BOUNDARY LAYER AT A CURVED CORNER

Abstract

The necessity and the practical importance of an understanding of the boundary layer formation at a curved corner have been emphasized, and recent investi-gations on corner boundary layer are briefly reviewed. An experimental study was made on the development of the boundary layer at a three-dimensional curved. corner formed by an orthogonal intersection of two identical cylindrical surfaces. A non-recirculating air duct of square cross-section was used for obtaining the flow past such a curved corner. Mean values of the pressure and velocity were measured for the Reynolds number of the uniform duct flow varying from 1.2 x 10-5 to 4.? x 105. Measurements were made for both laminar and turbulent boundary layers. The turbulent boundary layer was artificially stimulated by means of isolated sand grain roughness, fixed in two rows at some upstream station. The velocity profiles within the boundary layer away from the corner were found to be two dimen-sional in nature and they were irregular at the corner. This irregularity which was observed both for the laminar and turbulent boundary layers was due to secondary currents. The secondary currents arise as a consequence of the curvature in flow in two mutually perpendicular planes, and in the case of turbulent boundary layer they become stronger due to an unbalanced lateral pressure gradient set up by the Reynolds stresses at the free-stream edge of the boundary layer. The undulating velocity profile in the corner grows systematically with the distance along the arc length for both laminar and turbulent boundary layers . The displacement and momentum thicknesses of the boundary layer were computed by integrating graphically the Experimental data of the velocity profiles. The boundary-layer growth was shown in terms of these thickness parameters