Micro-scale three-dimensional Navier-Stokes investigation of laminar flow control suction hole configurations

The flow field induced in a laminar boundary layer by the application of surface suction through micro-perforations is investigated by solving the compressible, laminar, Navier-Stokes equations. A method has been developed to analyse single and multiple rows of holes, at transonic cruise conditions. The geometric parameters considered are hole diameter, inlet and bore shape, and inclination to the surface. The flow parameters comprise of the boundary layer displacement thickness and suction mass flow rate through the hole. A variety of flow field patterns and features are observed; including longitudinal vortices, streamline curvature, large crossflow velocities, inherently unstable velocity profiles and a recirculation region at the hole entrance. Although the hole inlet shape has a minimal effect on the induced flow field the level of streamwise vorticity is increased for inclined holes. The pressure drop and mass flow rate characteristics of a HLFC micro-perforation are found to be insensitive to the hole inlet shape and the ratio of hole diameter to boundary layer displacement thickness. Conical bore holes provide substantial static pressure recovery. The size and shape of the sucked streamtube, which is currently used to predict the critical suction velocity, is also determined. For multiple row of holes, the flow field characteristics are shown to be influenced by significant inter-hole effects.