Direct Numerical Simulation of Receptivity to Roughness in a Swept-Wing Boundary Layer at High Reynolds Numbers

Direct numerical simulations (DNS) are performed to examine the receptivity to roughness in a spatially developing three-dimensional boundary layer over an infinite-swept natural-laminar-flow wing at a freestream Mach number of 0.75 and a chord Reynolds number of approximately 25 million based on the long, swept chord. Stationary crossflow disturbances are excited by applying either critically spaced discrete cylinders of micron size or naturally occurring distributed roughness in the leading-edge region. The DNS data show that the spanwise spectral content of the excited crossflow disturbances is highly dependent upon the shape of roughness elements, and the initial growth of the crossflow structures is a nonlinear function of the element height. The linear growth rate of the excited crossflow disturbances predicted by DNS shows good agreement with linear parabolized stability equations. The receptivity study lays the foundation for investigating the stabilization of the naturally most unstable steady crossflow mode by using spanwise periodic DREs.