Large eddy simulation of enhanced heat transfer in grooved channel with pulsating flow corresponding to hydrodynamic frequency

This paper presents a numerical investigation on flow and heat transfer in a grooved channel formed by 9 rectangular blocks with steady and pulsating flow. Large eddy simulation is used to simulate the hydrodynamic instability in steady flow and heat transfer enhancement for pulsating flow. The simulations for steady flow at Re=700, 1500, 2500, are firstly conducted, showing that there are 23Hz, 70Hz and 130Hz natural frequencies fN induced by hydrodynamic instability (corresponding to Strouhal number StN=0.876, 1.243, 1.385) behind the first block, which disappear quickly with the flow development. A natural frequency fN of 34Hz (StN=1.295) is found only at Re=700 and it can be maintained and amplified by groove structures. Subsequently, a sinusoidal pulsating flow is applied, with the forcing frequency StF equal to the natural frequency StN in steady flow and the dimensionless amplitude A fixed at 0.2. Flow and thermal performance of the grooved channel is studied under the pulsating condition. A periodic process of vortex generation-shedding-fusion is found behind each block and the fluid in the channel has higher turbulent kinetic energy than that under the steady condition. Ultimately, compared with the thermal and pressure-drop performance between steady and pulsating flow, the enhancement of time-average Nusselt number ranges from 48.08%, 15.64%, 8.61% and time-average friction factor increases by about 40% at Re=700, 1500, 2500. The thermal performance factor is increased by 30.96% and 4.20% at Re=700, 1500 but is reduced slightly by 3.48% at Re=2500. It indicates that the augmentation of heat transfer through pulsating flow is significant at low Reynolds numbers.