FLUID-FLOW AND HEAT-TRANSFER IN A PERIODICALLY DIVERGING-CONVERGING TURBULENT DUCT FLOW

Experiments have been performed to investigate the effects of pressure gradient on the fluid flow and heat transfer in duct flow. Air flow in a fully developed turbulent state was decelerated through a linearly diverging section, and then accelerated through a linearly converging section. Two different ducts were tested, whose acceleration parameter K in the accelerating section was 2.2 X 10(-6) and 4.5 x 10(-6). The wall static pressure, the heat transfer coefficient and fluctuations of streamwise velocity as well as the time-averaged velocity profiles were measured. The heat transfer coefficient and turbulence intensity in the converging section were considerably lower than those in the diverging section, and the viscous sublayer expanded in the converging section. The behavior of the increase or decrease of the heat transfer coefficient was similar to that of the turbulence intensity in the near-wall region.