ID 372

Key aspects in the implementation of digital processors’ algorithms used in Laser Doppler Velocity and Phase Doppler Anemometry

 

Abstract:

Laser Doppler velocimetry (LDV or LDA) as well as Phase Doppler Anemometry (PDA or PDPA or PDI) are well-proven techniques that can measure fluid velocity (LDV) as well as both velocity and size (PDPA) accurately and non-invasively. Measurements are made at a point (a small, non-intrusive optical probe volume) defined by the intersection of two laser beams. As a particles pass through the probe volume, they scatter light from the beams into either a single detector (LDV) or into a multi-detector receiving probe (PDPA), strategically located at an off-axis collection angle. The frequency of the resulting Doppler Burst Signal is directly proportional to the particle velocity, while the phase shift between the between the Doppler burst signals from different detectors is proportional to the size of the spherical particles. Digital signal processing techniques are used via high-end electronics to extract accurate flow and size information in both complex and challenging fluid mechanics’ flows. Some of the key aspects that are important to the performance of signal processors will be presented and further discussed. Limitations of the theoretical approaches in evaluating the processing techniques are also outlined. Simulations have been carried out to examine the influence of some of the parameters not covered by the analytical approaches. The robustness of the auto-correlation technique with quadrature mixing is demonstrated through simulations. The advantage of adapting a processing technique that is well suited to the nature of the signal, as well as the importance of pre-processing or conditioning the input to be properly positioned for the algorithm are pointed out. Finally the benefits of the auto-correlation technique are proven through experimental measurements.