Numerical Investigation Of Flow And Enhanced Heat Transfer Of Supercritical Hydrocarbon Fuel With Dimples

Regenerative cooling,which applies supercritical fuel as coolant,is crucial for the thermal protection of hypersonic propulsion systems and liquid-propellant rocket engines.How to improve the cooling efficiency to ensure the safty of the viechle has becoming the key issue.Numerical investigations of the flow and heat transfer characteristics of hydrocarbon fuel in rectangular mini cooling channels in wichi dimples are applied to one wall as heat transfer enhancement devices are conducted.Meanwile,large eddy simulation of heat transfer of supercritical fuel is also conducted.Firstly,a 3-dimensional Reynolds-averaged numerical model is developed based on a single cooling channel of a scramjet.The thermophysical properties of supercritical hydrocarbon fuel are calculated with UDF.With dimples in the cooling channel,the heat transfer rate is 1.64 times that of smooth channel,while the pressure drop penalty is only 1.33 times that of the smooth channel.The thermal stratification of an asymmetrically heated regenerative cooling channel is greatly allevieated by dimples.Heat transfer deterioration in the smooth channel is caused by the formation of ‘M-shaped’ velocity profile which reduces the production of turbulence.While in the dimpled channel,the heat transfer directly deteriorates due to the rapid decrease of fuel density,although velocity gradient grows in the channel length.Then,the effects of depth-to-diameter ratio of spherical dimples,channel height,and shapes of dimples on the heat transfer performance of dimpled channel are numerically investigated.The results reveal that the dimples with depth-to-diameter ratio of 0.2 has the best overall heat transfer pereformance.Decreasing the channel height is beneficial for the heat transfer in the channel.Among the 3 different types of dimple shapes,the teardrop dimple performs the best to cool the channel wall,while the front-protruded dimple has slightly lower heat transfer level but beter than the spherical dimple.The middle-protruded dimple has the lowest heat transfer rate among all the dimples.Finnally,large eddy simulation of heat transfer of supercritical fluid in a vertical tube with the influence of buoyancy force is conducted.Through detailed comparision with DNS data,results show that the main reason of the deviation with the DNS results can be attributed to the useage of constant subgrid scale Prandt number for the calculation of subgrid scale enthalpy flux in the filtered engery equation.Large eddy simulation of the flow and heat transfer characteristics in a dimpled channel revealed the unsteady statistics and vortex structures.The streamwise vortices forms in the separated shear layer which is quite unstable.The the vortices are shed downstream and gradually turned in to a horsesheo vortex.The horseshoe vortices interact with the main flow and become streamwise vortices.Time-averaged results give further insight into the flow structu re and the heat transfer enhancement mechanism of dimples.