Effects of Particle Loading on Turbulent Flow in a 90° Elbow

Introducing a second phase into a turbulent flow changes its complex nature by modifying the turbulent fluctuations. Experimental data at high volume concentrations are limited due to the presence of the particles which degrade optical clarity. Optical clarity can be restored using refractive index matching (RIM) where the refractive indices of the secondary and continuous phases are matched. In this work, super absorbent hydrogel particles were used to create an index matched system. These particles absorb up to 500x their weight in water, and are therefore inherently index matched and neutrally buoyant. Turbulent flows at Re=11,500 and 115,000 through a sharp edged 90° elbow were studied using PIV. Mean and fluctuating (rms) velocities were measured in the presence of 0 to 5% of hydrogel particles. The results showed little variation due to the presence of the particles. These results are put into context by discussing the parameters used to predict turbulence modulation, most of which predicted attenuation of the rms velocities. A possible explanation for the observed behavior was the low values for the ratio of the slip velocity between the phases to the mean fluid velocity which has been shown to affect turbulence modulation in prior work.