DEVELOPMENT OF SQUARE NOZZLES FOR SUPERSONIC LOW-DISTURBANCE WIND TUNNELS

Two Mach 2.4 nozzles with square test sections have been designed and analyzed, as part of an effort to develop low-disturbance facilities f or laminar-now control for high-speed civil transport, The mean flows have been simulated using a finite volume, central-differencing scheme to solve the thin-layer Navier-Stokes equations, Substantial crossflo w exists in the boundary layers of both nozzles. The crossflow changes direction about halfway between the throat and exit, because of a cha nge in the sign of the crossflow pressure gradient, S-shaped crossflow profiles are present in this region, just as on a swept wing, Both th e standard crossflow Reynolds number and the new Reed and Haynes trans ition estimator predict transition to occur in the throat as well as n ear the exit. An analysis of the crossflow pressure gradients in the t ransonic throat region indicates that streamwise curvature has only a weak effect on the crossflow pressure gradient. Further research on cr ossflow-induced transition will have to be carried out before these no zzles will be suitable for low Mach number quiet-tunnel designs.