Stationary crossflow instability on an infinite swept wing

The Swept Laminar Flow Wing has long been a goal for aerodynamic scientists and engineers. Here the ideas of Laminar Flow Control (LFC) are applied to delay transition and maintain laminar flow over a much larger fraction of a wing surface. When applied to a swept wing, a configuration adopted by current-generation civil-transport aircraft, a significant reduction in drag and substantial increase in energy efficiency could result. To successfully apply this technology, a thorough knowledge and understanding of the transition process on the swept wing is necessary. Because the boundary-layer flow over a swept wing is highly three-dimensional (3-D), streamwise co-rotating crossflow vortices exist, which strongly affect the transition of laminar flow to turbulent. In this work, the stability of the flow over a 70 degree swept, infinite-span wing is examined both by quasi-parallel linear stability theory and by numerically solving the 3-D unsteady incompressible Navier-Stokes (N-S) equations in primitive-variable form. Near the leading edge, steady blowing and suction of chosen wavelength in the spanwise direction is introduced on the wall surface to simulate surface irregularity and generate an instability. The linear stability problems are solved by a Chebyshev-collocation method, while the 3-D full N-S simulation is accomplished by a Fourier-spectral/finite-difference/multiple-grid scheme (developed by the author), which is shown to be accurate and robust. Results of the linear stability analyses indicate that the convex wall curvature has a stabilizing effect while the streamline curvature has a destabilizing effect on the stationary crossflow vortices. The results of direct N-S simulation support the so-called crossflow/crossflow structure which is a consequence of nonlinear interaction near the wall. Strong spanwise modulation of the streamwise-velocity profiles results in the appearance of multiple inflection points. A detailed comparison of the N-S calculation with linear theory and experimental results is provided.