Acceleration Measurement Using the Laser Doppler Technique by

many Generally, the laser Doppler and phase Doppler techniques are considered point measurement techniques, because they achieve a high enough spatial resolution that the measured quantities can be considered constant over the transit time of the tracer particle or dispersed particle through the measurement volume. In most applications this is an appropriate assumption and the signal processing must provide only one single value of each velocity component or particle size for each particle. However, in some situations this may not be sufficient. The phase difference in a phase Doppler system can vary when an oscillating droplet passes through the measurement volume. Appropriate signal processing can provide considerable information about droplet shape and oscillation frequency/state by estimating these phase difference variations within one signal. Similarly, a tracer particle or dispersed particle under acceleration results in a change of Doppler signal frequency during passage through the detection volume of a laser Doppler system (figure 1). This information can be interpreted directly as the material derivative of the particle velocity, and is an important quantity in the formulation of Lagrangian stochastic models for simulating turbulent flows in which transport is of primary interest. However, existing signal processors for the laser Doppler technique do not attempt estimates of this frequency variation, despite the fact of that most processors are now fully digitally based and could implement — possibly in firmware — virtually any parameter estimator. Acceleration can be measured using a laser Doppler system by estimating the change of signal frequency with time. Three estimators are introduced for estimating the acceleration parameter from Doppler signals (figure 2). The performance is evaluated by examining the bias and comparing the variance to the Cramér-Rao Lower Bound. Validation experiments are performed in a laminar stagnation flow. −1.5 −