Some experiments with sonic throats downstream from the working-section of a slotted-wall high-speed tunnel

Abstract

Tests have been made in the National Physical Laboratory 9-in. × 3-in. High-Speed Tunnel to investigate the use of sonic throats downstream from the working-section of a slotted-wall high-speed tunnel employing diffuser suction. It was found that such throats behaved at subsonic speeds in a manner similar to their behaviour in a solid-wall tunnel. The Mach number in the working-section was approximately that to be expected from the ratio of the area between walls, at the beginning of the slots, to the area at the throat. Tests were made with various configurations, including the conditions which could be expected on the 18-in. × 14-in. and 36-in. × 14-in. High-Speed Tunnels at the N.P.L. It was found that the throat mechanisms at present used with the subsonic liners on these tunnels should work satisfactorily, and that the power required should be of the same order as that required to run the unchoked slotted walls at unit Mach number. Information has also been obtained on the beneficial effects to be obtained from (a) an improvement in the pressure recovery downstream from the parallel slotted length of the working-section and (b) a reduction in the slope of the upstream face of the sonic throat.