Visualizing supersonic inlet duct unstart using planar laser Rayleigh scattering

• Published in: Experiments in fluids 2011-06, Vol.50 (6), p.1651-1657
• Main Authors: Do, Hyungrok, Im, Seong-kyun, Mungal, M. Godfrey, Cappelli, Mark A.
• Format: Article
• Language: English
• Subjects: Boundary layer; Compressible flows; shock and detonation phenomena; Downstream effects; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Exact sciences and technology; Fluid dynamics; Fluid- and Aerodynamics; Fundamental areas of phenomenology (including applications); Heat and Mass Transfer; Instrumentation for fluid dynamics; Lasers; Physics; Rayleigh scattering; Research Article; Separation; Shock-wave interactions and shock effects; Turbulent boundary layer; Upstream; Wind tunnels
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-010-1028-4

Planar laser Rayleigh scattering (PLRS) from condensed CO 2 particles is used to visualize flow structure in a Mach 5 wind tunnel undergoing unstart. Detailed flow features such as laminar/turbulent boundary layers and shockwaves are readily illustrated by the technique. A downstream transverse air jet, inducing flow unchoking downstream of the jet, is injected into the free stream flow of the tunnel, resulting in tunnel unstart. Time sequential PLRS images reveal that the boundary layer growth/separation on a surface with a thick turbulent boundary layer, initiated by the jet injection, propagates upstream and produces an oblique unstart shock. The tunnel unstarts upon the arrival of the shock at the inlet. In contrast, earlier flow separation on the opposite surface, initially supporting a thin laminar boundary layer, is observed when a jet induced bow shock strikes that surface. The resulting disturbance to this boundary layer also propagates upstream and precedes the formation of an unstart shock.