SHROUD TECHNIQUE USING THE TRANSIENT METHOD FOR LOCAL HEAT TRANSFER MEASUREMENTS

Abstract

A new technique for measuring local heat transfer coefficients on complex-shaped models is described. This technique is referred to as the shroud technique and is a variation on the well-known transient method. The technique involves preheating a model inside a shroud while it is installed in a wind tunnel. The shroud is then ejected, exposing the model to ambient temperature air. The transient temperature on the surface of the model is measured using liquid crystals and recorded with a video system. Although an infinite variety of model shapes can be used, measurements on a cylinder in cross-flow are used to demonstrate this technique. The measurements are compared with earlier measurements, which used different techniques. Good agreement is found at the stagnation point and in the front laminar boundary-layer region. In the separation region, the heat transfer rate is dependent an the thermal boundary condition, which in the transient method is affected by the selection of the nondimensional liquid crystal temperature. In the wake region, it was found that the results depend on the flow development time relative to the transient measurement time.