An investigation of the influence of the size distribution of seeding particles on LDA velocity data in the vicinity of a large velocity gradient

Abstract

The influence of the properties of the size distribution of seeding particles on the results of laser Doppler anemometry (LDA) velocity measurements in the vicinity of a large velocity gradient downstream of an aerodynamic shock is studied numerically. Accounting for the differing velocity lag of particles of different sizes the average velocity and the pertaining rms values are determined in the relaxation region within which the particles adjust towards the changed flow velocity downstream of theshock. It is shown how the average velocity and the rms value depend on the mean particle size and the density of the particle material. It is demonstrated in a numerical simulation how the LDA system's "amplituede limit", which can offer a means of excluding the contribution of large particles towards the experimental results, affects the average velocity and the rms value to be measured in the relaxation region. A good qualitative agreement of the numerical and the experimental results is found.