Preferential concentration of heavy particles in a turbulent channel flow

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Abstract
An investigation of the instantaneous particle concentration at the centerline of a turbulent channel flow has been conducted. The concentration field was obtained by digitizing photographs of particles illuminated by a spanwise laser sheet and identifying individual particles. The resulting distribution was then compared to the expected distribution for the same number of particles randomly distributed throughout the volume. Significant departures from randomness have been found and the differences are strongly dependent on the time constants of the particles. Five different particle classes were investigated and the maximum departure from randomness was found when the ratio of the particle’s aerodynamic response time to the Kolmogorov time scale of the flow was approximately one. The length scales of the particle clusters were found to change with the particle size. The correlation dimension was used to produce a single parameter describing the degree of concentration regardless of the scale on which it occurs. The spacing between particle clusters was also investigated and found to be much larger than the scales on which concentration occurs.