Laser anemometry based on collective scattering: the effects of propagating and nonpropagating fluctuations

Abstract

Laser anemometry, as it is commonly applied, requires particles. However, in certain types of high-speed flows and plasma flows no particles are present. Collective light-scattering may then be applied to measure fluid or plasma velocity. A new hybrid scheme has been proposed; the scheme allows for better axial resolution than that which has previously been demonstrated. The effects of propagating and nonpropagating fluctuations on the expected cross-correlation functions are investigated. The correlation function will, in general, be asymmetric and will consist of three identifiable peaks: two caused by (counter) propagating fluctuations and one caused by nonpropagating fluctuations. Thermal diffusivity causes the maximum of the ‘nonpropagating peak’ to be displaced relative to the case of no diffusivity.