Effect of Reynolds number on leading edge vortex for a wing in unsteady motion

Abstract

The present study focuses on investigating the persistence of delayed stall for Micro Air Vehicles at Re-34,000. The motivation behind present research is to find out the effect of Reynolds number on aerodynamic force production and formation of leading edge vortex on a wing in unsteady motion. Computations are done on a corrugated wing in sweeping motion and pure translation at Reynolds number 3500 and 34,000. For sweeping motion, at 10 degree angle of attack, flow remain attached to the wing with no signs of leading edge vortex and the force coefficients at Re 34000 were higher than Re 3500 throughout the sweeping motion. For sweeping motion, at angle of attack of 40°, delayed stall continued to manifest itself at Re 34000. At Re 34000, the size of leading edge vortex was comparatively small but the strength of leading edge vortex core was relatively more and signs of vortex break down were eminent at 90 percent of wingspan. However, at Re 3500, signs of vortex break down were observed at 70 percent of wingspan. In pure translation, “stall absent” mechanism was not seen at any Re, as leading edge vortex was formed and it then shed into the wake. In short, it can be concluded that delayed stall continues to act as lift enhancement mechanism for MAV but flow structure and span wise vortex break down pattern changes with the change in Reynolds number.