| 1. |
- Hemida, Hassan, 1972, et al.
(författare)
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LES study of the influence of the vortex generators on cooling of surface-mounted cubes
- 2007
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Ingår i: 1st International Conference on Thermal Issues in Emerging Technologies, Theory and Applications, Proceedings - ThETA1, Cairo, Egypt, 3-6 January 2007. - 1424408970 ; , s. 55-62
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Konferensbidrag (refereegranskat)abstract
- The influence of vortex generators on the enhancement of heat transfer from a wall-mounted cube matrix was investigated by numerical simulation using finite-volume method. The momentum and convective heat transfer equations were discretized and solved using large-eddy simulation. The numerical simulation was performed on a fully developed turbulent flow over one cube mounted in the middle of a cube matrix. Constant heat flux was generated from the cubes. Periodic boundary conditions were applied in both the streamwise and the spanwise directions. In order to study the influence of vortex generator on the flow structures and heat transfer coefficient, the flow and the convective heat transfer equations were solved around two cube configurations: a smooth cube and a cube with vortex generator attached to its surface. The vortex generator used in this investigation is a simple rib attached to the top and the side walls of the cube close to the streamwise edge. The flow Reynolds number based on the bulk velocity and the height of the channel was 13000. Standard Smagorinsky subgrid-scale model was used to model the unresolved scales and heat fluxes. The LES results were compared with the experimental results and good agreement was obtained. Numerical flow visualization was used to provide a better insight into the flow structures and heat transfer coefficient around the cubes. The LES results showed that the flow in the boundary layer around the cube with vortex generator is more turbulent and unsteady than the flow around the smooth cube without the vortex generator. More turbulent structures are generated close to the surface of the cube resulting in a good mixing of heat and hence high heat transfer coefficient
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| 2. |
- Qiao, Zengxi, 1986, et al.
(författare)
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Trailing edge actuation for a bluff body at moderate yaw optimized with a genetic algorithm
- 2023
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Ingår i: Physics of Fluids. - 1089-7666 .- 1070-6631. ; 35:12
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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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| 3. |
- 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. ; , 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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| 4. |
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| 5. |
- 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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| 6. |
- Qiao, Zengxi, 1986, et al.
(författare)
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Multi-frequency aerodynamic control of a yawed bluff body optimized with a genetic algorithm
- 2021
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 212
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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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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- Han, Xingsi, 1981, et al.
(författare)
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Very Large Eddy Simulation of Passive Drag Control for a D-Shaped Cylinder
- 2013
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Ingår i: Journal of Fluids Engineering, Transactions of the ASME. - : ASME International. - 1528-901X .- 0098-2202. ; 135:10
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Tidskriftsartikel (refereegranskat)abstract
- The numerical study reported here deals with the passive flow control around a two-dimensional D-shaped bluff body at a Reynolds number of Re=3.6×104. A small circular control cylinder located in the near wake behind the main bluff body is employed as a local disturbance of the shear layer and the wake. 3D simulations are carried out using a newly developed very large eddy simulation (VLES) method, based on the standard k − ε turbulence model. The aim of this study is to validate the performance of this method for the complex flow control problem. Numerical results are compared with available experimental data, including global flow parameters and velocity profiles. Good agreements are observed. Numerical results suggest that the bubble recirculation length is increased by about 36% by the local disturbance of the small cylinder, which compares well to the experimental observations in which the length is increased by about 38%. A drag reduction of about 18% is observed in the VLES simulation, which is quite close to the experimental value of 17.5%. It is found that the VLES method is able to predict the flow control problem quite well.
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