Experimental Studies of Separation on a Two-Dimensional Airfoil at Low Reynolds Numbers

TLDR

The study used a low‑speed smoke‑visualization wind tunnel to examine laminar separation, transition, and turbulent reattachment on a NACA 663‑018 airfoil, measuring lift and drag over Reynolds numbers 40–400 000, and testing surface roughness and acoustic excitation to influence the boundary layer. The experiments revealed how angle of attack and Reynolds number affect separation characteristics and airfoil performance, with flow visualization correlating to force measurements. Key symbols include c (chord), cd (drag coefficient), cf (lift coefficient), Cp (pressure coefficient), R (reattachment location), Rc (Re based on chord), U (velocity), x/c (non‑dimensional chord position), a (angle of attack), and v (kinematic viscosity).

Abstract

The laminar separation, transition, and turbulent reattachment near the leading edge of a two-dimensional NACA 663 -018 airfoil were investigated using a low-speed, smoke visualization wind tunnel. Lift and drag force measurements were made using an external strain gage balance for a chord Reynolds number range of 40,GOO400,000. An extensive flow visualization study was performed and correlated with the force measurements. Experiments were also conducted with distributed surface roughness at the leading edge and external acoustic excitation to influence the development of the airfoil boundary layer. This study delineates the effects of angle of attack and chord Reynolds number on the separation characteristics and airfoil performance. Nomenclature c = model chord cd = section profile drag coefficient (uncorrected) cf = section lift coefficient (uncorrected) Cp = pressure coefficient / = acoustic frequency, Hz R = reattachment location Rc = Reynolds number based on chord length, U^ civ S = separation location T = location of approximate end of transition £/«, = freestream velocity x/c = nondimensional distance along chord a = angle of attack v - kinematic viscosity