TRANSIENTS IN FLOW AND LOCAL HEAT-TRANSFER DUE TO A PRESSURE WAVE IN PIPE-FLOW

The effect of a pressure wave on the turbulent flow and heat transfer in a rectangular air flow channel has been experimentally studied for fast transients, occurring due to a sudden increase of the main flow b y an injection of air through the wall. A fast response measuring tech nique using a hot film sensor for the heat flux, a hot wire for the ve locities and a pressure transducer have been developed. It was found t hat in the initial part of the transient the heat transfer change is i ndependent of the Reynolds number. For the second part the change in h eat transfer depends on thermal boundary layer thickness and thus on t he Reynolds number. Results have been compared with a simple numerical turbulent flow and heat transfer model. The main effect on the flow c ould be well predicted. For the heat transfer a deviation in the initi al part of the transient heat transfer has been found. From the turbul ence measurements it has been found that a pressure wave does not infl uence the absolute value of the local turbulent velocity fluctuations. They could be considered to be frozen.