Methods to control low frequency pulsation in open-jet wind tunnel

Low frequency pulsation affects both aerodynamic and acoustic measurements in an open jet wind tunnel. Avoiding it and establishing a good experiment environment are primary concerns for the wind tunnels. The characteristics of the low frequency pulsation and a combination control method of changing angles of the collector flaps and opening a hole in the test section chamber above nozzle were researched in a 1:15 model wind tunnel. On the basis of the method, two new control methods that are based on a Helmholtz resonator and addition pipes connected with airline of wind tunnel were put forward and validation tests were done. The results show that although the method can reduce the magnitude of the pulsation, the control effect is not the acme of perfection. The new methods effectively reduce the pulsation in different wind speeds and frequency ranges, and they can make the pulsation to keep a stable level in whole wind speeds, which is beneficial to the application of a full scale wind tunnel.