Experimental and computational investigation of heat fluxes in a supersonic diffuser

Abstract

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...

Conceptual Design Model of High-Altitude Test Stand for Rocket Engines

“…Cooling of the supersonic diffuser has been studied. 14,15) Supersonic combustion gas flow decelerates to subsonic through the pseudo-shock. The general estimation formula for heat transfer is not effective in the pseudo-shock region.…”

Experimental Study of Heat Flux in the Pseudo-shock Region

“…Studies have been conducted for prediction of the heat transfer in supersonic diffusers. Back et al 2) and Zaikovskii et al 3) reported on heat transfer in supersonic diffusers. Back and Cuffel gave an empirical equation between wall static pressure and heat transfer coefficient in the shock wave impingement on the turbulent boundary layer.…”