Effect of geometry parameters on flow field quality in a transonic slotted wind tunnel

Numerical simulation method is applied to studying the effect of the re-entry flap angle, slot diverging angle and slot shape on the flow field quality in a transonic slotted wind tunnel. Boundary conditions at the inlet and outlet of the tunnel are introduced, and also, similarity parameters are obtained through dimensional analysis. The results show that a sonic throat will be formed at the leading edge if the re-entry flap is closed, leading to the inability to establish stable supersonic flow at the test section. When the re-entry flap is open, the slot outflow which comes from the plenum is the main disturbance source of the flow field and could be wakened with a larger slot diverging angle. All the components affect the flow field quality by strengthening or wakening the slot outflow while the slot shape is the most sensitive. An optimization approach based on free form deformation (FFD) method is adopted and therefore a slot shape which is applicable to cases from 0.8 to 1.2 Mach number in test section is obtained. Results of the optimization show that most of the slot outflow which occurs in the original configuration has been eliminated and the mean square error of Mach number distribution at the test section is reduced by an order of magnitude, proving that the optimization approach is reasonable and practicable.