Author(s)

R. W. Derksen, M. Agelinchaab & M. Tachie

Abstract

This paper presents our work of an experimental examination of the flow over a NACA 0012 Airfoil at low Reynolds numbers and large angle of attack using particle imaging velocimetry. The Reynolds numbers examined were 5,000, 30,000, and 60,000, while the angles of attack ranged from 8 to 12 degrees in 2 degree increments. This work was motivated by reports that lift and drag measurements for airfoils operating at Reynolds numbers less than roughly 40,000 could not be made due to flow unsteadiness. This is puzzling in that the flow should be laminar at these Reynolds numbers, which are an order of magnitude lower than the flat-plate transition Reynolds number of 500,000. To this end we examined a sequence of flow field measurements of the instantaneous velocity field. We observed mean streamline patterns that were very representative of those we would find for a strictly steady flow, however a random pattern of significant fluctuations in the velocity and vorticity were observed. The intensity of these fluctuations increased with Reynolds number and angle of attack. Keywords: aerodynamics, low Reynolds number flow, particle imaging velocimetry. 1 Introduction Historically, interest in low Reynolds number aerodynamics has been restricted to model radio controlled aircraft applications and did not garner a great deal of scientific interest. This situation is changing with the interest in small unmanned aerial vehicles, predominantly for military purposes. As such, our understanding of low Reynolds number flow over airfoils is limited to a few sources that are

Keywords

aerodynamics, low Reynolds number flow, particle imaging velocimetry.