Choice of Particles and Particle Generation

Abstract

The laser Doppler technique relies on the presence of particles in the flow, which not only follow all flow velocity fluctuations but are also sufficient in number to provide the desired temporal resolution of the measured flow velocity (section 7.1). Of course it is desirable that these tracer particles are at the same time good light scattering centers, since this improves the signal quality for a given incident laser power. The scattering characteristics of particles will not be addressed in this chapter, but is discussed in detail in chapter 4. In any case, the fact that flow tracking demands small particles and light scattering improves with increasing particle size already suggests the necessity for a compromise or possibly an optimization for given flow characteristics.