Development of square nozzles for supersonic low-disturbance wind tunnels

Abstract

Two Mach 2.4 nozzles with square test sections have been designed and analyzed, as part of an effort to develop low-disturbance facilities for laminar-flow control for high-speed civil transport. The mean flows have been simulated using a finite volume, central-differencing scheme to solve the thin-layer NavierStokes equations. Substantial crossflow exists in the boundary layers of both nozzles. The crossflow changes direction about halfway between the throat and exit, because of a change in the sign of the crossflow pressure gradient. S-shaped crossflow profiles are present in this region, just as on a swept wing. Both the standard crossflow Reynolds number and the new Reed and Haynes transition estimator predict transition to occur in the throat as well as near the exit. An analysis of the crossflow pressure gradients in the transonic throat region indicates that streamwise curvature has only a weak effect on the crossflow pressure gradient. Further research on crossflow-induced transition will have to be carried out before these nozzles will be suitable for low Mach number quiet-tunnel designs.