Turbulent Structure of an Intermittent Region of a Turbulent Boundary Layer Interacting with Controlled Longitudinal Vortex Arrays in a Free Stream.

Abstract

Conditional averaged patterns on the outer layer of a turbulent boundary layer have been investigated in order to understand the development process of a boundary layer interacting with spanwise periodic longitudinal vortex arrays which is artificially generated in a free stream. Two parameters, nemely, the spanwise periodicity of the longitudinal vortex arrays L/S and the arrangement height of airfoil arrays, were independently varied for five cases. Intermittency factor profiles revealed the effect of pairs of counterrotating secondary flows which showed the downwash flow for the midspan of the airfoil, and conversely, the upwash flow for the center slice of neighbouring airfoils. Intermittency factors are strongly affected by the spacing between neigbouring airfoils. The value of the intermittency factor decreases in the inner layer with increasing L/S at the midspan of the airfoil.