Measurements of Mean Velocity and Mass Exchange in a Separated Recirculating Flow

Abstract

Experimental measurements were taken in a closed, recirculating, turbulent separated flow. The experiments were made to elucidate the mass and momentum exchange mechanisms between the throughflow and the recirculating flow in a combustor that had previously been developed for burning heavy fuels without a flame tube. Mean velocity measurements are presented for the cold flow field and these are used to derive a detailed streamline pattern. The three-dimensional shear layer surface that divides the recirculating flow from the throughflow is analyzed in detail and the variation of momentum exchange coefficient along its development length is derived. Mass exchange data show that the variation of mass transport along the mixing layer is similar to the variation of momentum transport. Overall features of the exchange processes are shown to be similar to those in simple two-dimensional, nonducted mixing flows if allowance is made for the three dimensionality of the present layers. However, it is also shown that there are significant quantitative differences between the two types of flow. The overall mass exchange rate between the two flow regions was found to be one-third of the mass rate supplied to the combustor and this is a typical figure for conventional designs.