Monitoring the Wake of Low Reynolds Number Airfoils for Their Aerodynamic Loads Assessment

Experimental investigations are carried out to explore the aerodynamic performance and vortex shedding characteristics of S۵۰۱۰ and E۲۱۴ airfoil-based wings to provide guidance for the design of MAVs and other low-speed vehicles. Force and wake shedding frequency measurements are carried out in a subsonic wind tunnel in the Reynolds number (Re) range of ۴ × ۱۰۴ - ۱ × ۱۰۵. The measurements with increasing Re show that the slope of the lift curve in the linear region increases by ۱۴% for S۵۰۱۰, while this increment is ۱۱% for E۲۱۴. The peak lift coefficient of both airfoils reduces with reducing Re. For lower pitch angles, the influence of Re on drag coefficients is less significant, but at higher angles, the drag increases as the Re drops. Unlike pre-stall mountings, the pitch-down propensity of the airfoil enhances in the post-stall region for high Re flows. Moreover, the frequency of shed vortices reduces with rising angle of attack at a given Re. In contrast, the Strouhal number almost remains constant with varying Re at a fixed angle of attack. For S۵۰۱۰ and E۲۱۴ airfoils, the Strouhal number is noticed to vary between ۰.۶۸ - ۰.۳۶ and ۰.۵۸ - ۰.۳۶, respectively, for pitch angle variation of ۱۲°- ۲۸°. The airfoils show a higher Strouhal number than the bluff body wakes, but this difference decreases for high angles of attack mountings. This finding reveals that the wake structure of the airfoil at a high post-stall angle behaves as bluff body wakes.

کلیدواژه ها:

Wind tunnel measurement ، Low Reynolds number ، S۵۰۱۰ and E۲۱۴ airfoils ، Aerodynamic characteristics ، Vortex shedding frequency ، Strouhal number