Experimental and Numerical Study of Internal Flow through a Rotating Duct

Several rotorcraft applications such as circulation control and tip jet-driven rotors involve internal spanwise flow along a ducted rotor blade. The primary goal of this work was to study a self-pumping pneumatically driven duct flow by both generating a quasi one-dimensional model for such flows and providing a validation data set for rotorcraft applications. The flow behavior inside a 1.32-m-long cylindrical duct, with a duct cross-sectional diameter of 52 mm, and rotating at speeds up to 1050 RPM was studied. Spanwise pressure distribution, duct velocity, hub forces, and moments from the numerical model showed good correlation with experiments. A considerable internal mass flow rate (similar to 0.3 kg/s) was also observed for a steadily rotating duct. In the presence of a time-varying valve at the inlet, transient spanwise pressure variations showed periodic fluctuations in pressure that diminished once the valve was fully open. The experimental results were compared with results of two computational models-a quasi one-dimensional finite volume Euler equation solver and a full three-dimensional computational fluid dynamics solver. The ability to model a range of boundary conditions, time-varying duct cross-sectional area to simulate a flow control valve, frictional losses, duct sweep, and centrifugal as well as Coriolis effects on the flow is included. The experiments revealed key information about pressure at the duct's outlet. It was observed that when the duct's inlet is closed, the duct's outlet pressure is less than its ambient value. The knowledge of these boundary conditions is key in modeling flow through rotating ducts.