Turbulence modulation by large ellipsoidal particles: Concentration effects

We use laboratory measurements to study how suspended ellipsoidal particles affect the velocity statistics of a turbulent flow. The ellipsoids have size, time, and velocity scales corresponding to the inertial subrange of the turbulence and are nearly neutrally buoyant. These characteristics make them likely candidates for two-way interactions with the fluid (i.e.; they influence the flow and are influenced by it). We vary the volume fraction of suspended ellipsoids and observe the effects on one- and two-point velocity statistics in the fluid phase. Measurements at two different heights indicate that particle buoyancy (0.5 % denser than the ambient fluid) significantly changes volume fraction. We see that particles' effect on turbulent kinetic energy is a non-monotonic function of the volume fraction. We also find that particles' presence causes a redistribution of velocity variance from large scales to small scales within the inertial subrange, i.e.; the slope of power spectra is flatter than in the single-phase case. © 2013 Springer-Verlag Wien.