Measurements in liquid flows: Refractive index matching

Various measurements in fluid flows are given and laser Doppler velocimeter measurements are discussed. The necessity of refractive index matching in special cases is discussed. Two related questions are addressed: In which cases is the beam separation spatially independent, and what can be measured without refractive index matching? What methods exist to eliminate the refractive index influence and which fluids can be used are other questions that are discussed. Measurements with matched refractive indices are presented in bubble flows, stirred tanks, nuclear reactor fuel bundles, solid-liquid two phase flows, and pipe flows with high molecular polymers.