Design of a Novel Photomultiplier Power Supply for Laser Doppler Velocimetry Measurement in Fl ow Boundary Layers

In the context of fluid dynamics studies for aerospace industry, laser Doppler velocimetry (LDV) technique is employed, especially for fluid velocity measurements in the immediate vicinity of aircraft surfaces called boundary layer (BL). One of the major problems in this case is caused by high level light intensity reflected by these surfaces, thus disturbing the behavior of photomultipliers (PM), which are the main sensors used for LDV measurements. In this paper, we describe a new PM power supply for LDV in flow boundary layers, specially designed to, firstly, suppress the large DC light intensity caused by reflections and, secondly, to amplify the AC LDV signal. A theoretical model is also proposed to assess the bias and variances of Doppler frequency estimations. This model takes into account the corpuscular nature of light to represent the large level additive shot-noise caused by wall reflections. Furthermore, an experimental setup has been built to validate our theoretical model. Experimental results are given and show that the proposed system makes great improvements, in comparison with classical power supply, in terms of rate of velocity measurements and standard deviation of Doppler frequency estimations