Tohoku University, 6-6-01 Aramaki-Aoba, Sendai, 980-8579, Japan
Seikei University, 3-3-1 Kichijoji-Kitamachi, Musashino-shi, Tokyo, 180-8633, Japan
The receptivity of the Blasius boundary layer over a semi-inﬁnite ﬂat plate with an elliptic leading edge and of aspect ratio ﬁve was investigated using a direct numerical solution of two-dimensional Navier-Stokes equations. The result of the computation where the slip condition is applied to the ﬂuctuating component of velocity at the wall surface is compared with that of an ordinary computation using a nonslip condition. Another numerical experiment is performed where no vorticity ﬂuctuation is supplied from a freestream while prerecorded values of vorticities at the wall in response to the passage of convecting ﬂuctuations are used as the wall vorticity boundary condition. It is shown that vorticity ﬂuctuations in the boundary layer can be classiﬁed according to their wavelengths. Waves with longer wavelengths originate from the freestream, whereas waves with shorter wavelengths close to T-S waves originate from the surface of the plate. In another numerical experiment, the slip boundary condition against the ﬂuctuation component of vorticity is applied to the limited area of the wall surface. The aim of the study is to determine the part of the elliptic leading edge or ﬂat plate that induces vorticity ﬂuctuations, thereby resulting in the creation of T-S waves. The numerical results show that the contribution of vorticity ﬂuctuations originating from the juncture is the most crucial, whereas the vorticities supplied in the elliptic leading-edge surface negatively affect the amplitude of vorticity ﬂuctuations inside the boundary layer. And, the stagnation section did not show positive contribution.