Spanwise Variation of Turbulent Flowfield for the Turbulent Boundary Layer Interacting with Controlled Longitudinal Vortex Arrays

Abstract

A vortical structure within a turbulent boundary layer and spanwise variation of turbulent flowfield have been investigated for further understanding of the development of the turbulent boundary layer interacting with the spanwise periodic longitudinal vortex arrays which are artificially generated in a free stream. One of the parameters, spanwise periodicity of longitudinal vortices L/S (L denotes the spanwise distance between neighboring airfoils, S the airfoil span), rules both magnitude and streamwise path of secondary vortices caused within the turbulent boundary layer. As a result, whether the turbulent quantities show linear or nonlinear interaction significantly depends on the value of L/S. Therefore, in cases where L/S < 1, although the spanwise distortion of turbulent quantities in the outer region is not marked, those spanwise periods change in the streamwise direction due to the rapid vortex diffusion following corotating merging vortices. However, in cases where L/S &gsim; 1, turbulent quantities show a noticeable spanwise periodic variation corresponding to the arrangement of airfoil elements, and these spanwise periods are strictly maintained. Comparing the spanwise variations of the turbulent flowfield with those of the mean flowfield, mechanisms of spanwise variation of the turbulent boundary layer are discussed.