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In particle-laden turbulent flows the turbulence in carrier fluid phase getsaffected by the dispersed particle phase for volume fraction above $10^{-4}$and hence reverse coupling or two-way coupling becomes relevant in that volumefraction regime. In a recent study by Muramulla $et.al.^1$, a discontinuousdecrease of turbulence intensity is observed in a vertical particle-ladenturbulent channel-flow for a critical volume fraction O($10^{-3}$). Thecollapse of turbulent intensity is found out to be a result of catastrophicreduction of turbulent energy production rate. Mechanistically, particle-fluidcoupling in particle-laden turbulent Couette-flow differs from that in a closedchannel flow. In this article, the turbulence modulation in Couette-flow byinertial particles is explored through two-way coupled DNS where particlevolume fraction ($\phi$) is varied from $1.75\times10^{-4}$ to$1.05\times10^{-3}$ and Reynolds Number based on half-channel width ($\delta$)and wall velocity ($U$) ($Re_{\delta}$) is $750$. The particles are heavy pointparticles with $St\sim367$ based on fluid integral time-scale represented by$\delta/U$. A discontinuous decrease of fluid turbulence intensity, mean squarevelocity and Reynolds stress is observed beyond a critical volume fraction$\phi_{cr}\sim7.875\times10^{-4}$. The drastic reduction of shear production ofturbulence and in turn the reduction of viscous dissipation of turbulentkinetic energy are two important phenomena for the occurrence of discontinuoustransition similar to channelflow. The step-wise particle injection andstep-wise removal study confirms that it is the presence of particles which ismajorly behind this discontinuous transition.

Dynamics of particle-laden turbulent Couette flow. Part1: Turbulence modulation by inertial particles