A large-scale matched index of refraction flow facility for LDA studies around complex geometries

Useage of laser-Doppler anemometry (LDA) requires optical access to the flow field of interest. This has not always proved easy, as in the case of complex geometries or very near-wall boundary layer measurements. One solution is to employ a solid material and fluid with the same refractive index. In this case, there is no optical interference of the solid with the LDA. Although this technique is not new, previous studies have been limited to small flow apparatus and relatively unpleasant fluids. A large-scale flow tunnel has now been constructed, permitting matched index of refraction LDA measurements in difficult geometries, higher Reynolds numbers, and increased spatial resolution in the measurements. This paper describes the facility and fluid flow quality, and presents some preliminary results for very near-wall measurements of a transitional boundary layer behind a roughness element. Received: 13 March 2000/Accepted: 30 July 2000