| 1. |
- Rao, Anirudh Narayan, 1985, et al.
(författare)
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Influence of the numerical schemes on the flow states of a simplified heavy vehicle
- 2018
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Ingår i: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816. ; 2018-July, s. 731-734
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Konferensbidrag (refereegranskat)abstract
- Recent experiments [1, 2] in the wake of a simplified heavy vehicle (also know as a ground transportation system (GTS)) have shown that the flow topology remains invariant over a large range of Reynolds numbers [3.8 × 10 4 − 2.8 × 10 6 ]. This allows numerical techniques such as large eddy simulations (LES) to accurately predict the flow topology at low Reynolds numbers. While LES requires grids of higher spatial resolution; hybrid RANS/LES turbulence models are an alternate choice, where, accurate prediction of the flow is possible on coarser grids ([3, 4]). Numerical simulations are performed using LES and a hybrid turbulence model - partially-averaged Navier–Stokes (PANS) equations at Re H = 3.8 × 10 4 for a unified tractor-trailer geometry to compare the flow topologies in the near wake. The influence of the numerical schemes on the flow topology in the symmetry plane which is susceptible to bi-stable flow is investigated using PANS, and compared with the results from LES.
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| 2. |
- Xu, Kewei, 1992, et al.
(författare)
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Drag reduction of ship airflow using steady Coanda effect
- 2022
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 266
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Tidskriftsartikel (refereegranskat)abstract
- This paper studies the steady Coanda effect for reducing the aerodynamic drag of the Chalmers ship model (CSM) using Large Eddy Simulation (LES) with Wall-Adapting Local-Eddy Viscosity (WALE) model. The flow control mechanism is explored, and the analysis of energy efficiency is conducted to evaluate the net benefit of the flow control. Validating the numerical methods, the predicted aerodynamic drag of the ship and pressure coefficients distribution on the baseline CSM agree well with the experimental measurements and the maximum discrepancy is 4.2%. In creating the flow control models, the hanger base of the baseline CSM is modified with a Coanda surface and two different sizes of jet-blowing slots, 1%h (hanger height) and 2%h, respectively. A drag reduction of 5.34% is achieved by the 1%h slot-size case. The 2%h slot-size case further increases the drag reduction to 6.22% but has doubled power consumption. It is found that vectoring vorticity towards the low-speed area on deck is effective for enhancing the energization. Finally, the analysis of energy efficiency indicates that the net benefit is achieved in both flow control cases, and the case with the 1%h slot size is 11.9% more efficient due to a stronger Coanda effect.
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| 3. |
- Adamu, Abdulmalik, et al.
(författare)
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An investigation of superstructure length on bi-stable ship wake flow
- 2024
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Ingår i: Ocean Engineering. - 0029-8018. ; 312
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Tidskriftsartikel (refereegranskat)abstract
- The variation in the geometry of a ship model has the potential to eliminate the flow asymmetry in ship wake and improve its aerodynamic performance. This study investigates the impact of the length of superstructure on the wake flow bi-stability of the ship model using IDDES at Re = 8 × 104. Also, this article studied the effect of ship's funnel structure using two models, with and without funnel, on the wake flow asymmetry, providing smooth transition into the study of the length of superstructure. The result indicates that when the funnel is removed, the length of flow reattachment after separation at the hanger increases for the top step and decreases for the second step for the case with no funnel. The asymmetric flow at wake persists, however, the configuration is different, showing difference in flow state. When the length of the superstructure is reduced, the turbulence at the wake increases, the size of recirculation bubble at the flight deck and behind the stern reduces and the overall pressure area decreases significantly. Behind the stern, all three cases indicate an asymmetrical flow, however, compared to Case 1, the asymmetry at the flight deck in Case 2 is weak, while a symmetrical flow is achieved with Case 3. Consequently, this research proposes a novel approach to improving wake flow and ensure safe aircraft take-off and landing operations on the ship deck.
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| 4. |
- Zhang, Jie, et al.
(författare)
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Assessment of URANS, SAS, and IDDES on the bi-stable wake flow of a generic ship
- 2023
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Ingår i: Ocean Engineering. - 0029-8018. ; 286
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Tidskriftsartikel (refereegranskat)abstract
- The present study aims to assess the prediction ability of URANS (unsteady Reynolds-averaged Navier-Stokes), SAS (scale-adaptive simulation), and IDDES (improved delayed detached-eddy simulation) on the naturally asymmetric flow of a generic ship model. The inlet velocity gives a Reynolds number of 8 × 104 based on the ship width. Experimental results are used as the baseline to judge the accuracy of these modelling techniques. The findings indicate that all techniques can predict the flow asymmetry of the ship wake, although URANS is less accurate due to its inability to resolve small-scale flow structures. Furthermore, IDDES is found to be more accurate than SAS considering the extent of wake asymmetry. Therefore, IDDES is recommended when higher accuracy is needed despite its higher computational demand.
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| 5. |
- 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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| 6. |
- Rao, Anirudh Narayan, 1985, et al.
(författare)
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An LES investigation of the near-wake flow topology of a simplified heavy vehicle
- 2019
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Ingår i: Flow, Turbulence and Combustion. - : Springer Science and Business Media LLC. - 1573-1987 .- 1386-6184. ; 102:2, s. 389-415
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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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| 7. |
- Minelli, Guglielmo, 1988, et al.
(författare)
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A LES Study on the Effect of Periodic Gusts on a Truck Model
- 2017
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Ingår i: Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2017.
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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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| 8. |
- Minelli, Guglielmo, 1988, et al.
(författare)
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Validation of PANS and active flow control for a generic truck cabin
- 2017
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 171, s. 148-160
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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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| 9. |
- Östh, Jan, 1985, et al.
(författare)
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A study of the aerodynamics of a generic container freight wagon using Large-Eddy Simulation
- 2014
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Ingår i: Journal of Fluids and Structures. - : Elsevier BV. - 1095-8622 .- 0889-9746. ; 44, s. 31-51
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Tidskriftsartikel (refereegranskat)abstract
- In this work simulations using the Large Eddy Simulation technique have been made of the flow around a generic container freight wagon model. The model consists of one 11.8 m standard length container placed on a wagon. Details of the undercarriage such as wheels are included, but the container is generic and smoothed in comparison to a real freight wagon. The Reynolds number of the flow is 105 based on the container width of 2.354 m. Two cases have been considered in the study, one case where the wagon is standing alone and one case where it is submerged into a train set with wagons ahead and behind the wagon. The latter case is simulated using periodic boundary condition. Both the time-averaged and the instantaneous flow around the wagon for the two cases are described. For the single wagon case, it is found that the separation bubble formed on the roof of the container oscillates back and forth in the streamwise direction and that this oscillation is in phase with oscillations found in the upper shear layer of the ring vortex in the wake. The mechanism that is causing the synchronization of the oscillations of the separation bubble at the front and the upper shear layers in the wake is found to be waves of vorticity being shed from the separation bubble. The time-averaged ring vortex in the near wake of the single wagon is found to be inclined due to the disturbance of the undercarriage details on flow in the lower shear layer. The lower center of the ring vortex is located closer to the base face than the upper center. The drag coefficient of the wagon in the periodic case was found to be only 10% of that of the single wagon case. This is due to two symmetrical counter-rotating vortices found in the gaps which make the train set appear as a single body to the oncoming flow and shielding the wagon from any direct impingement of the flow. The counter-rotating vortices in the gap are found to inhibit periodic oscillations in the lateral direction. These oscillations cause vortical structures to form by the air that is pushed out from the gap and these flow structures cause a dominating oscillation of non-dimensional frequency St=0.12 in the side force signal.
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| 10. |
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