| 1. |
- Basara, Branislav, 1964, et al.
(författare)
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Calculations of turbulent flow through a staggered tube bank
- 2017
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Ingår i: Proceedings of the Thermal and Fluids Engineering Summer Conference. - 2379-1748. ; 2017-April, s. 1563-1566
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Konferensbidrag (refereegranskat)abstract
- The primary aim of this paper is to numerically investigate the crossflow in a staggered tube bank by using a variable-resolution method. Experimental data of Simonin and Barcoude (1988) is available in the ERCOFTAC database. There are also few ERCOFTAC workshops, e.g. 1993, 19999, which were considering this test case primarily for checking the performance of the Reynolds-Averaged Navier-Stokes (RANS) models. Therefore, there are number of results with very different models which can be found in the literature. The work presented here aims to add one more set of results but this time with recently advanced variable resolution method, namely the Partially-Averaged Navier-Stokes (PANS). This method (Girimaji, 2006) belongs to so called bridging or seamless methods. The PANS approach adjusts seamlessly from the Reynolds-Averaged Navier-Stokes (RANS) to the Direct Numerical Solution (DNS) of the Navier-Stokes equation. The results are largely improved by using the PANS as for example shown in Basara (2015). This turbulence bridging method is derived from the RANS model equations. It inevitably improves results when compared with its corresponding RANS model if more scales of motions are resolved. This is done by varying the unresolved-to-total ratios of kinetic energy and dissipation. In the practice, the parameter which determines the unresolved-to-total kinetic energy ratio is defined by using the grid spacing and calculated integral length scale of turbulence. When the grid size is smaller, then more of the turbulent kinetic energy can be resolved. Usually, the integral scale of turbulence is obtained by summing up resolved turbulence, calculated as difference between instantaneous filtered velocity and the averaged velocity field, and unresolved turbulence obtained from its own equation. The turbulence model adopted in the present PANS variant is the four-equation ζ - f formulation (Hanjalic et al., 2004) which is the variant of more known v2-f model based on the elliptic relaxation concept.). As this model represents a practical and accurate RANS choice for a wide range of industrial applications, especially when used in conjunction with the universal wall approach (Popovac and Hanjalic, 2007, Basara, 2006), its PANS variant therefore guarantees that the proper near-wall model is used when fkis of a higher value. Therefore, the near-wall PANS variant of Basara et al. (2011) was used in the present study. The PANS model is implemented into the commercial CFD code AVL FIRE (AVL FIRE Manual, 2011).
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| 2. |
- Dong, Tianyun, 1990, et al.
(författare)
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Numerical investigation of a high-speed train underbody flows: Studying flow structures through large-eddy simulation and assessment of steady and unsteady Reynolds-averaged Navier-Stokes and improved delayed detached eddy simulation performance
- 2022
-
Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 34:1
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Tidskriftsartikel (refereegranskat)abstract
- The underbody flow of a truncated, 1:10 scaled, CRH380A model is investigated at Re = 2.78 × 105 in this paper. The large-eddy simulation (LES) is used to study the main features of the development of the underbody flow under the snowplow, in the bogie/cavity region and after the cavity (equip-cabin region). A grid independence study and a validation against experimental data have been done prior to the investigation. The snowplow region is dominated by a pair of separated counter-rotating vortices, which further affects the downstream flow. A strong shear layer is observed in the cavity region, and the turbulent flow is intensively triggered by the shear instability and the complex bogie components within the cavity region. The equip-cabin region allows the turbulent flow to develop without any disturbance, decreasing the turbulence intensity. Moreover, the steady and unsteady Reynolds-averaged Navier-Stokes (RANS, URANS) model and the improved delayed detached eddy simulation (IDDES) are used to compute the same flow, and to compare the results to LES. The solution differences, in terms of aerodynamic forces and the underbody flow state, are analyzed. Specifically, the minimum velocity discrepancy, at line2, between RANS (URANS) and LES is 14.4%, while IDDES is 3.6%. The solution accuracy vs the computational cost is also reported.
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| 3. |
- Dong, Tianyun, et al.
(författare)
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The effect of ground clearance on the aerodynamics of a generic high-speed train
- 2020
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Ingår i: Journal of Fluids and Structures. - : Elsevier BV. - 1095-8622 .- 0889-9746. ; 95
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Tidskriftsartikel (refereegranskat)abstract
- The influence of ground clearance on the flow around a simplified high-speed train is investigated in this paper. Four clearance heights are studied using IDDES. After a grid independence study, the results of the simulations are validated against experimental data present in the literature. It is found that the drag decreases when reducing the clearance gap from the baseline height to a possibly critical height, while drag remains constant when the clearance is lower than this critical height. The negative lift (downforce) increases with the decreasing of the clearance gap. The flow is particularly influenced by the gap height at the underbody and wake regions, where a lower underbody velocity and a higher wake velocity are observed with lower clearance down to case h2. Therefore, the different topologies of the wake are presented and described. Particular attention is paid to the description of the wake flow and to the position and the formation of the flow mixing region. Specifically, with decreasing clearance, the mix of the tail downwash and underbody flows happen earlier, and the core of the counter-rotating vortices in the wake tends to develop with an increasing height trend. Overall, aerodynamic performance and flow structure descriptions show positive and negative effects when decreasing gap clearances, which should be taken into account for new design strategies.
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| 4. |
- Dong, Tianyun, et al.
(författare)
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The effect of reducing the underbody clearance on the aerodynamics of a high-speed train
- 2020
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- The effect of lowering the ground clearance, on train aerodynamics is investigated using IDDES. The high speed train geometry with its full underbody complexity is used in the investigation. The clearance is reduced by installing extra panels on the track. The numerical results are verified and validated by a grid independence study and experimental data. This work shows that, when lowered the clearance, the underbody velocity at the head car decreases, while the underbody velocity at the middle and tail car increases. The reduced clearance barely affects the time-averaged slipstream at 3 m away from the center of track. However, at a closer distance to the train body, the difference in velocity is observed to reach up to 50% between the two clearance configurations and the clearance has an opposite effect on the trackside and platform slipstream. Based on the analysis of ensemble-averaged slipstream, lowering the underbody clearance, the characteristic air speed at the trackside and platform height increases by 2.0% and 6.7%, respectively. The total drag is almost unaffected by the clearance, but the changed distribution of the drag indicates a larger drag depends on the bogie structure if longer grouped train is used. The total lift decreases 25.9% after the clearance is reduced. Specifically, 4.1% of the negative lift is increased at the head car, while the positive lift decreases 92.7% and 1.8% for the middle and tail car, respectively. Overall it is shown that reducing the underbody clearance barely affect the slipstream at standard positions, but affects more aerodynamic loads of the train.
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| 5. |
- He, Kan, et al.
(författare)
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Assessment of LES, IDDES and RANS approaches for prediction of wakes behind notchback road vehicles
- 2021
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 217
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Tidskriftsartikel (refereegranskat)abstract
- The capability of Large Eddy Simulations (LES), Improved Delayed Detached Eddy Simulations (IDDES) and Reynolds-Averaged Navier–Stokes Equations (RANS) to predict the flow behind notchback Ahmed body is investigated in the present paper. Simulations consider two specific models, with effective backlight angles of β1=17.8° and β2=21.0°, respectively. The focus of the study is on the prediction of the expected lateral asymmetry or symmetry of the near-wake flows. Results show that IDDES using coarse computational grids predicts the flow in agreement with LES using finer computational grids. RANS results in inaccurate flow predictions, attributed to its steady formulation relying on turbulence modelling being incapable of dealing with the studied flow. Modal analysis applying Proper Orthogonal Decomposition (POD) suggests the consistency of the wake dynamics between IDDES and LES. The presence of the wake bi-stability is validated by the wind tunnel experiment.
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| 6. |
- He, Kan, 1991, et al.
(författare)
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Floor motion's influence on wake asymmetry of a notchback bluff body
- 2022
-
Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 34:3
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Tidskriftsartikel (refereegranskat)abstract
- Large eddy simulations are used to explore the influence of floor motions on asymmetric flows around a notchback bluff body. The focus of this study is on the aerodynamic forces and the extent of natural wake asymmetry presented under moving and stationary ground conditions. The different ground condition has a notable influence on the aerodynamic force and the surrounding pressure distribution of the body. On the other hand, the wake asymmetry, known to be a sensitive phenomenon, is not evidently affected by the floor motion. However, quantitative analysis of the averaged and the statistic flow still suggests slight differences in the degree of wake asymmetry between the two ground conditions. Modal analysis applying proper orthogonal decomposition confirms that the asymmetric wake dynamics and the wake shedding frequency are not sensitive to the floor motion. The accuracy of the numerical simulation is established by a grid-independence study.
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| 7. |
- He, Kan, et al.
(författare)
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Influence of the rounded rear edge on wake bi-stability of a notchback bluff body
- 2021
-
Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 33:11
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Tidskriftsartikel (refereegranskat)abstract
- The wake bi-stability behind notchback Ahmed bodies is investigated by performing wind tunnel experiments and large eddy simulations (LESs). The focus of this study is on the suppression of bi-stable wakes achieved by rounding the roof's trailing edge of the body. The suppression effect is found to depend on the Reynolds number (R e). The wake behind a sharp edge remains bi-stable for all tested R e. However, for a rounded edge with small radius, wake bi-stability at R e = 0.5 × 10 5 and wake symmetrization with 0.75 × 10 5 ≤ R e ≤ 1.5 × 10 5 are observed. Increasing R e with R e ≥ 1.75 × 10 5, the wake returns to the bi-stable state. Particularly, with R e ≥ 2 × 10 5, a stable asymmetric wake state with no switches is observed for long periods. Performing LES confirms the expected wake asymmetry at R e = 0.5 × 10 5 and symmetry at R e = 1 × 10 5 for the case of rounded edge with a small radius. Besides, another wake symmetry is observed for the rounded edge with a large radius at R e = 0.5 × 10 5. For the two wake symmetries shown in the LES results, the symmetrization is attributed to wake suppression in the notchback region, forcing the flow separation from the rear roof to attach to the slant on both sides of the body.
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| 8. |
- He, Kan, et al.
(författare)
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Numerical investigation of the wake bi-stability behind a notchback Ahmed body
- 2021
-
Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 926, s. A36-1-A36-29
-
Tidskriftsartikel (refereegranskat)abstract
- Large-eddy simulations are used to investigate the origin of the wake asymmetry and symmetry behind notchback Ahmed bodies. Two different effective backlight angles, beta(1) = 17.8 degrees and beta(2) = 21.0 degrees, are simulated resulting in wake asymmetry and symmetry in flows without external perturbations, in agreement with previous experimental observations. In particular, the asymmetric case presents a bi-stable nature showing, in a random fashion, two stable mirrored states characterized by a left or right asymmetry for long periods. A random switch and several attempts to switch between the bi-stability are observed. The asymmetry of the flow is ascribed to the asymmetric separations and reattachments in the wake. The deflection of the near-wall flow structures behind the slant counteracting the asymmetry drives the wake to be temporarily symmetric, triggering the switching process of the bi-stable wake. The consequence of deflection that forces the flow structure to form on the opposite side of the slant is the decisive factor for a successful switch. Modal analysis applying proper orthogonal decomposition is used for the exploration of the wake dynamics of the bi-stable nature observed.
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| 9. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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LES INVESTIGATION OF THE ASYMMETRY IN THE WAKE OF A GENERIC VEHICLE BODY
- 2013
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Ingår i: 4th International Conference on Jets, Wakes and Separated Flows, ICJWSF2013 IMECE 2013 September 17-21, 2013, Nagoya, JAPAN.
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Konferensbidrag (refereegranskat)abstract
- Large eddy simulations are used to investigate the emergence of flow asymmetry behind the symmetric geometry of a simplified notchback vehicle body. Two different angles of the backlight were simulated, resulting in asymmetric and symmetric flows in agreement with previous experimental observations. Simulations were made at Reynolds numbers 10^4, 3 x 10^4 and 5 x 10^4 based on the incoming velocity and the height of the body. The Reynolds number dependency of the asymmetry phenomenon was observed when the Reynolds number was changed from 10^4 to 3 x 10^4. The LES results are used to present a new picture of the time-averaged flow around the notchback geometry. The instantaneous flow was found to contain regular shedding of the horse-shoe vortices from the deck at the nondimensional frequency of St=0.42, in agreement with previous experimental observations.
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| 10. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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Partially-Averaged Navier-Stokes simulation of the flow around simplified vehicle
- 2015
-
Ingår i: AIP Conference Proceedings. - : AIP Publishing LLC. - 1551-7616 .- 0094-243X. - 9780735412873 ; 1648, s. Art. no. UNSP 030019-
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Konferensbidrag (refereegranskat)abstract
- This paper presents Partially-Averaged Navier-Stokes (PANS) simulation of the flow around generic vehicle atdifferent yaw angles. The results of PANS show not only excellent agreement with the experimental data but also largesavings in the computer effort compared to LES predictions. Simulations on several computational grids show that PANSadapts to the existing grid making the prediction accurate on affordable computational grids.
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| 11. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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PARTIALLY-AVERAGED NAVIER- STOKES SIMULATIONS IN ENGINEERING FLOWS
- 2018
-
Ingår i: Proceedings of the Thermal and Fluids Engineering Summer Conference. - 2379-1748. - 9781567004724 ; 2018-March, s. 543-546
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Konferensbidrag (refereegranskat)abstract
- This paper presents the most recent applications of the Partially-Averaged Navier-Stokes equations for engineering flows together with the review of the previous work in the field. Partially-Averaged Navier Stokes (PANS) simulation has been successfully used for several different applications of flows around ground vehicles. Examples of flows studied using PANS are that of the flow around square-back Ahmed body, flow around simplified passenger vehicle influenced by crosswinds, flow around simplified intercity trains, to the influence of passive and active flow control on the reduction of the aerodynamic drag on simplified vehicles. The idea of the application of hybrid methods such as PANS is to decrease the resolution requirements that are needed in turbulence resolving simulations such as LES. The resolution requirements of LES are normally very high in the near-wall regions, and this is where the PANS method is expected to activate more turbulence modelling, and thereby decrease the computational effort. The PANS method used by the authors is based on the variable switching coefficient that regulates the amount of the turbulence modelling in the simulation. Previous studies have shown that such implementation of PANS is in line with the requirements that PANS should adapt to the computational grid. The most recent predictions range from simplified ground vehicle flow, flow around a freight train locomotive to the investigation of active flow control for trucks and ships. The new predictions show good agreement with the experimental observations.
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| 12. |
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| 13. |
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| 14. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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Partially-Averaged Navier-Stokes Simulations of Flows Around Generic Vehicle at Yaw
- 2016
-
Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2016-April:April
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Tidskriftsartikel (refereegranskat)abstract
- Partially-Averaged Navier-Stokes Simulations (PANS) were made of flow around a generic vehicle influenced by side wind at four different yaw angles to investigate the prediction capabilities of PANS. Comparisons with results of LES show clear advantages of PANS in predicting pressure-induced separation resulting in the trailing vortices aligned with the direction of the flow. Poorer agreement was obtained in the near wake when the boundary layer separates at the end of the surface at the rear end. A possible explanation for the lack of accuracy at the rear end of the body was found in the formulation of the switching coefficient fk which produces too low values resulting in too low eddy viscosity in this region.
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| 15. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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Partially-averaged Navier–Stokes simulations of two bluff body flows
- 2016
-
Ingår i: Applied Mathematics and Computation. - : Elsevier BV. - 0096-3003 .- 1873-5649. ; 272, s. 692-706
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Tidskriftsartikel (refereegranskat)abstract
- The paper discusses the PANS model in the framework of engineering applications of bluff body flows. Comparisons with the resolving LES technique and URANS of a three dimensional bluff body flow are made for a better understanding of the behavior of PANS model in these flows. Several implementation issues of PANS such as fk variable in space and time, the influence of the inlet boundary conditions and discretization scheme are discussed. The reference comparison with LES and URANS displays the differences between the methods in the complex interaction between the resolved and the modeled coherent flow scales. The PANS model is compared with competing techniques of LES, DES and RANS for challenging flow around a generic vehicle at yaw. The remaining problems and the possible directions in the improvement of the PANS model are discussed.
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| 16. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
-
RECENT Experiences of PANS predictions in vehicle aerodynamics
- 2016
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Ingår i: 26th JUMV International Automotive Conference Belgrade 19/20 April 2017.
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Konferensbidrag (refereegranskat)abstract
- This paper presents recent applications of the Partially-averaged Navier-Stokes equations for external vehicle flows. The flow predictions range from simplified ground vehicle flow, flow around a freight train locomotive to the investigation of a simplified truck at yaw, and active flow control. The new predictions show good agreement with the experimental observations. The results of the PANS simulations are used to study the differences between the quasi-steady and dynamic change of the yaw for the flow around a simplified truck cabin. Furthermore, active flow control was implemented with the aim to suppress the separations around the front A pillars of a simplified truck using PANS.
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| 17. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
-
Status of PANS for bluff body aerodynamics of engineering relevance
- 2015
-
Ingår i: Notes on Numerical Fluid Mechanics and Multidisciplinary Design. - Cham : Springer International Publishing. - 1612-2909 .- 1860-0824. ; 130, s. 399-410
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Tidskriftsartikel (refereegranskat)abstract
- This paper is a review of the use of Partially-Averaged Navier-Stokes (PANS) simulations for various bluff body flows of engineering relevance. The application range from flows around generic bluff bodies such as a finite cylinder to flows around simplified road vehicles, trains and landing gears. Active flow control of bluff body flow is one of important application of PANS discussed in this paper. Judgment of the PANS performance is made in comparison with LES and other numerical techniques such as DES and RANS. The review illustrates the success of PANS and its advantage over LES in several bluff body flows, such as the flow around a rudimentary landing gear and the flow around finite cylinder. It also shows that there is a need of improvement in existing PANS methodology with variable fk in flows with varying boundary conditions.
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| 18. |
- Krajnovic, Sinisa, 1970, et al.
(författare)
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The status of PANS for bluff body aerodynamics of engineering relevance.
- 2014
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Ingår i: In 5th Symposium on Hybrid RANS-LES Methods, TEXAS, A&M University, College Station, Houston, USA, 19-21 March, 2014.
-
Konferensbidrag (refereegranskat)abstract
- This paper is a review of the use of Partially-Averaged Navier-Stokes (PANS) simulations for various bluff body flows of engineering relevance. The application range from flows around generic bluff bodies such as a finite cylinder to flows around simplified road vehicle, trains and landing gears. Active flow control of bluff body flow is one of important application of PANS discussed in this paper. Judgment of the PANS performance is made in comparison with LES and other numerical techniques such as DES and RANS. The review illustrates the success of PANS and its advantage over LES in several bluff body flow, such as the flow around a rudimentary landing gear and the flow around finite cylinder. It also shows that there is a need of improvement in existing PANS methodology with variable $f_k$ in flows with varying boundary conditions.
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| 19. |
- Miao, Xiujuan, et al.
(författare)
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Aerodynamic performance of a high-speed train passing through three standard tunnel junctions under crosswinds
- 2020
-
Ingår i: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- The aerodynamic performance of a high-speed train passing through tunnel junctions under severe crosswind condition was numerically investigated using improved delayed detached-eddy simulations (IDDES). Three ground scenarios connected with entrances and exits of tunnels were considered. In particular a flat ground, an embankment, and a bridge configuration were used. The numerical method was first validated against experimental data, showing good agreement. The results show that the ground scenario has a large effect on the train's aerodynamic performance. The bridge case resulted in generally smaller drag and lift, as well as a lower pressure coefficient on both the train body and the inner tunnel wall, as compared to the tunnel junctions with flat ground and embankment. Furthermore, the bridge configuration contributed to the smallest pressure variation in time in the tunnel. Overall, the study gives important insights on complicated tunnel junction scenarios coupled with severe flow conditions, that, to the knowledge of the authors, were not studied before. Beside this, the results can be used for further improvements in the design of tunnels where such crosswind conditions may occur.
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| 20. |
- Minelli, Guglielmo, 1988, et al.
(författare)
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A Flow Control Study of a Simplified, Oscillating Truck Cabin Using PANS
- 2018
-
Ingår i: Journal of Fluids Engineering, Transactions of the ASME. - : ASME International. - 1528-901X .- 0098-2202. ; 140:12
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Tidskriftsartikel (refereegranskat)abstract
- This work presents an application of the partially averaged Navier–Stokes (PANS) equations for an external vehicle flow. In particular, the flow around a generic truck cabin is simulated. The PANS method is first validated against experiments and resolved large eddy simulation (LES) on two static cases. As a consequence, PANS is used to study the effect of an active flow control (AFC) on a dynamic oscillating configuration. The oscillation of the model represents a more realistic ground vehicle flow, where gusts (of different natures) define the unsteadiness of the incoming flow. In the numerical study, the model is forced to oscillate with a yaw angle 10 deg > β > –10 deg and a nondimensional frequency St = fW/Uinf = 0.1. The effect of the periodic motion of the model is compared with the quasi-static flow condition. At a later stage, the dynamic configuration is actuated by means of a synthetic jet boundary condition. Overall, the effect of the actuation is beneficial. The actuation of the AFC decreases drag, stabilizes the flow, and reduces the size of the side recirculation bubble.
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| 21. |
- Minelli, Guglielmo, 1988, et al.
(författare)
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A LES Study on the Effect of Periodic Gusts on a Truck Model
- 2017
-
Ingår i: Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2017.
-
Konferensbidrag (refereegranskat)abstract
- This work presents an application of the Large Eddy Simulation Coherent Structures Model (LES-CSM) equations for an external vehicle flow. In particular, the flow around a generic truck is simulated. The model is forced to oscillate in order to represents a more realistic ground vehicle flow condition, where gusts (of different natures) define the unsteadiness of the incoming flow. In this numerical study, the Reynolds number is Re = 4 × 10 4 based on the width of the model W = 0.152 and the incoming velocity U inf = 4.26m/s. The model is forced to oscillate with a yaw angle 10 ◦ > β > −10 ◦ and a non-dimensional frequency St = f W/U inf = 0.06.The effect of the periodic motion of the model is compared with the quasi-static flow condition. Overall, the effect of oscillation changes drastically the flow, arising an hysteresis behaviour and complete different features, when compared to the static configuration. This study is relevant to better understand real flow conditions, with the ultimate goal to implement an effective active flow control strategy for aerodynamic drag reduction.
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| 22. |
- Minelli, Guglielmo, 1988, et al.
(författare)
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Active Aerodynamic Control of a Separated Flow Using Streamwise Synthetic Jets
- 2019
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Ingår i: Flow, Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1573-1987 .- 1386-6184. ; 103:4, s. 1039-1055
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Tidskriftsartikel (refereegranskat)abstract
- LES simulations at Re=1×10^5 and wind tunnel experiments at Re=5×10^5 were con-ducted to investigate the beneficial effect of an active flow control (AFC) technique on theaerodynamic performance of a simplified truck geometry. The paper involves the investiga-tion of a synthetic jet actuator characterized by periodic blowing and suction that defines azero net mass flux flow control mechanism. The actuation aims to suppress the flow sep-aration occurring at the A-pillar (front rounded corner) of a truck cabin. The work flow isdefined as it follows. First, LES at low Reynolds number are conducted for different dispo-sition of the actuation slots. The results show a beneficial effect when the actuation slots arepositioned in streamwise direction compared to spanwise (vertical) direction. Second, basedon the previous considerations, wind tunnel experiments are conducted to verify and sup-port the numerical findings. Both numerical solutions and experimental data show the sametrend and the superiority of the streamwise slots actuation when compared to traditional ver-tical slot actuation. In particular, this work shows the weakness of a vertical slot actuation,when its location is not optimized. A small change in its positioning greatly worsen the effi-cacy of the separation control in terms of drag reduction and separation bubble length. Theslot location directly affects the length of the separated flow region which its reduction canvary between 40–70% based on the positioning. Conversely, a streamwise actuation, span-ning a larger portion of the curvature of a rounded A-pillar, is not affected by this behaviourand contributes up to 80% of the recirculation bubble reduction measured in the unactuatedcase. The effect of the location change and the orientation of a zero net mass flux jet slot istherefore investigated and discussed in this work.
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| 23. |
- Minelli, Guglielmo, 1988
(författare)
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Active Flow Control for Reducing Drag on Trucks: from Concept to Full Scale Testing
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is no doubt that road vehicle transportation is needed to improve efficiency, to reduce power consumption and to contribute to a sustainable mobility. Aerodynamics plays a crucial role in this, and its optimization can have a significant impact on fuel efficiency. The work reported in this thesis thus investigates the applicability of an active flow control technique able to improve the aerodynamic performance of trucks.CFD simulations and wind tunnel experiments are conducted to explore the potential of such a device. The process starts with a preliminary LES study (Re = 1 × 10^5 ) and ends with a proof of concept full scale test of a real truck (Re = 3.5 × 10^6 ). The PANS method and scaled model wind tunnel experiments were essential to bridge the initial preliminary findings to the final full scale test. PANS was first validated (using in-house experimental data and data from test cases) and then used to simulate the efficacy of AFC at higher Re (Re = 5 × 10^5 ), introducing realistic flow conditions (wind gusts).In addition, wind tunnel experiments of a scaled, simplified truck cabin were used to demonstrate the applicability of the control. The results focus on two main points. First, synthetic jets were shown to be an effective and low energy consumption technique to control a pressure induced separated flow and for reducing drag on trucks. Second, PANS was shown to be an interesting method for industrial applications. Its capability to resolve unsteady flow cases preserving the accuracy of the flow structures prediction is shown, even when meshes are relatively coarse.
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| 24. |
- Minelli, Guglielmo, 1988, et al.
(författare)
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ACTIVE FLOW CONTROL FOR TRUCKS: FROM THEORY TO PRACTICE
- 2017
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Ingår i: Svenska Mekanikdagarna, Uppsala, 12-13 juni 2017.
-
Konferensbidrag (refereegranskat)abstract
- The possibility to actively control the external aerodynamic of vehicles is an attractive yet challenging solution to decrease the aerodynamic drag and the fuel consumption. The workflow that describes the implementation of an Active Flow Control (AFC), for the suppression of theseparated flow at the A-pillar of a truck, is condensate in this paper. The presented work spans the process from a theoretical verification of the method to a preliminary implementation of an AFC on a real full-scale truck cabin. The study involves CFD and experimental work, including aerodynamic test in a full-scale wind tunnel. The milestones of this process are listed below:- Identification of the problem, Fig. 1.- Preliminary CFD (LES) study, Fig. 2.- CFD (PANS) study of a simplified truck cabin model, Fig. 3.- Experiments on a simplified cabin model and actuation of the flow, Fig. 4.- Full-scale preliminary test (cabin), Fig. 5.- Future: full-scale wind tunnel test (force measurements), cabin + trailer.- Future: piezo electric actuators.
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| 25. |
- Minelli, Guglielmo, 1988, et al.
(författare)
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Actuation of the flow field around a frontstep with a rounded leading edge
- 2015
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Ingår i: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816. ; 0
-
Konferensbidrag (refereegranskat)abstract
- Large Eddy Simulations (LES) are conducted to study the actuated flow field around a bluff body.The model is a simplification of a section of a truck cabin. The aim is to model the separation of the flow actingat the front part, the so called A-pillar. LES data show the connection between orientation and frequency of the actuation in comparison with drag reduction and separation mechanism. The flow is post processed using modal and frequency decompositions. Relevant results in terms of drag coefficient reduction were observed for the actuated flow. An optimal actuation in terms of induced frequency and drag reduction is also found.
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| 26. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Aerodynamic flow control for a generic truck cabin using synthetic jets
- 2017
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 168, s. 81-90
-
Tidskriftsartikel (refereegranskat)abstract
- This experimental work presents the achievement in drag reduction with the use of active flow control (AFC) for a generic bluff body. Experiments were done in the Chalmers University closed loop wind-tunnel at Reynolds number . The is based on the undisturbed velocity m/s and the width of the model m. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the rounded vertical side edges. The pressure induced separation reproduces the flow detachment occurring at the front A-pillar of a real truck. The investigation of the unactuated and actuated flow was conducted by means of time-resolved particle image velocimetry (PIV). Loudspeakers were used as the actuation device. These were characterized before the actuation study, highlighting an interesting analogy between actuation frequency and jet vortex pair size. The effects of different actuations were evaluated with hot wire anemometry. The effect of the actuation was studied using phase averaging and modal analysis. A notable reduction of the side recirculation bubble was observed. The nature of the separation mechanism was investigated and related to different actuation frequencies spanning the range . As for the , the non-dimensional frequency is based on the undisturbed velocity and the width of the model W.
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| 27. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
An aeroacoustic study of the flow surrounding the front of a simplified ICE3 high-speed train model
- 2020
-
Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 160
-
Tidskriftsartikel (refereegranskat)abstract
- A numerical study using IDDES is carried out to investigate the aerodynamic and the aeroacoustic response of a simplified ICE3 high-speed train model. The work focuses on the front part of the train and, in particular, on the first bogie cavity. The choice is justified by a literature survey which shows that this part of the train is the principal contributor of critical noise pollution created at pass-by in populated areas. Detailed CFD can provide useful insight and be of great importance in the identification of noise generation mechanisms and their relation with the flow structures. Results show the formation of two main aerodynamic structures with a clear relation to the aeroacoustic response calculated on the train and ground surfaces. Simulations were made at Re=1.8×105 and M=0.058 to match the experimental observations found in literature and generate a set of benchmark data for future investigations.
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| 28. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Bluff Body Flow Control Using a Genetic Algorithm Optimization
- 2019
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This first preliminary study highlights few important points: • ML techniques applied to flow control show impressive and sometimes surprising results concerning actuation strategies • A very weak actuation applied at the front rounded cor- ner of the body is able to strongly influence the body wake and sets the starting point for the following future steps: • The backtracking of the evolution results finding pat- terns to explain the flow physics brought by the actuation • The application of the GA to a 3D geometry • The application of a linear genetic programming (LGP) to generate a higher degree of freedom actuation signal
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| 29. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Development of Active Flow Control for Trucks
- 2018
-
Ingår i: Proceedings of the Thermal and Fluids Engineering Summer Conference. - 2379-1748. ; 2018-March
-
Konferensbidrag (refereegranskat)abstract
- The possibility to actively control the external aerodynamic of vehicles is an attractive yet challenging solution to decrease the aerodynamic drag and the fuel consumption. The work flow that describes the implementation of an Active Flow Control (AFC), for the suppression of the separated flow at the A-pillar of a truck, is summarised in this paper. The presented work spans from a theoretical verification of the method to a preliminary implementation of an AFC on a real full-scale truck cabin. The study involves numerical (CFD) and experimental work, including aerodynamic test in a full scale wind tunnel. The initial CFD simulations of a simplified A-pillar were performed using turbulence resolving numerical method large-eddy simulations (LES). A second step consisted in simulation of a simplified truck cabin using hybrid Partially-Averaged Navier-Stokes simulations (PANS). The AFC was created using synthetic jets produced by the use of loudspeakers mounted in the A-pillars of the model. The numerical and experimental investigations were used to optimise the actuation parameters leading to maximum drag reduction. The final step of the validation of the AFC concept was achieved with a full scale test experimental campaign of a Volvo Truck cabin equipped with the studied AFC device.
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| 30. |
- Minelli, Guglielmo, 1988
(författare)
-
Drag Reduction by means of Active Flow Control Applied on a Generic Truck A-pillar: a Numerical and Experimental Study
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall goal of this thesis is to isolate and control the flow mechanism characterizing the flow separation occurring at the A-pillar of a truck. The study aims to gain knowledge of the flow physics of the separation mechanism, and to eventually suppress the afore mentioned separation by means of an Active Flow Control.State of the art unsteady numerical simulations and experiments are both employed to carry out this work. LES are performed at Re = 1 × 10 5 and post processed (by meansof POD and FFT), to study the physics of the flow structures. Further, the hybrid PANS method is tested on several bluff body flows evaluating limits and qualities. The use of a hybrid technique as such is necessary to minimize the computer resources, while still being able to simulate a ”close to reality” Re. In the last part of the work, PANS are validated against wind tunnel experiments on a 3-D generic truck cabin. In the latter part PANS simulations are also employed to conduct an optimization study of the actuation frequency.
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| 31. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
EXPERIMENTAL AND NUMERICAL INVESTIGATION OF ACTIVE FLOW CONTROL ON A GENERIC TRUCK CABIN
- 2016
-
Ingår i: 11TH INTERNATIONAL ERCOFTAC SYMPOSIUM ON ENGINEERING TURBULENCE MODELLING AND MEASUREMENT.
-
Konferensbidrag (refereegranskat)abstract
- This work presents the achievement in drag reduction by use of Active Flow Control (AFC) on a generic bluff body. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the rounded vertical front corner. The pressure induced separation reproduces the flow separation occurring at the front A-pillar of a real truck.Hybrid Partially Averaged Navier-Stokes (PANS) simulations are compared with wind tunnel experiments.The Reynolds number for both simulations and experiments is Re = 5×10^5 based on the inlet velocity Uinf and the width of the model W = 0.4 m. A validation of the hybrid CFD model on two flow configurations is followed by a CFD study on the optimal actuation frequency able to minimize the aerodynamic drag. PANS accurately predicts the flow field measured in experiments and a notable drag reduction by means of AFC is observed in a numerical study.
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| 32. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
FLOW CONTROL FOR A GENERIC TRUCK CABIN USING SYNTHETIC JET
- 2017
-
Ingår i: European Drag Reduction and Flow Control Meeting – EDRFCM 2017 April 3–6, 2017, Rome, Italy.
-
Konferensbidrag (refereegranskat)abstract
- Active flow control can be applied using a various number of approaches. The general, yet ultimate, goal is to use a control strategy able to actively manipulate a separated flow.Reattachment or deflection of the shear layer is of main importance to enhance the aerodynamic performance of blunt and aerodynamic bodies. The experiments presented in this paper show the achievements of a synthetic jet used to mitigate and eventually suppress the recirculation bubble occurring at the A-pillars of a truck, Fig. 1a. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the rounded vertical front corners. The pressure induced separation reproduces the flow detachment occurring at the front A-pillars of a real truck. Figures and dimensions of the model are presented in Figs. 1 (b and c), 2, and Tab. 1, respectively. Time resolved PIV was employed to investigate the flow (Re = 5 × 10 5 ), Fig. 3. The snapshots were post processed using modal and phase averaged analyses.
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| 33. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Flow control for a simplified truck using an array of streamwise synthetic jets
- 2018
-
Ingår i: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816. - 9781567004687 ; 2018-July, s. 665-676
-
Konferensbidrag (refereegranskat)abstract
- LES simulations at Re = 1 × 10^5 and wind tunnel experiments at Re = 5 × 10^5 were conducted to investigate the beneficial effect of an active flow control (AFC) technique on the aerodynamic performance of a simplified truck geometry. The paper involves the investigation of a synthetic jet actuator characterized by periodic blowing and suction that defines a zero net mass flux flow control mechanism. The actuation aims to suppress the flow separation occurring at the A-pillar (front rounded corner) of a truck cabin. The work flow is defined as follow. First, LES at low Reynolds number are conducted for different disposition of the actuation slots. The results show a beneficial effect when the actuation slots are positioned in streamwise direction compared to spanwise (vertical) direction. Second, based on the previous considerations, wind tunnel experiments are conducted to verify and support the numerical findings. Both numerical solutions and experimental data show the same trend and the superiority of streamwise aligned AFC slots.
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| 34. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
LES and PANS of turbulent flow through a staggered tube bundle
- 2017
-
Ingår i: American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM. - 0888-8116. - 9780791858059 ; 1B-2017
-
Konferensbidrag (refereegranskat)abstract
- Two unsteady numerical techniques, Partially-AveragedNavier Stokes (PANS) and Large Eddy Simulation (LES), areused to predict the flow in a tube bundle. The results were compared with the existing experimental data. Both methods predicted the flow in a relatively good agreement with the experimental data although the PANS simulation used only fifty percent of the computational nodes compared to the LES. The results of the simulations are used to study the unsteadiness in the flow and identify a dominant frequency of the flow.
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| 35. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Numerical Investigation of Active Flow Control Around a Generic Truck A-Pillar
- 2016
-
Ingår i: Flow, Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1573-1987 .- 1386-6184. ; 97:287, s. 1-20
-
Tidskriftsartikel (refereegranskat)abstract
- Large Eddy Simulations (LES) are conducted to study the actuated flow field around a bluff body. The model is a simplified section of a truck. The aim of the work is tomodel the separation of the flow acting at the front rounded corners, the so called A-pillars, and to minimize the separation of the flow by means of Zero Net Mass Flux synthetic jets.LES data show the interaction of the flow main structures, the separation mechanism and the effects of the actuation on the flow field. The flow is post processed using modal and frequency decompositions. Relevant results in terms of drag reduction were observed for the actuated flow. The principle flow mechanisms are discussed and an optimal actuation frequency, in terms of induced fluctuations and drag reduction, is identified.
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| 36. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Numerical Investigation of the Actuated Flow on a Bluff Body
- 2016
-
Ingår i: Springer Proceedings in Physics. - Cham : Springer International Publishing. - 0930-8989 .- 1867-4941. ; 185, s. 295-302
-
Konferensbidrag (refereegranskat)abstract
- Large Eddy Simulations (LES) are conducted to study the Active Flow Control (AFC) of the separation of the boundary layer on a rounded leading edge frontstep. This bluff body imitates the flow around a section of a simplified truck cabin and focuses on the separation arising at the front rounded corner, the so called A-pillar. The LES data show the connection between the actuation and drag reduction. The actuated and unactuated flows are analysed using modal decomposition and frequency analysis. Different configurations are tested and a strong influence of the actuation on both drag reduction and separation mechanism was observed. Relevant results, in terms of drag coefficient and recirculation bubble reduction, are achieved when the flow is actuated. LES shows an increased unsteadiness in the flow, introduced by the actuation. An analysis that investigates the connection between actuation and induced unsteadiness is presented.
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| 37. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
PANS study of the flow around an oscillating, simplified truck cabin with flow control
- 2017
-
Ingår i: American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM. - 0888-8116. - 9780791858059 ; 1B-2017
-
Konferensbidrag (refereegranskat)abstract
- This work presents an application of the Partially-AveragedNavier-Stokes equations for an external vehicle flow. In particular, the flow around a generic truck cabin is simulated. The PANS method is first validated against experiments and resolved LES on two static cases. As a consequence, PANS is used to study the effect of an active flow control (AFC) on a dynamic oscillating configuration. The oscillation of the model represents a more realistic ground vehicle flow, where gusts (of different nature) define the unsteadiness of the incoming flow. In the numerical study, the model is forced to oscillate with ayaw angle 10 ◦ > β > −10 ◦ and a non-dimensional frequencySt = fW /U in f = 0.1. The effect of the periodic motion of the model is compared with the quasi-steady flow condition. At a later stage, the dynamic configuration is actuated by means of a synthetic jet boundary condition. Overall, the effect of the actuation is beneficial. The actuation of the AFC decreases drag, stabilises the flow and reduces the size of the side recirculation bubble.
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| 38. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
PANS Validation and Active Flow Control for a Simplified Truck Cabin
- 2017
-
Ingår i: 16th European Turbulence Conference, 21-24 August, 2017, Stockholm, Sweden.
-
Konferensbidrag (refereegranskat)abstract
- Active Flow Control (AFC) can be applied using a various number of approaches. The general, yet ultimate, goal is to use a control strategy able to actively manipulate a separated flow. Reattachment or deflection of the shear layer is of main importance to enhance the aerodynamic performance of blunt and aerodynamic bodies. The paper presents a numerical and experimental study of the suppression of the recirculation bubble occurring at the side of a generic truck cabin (A-pillar separation) at Re = 5 × 10 5 . In this work the hybrid Partially Averaged Navier-Stokes (PANS) method was used.The aim of the present study is twofold: to validate the PANS method against in-house experiments and a resolved LES simulation, and to simulate the effect of an AFC on a heavily separated turbulent flow. Figure 1 shows the dimension of the computational and experimental domains (a and b) and the observed window in both experiments and simulations (c and d). The results show a good flow prediction by PANS even when the computational domain is drastically coarsened, Fig. 2. Velocity and Reynolds stress profiles, as well as modal and frequency analysis will be compared for a full validation.The AFC effect shows a drastic decrease of the side recirculation bubble, Fig. 3. The separation is observed to be receptive to the control and it locks to the specific actuation frequency when the latter is in the "receptive band". The flow reaches a frequency independent behaviour when the actuation frequency exceeds this range.
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| 39. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Upstream actuation for bluff-body wake control driven by a genetically inspired optimization
- 2020
-
Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 893
-
Tidskriftsartikel (refereegranskat)abstract
- The control of bluff-body wakes for reduced drag and enhanced stability has traditionally relied on the so-called direct-wake control approach. By the use of actuators or passive devices, one can manipulate the aerodynamic loads that act on the rear of the model. An alternative approach for the manipulation of the flow is to move the position of the actuator upstream, hence interacting with an easier-to-manipulate boundary layer. The present paper comprises a bluff-body flow study via large-eddy simulations to investigate the effectiveness of an upstream actuator (positioned at the leading edge) with regard to the manipulation of the wake dynamics and its aerodynamic loads. A rectangular cylinder with rounded leading edges, equipped with actuators positioned at the front curvatures, is simulated at. A genetic algorithm (GA) optimization is performed to find an effective actuation that minimizes drag. It is shown that the GA selects superharmonic frequencies of the natural vortex shedding. Hence, the induced disturbances, penetrating downstream in the wake, significantly reduce drag and lateral instability. A comparison with a side-recirculation-suppression approach is also presented, the latter case being worse in terms of reduced drag (only 8 % drag reduction achieved), despite the total suppression of the side recirculation bubble. In contrast, the GA optimized case contributes to a 20 % drag reduction with respect to the unactuated case. In addition, the large drag reduction is associated with a reduced shedding motion and an improved lateral stability.
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| 40. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Using horizontal sonic crystals to reduce the aeroacosutic signature of a simplified ICE3 train model
- 2021
-
Ingår i: Applied Acoustics. - : Elsevier BV. - 0003-682X .- 1872-910X. ; 172
-
Tidskriftsartikel (refereegranskat)abstract
- The design of noise barriers for high-speed trains is challenging due to the flow interaction between the train body and barriers. A failed design could affect the flow that in turn introduces additional aerodynamic loads to the train and generates extra noise. This study is the first investigation to numerically explore the detailed effects of noise barriers on high-speed trains. In particular, horizontal sonic crystals are compared to vertical, closed at the ground barriers in order to investigate the detailed effects of different noise screens on high-speed trains. The compressible IDDES is used to simulate the flow. The focus of this study is twofold. The first is to test if an alternative barrier typology can effectively reduce the noise signature, without having an impact on the train’s aerodynamic performance. The second is to explore the connection between the near-field velocity fluctuations and the far-field noise. A few specific tonal frequency components have been commonly reported but not clearly explained in the literature. It is unclear if the specific tonal components are less dependent on the Reynolds numbers, although, in general, energetic flow structures are dependent on inflow speeds. Concerning the noise reduction, the results show that the sonic crystal barrier case has a significantly better performance. A modal analysis is used to explore the causes of the tonal peaks and the association of the underbody swirling vortices to the far-field noise is described.
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| 41. |
|
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| 42. |
- Minelli, Guglielmo, 1988, et al.
(författare)
-
Validation of PANS and active flow control for a generic truck cabin
- 2017
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 171, s. 148-160
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a drag reduction study using active flow control (AFC) on a generic bluff body. The model consists of a simplified truck cabin, characterized by sharp edge separation on top and bottom edges and pressure induced separation on the two other rounded vertical front corners. The pressure induced separation reproduces the flow detachment occurring at the front A-pillar of a real truck (Schuetz, 2015). The prediction of the flow field by partially averaged Navier-Stokes (PANS) simulations, conducted on a relatively coarse mesh, is validated against wind tunnel data (pressure measurements and particle image velocimetry (PIV)) and resolved large eddy simulations (LES) data. The Reynolds number for both simulations and experiments is Re=5×10^5 (which corresponds to 1/6 of a full scale truck Re) based on the inlet velocity Uinf and the width of the model W=0.4m. A validation of PANS results is followed by a CFD study on the actuation frequency that minimizes the aerodynamic drag and suppresses the side recirculation bubbles. PANS accurately predicts the flow field measured in experiments and predicted by a resolved LES. The side recirculation bubble of a simplified truck cabin model is suppressed almost completely and a notable drag reduction by means of AFC is observed.
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| 43. |
- Obara, K., et al.
(författare)
-
Large eddy simulation of a tornado flow around a train
- 2019
-
Ingår i: ERCOFTAC Series. - Cham : Springer International Publishing. - 1382-4309 .- 2215-1826. ; 25, s. 587-593
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- A tornado is a destructive rotating column of air extending from a cloud to the ground. It may kill people and damage property. Also there are possibilities of derailment of trains. Some train-turnover accidents are suspected to have been caused by tornadoes in Japan. For instance, a train of the JR Uestu line was overturned by a gust in 2005. According to the accident analysis, a tornado or downburst probably generated the gust (Aircraft and railway accidents investigation commission: Railway accident analysis report RA2008 -4 (2008), (in Japanese), [1]). In 2006, a train of the JR Nippo line was overturned by a tornado (Aircraft and railway accidents investigation commission: Railway accident analysis report RA2008 -6 (2008), (in Japanese), [2]).
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| 44. |
- Obara, Kohei, et al.
(författare)
-
LARGE EDDY SIMULATION OF A TORNADO FLOW AROUND A TRAIN
- 2017
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A tornado is defined as a destructive rotating column ofair extending from a cloud to the ground. Tornadoes cancause derailment or overturning of trains. At least three train-turnover accidents in Japan are suspected to have beencaused by tornadoes or crosswinds. Some experiments and simulations about effects of a crosswind have been studied [1].However there are almost no studies about the aerodynamic forces acting on a train by a tornado. Therefore, the large eddy simulation (LES) and the experiments were conducted to investigate how a tornado flow acts on a train and the results were compared.
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| 45. |
- Obara, Kohei, et al.
(författare)
-
Numerical simulation of flow around a train passing through a tornado
- 2017
-
Ingår i: International Conference on Fluid Flow, Heat and Mass Transfer. - : Avestia Publishing. - 2369-3029.
-
Konferensbidrag (refereegranskat)abstract
- A tornado is one of the most powerful weather phenomena. It has high wind velocity and often brings serious damages to our lives. It also might has power to overturn trains. Actually at least three train overturn accidents in Japan were probably caused by tornadoes. Although numerous studies have been conducted to clarify the nature of tornado and its effects on civil engineering structures, only a few studies have been examined the effects of the tornado on moving vehicles [1]. Thus we investigated the flow around a train passing through a tornado by a numerical simulation. The compressible Reynolds Averaged Navier-Stokes equations are solved with the k-ξ-f turbulence model [2] using a commercial finite volume solver, AVL FIRE. A boundary condition was defined based on a set-up of our previous experiment [1]. The maximum tangential velocity and the core radius of the tornado were set at 8 m/s and 100 mm, respectively. The swirl ratio was set at 0.8. A 1/40 scale vehicle was set to travel through the tornado at a speed of 4 m/s. The Reynolds number based on the maximum tangential velocity and the train width is 3.8x104. A deforming and sliding mesh method [3] was employed to achieve a scenario that the train runs through the tornado. First, in order to check the numerical accuracy, the velocity and the pressure profiles of the tornado itself were compared with those of the experimental data and the analytical model of the tornado - the Rankin vortex model. The results showed good agreements. And then, time histories of the side and lift forces acting on the train were compared with the experimental data. The computational results agreed well with the experimental results. The side force acting on the train changed its direction from negative to positive while passing through the tornado. Finally, the flow field around the train in the tornado were analysed. The analysis showed that the flow field changed moment by moment depending on the position of the train in the tornado and the resulted air forces acting on the vehicle varied.
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| 46. |
- Obara, Kohei, et al.
(författare)
-
Simulating the flow around a train passing through a tornado
- 2020
-
Ingår i: JOURNAL OF ADVANCED SIMULATION IN SCIENCE AND ENGINEERING. - : Japan Society for Simulation Technology. - 2188-5303. ; 8:1, s. 12-26
-
Tidskriftsartikel (refereegranskat)abstract
- A flow simulation was developed to understand the flow surrounding a train that was passing through a tornado and the resulting aerodynamic forces acting on the vehicle. Unsteady Reynolds averaged Navier-Stokes equations were solved to reproduce a previously-conducted laboratory experiment, in which a model train runs through a stationary tornado-like swirling flow. The simulation reproduced the unsteady aerodynamic forces acting on the train reported in the experiment. Furthermore, the computation successfully revealed how the flow field changes as a train passes through a tornado-like swirling flow.
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| 47. |
- Qiao, Zengxi, 1986, et al.
(författare)
-
Multi-frequency aerodynamic control of a yawed bluff body optimized with a genetic algorithm
- 2021
-
Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 212
-
Tidskriftsartikel (refereegranskat)abstract
- This experimental work aims to investigate the manipulation of a bluff body flow with a yaw angle of 10° based on a genetic algorithm optimization. Two loudspeakers are used to generate zero-net mass-flux jets through streamwise slots, which span a large portion of the rounded A-pillars of the bluff body. The actuations produce a maximum drag reduction of 17% and 2% for the leeward and windward side control, respectively. The genetic algorithm has found two typical frequencies to separately drive the actuators on the windward and leeward sides. The drag reduction is 20% under the optimal control law, 3% larger than the 17% attained from the reference single frequency control. In addition, a beneficial effect is observed when considering energy efficiency, which increases by 30% in the optimal control compared to the single frequency control. The drag spectra and velocity mapping in the wake are measured with and without control, and, based on the measurement, the underlying flow mechanism behind the control is proposed.
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| 48. |
- Qiao, Zengxi, 1986, et al.
(författare)
-
Trailing edge actuation for a bluff body at moderate yaw optimized with a genetic algorithm
- 2023
-
Ingår i: Physics of Fluids. - 1089-7666 .- 1070-6631. ; 35:12
-
Tidskriftsartikel (refereegranskat)abstract
- This experimental work is conducted to manipulate the wake to reduce aerodynamic drag using the actuations on the trailing edges of a bluff body at a yaw angle of 10°. Two loudspeakers are separately installed into the vertical trailing edges of the vertical base, creating a zero-net mass-flux jet through vertical slots. A maximum drag reduction of 2% and 1.5% is produced by the single actuation on the windward and leeward side, respectively. When the genetic algorithm is introduced to optimize the actuations on both sides, a drag reduction of 7% is obtained. Thus, the energy efficiency of the entire control system is greatly improved by 80% compared to the best single actuation. The underlying flow mechanism behind the effective parameters is proposed according to the analyses of the drag spectra and the hot-wire data measured with and without control. The genetic algorithm provides a promising optimization strategy for the better control performance of trailing edge actuation on a yawed bluff body. Furthermore, this strategy may have the engineering potential to reduce the drag of ground transport vehicles for a large range of operating conditions. Therefore, this research is expected to save energy consumption and improve traveling safety for the aerodynamic control of vehicles.
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| 49. |
- Rao, Anirudh Narayan, 1985, et al.
(författare)
-
An LES investigation of the near-wake flow topology of a simplified heavy vehicle
- 2019
-
Ingår i: Flow, Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1573-1987 .- 1386-6184. ; 102:2, s. 389-415
-
Tidskriftsartikel (refereegranskat)abstract
- Recent experimental investigations of McArthur et al (2016) in the wake of a simplified heavy vehicle or commonly known as the ground transportation system (GTS) model has shown that the flow topology is invariant over a large range of Reynolds numbers [2.7 × 104 − 2 × 106]. Numerical simulations are performed to investigate the initial flow topology at a Reynolds number of 2.7× 104, using well-resolved large eddy simulations (LES). In the vertical midplane behind the GTS, a flow state which is anti-symmetric to that reported in McArthur et al (2016) is observed here, thereby, confirming the possibility of occurrence of the complementary bi-stable flow state. The occurrence of this bi-stable state does not depend on the ground clearance between the GTS and the ground plane, as a similar flow topology is observed at both small and large gap heights. Furthermore, the flow topology in the vertical midplane is also found to be insensitive to the incoming flow for small yaw angles. However, complex flow behaviour is observed in the wake for larger yaw angles, where the flow topology in the vertical midplane becomes nearly symmetric, while an asymmetric flow topology is now observed in the lateral midplane in the near wake. Furthermore, the corner vortices which originate from either side at the front of the model merge in the far wake, leading to a large vortex structure nearly equal to the height of the model. The near-wake topology of the GTS is analysed and compared with previous studies for a range of scenarios, and the forces on the GTS are computed.
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| 50. |
- Rao, Anirudh Narayan, 1985, et al.
(författare)
-
BI-STABLE STATES IN THE WAKE OF A 35 ◦ AHMED BODY AT YAW
- 2017
-
Ingår i: Int. Conf. on Jets, Wakes and Separated Flows.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Recent experimental observations by in the wakeof a 35 ◦ back slant Ahmed body reveal the exis-tence of two stable states when the body is yawed[1]. The two flow states, flow state I and flowstate II, are confirmed numerically by using thepartially-averaged Navier–Stokes (PANS) formu-lation on unstructured meshes. Flow state I corre-sponds to a low drag/low lift state with the flowbeing fully separated, while flow state II corre-sponds to a high drag/high lift state, with the flowseparating and reattaching over the back slant.For the Ahmed body at zero yaw angle (β = 0 ◦ ),flow state I is observed. This flow state is observedas the yaw angle is increased up to |β| ≃ 12.5 ◦ .As the yaw angle is increased beyond |β| = 12.5 ◦ ,flow state II is observed. These findings are ingood comparison with the experimental observa-tions of [1].
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