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Two-phase turbulent Taylor-Couette (TC) flow is simulated using anEuler-Lagrange approach to study the effects of a secondary phase dispersedinto a turbulent carrier phase (here bubbles dispersed into water). Thedynamics of the carrier phase is computed using Direct Numerical Simulations(DNS) in an Eulerian framework, while the bubbles are tracked in a Lagrangianmanner by modelling the effective drag, lift, added mass and buoyancy forceacting on them. Two-way coupling is implemented between the dispersed phase andthe carrier phase which allows for momentum exchange among both phases and tostudy the effect of the dispersed phase on the carrier phase dynamics. Theradius ratio of the TC setup is fixed to $\eta=0.833$, and a maximum innercylinder Reynolds number of $Re_i=8000$ is reached. We vary the Froude number($Fr$), which is the ratio of the centripetal to the gravitational accelerationof the dispersed phase and study its effect on the net torque required to drivethe TC system. For the two-phase TC system, we observe drag reduction, i.e.,the torque required to drive the inner cylinder is less compared to that of thesingle phase system. The net drag reduction decreases with increasing Reynoldsnumber $Re_i$, which is consistent with previous experimental findings (Muraiet al. 2005, 2008). The drag reduction is strongly related to the Froudenumber: for fixed Reynolds number we observe higher drag reduction when $Fr <1$ than for with$ Fr > 1$. This buoyancy effect is more prominent in low $Re_i$systems and decreases with increasing Reynolds number $Re_i$. We trace the dragreduction back to the weakening of the angular momentum carrying Taylor rollsby the rising bubbles.

Drag reduction in numerical two-phase Taylor-Couette turbulence using an Euler-Lagrange approach