Measurement of acceleration using the laser Doppler technique

Abstract

Acceleration can be measured using a laser Doppler system by estimating the change of signal frequency with time. This acceleration corresponds directly to the material derivative of flow velocity, and is an important quantity in the formulation of Lagrangian stochastic models for simulating turbulent flows in which transport is of primary interest. A non-parametric (FFT based) and a direct parametric estimator are introduced for estimating the acceleration parameter from Doppler signals. The estimators' performance is evaluated by examining their bias and comparing their variance to the Cramér-Rao lower bound. The non-parametric estimator with a window function proves to be accurate, robust and computationally fast. Validation experiments are performed in a laminar stagnation flow and measurements in a turbulent jet are used to demonstrate the application of the new estimators. The numerical values of the measured acceleration are high, but agree well with expectations.