A Sub-Miniature Laser-Doppler Velocimeter for High Speed Flow Measurements

A new laser-Doppler velocimeter (LDV) for high speed flow measurements (three-dimensional flows with speeds greater than 610 m/s) is being developed based in-part upon an existing low speed instrument capable of high resolution, near surface velocity vector measurements. The key technology for the instrument is a sub-miniature laser-Doppler velocimeter (SMLDV); a similar low-speed version of which has been used effectively in past work to obtain novel measurements from within a small model in a low speed wind tunnel (Byun and Simpson 2006). The instrument is based upon the LDV technique but with enhancements that allow ultra-miniaturization, operation through curved access windows, remote operation, robust performance even with low signal-to-noise ratios as may be encountered in some high speed flows, and particle acceleration measurements. To this end, the SMLDV is an extended LDV concept that may be deployed inside models with nearly arbitrary surface curvature to obtain high resolution three-component velocity and acceleration statistics profiles throughout the boundary layer of the model. The current paper is divided into two parts. In the first part, the robust design and operating capabilities of the SMLDV for inmodel measurements at high speeds are discussed. In the second part, an important potential application for the SMLDV utilizing the capability to measure turbulent flow accelerations is highlighted including aspects of signal processing and application-oriented descriptions of acceleration-related flow physics.