Experimental study of sudden expansion in pipe flow

Abstract

An Experimental Study of Sudden Expansion in Pipe Flow Flow through a sudden expansion, though the simplest and perhaps the earliest problem of fluid flow separation, still leaves much to be understood. The sudden expansion represents the special case of co-flow jets with zero secondary stream velocity. Flow through axisymmetric sudden expansion in a pipe has been investigated experimentally with air as the flow medium for an area ratio of approximately 11, in the Reynolds number range 0.8�5?1.3�50.8 \times 10^5 - 1.3 \times 10^50.8�5?1.3�5. Mean velocity and static pressure variations across the pipe have been obtained at several traverse stations downstream. The separation streamline has been obtained and the location of the reattachment point and secondary separation are compared with the results of other experiments. The assumption of self-preservation of the velocity profile has been checked and compared with those of a free jet and co-flowing jet. The static pressure contours in the flow field have been obtained and the minimum static pressure appears to be associated with the regions of maximum shear. The assumption of constant base pressure on the separation face, often made in elementary momentum analysis, is found to be surprisingly good. The Borda-Carnot estimation of energy loss is substantiated by the experimentally determined variation of energy along the pipe.