Numerical and Experimental Study of Centrifugally-Driven Flow inside a Rotating Duct for Rotorcraft Application

Rotor blades experience very high centrifugal forces that can be utilized to pump air to the outboard region of the blade through an internal duct, which can be used for flow control. Analysis or design of such systems requires accurate prediction capability. In order to validate current Reynolds Averaged Navier-Stokes CFD methodologies, an experiment was performed using a rotating pipe as a simplified ducted blade, and simulation results were compared to the measured data. A quasi-one-dimensional (Q1D) code was also compared to experimental data as a lower order simulation tool that can provide faster solutions more appropriate for rapid design iterations. The test and simulations include several combinations of steady inlet and exit conditions as well as an unsteady inlet valve operation condition at several rotational speeds. The Q1D code showed good correlation for steady inlet and exit conditions with boundary conditions obtained from experiment. Navier-Stokes CFD methods also showed good agreement with measured data for pressure and mass flow rate at most conditions, while properly capturing complex flow features including separation, secondary swirl flow, and tip-flow interactions. The Kinetic Eddy Simulation and the Spalart-Allmaras turbulence models were tested to examine solution sensitivity under the complex flow environment. The two turbulence models showed similar results, except when the inlet valve was closed, in which case, the Kinetic-Eddy-Simulation model showed better correlation.