Experimental Study on the Influence of Frequency Ratio on Thrust and Vortex Structure of a Pitching Wing in a Periodic Flow

Abstract

The purpose of this study is to investigate the influence of the frequency ratio on the thrust and the vortex street in a periodic flow. The periodic flow is the model of an unsteady freestream velocity, and the frequency ratio is defined as the frequency of pitching wing divided by that of the periodic flow. The thrust and the vortex street are measured by a load cell and particle image velocimetry (PIV), respectively. In this study, the pitching wing is modeled as a NACA 0012 airfoil pitching sinusoidally at a Reynolds number of 4000. We compare a steady with the periodic flow to find the difference in the thrust and the vortex street at frequency ratios of 1, 2, and 3. Furthermore, FFT analysis of the thrust is conducted to investigate the difference in more detail. It is found that the thrust and vortex street are more affected by periodic flow at the low-frequency ratio than at the high-frequency ratio.