| By combining the merits of high thrust-to-weight ratio liquid rocket engine and high specific impulse dual-mode ramjet engine,the Rocket Based Combined Cycle(RBCC)engine can realize the high efficiency of performance in wide range of speed and altitude and it is one of the ideal propulsion systems in the future areas of reusable near space aerocraft and space vehicle.However,the RBCC engine confronts much more severe thermal load compared with the liquid rocket and scramjet engine.Due to the wide range of RBCC engine,the thermal environment reflects strong time and spatial characteristics at different operation modes.Therefore,the thermal proctection system design is no longer a component level technology,but a system level design based on multi-mode operating conditions.It is urgent to develop the research of flow and heat transfer mechanisms in regenerative cooling process of RBCC engine based on hydrocarbon fuel,so as to improve the developments of the key technologies related to regenerative thermal protection system design of combined cycle engine.Under the background of Mach 5?6 long-range cruise mission of near space hypersonic vehicle,a one-dimensional analysis method and a three-dimensional numerical simulation model are developed to study the thermal protection system of RBCC engine.This paper obtains the specific thermal environment characteristics at different operation mode of RBCC engine and investigates the flow and heat transfer processes of supercritical hydrocarbon fuel based on the complex thermal load of RBCC engine and reveals the mechanism of non-uniform distribution in parallel cooling channels under uneven thermal boundary.An innovative self-adaptive method for improving heat sink utilization efficiency of hydrocarbon fuel in regenerative thermal protection system of combined cycle engine is proposed.Moreover,a regenerative cooling system of a combustor variable RBCC engine is completed.The main contents and conclusions of this paper are as follows:(1)The thermal environment characteristics of two types of RBCC flowpath scheme based on thermal throat and geometric throat are obtained.Through the three-dimensional numerical simulation with constant wall temperature,the thermal loads of ramjet and flame holders of different flowpath schemes at different locations and under different Mach numbers are compared in detail.The effect of wall temperature on the thermal load of RBCC engine is also investigated to provide guidance in the initial stage of RBCC engine design.(2)A one-dimensional analysis model and a three-dimensional numerical model are established.These two models consider the conjugate heat transfer between the fluid and solid zones,the variable thermo-physical properties of supercritical hydrocarbon fuels and the endothermic pyrolysis reaction,and the one-dimensional analysis model can be employed in the initial stage of regenerative cooling channels' design while the three-dimensional numerical model for single cooling channel and multi cooling channels can give more details of flow and heat transfer processes.These two models are validated through the electrically heated tube test and can be employed for the following investigations.(3)Effects of coolant inlet temperature and wall heat flux on the flow and heat transfer characteristics of a single curved cooling channel are obtained.Through the three-dimensional numerical simulation,the secondary flow in cooling channel and its effect on heating wall are analyzed,the results show that the pyrolytic reaction can improve the intensity of vortex and reduce the transverse temperature diference by 6.5%.And the increasing inlet temperature also decreases the transverse temperature difference.But the fluid-solid conjugate model would mitigate the transverse temperature difference in unilateral heating model due to the conduction in the solid zone.(4)An innovative self-adaptive method for improving heat sink utilization efficiency of hydrocarbon fuel in regenerative thermal protection system of combined cycle engine is proposed.Through the numerical simulation of multi-channels,the severely non-uniform flow distribution between parallel cooling channels are captured and this non-uniform distribution is very sensitive to the thermal boundary.A self-adaptive method for improving flow distribution in parallel channels based on the flow characteristics of adjacent cooling channels is proposed,the adaptive mini-structure improves the mass flow uniformity between parallel channels by forming a jet flow through the mini-structure and the backward recirculation region created by the jet flow,these two characteristics adaptively change the flow area in the low heat flux channel and create a virtual throat after the adaptive mini-structure which decreases the mass flow rate in low heat flux channel and achieves better uniformity.Also,the effects of the number,location of adaptive structure and wall heat flux on the improvement degree are studied.(5)A strategy for the axial flowpath design of coolant is established based on one-dimensional analysis method.Based on the thermal environment characteristics of thermal throat and geometric throat RBCC engines,the different flowpaths of the coolant are analyzed,and it shows that coolant flowpath can improve the walls' overall temperature uniformity.(6)The design of regenerative cooling system of a geometric variable RBCC combustor is completed.Based on the thermal environment of wide range RBCC engine and the above research results of flow and heat transfer processes in cooling channels,the asynchronous iterative design of regenerative cooling channels is carried out and its effectiveness is validated by three-dimensional numerical simulation. |
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