Convective heat transfer in a convergent-divergent nozzle

Abstract

The results of an experimental investigation of convective heat transfer from turbulent boundary layers accelerated under the influence of large pressure gradients in a cooled convergent-divergent nozzle are presented. The investigation covered a range of stagnation pressures from 30 to 250 psia, stagnation temperatures from 1030° to 2000°R, and nozzle-inlet boundary-layer thicknesses between 5 and 25 per cent of the inlet radius. The most significant unexpected trend in the results is the reduction in the heat-transfer coefficient, below that typical of a turbulent boundary layer, at stagnation pressures less than about 75 psia. As expected, the results include a maximum in the heat-transfer coefficient upstream of the throat where the mass flow rate per unit area is largest, and a substantial decrease of the heat-transfer coefficient downstream of the point of flow separation which occurred in the divergent section of the nozzle at the low stagnation pressures. A reduction of about 10 per cent in the heat-transfer coefficient resulted from an increase in the inlet boundary-layer thickness between the minimum and maximum thicknesses investigated.Heat-transfer predictions with which the data were compared either incorporate a prediction of the boundary-layer characteristics or are related to pipe flow. At the higher stagnation pressures, predicted values from a modification of Bartz's turbulent-boundary-layer analysis are in fair agreement with the data. As a possible explanation of the low heat transfer at the lower stagnation pressures, a parameter is found which is a measure of the importance of flow acceleration in reducing the turbulent transport below that typical of a fully turbulent boundary layer.