On the speed of progressive waves in gust-tunnels of the QMC-type

Abstract

SummaryIn the Queen Mary College gust-tunnels, unsteady flows are generated by oscillating flaps attached to the downstream upper and lower surfaces of the contraction nozzle of a semi-open test section, open-return, low-speed wind-tunnel. The flow perturbations produced on the mainstream of velocityU∞, are of the travelling-wave type, with wave-velocityQ. Attention is drawn to the contradictory early measurements ofQ/U∞. New data are presented which showQ/U∞apparently diminishing along the tunnel axis from a high value near the nozzle exit to an asymptotic value of about 0·6 far downstream. Using a digital phase meter especially developed for the purpose it is shown that the explanation for this behaviour lies in the two-dimensional nature of the wave process in the region of the flaps.

Localized drag modification in a laminar boundary layer subject to free-stream travelling waves via critical and Stokes layer interactions

“…But because the mean velocity profile was assumed fixed, this numerical approach was not able to resolve the streaming behaviour or the effect of the perturbations on the mean skin friction. Moreover, the experimental characterization of the disturbances used in Patel (1975) was subsequently re-examined by Ishaq & Bernstein (1987), who noted technical issues with the accuracy of the reported phase speeds, making exact theoretical comparisons difficult. Choi et al (1996) used both boundary layer and full Navier-Stokes numerical solutions, and also reported difficulty matching the experiments of Patel (1975).…”