Angular momentum transport and its scaling in co-rotating suspension Taylor-Couette flow

Torque measurements are carried out to elucidate the global response of a neutrally buoyant, non-colloidal suspension in the co-rotation regime (i.e., the rotation ratio Ω = ωo/ωi > 0, with ωo and ωi being the angular speeds of the inner and outer cylinders, respectively) of Taylor-Couette flow (TCF) up to a shear Reynolds number of Res ≤ 1000 and particle volume fraction of ϕ ≤ 0.2. The dimensional torque increases with increasing particle loading for all Ω ≤ 0.65, however, the maximum of dimensionless angular momentum (pseudo Nusselt number) occurs at intermediate values of Ω ∈ (0.3, 0.5), depending on the values of Res and ϕ. The pseudo-Nusselt number in the co-rotation regime is found to follow the master scaling relation proposed by Alam and Ghosh [Phil. Trans. R. Soc. A 381, 20220226 (2023)] in the counter-rotation regime (Ω < 0). The e↵ect of co-rotation on torque scaling is also discussed.