Flow Stabilization in a Transonic Wind Tunnel with a Second Throat

Abstract

A second throat has been used to stabilize the ow in the test section of an induction-driven transonic wind tunnel. Different second throat con gurations were attempted by employing simple wall-xed aps and a centerline-xed strut, and their ef ciency based on the duration of stable test section ow was examined. Generally, a longer duration of stable ow could be achieved when the tunnel was operated with a second throat than without one. Moreover, a longer run time was achieved with the wall-xed aps than with the center strut. The performance of the center strut was so poor that it raised concerns about the installation of the sting support, which is usually installed in the same manner as the center strut. It was also found that when the aps were installed vertically on the sidewalls the low-momentum reentry ow from the plenum chamber reduced the effectiveness of the aps in choking the ow. The performance was greatly improved by repositioning the aps horizontally and directly behind the reentry region. However, there was an upper limit to the effectiveness of the aps in choking the ow. Beyond a certain injector total pressure the effective cross-sectional area of the diffuser at the injector's location was reduced by the jet, turning it into the effective throat area. The cross-sectional area at the second throat is rendered ineffective, causing the Mach number in the test section to temporarily drop.

A numerical optimization of high altitude testing facility for wind tunnel experiments

“…Its main objective is to choke the flow at a location downstream of the test section to effectively freeze the flow in the test section. 15 After each run the vacuum tank is evacuated by vacuum pumps and the air is compressed, dried, and sent into the high pressure system. If the weight flow available is much larger than the weight flow required for the high Mach number test, then an air ejector is used in place of a vacuum tank.…”