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NONLINEAR RECEPTIVITY TO OBLIQUE VORTICAL MODES IN FLOW PAST AN ELLIPTIC LEADING EDGE

Lars-Uve Schrader
Department of Mechanical Engineering University of Ottawa, ON, Canada K1N 6N5

Luca Brandt
Linné Flow Centre, KTH Mechanics, Osquars backe 18, SE-100 44 Stockholm, Sweden

Catherine Mavriplis
Department of Mechanical Engineering, University of Ottawa, ON, Canada, K1N 6N5

Dan S. Henningson
Linne FLOW Centre and Swedish e-Science Research Centre (SeRC) KTH Mechanics, Royal Institute of Technology SE-100 44 Stockholm, Sweden

Аннотация

Boundary layer receptivity to pairs of unsteady oblique freestream vortical modes is studied in direct numerical simulation of flow over a flat plate with an elliptic leading edge. The freestream is perturbed by three types of oblique Fourier modes, differing in the magnitude of the three vorticity components. The vortical modes excite steady boundary layer streaks, and the associated receptivity mechanism is nonlinear in the forcing amplitude. Leading edges with two different aspect ratios are considered. It is found that the streak amplitudes obtained are largely unaffected by the leading edge bluntness. Whereas linear receptivity is the predominant mechanism at low forcing frequencies, the nonlinear mechanism becomes important when high-frequency vortices are present in the freestream. Nonlinear receptivity is therefore expected to contribute significantly to the excitation of boundary layer streaks by freestream turbulence.