Non - contact boundary layer profiler using low - coherence self - referencing

A spatially self–referencing velocimetry system based on low–coherence interferometry has been developed. The measurement technique is contactless and relies on the interference between back–reflected light from an arbitrary reference surface and seeding particles in the flow. The measurement location and the flow velocity are measured relative to the reference surface’s location and velocity, respectively. Scanning of the measurement location along the beam direction does not require mechanical movement of the sensor head. The reference surface (which can move or vibrate relative to the sensor head) can be either an external object or the surface of a body over which measurements are to be performed. The absolute spatial accuracy and the spatial resolution only depend on the coherence length of the light source (tens of microns for a superluminescent diode). The prototype is an all–fiber assembly. An optical fiber of arbitrary length connects the self–contained optical and electronics setup to the sensor head. Proof–of– principle measurements in water (Taylor–Couette flow) and in air (Blasius boundary layer) are reported in this paper.