Nonlinear receptivity of leading-edge ow to oblique free-stream vortical modes
2010 (English)Report (Other academic)
Boundary-layer receptivity to pairs of unsteady oblique free-stream vortical modes is studied for flat-plate flow using direct numerical simulation (DNS). This kind of forcing gives rise to steady boundary-layer streaks and the associated receptivity mechanism is nonlinear in the forcing amplitude. The flat plates considered feature elliptic leading edges with two different aspect ratios, allowing for the study of leading-edge bluntness effects on the receptivity. The free stream is perturbed by three types of unsteady oblique Fourier modes upstream of the leading edge. These modes differ in the magnitude of the three vorticity components. It is found that the bluntness of the leading edge hardly affects the streak amplitudes obtained. This observation also holds for oblique waves with vertical vorticity alone and is in contrast to the linear receptivity to this kind of modes, which is known to depend strongly on the leading-edge shape. While being irrelevant at low frequencies the nonlinear receptivity mechanism becomes important for high-frequency free-stream vortices to which the boundary layer is linearly non-receptive. Although the linear receptivity mechanism for zero- or low-frequency forcing is more efficient in producing disturbance streaks than the nonlinear receptivity to high-frequency disturbances, the nonlinear mechanism is expected to contribute significantly to the boundary-layer receptivity to free-stream turbulence.
Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , 15 p.
Fluid Mechanics and Acoustics
IdentifiersURN: urn:nbn:se:kth:diva-25504OAI: oai:DiVA.org:kth-25504DiVA: diva2:358821
QC 201010252010-10-252010-10-252010-10-25Bibliographically approved