Investigation Of Heat Transfer Characteristics In Regenerative Cooling Scramjet Start-up Stage

Heat transfer characteristics of kerosene in regenerative cooled scramjet start-up stage were investigated. Theoretical analysis, numerical simulation and experimental verification was applied to investigate the characteristics of heat transfer and the relationship between the parameters of the cooling channel and the performance of the heat transfer ability under unstable, low-heat-flux condition.The numerical simulation part was based on the kerosene property model calculated by NIST-SUPERTRAPP. Cooling channels of different parameters were simulated to observe the relationship of the parameters of the cooling channel and the performance of the heat transfer ability. Results show that the thinner the wall is, the larger the width to height ration is, the faster the flow speed is, the better the performance of heat transfer ability is.Radiation heating method was applied to simulate the heat transfer between the hot gas and the inner-wall of the scramjet. Results show that the three-section phenomenon of the curve under the usage of nozzle; under the same flow rate, no matter preheating or not, the same stable state will be achieved if the throat of the nozzle is the same, and preheating can eliminate the time needed to achieve the stable state; special heat transfer phenomenon under near-supercritical pressure is due to the inconsistency of the first derivative of the specific heat under near-supercritical pressure; the first-decrease-and-then-increase phenomenon of the gradient of the oil temperature curve is due to the same phenomenon of specific heat near critical point, and the curve becomes smooth as the pressure rises is due to and the shift of specific heat becomes smooth as the pressure rises; the low-frequency vibration of pressure phenomenon was due to the density wave instability of the two-phase instabilities, and the vibration period is the same or twice as the time kerosene stays in the channels.Eight single-channel panels of the same area and different parameters were designed. Unstable energy transfer process was analyzed, fin-efficiency, efficient heat transfer area, thickness of inner-wall, shape of cross section, heat transfer coefficient were analyzed and deduced, and numerical simulations results, theoretical analysis results and experiment results were compared. Results show that heat transfer enhancement of the fin is due to the enlargement of the heat transfer area, and the perfect fin should reach the maximum value of multiplying the area and the fin-efficiency; the thinner the inner wall is, the smaller the heat conduction resistance is, and the higher the heat transfer ability is; the better performance of the trapezium-shaped channel is due to the high fin-efficiency of the trapezium-shaped fin; to enhance the heat transfer coefficient, the better way is to increase the flow speed, and it can be obtained by decreasing the area of the cross section, but it results the reduce of the effective heat transfer area; the increase of the temperature which has a positive feedback on heat transfer ability is due to the increase of the specific heat as the temperature rises.