Zhi Gang Yang

The Influence of Rotating Wheels on Vehicle Aerodynamics

Full scaled simplified model and production vehicle were applied to make a research on the local and global flow characteristics. Two different conditions including stationary and rotation were employed in computational simulation by steady RNS Navier-Stokes calculation. Further, detailed analysis on flow, surface pressure coefficient, drag coefficient and lift coefficient affected by rotating wheel figure out that rotating wheel has a significant influence on the flow around wheel and vehicle. Pressure difference, drag coefficient and lift coefficient are decreased by rotation, which improve aerodynamic performance.

Comparison of different ground simulation systems on the flow around a high-speed train

The influence of different ground simulation systems on the air flow around a high-speed train with zero yaw angle is investigated. Force values, force development graphs, surface pressures, the underbody flow and the wake are studied in detail with Computational Fluid Dynamics, which is initially validated by wind tunnel testing. It shows that the stationary ground has severe deviations from the full moving ground on the aerodynamic performance due to the inaccurate pressure distribution on the underbody. This is mainly attributed to the high level of interaction between the underbody and the boundary layer development. In addition, a ground boundary layer separation bubble can be observed under the tail end of the train for the stationary ground on account of insufficient energy to overcome the increasing adverse pressure gradient. In order to guarantee a correct underbody flow, a partially moving ground is proposed, including the “3-moving ground” and the “1-moving ground”. Such ground simulation systems are well compatible with the fixed rail tracks and the bottom support struts compared to the full moving ground. As a conceivable method to reduce the influence of the boundary layer, raising the high-speed train model with different ground clearances is also studied. Overall, the 3-moving ground is suggested to be the best choice for the ground simulation systems in high speed train wind tunnel testing.

Application of Response Surface Model on Aerodynamic Characteristic of Airfoil

To reduce the computational resources, experimental design and response surface method (RSM) were employed to investigate the aerodynamic drag coefficient (CD) and lift coefficient (CL) of airfoils by using CFD methods. The selection of sample points, development and validation of response surface model and the effects of different sample points on approximation model were discussed. The results indicates that the number and distribution of sample points have a significant impact on model accuracy and optimize results. Also this method can greatly reduce calculation amount.

Design for Wind Tunnel Testing of Scaled Model by CFD Method

The numerical investigations presented in this paper deal with wind tunnel testing scheme design for 1/4 scaled MIRA model including supporting system. Based on the structure of aerodynamic and aero-acoustic full scale wind tunnel, using computational fluid dynamics (CFD), focus on MIRA model and supporting system, the drag force of scaled models and supporting system were calculated. By comparing with the wind tunnel testing results and drag force coefficient of reference, it is certain that the wind tunnel testing scheme is available and effective and that the value calculated by CFD is in good agreement with experiments.

Numerical Simulation of Unsteady Flow around Ahmed Body with Active Flow Control

The numerical investigations presented in this paper deal with active flow control approach at the rear end of the Ahmed body model with the slant angle of 25°.Results of the velocity, pressure and vorticity field demonstrate the main reasons that cause the pressure drag. The influence of the spanwise and streamwise vortices rolling up from the slant and the edges on the recirculation zone behind the body is examined. A control slot is set on the separated line at the conjunction of the roof and the slant. Two different actuation concepts by blowing and suction steady jets through the slot lead to a drug increase of 5.61% and a drug reduction of 13.20% with the efficiency of 12.53% respectively.

CFD Research and Investigation of 2011 P4/5 Competition Rear Wing

In order to analyze the influence of the rear wing of a competition race car on the aerodynamics of the whole vehicle, computational fluid dynamics simulations have been performed. Rear wing is set by two elements, a main plate and a flap. Their relative position and the angle of attack of these elements influence the aero- performances in terms of downforce and drag generated; 12 different configurations have been generated, modifying the angle of attack and the slot gap. 3D mesh has been generated from the geometrical model of the vehicle, and air flow around the vehicle and on the rear wing has been evaluated through a CFD commercial software. It has been proved that steeper angles of attack of the mainplate and of the flap contribute to generate more downforce until a certain point; when angle of attack reaches a critical value, the downforce no longer increases and the drag still keep high values.

Comparative Study on Aerodynamic Noise of Dimensionally Similar Locomotive Models of High Speed Trains

This study is focused on the locomotive of high speed train. First, wind tunnel test is used to verify the credibility of numerical results. Then, in order to compare the difference of aerodynamic noise generated by different size locomotive, dimensionally similar models of 1/8th, 1/12th and 1/15th scale are studied by using numerical simulation, including stationary aerodynamic characteristics, fluctuation characteristics of unsteady flow, noise source distribution on surface and far-field noise spectral characteristics. Based on the result of pressure fluctuation, it is noted that the difference between 1/15th and 1/8th scale model is larger in individual parts, including the separation zone in the roof and the edge of window. In addition, according to the far-field noise calculation, the result of 1/12th scale model is better than 1/15th scale model. From the results mentioned above, 1/15th or much smaller scale model should not be used in wind tunnel test as possible.

Analysis of Structure Dynamic Characteristics of a Metal Plate

Modal analysis is a modern method to study structure dynamic characteristics. In this paper, computational modal analysis with Finite Element Method is applied to simulate an aluminum plate with the dimension of 160mm*240mm*1.5mm under different boundary conditions (Including free boundary condition and fixed boundary condition). The results of structure natural frequencies and mode shapes of this plate show obvious difference between the two boundary conditions.

Analysis of Rear Window Buffeting Characteristics Using a Production Sedan

In this paper rear left side window buffeting characteristics of a production sedan under different yaw angles and different window opening sizes are investigated through full-scale aeroacoustic wind tunnel tests. By yaw angle -10 degree, as driver position on the lee side, the resonance peak SPL is much less than that by yaw angle 0 or +10 degree and the corresponding frequency is also some lower than that by yaw angle 0 or +10 degree. As window opening size turns small, the resonance peak SPL decreases. By side window with 25% opening size, the peak SPL is much less than that by side window with 50% or 100% opening size. In addition, the corresponding frequency is also some lower than that by side window with 50% or 100% opening size. Different test positions at the front row or back row show very similar buffeting characteristics.

The Effects of Different Support Forms on the Aerodynamic Characteristics of the High-Speed Train Model

By the method of computational fluid dynamics (CFD), this paper calculates the aerodynamic parameters of one complex high-speed train model which adopts different support forms when the reference velocity is 70m/s under different operating conditions. It also analyses the support interference mechanism from the point of flow field structure. The results show that the distributed cylinder support form causes least interference on the model, while the single big cylinder support forms change the flow field structures much which leads to much change of the aerodynamic parameters of the model. The distributed cylinder support form can be applied as a good support form for the high-speed train wind tunnel tests.