Numerical prediction of unsteady aerodynamics for a ducted fan micro air vehicle

In this paper, the unsteady aerodynamics of a ducted fan micro air vehicle is investigated using an unstructured overset grid technique and momentum source method. The in-house programmed compressible Navier–Stoke solver is preconditioned for low Mach number flow regime, and a dual time-stepping strategy is employed to guarantee the computing accuracy and efficiency. Momentum source items are added in the Navier–Stoke solver to replace the contra-rotating propellers in numerical simulation which simplify the inherently unsteady flow into a quasi-steady one. The developed method was verified and validated as a reliable tool for predicting the unsteady aerodynamic performance in low Reynolds flow regime. The effects of reduced frequency, flight velocity and propeller speed on the aerodynamic performance of the ducted fan micro air vehicle are evaluated in this paper. Results show that the hysteresis effect of aerodynamic coefficient increases as induced frequency, freestream velocity and propeller speed increases.