Research on asymmetric field flow in the subsonic second throat

China will consider the construction of large transonic wind tunnels and develop fi-ner wind tunnel test simulation techniques to meet the needs of future advanced aircraft develop-ment.As an effective means to control the Mach number,the second throat is considered to be one of the key technologies to enhance the ability of transonic wind tunnel.In this paper,we i-dentify the asymmetric field flow in the second throat by the CFD simulation.Then we design and manufacture a new second throat section with variable center subject for the model wind tun-nel.The wind tunnel test results show that the asymmetriy field flow occurs in the second throat when the total pressure reaches a certain value,which can be forward transmitted to affect the quality of the test section flow.Finally,we design a new kind of second throat which would not generate the asymmetric field flow by the CFD method.