Convective heat transfer in pulsed separated flows

The present paper describes the numerical modelling of turbulent flow and convective heat transfer for two cases of forced unsteady separated flows: periodically oscillating flow through an abrupt pipe expansion, and flow over a backward facing step with periodic injection and ingestion through a slot at the separation corner. In both cases the flow Reynolds numbers are reasonably high and emphasis is placed on the resulting heat transfer rates in the separated and recovery regions of the flow. The present work tests the two-equation linear k -e scheme (Launder and Sharma, 1974) ; a modified two-equation non-linear k -e (Craft et al., 2005), and a simple DSM model (Iacovides et al., 1999) in conjunction with the Reynolds-averaged momentum (URANS) and temperature equations. The Crank-Nicholson and bounded QUICK schemes have been used in all computations and tests were carried out to ensure grid and time-step independency of the results. The imposed unsteadiness enhances the coherence of the separated shear layers and reduces the reattachment lengths. All the models are shown to broadly capture this effect, with the non-linear eddy viscosity scheme giving better quantitative agreement with available experimental data. Key words: Eddy-viscosity model, DSM, Convective heat transfer, Imposed unsteadiness, URANS.