Flow And Heat Transfer Of Kerosene Flowing Inside The Regenerative Cooling Channels Of Scramjet At Near-critical Pressures

The flow and heat transfer of RP-3 kerosene flowing at near critical pressures have been studied in this paper.Research focuses on the heat transfer of kerosene at near critical pressures and the generating mechanism and stability boundaries of thermo-acoustic instability.The influences of thermo-acoustic instability on the flow and heat transfer characteristics also have been studied,and correlations for steady heat transfer and thermo-acoustic instable heat transfer were put forward.The heat transfer of kerosene at near critical pressures can be classified as initial heat transfer,normal heat transfer,and pseudo-boling heat transfer.The initial heat transfer is mainly influenced by entrance effect coupled with flow and pseudo-boling.The pseudo-boling heat transfer is similar with boiling heat transfer,and is related to folw.Because of the difficulty in studying thermo-acoustic instability under supercritical pressure,the thermo-acoustic instability under subcritical pressure is studied firstly.The results indicate that thermo-acoustic instability is a kind of dynamic instability which is generated during the system transforming between instable state and stable state.And the transformingprocedureis driven by positive feedback and negative feedback.Secondly,the thermo-acoustic instability under supercritical pressure is studied.The results indicate that the varying trends of thermo properties at supercritical pressure are similar to that at subcritical pressure.And the generating procedure of thermo-acoustic instability under supercritical pressure is same to that under subcritical pressure.Thus the generating mechanism of thermo-acoustic instability at subcritical pressure can be applied to thermo-acoustic instability under supercritical pressure.To understand the stability boundaries,the threshold heat flux of thermo-acoustic was firstly studied.The parametric investigationsindicate that the thermo-acoustic instability is promoted by an increase in mass flow rate and inlet temperature while is restrained by an increase in operating pressure.Then two dimensionless parameters,namely,sub-pseudo-critical number and true trans-pseudo-critical number were used to study the boundary of the thermo-acoustic instability.The result reveals that the system stability is significantly enhanced by increasing operating pressure.The instable area decreases obviously with increasing inlet temperature.And mass flow rate has no obvious effects on the system stability.Based on the experimental results,a correlation of threshold heat flux was put forward.In the investigation on the influence of thermo-acoustic instability on the flow characteristics,the pressure drop fluctuations were used to represent the characteristics of thermo-acoustic instability.The influence of thermo-acoustic instability on the heat transfer characteristics is studied.And the method of studying the heat transfer characteristics of thermo-acoustic instability was put forward.The heat transfer characteristics are significantly enhanced by thermo-acoustic instability,which is restrained by an increase in mass flow rate and inlet temperature.Based on the experimental results,new correlations for steady heat transfer and thermo-acoustic instable heat transfer were put forward,and the accuracy is improved a lot.