Theoret. Comput. Fluid Dynamics (1992) 3:369-380 Theoretical andComputational FluidDynamics O Springer-Verlag 1992 Temporal Development of Turbulent Boundary Layers with Embedded Streamwise Vortices 1 Hossein Esmaili and Ugo Piomeili Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, U.S.A. Communicated by M.Y. Hussaini Received 23 January 1992 and accepted 30 March 1992 Abstract. The interaction of streamwise vortices with turbulent boundary layer has been investi- gated using large-eddy simulation. The initial conditions are a pair of counterrotating Oseen vortices with flow between them directed toward the wall (common-flow-down), superimposed on various instantaneous realizations of a turbulent boundary layer. The time development of the vortices and their interaction with the boundary layer are studied by integrating the filtered Navier-Stokes equations in time. The most important effects of the vortices on the boundary layer are the thinning of the boundary layer between vortices (downwash region) and the thickening of the boundary layer in the upwash region. The vortices first move toward the wall as a result of the self-induced velocity, and then apart from each other because of the image vortices due to the solid wall. The Reynolds stress profiles highlight the highly three-dimensional structure of the turbulent boundary layer modified by the vortices. The presence of significant turbulent activity near the vortex center and in the upwash region suggests that localized instability mechanisms in addition to the convection of turbulent energy by the secondary flow are responsi- ble for this effect. High levels of turbulent kinetic energy and secondary stresses in the vicinity of the vortex center are also observed. The numerical results show good agreement with experimen- tal results. 1. Introduction Streamwise vortices occurring in engineering applications may be divided into two categories, natural and artificial. Examples of naturally occurring streamwise vortices are the trailing vortices from aircraft wings that may interact with other aircraft in the wake of the original one, the vortex pair formed downstream of obstacles protruding in a boundary layer as the spanwise vortex lines are turned through an angle equal to the flow turning angle, thus producing two counterrotating vortices, the streamwise vortices generated in curved ducts, etc. Vortices are often introduced in boundary layers artificially: as high-momentum fluid from the free stream is convected toward the solid wall and low-momentum fluid is carried into the free stream, the intense mixing between the high and low-momentum streams can delay separation. Taylor (1923) first observed longitudinal vortices between rotating concentric cylinders. In his 1 This work was supported by the Office of Naval Research under Grant N00014-89-J-1638. Computer time was supplied by the San Diego Supercomputing Center. 369