Visualization of the quiet test region in a supersonic wind tunnelusing luminescent paint

摘要

A temperature-sensitive luminescent paint technique has been usedto visualize boundary-layer transition on a 10-degree cone model in the0.2-m Supersonic Wind Tunnel at National Aerospace Laboratory. Aluminescent paint based on EuTTA was applied on the model surface usingairbrush. The paint coating was excited by a Xenon light and theluminescence image was acquired using a high resolution cooled-CCDcamera. To enhance thermal signature across transition, tunnel flow washeated by a sudden shutdown of cooling water supply to heat exchanger.Two images were taken for each condition, one is transient image takenin heating process and the other is reference image taken in steadycondition. By ratioing these two images, global transition patterns onthe cone have been visualized as the edges of brightness. Fromtransition images at various model locations in the test section, it wasfound that transition remains at a fixed spatial location with respectto the tunnel. This indicates that the cone transition is induced byradiated noise propagating from turbulent boundary layers on the tunnelwalls. Effects of the stagnation pressure were also studied over therange from 55 to 150 kPa. The extent of quiet test region was found tobe strongly sensitive to the pressure or unit Reynolds number. At theNAL 0.2-m SWT, natural transition did not occur on the cone at lowervalues of unit Reynolds number