Investigation of Compressible Turbulent Boundary Layer with Large Adverse Pressure Gradient

Abstract

Until recently the characteristics of the turbulent boundary layer were investigated in supersonic and hypersonic flows around the surfaces with a longitudinal curvature. However they dealt with two-dimensional [1] or axisymmetric [2] flows. At the same time we do not possess data on the state of the boundary layer in the internal conic flows with longitudinal surface curvatures. These very complicated flows are extremely difficult to calculate due to the joint influence of the adverse pressure gradient, flow lines curvatures, volume compression. The task becomes even more complicated if the axial symmetry is eliminated and the flow becomes three-dimensional. Elaboration and verification of the calculation methods requires reliable experimental data. The purpose of this research is to obtain such data fog the Mach numbers ranging from 2 to 6 at Reynolds of (6..60) 106 1/m. Mesurements of mean characteristics of the threg-dimensional boundary layer were made on a model which is a 900-section of the internal axisymmetric flow (the Laval inverse nozzle) (Fig.1). The experiments were carried out on the models both with the limiting plates and without them. A pressure increase by a factor of 3 to 26 was achieved (at Mach numbers ranging from 2 to 6 respectively) over the length of 24 8 mm. In all the experiments the formation of the boundary layer began at the leading edge of the model. As a result the layer thickness did not exceed 2 mm before the curved surface, its maximum thickness at the end of the compression region being 5.15 mm. The application of the artificial turbulization resulted in a 20–30% increase of the layer thickness. To compare the obtained characteristics of the boundary layer with the data for a two-dimensional flow similar investigations were carried out on a two-dimensional model whose longitudinal contour exactly corresponded to the contour of the above mentioned model.