TY - GEN

T1 - Numerical investigation of separation for airfoils at low Reynolds numbers

AU - Gross, A.

AU - Fasel, H. F.

PY - 2010/12/2

Y1 - 2010/12/2

N2 - The present study is concerned with the Aeromot 200S Super Ximango motor glider for which we built two 1:5 scale dynamically scaled models. For a two-dimensional section of its wing, which has a modified NACA 643-618 airfoil, we computed the unsteady time-dependent flow for two chord Reynolds numbers, 64,200 and 322,000. At Re=64,200, the wing tip Reynolds number at model takeoff speed, most of the turbulent energy spectrum can be captured using direct numerical simulations and turbulence modeling is not required. For α = 8.64deg laminar separation occurs near the maximum thickness resulting in a considerable performance loss. As the angle of attack is increased a leading edge bubble forms. The turbulent boundary layer downstream of the bubble is more resistant to separation resulting in a considerable performance recovery. For even higher angles of attack the leading edge bubble "bursts" and performance is once again lost. At Re=322,000, the model cruise Reynolds number based on mean aerodynamic chord, computer limitations prohibit direct numerical simulations and necessitate turbulence modeling. We employed filter-based Reynolds-averaged Navier-Stokes for simulations at an angle of attack of 13.2deg. The flow again separates near the maximum thickness location. In a separate simulation we show how performance can partially be recovered by harmonic blowing through a spanwise slot near the leading edge of the airfoil.

AB - The present study is concerned with the Aeromot 200S Super Ximango motor glider for which we built two 1:5 scale dynamically scaled models. For a two-dimensional section of its wing, which has a modified NACA 643-618 airfoil, we computed the unsteady time-dependent flow for two chord Reynolds numbers, 64,200 and 322,000. At Re=64,200, the wing tip Reynolds number at model takeoff speed, most of the turbulent energy spectrum can be captured using direct numerical simulations and turbulence modeling is not required. For α = 8.64deg laminar separation occurs near the maximum thickness resulting in a considerable performance loss. As the angle of attack is increased a leading edge bubble forms. The turbulent boundary layer downstream of the bubble is more resistant to separation resulting in a considerable performance recovery. For even higher angles of attack the leading edge bubble "bursts" and performance is once again lost. At Re=322,000, the model cruise Reynolds number based on mean aerodynamic chord, computer limitations prohibit direct numerical simulations and necessitate turbulence modeling. We employed filter-based Reynolds-averaged Navier-Stokes for simulations at an angle of attack of 13.2deg. The flow again separates near the maximum thickness location. In a separate simulation we show how performance can partially be recovered by harmonic blowing through a spanwise slot near the leading edge of the airfoil.

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M3 - Conference contribution

AN - SCOPUS:78649453284

SN - 9781617389221

T3 - 40th AIAA Fluid Dynamics Conference

BT - 40th AIAA Fluid Dynamics Conference

T2 - 40th AIAA Fluid Dynamics Conference

Y2 - 28 June 2010 through 1 July 2010

ER -