Investigation Of Regulation On Heat Transfer And Resistance Characteristics Of Supercritical Hydrocarbon Fuel Based On Micro-disturbing Structures

The hypersonic propulsion system is aiming at high Mach number(Ma8+)nowadays,leading to dramatic heat load for the thermal protection system.High Mach number flight increases the relative heat load of the cooling system,which aggravates the thermal stratification inside the regenerative cooling channel,wastes the effective cooling capacity of propellant,easily induces heat transfer deterioration of hydrocarbon fuel and make the flow distribution more uneven.Aiming at the cooling channel with high heat-to-mass flux ratio in the thermal protection system of scramjet engine,this study explores the regulation method based on the micro-disturbing structures for the heat transfer and flow resistance characteristics of supercritical pressure hydrocarbon fuel.Firstly,the influence of micro-disturbing structures on the heat transfer characteristics of hydrocarbon fuel in the regenerative cooling channel with high heat-to-mass flux ratio are investigated.For the turbulent flow with strong propert ies change in the unilateral heated channel,the heat transfer enhancement of micro-disturbing structures are relying on the effective increment of transverse secondary flow intensity.Meanwhile,the regulation of micro-disturbing structures for hydrocarbon fuel in different temperature regions are different.Compared with the subcritical and supercritical temperature regions,the dramatic properties change in transcritical temperature region leading to a strong shear layer in the vicinity of heated wall,which significantly promotes the heat transfer enhancement of micro-disturbing structures to the hydrocarbon fuel flow in transcritical temperature region,especially at high heat-to-mass flux ratio.When thermal cracking reaction occurs,due to the turbulence time scale being 3-6 orders of magnitude lower than the cracking reaction,the low-density layer near the wall exacerbates the thermal stratification in the cooling channel.Thus,the heat transfer enhancement of micro-disturbing structures for the cracking fuel flow is not obvious.However,micro-disturbing structures could significantly reduce the nonuniformity of the fuel heat sink,which helps to fully utilize the physical heat sink of hydrocarbon fuels.Therefore,the fuel heat sink utilization rate is improved.The parallel studies shows that when the micro-ribs are as:h_r/H=0.15,p_r/e=10,the convective heat transfer factor could be increased by 106%compared with smooth channel,where the nonuniformity of physical heat sink is reduced by 20%.Secondly,the influence of micro-disturbing structures on the flow resistance characteristics of hydrocarbon fuel in the regenerative cooling channel with high heat-to-mass flux ratio are investigated.Due to the dual effects of dramatic property change and thermal stratification,the flow resistance characteristics vary in different temperature regions.In the subcritical temperature region,the channel pressure loss decreases with the increasing heat flux;in the transcritical temperature region,when heat flux increases,the pressure loss firstly decreases and then increase;in the supercritical temperature region,the channel pressure loss increases linearly with the increasing heat flux.When thermal cracking reaction occurs,the pressure loss increases nonlinearly.In this case,micro-disturbing structures can significantly reduce the sensitivity of channel pressure loss to various heat fluxes and eliminate the nonlinearity.The parallel studies shows that when the optimal micro-rib parameters are as:h_r/H=0.15,p_r/e=10,which can reduce the flow resistance sensitivity in the transcritical temperature region by 95%,where the channel pressure loss is just increases by 1.05～2.06 times.Even when thermal cracking reaction occurs,micro-rib could reduce the the flow resistance sensitivity by 64%～87.4%,with only 0.75～2.08times increment of pressure los.In the cooling channel with severe thermal stratification,there exists a synergistic regulation characteristics between the heat transfer enhancement and flow resistance for transcritical hydrocarbon fuel.Besides,there also exists a synergistic regulation characteristics between the heat sink utilization and flow resistance for cracking hydrocarbon fuel.The reason lies on the facts that the micro-disturbing structures have similar regulation to the transverse secondary flow intensity,axial velocity gradient,and turbulent energy dissipation rate.Based on this,for the simplified dual-channel,the study shows that under severe heat flux deviation,micro-rib could reduce the mass flow rate deviation by 30%～70%,where the channel pressure loss only increases 17%～40%.The results concludes that the micro-disturbing structures have good regulation for floe distribution in parallel cooling channels,which provides a new method for the fuel flow distribution in the regenerative cooling channel for high Mach number scramjet engines.