Study on the disturbance effect of pulsating flow and heat transfer in self-excited oscillation shear layer

Abstract

The fluid movement motion has an important influence on the evolution of the pul?sating flow in the hot runner. Using the large eddy simulation numerical method, the instantaneous velocity, wall shear stress, boundary-layer thickness, and Nusselt number of hot runner section under different structural parameters at an inlet pressure of 5000 Pa were studied. The research results showed that the backflow vortex can be formed in the hot runner, and the fluid at the axis center of hot runner can form a pulsating flow under the squeezing action of the backflow vortex. The pulsating flow had a strong disturbance effect on the fluid around the axis center and accelerated the heat exchange between the fluid around the axis center and the wall. The disturbance effect of pulsating flow gradually strengthened with the flow of the main flow to the downstream. When d2/d1 was 1-1.8, the wall shear stress first increased and then decreased, and the wall heat transfer efficiency first increased and then decreased. The maximum wall shear stress was 36.4 Pa. When L/D was 0.45-0.65, the boundary-layer thickness first decreased and then increased, and the heat transfer efficiency first increased and then decreased. The minimum boundary-layer thickness was 0.392 mm and the maximum Nusselt number was 138. When d2/d1=1.4 and L/D=0.55, the maximum comprehensive evaluation factor reached 1.241, and the heat transfer efficiency was increased by 24.1%.