The Research Of Ground Effect In Automotive Wind Tunnel Based On Numerical Simulation

The ground boundary layer in automotive wind tunnel may change the experimental results, the over thick boundary layer may reduce the value of Cd and increase the value of Cl. In this paper, numerical simulation was used to study the boundary layer and ground effect in JiLin University's automotive wind tunnel. Compared with the result of real experiments, the characteristic of the ground effect simulated system was concluded, the air flow distribution in the test section and the experimental result influenced by the ground effect simulated system were also studied. In the paper the author also discussed something about the method how to simulate the exterior air flow with the experience in the real work.The air flow distribution under the auto body and the pressure control of moving belt were talked at the same time.Pay attention to the velocity gradient, boundary layer thickness, static pressure distribution and the angle of air flow, the base characteristic in JiLin university automotive wind tunnel was first studied. The result shown that it has a high quality of air flowing, but a over thick boundary layer existed near the test section floor. Because of that, some useful equipment should be taken to control the boundary layer thickness. Therefore the ground effect simulated system need to use.The situation of single moving belt working was studied. The characteristic of the test section air flow distribution in this ground effect simulated style was concluded. The working method of moving belt and its influence to the experiment result was summarized. As the result shown, the moving belt can reduce the thickness of boundary layer powerful. It can reduce the velocity gradient and change the air flow to a better flowing way. The use of moving belt may raise the value of Cd as a result of air flow distribution optimized. The moving belt working aero was a very lower position over the test section floor, the use of moving belt may caused the test section static pressure changed, but the tendency is very weak.The situation of single front suction working was studied. The characteristic of the test section air flow distribution in this ground effect simulated style was concluded. The working method of front suction and its influence to the experiment result was summarized. The result shown that the front suction may reduce the thickness of boundary layer. But it worked less useful than the moving belt. However, compared with the moving belt, the front suction can optimize a lager aero near the test section where the vehicle put. The unfavorable factor is the suction pressure can change the air distribution near the front of the test section, add the pressure gradient. If the suction pressure was too large, the pressure gradient will change the pressure of the vehicle. This could influence the pressure distribution in the auto body, increase the value of Cd.The situation of both using the moving belt and front suction working was also studied. The characteristic of the test section air flow distribution in this ground effect simulated style was concluded. The working method and its influence to the experiment result were summarized. This situation had the best boundary layer control effect. The velocity gradient was reduced; a higher quality of the air flow distribution in the test section was got.The ground effect simulated system can reduce the influence of boundary layer, raise the quality of air flow, a more virtual result could be got with it.