Numerical study of the effect of motion parameters on propulsive efficiency for an oscillating airfoil

A numerical study on an airfoil undergoing combined heaving and pitching motion in cruise condition to assess the effect of a range of kinematic parameters on the propulsive efficiency is presented. The study assesses the effect of parameters like oscillation frequency, pitch amplitude, and non-dimensional heaving amplitude on the propulsive efficiency of the airfoil and uses an in-house computational fluid dynamics code. The propulsive efficiencies of the foil in the frequency range of 1-30 Hz, pitch amplitude range of 3-19, and non-dimensional heave amplitude range of 0.1-0.9 were computed and compared in order to explore the relationship between kinematic parameters and propulsive efficiency. Results indicate that at smaller pitch amplitudes low efficiencies occur at lower frequencies and high efficiencies occur when frequencies and heave amplitudes are on higher side. The low propulsive efficiency regions disappear with increasing pitch amplitude and larger regions at higher frequencies and heave amplitudes show high efficiencies. When both heave amplitude and frequency are small, propulsive efficiency is less than 0.5; when heave amplitude range is from 0.2 to 0.7, high efficiency occurs at high frequencies, however, with increasing heave amplitudes, these high efficiencies occur at lower frequencies. When the range of frequency is from 8 Hz to 30 Hz, the size of high efficiency area first increases, then decreases. And we explore the reasons why the oscillation frequency, pitch amplitude, and non-dimensional heaving amplitude can affect the propulsive efficiency. Combinations of kinematic parameters for optimal propulsive efficiency have been identified.