Studies On Mechanism And Prediction Of Thermo-acoustic Oscillation And Heat Transfer Deterioration Of Aviation Kerosene At Supercritical Pressures

The scramjet engine works under an extremely harsh environment caused by the combustion heat and aerodynamic heat, and faces serious material thermal protection problem. The regenerative cooling takes the endothermic hydrocarbon fuel as a coolant and carries heat by physical and chemical heat sinks, which could efficiently solve this problem. In the regenerative cooling channels, since the operational pressure of hydrocarbon fuel is above its critical pressure, under a supercritical pressure, the special variations of thermo-physical properties lead to complex flow and heat transfer phenomena. Therefore, the research on the flow and heat transfer process of hydrocarbon fuel under supercritical pressures has a great significance on the regenerative cooling technology application.So far, although a number of studies have been conducted to examine the flow and heat transfer processes of hydrocarbon fuels under supercritical pressures, more fundamental investigations, especially for the mechanism and prediction of thermo-acoustic oscillation and heat transfer deterioration, still need to be perfected. Based on a combination of experimental and numerical analysis methods, in this paper, the related research, taking the RP-3 aviation kerosene as a research object, has been performed.Firstly, experimental investigations on unstable and stable flow and heat transfer of aviation kerosene at supercritical pressures in a vertical upward circular tube were performed. (l)For unstable flow and heat transfer conditions, the mechanism and critical condition of thermo-acoustic oscillation in the transition-flow region, as well as the quantitative prediction for heat transfer performance after thermo-acoustic oscillation, were investigated. Results indicate that when the fluid inlet Reynolds number is less than 4100, a periodic instability of viscous boundary layer occurs due to the thick thermal boundary layer, and thus leads to the thermo-acoustic oscillation. As the heat flux or pressure increases, the variation of viscosity with temperature tends to flatten, so that the oscillation is weakened. The transition process of thermal boundary layer is weakened with the increasing mass flux, and consequently the thermo-acoustic oscillation is also suppressed. Meanwhile, once the shaking wall temperature is higher than the pseudo-critical temperature, a periodic pseudo-boiling effect would further exacerbates the thermo-acoustic oscillation. The stability boundary has been described based on two dimensionless numbers of the trans-pseudo-critical number and the sub-pseudo-critical number, the prediction correlation and heat transfer correlation for thermo-acoustic oscillation were successfully developed. (2)For stable flow and heat transfer conditions, the mechanism of heat transfer deterioration, and the quantitative prediction for heat transfer, were analyzed. Results indicate that under low mass fluxes, the buoyancy and thermal acceleration cause the heat transfer deterioration in the transition-flow region, and the buoyancy induces the heat transfer deterioration in the turbulent-flow region. The heat transfer correlations, by amendment of buoyancy and thermal acceleration parameters which applied to the transition-flow region, and by amendment of buoyancy parameter which applied to the turbulent-flow region, were obtained. Under high mass fluxes, the buoyancy causes the heat transfer deterioration in the transition-flow region, and the pseudo-film boiling induces the heat transfer deterioration in the turbulent-flow region, two heat transfer correlations by amendment of density and thermal diffusivity which applied to the transition-flow and turbulent-flow regions have been respectively developed.Secondly, based on the reliability of numerical methods were fully verified, numerical studies on the convective heat transfer of aviation kerosene at supercritical pressures in vertical and horizontal circular tubes were performed. Compared with the experimental research, the difference is that the length of tubes were selected according to various heat fluxes, so as to obtain the whole flow and heat transfer process. (1)For vertical circular tubes, the mechanism and critical condition of heat transfer deterioration were analyzed. Results indicate that two types of heat transfer deterioration occur in the low and high bulk fluid temperature regions, respectively. The heat transfer deterioration with low bulk fluid temperature is caused by the thermal acceleration, and abnormal distributions of the near-wall turbulent kinetic energy and wall shear stress are observed. The heat transfer deterioration with high bulk fluid temperature is caused by the pressure imbalance, and abnormal distributions of the near-wall mass flux and radial velocity are observed, it can be considered as a pseudo-film boiling phenomenon. The action mechanism and critical condition of pseudo-film boiling effect were firstly developed, and its critical heat flux linearly increases with the mass flux or the operational pressure. (2)For horizontal circular tubes, the evolution characteristics of secondary flow, the effect mechanism of secondary flow on heat transfer deterioration, and the quantitative prediction of secondary flow effect, were analyzed. Results indicate that non-uniform heat transfer deterioration phenomenon along the tube circumference direction appears due to the strong secondary flow and pseudo-boiling effects in the pseudo-critical region, and the prediction correlation for heat transfer difference between the tube-top and tube-bottom by amendment of Grashof number was obtained.Finally, based on the actual structure and heating mode of regenerative cooling channel, numerical studies on the flow and heat transfer processes of aviation kerosene at supercritical pressures in a square channel with asymmetric heating on the top exterior wall surface, including constant heat flux and constant temperature, were performed. The coupling mechanism between wall heat conduction and heat transfer deterioration, and the quantitative prediction of heat flux at the inner-wall surfaces, were analyzed. (1)For constant exterior wall heat flux conditions, results indicate that the heat transfer deterioration occurs in the pseudo-critical region, featuring an increase of wall temperature and a decrease of heat flux, and the prediction correlations for abnormal heat flux distributions at the heating internal wall and the side internal wall by amendment of temperature were obtained. (2)For constant exterior wall temperature conditions, results indicate that the heat transfer deterioration occurs when the fluid specific heat capacity reaches the peak value, only featuring an abnormal decrease of heat flux. The correlations for heat flux prediction at the heating internal wall and the side internal wall by amendment of volumetric heat capacity were obtained.