PHASE VALIDATION CRITERIA OF SIZE MEASUREMENTS FOR THE PHASE DOPPLER TECHNIQUE

A validation procedure of the size measurements for the phase Doppler anemometer is proposed for a two and three photodetector system and is shown experimentally to reduce erroneous measurements due to unwanted Doppler signals caused by surface reflection rather than refraction t hrough the particles. This problem known as 'trajectory ambiguity' is caused by the Gaussian distribution of the incident laser beams when t he particle diameter is similar to the diameter of the probe volume of the anemometer. The three photodetector system is shown to improve fu rther the sizing accuracy of a two photodetector system by rejecting m easurements from signals with phase ratio values lying outside the exp ected value for spherical scatterers and which would otherwise have be en validated by the two photodetector system.