Large-scale longitudinal vortices in high-speed turbulent separated flows caused by relatively small irregularities at the model leading edges or at the model surfaces are investigated in this paper. Oil-flow visualization and infrared thermography techniques were applied in the wind tunnel tests at Mach numbers 3 and 5 to investigate the nominally 2-D ramp flow at deflection angles of 20°, 25° and 30°. The surface contour anomalies have been artificially simulated by very thin strips (vortex generators) of different shapes and thicknesses attached to the model surface. It is shown that the introduced streamwise vortical disturbances survive over very large downstream distances of the order of 104 vortex-generator heights in turbulent supersonic flows without pressure gradients. It is demonstrated that each vortex pair induced in the reattachment region of the ramp is definitely a child of a vortex pair, which was generated originally, for instance, by the small roughness element near the leading edge. The dependence of the spacing and intensity of the observed longitudinal vortices on the introduced disturbances (thickness and spanwise size of vortex generators) and on the flow parameters (Reynolds numbers, boundary-layer thickness, compression corner angles, etc.) has been shown experimentally.

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The internal structure of a turbulent flow in a boundary layer brings about an expressed two-layer character of flow with respect to the characteristic relaxation time of perturbations. The different relaxation times of perturbations in the internal and external parts of a boundary layer are not taken into account by the Boussinesq hypothesis, in which turbulence is determined by the usual law for a viscous liquid of dependence of stresses on the strain rate, which differs only in the renormalized viscosity coefficient [1].It was proposed to take account of the specific influence of the internal flow structure on the relaxation of perturbations using the Clauser parameter/3 = (5*dp/dx)/rw (dp/dx is the longitudinal pressure gradient, and 5* and rw are the displacement thickness and friction near the solid surface). The boundary layers in which/3 = const are called equilibrium boundary layers, according to Clauser, and those in which/3 5r const, nonequilibrium. Various attempts have been made to overcome the restrictions of the Boussinesq formula for calculating nonequilibrium boundary layers [1], in particular, by modifying the coefficient of turbulent viscosity ut [2, 3]. In calculations of heat exchange in supersonic flows with separation zones the relations accounting for the elevated level of turbulence in nonequilibrium layers were used [4, 5]. However, all these approaches, which consider the extrinsic aspect of the above phenomenon, have a number of limitations in applications, especially for heat exchange predictions.Models that allow for the orientational interaction of the vectors of the internal angular momentum and external force fields [6] make it possible to understand some reasons for the uniqueness of the vortex structure of turbulence [7] and simulate its influence in heat exchange calculations.A supersonic diffuser is one of the most thermally stressed elements of the various devices of aviation and rocket equipment. Owing to its small relative length (a/Di <~ t0, a and Di are the length and diameter of the diffuser), the presence of shock waves, and the formation of local separation zones, the turbulent boundary layer at the diffuser internal surfaces is essentially nonequilibrium.In the present work we present the results of an experimental study of a flow and heat exchange inside a subsonic diffuser, as well as a calculation of heat exchange coefficients along its generatrix on the internal surface. In contrast to [4, 5], the heat exchange in a nonequilibrium turbulent boundary layer is simulated on the basis of the considerations of nonequilibrium turbulence [7] using a specially constructed function that allows for the orientational effect of the main flow on large-scale turbulence. This function does not contain additional empirical constants and, therefore, agrees with the main idea of the asymptotic theory [8] of the relative law of heat exchange.1. Experimental Investigation. Experiments were carried out on a large-scale gasdynamic ramjet device designed for modeling internal processe...

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