热防护一直是高超声速飞行器与发动机研究的重要领域。随着飞行速度与发动机效率的不断提高，发动机承受的热载荷不断增大。特别是超燃冲压发动机凹腔稳焰装置、支板喷油装置等关键部件，均面临着恶劣的热环境，存在局部峰值热流，急需发展高效的冷却方法，使材料与结构处于安全使用温度范围内。目前超燃冲压发动机最常用的冷却方式是再生冷却。其以机载碳氢燃料作为冷却剂，导入冷却通道，以对流传热方式吸收结构热量。但传统的对流传热方式受限于燃料流量和冷却结构尺寸，对流传热性能难以满足发动机局部高温高热流区域的防热需求。冲击射流冷却作为一种高效的冷却方式，通过冲击孔形成高速射流以及旋涡结构，对需要冷却的壁面进行高效换热。以往关于冲击射流冷却的研究主要以简单介质如空气、水等为主，而关于复杂碳氢燃料冲击射流的研究极少。碳氢燃料如航空煤油，具有复杂的热物性变化与多物态转变过程。因此，研究航空煤油的冲击射流流动与传热特性、揭示流动机理是非常必要的。
    本文实验研究了不同冲击结构及流动参数条件下航空煤油冲击射流的传热效果及压差损失变化规律。采用云母电加热方法为实验测试件提供热载荷，通过测量实验件进出口温差、压降以及冲击冷却壁温等参数，基于能量、动量守恒分析得到煤油冲击射流的平均传热系数及压差系数。实验结果表明，与充分发展管道的对流传热相比，煤油冲击射流具有显著的传热增益效果，增益幅度超过100%。同时，冲击射流的压力损失与煤油工作压力相比很小。实验研究了射流雷诺数Re、冲击高度H、开孔率Af等参数对于传热系数及压力损失的影响规律，得到了努塞尔数及压差系数随流动及结构参数的变化关系式。并且基于强化效率因子指标，综合比较了冲击射流的传热效果与压力损失，确定了最优的冲击射流结构参数。
    结合数值方法，本文揭示了冲击射流传热强化的流动机理。采用雷诺平均方法结合SST k-ω湍流模型以及煤油10组分替代模型数值研究了不同工况下冲击射流的流动与传热特性。数值结果表明，煤油通过冲击孔形成高速射流冲击到冷却面，在孔下游区域形成典型的反向旋转对涡结构，并显著增强了湍动能，在冲击冷却面产生较强的传热效果；同时多股冲击射流之间的相互作用，进一步促进了传热效果。数值研究了雷诺数、冲击高度、开孔率、入口温度对煤油冲击射流流动及传热的影响机制。研究发现，冲击射流在高雷诺数条件下进入了自模区，流场参数具有相似性，并且压差系数不随雷诺数而改变。通过比较冲击高度的影响结果，确定了冲击射流的势流核长度，并分析了不同冲击高度情况下流动及传热性能。本文还数值研究了开孔率的影响。相同流量下，随着开孔率的增加，冲击射流的速度及湍动能不断减小，从而降低了传热系数及进出口压差。另外，通过研究高温煤油冲击射流的流动与传热特性，初步确定了传热系数二次峰产生的流动机理。 
    本文基于分离涡模拟方法，进一步研究了冲击射流流动与传热的非定常特性，得到了冲击射流由于剪切效应产生的脉动现象，获得了脉动的特征频率，并发现冲击冷却面上传热系数及摩擦力受到近壁面流动的影响，其脉动频率与冲击射流脉动频率基本保持一致。

    Thermal protection is always an important research field in the research of hypersonic vehicle and engine. With the continuous improvement of flight speed and engine efficiency, the thermal load of the engine is increasing gradually. In particular, key components such as cavity flame stabilizer and strut injector of scramjet engines are faced with harsh thermal environment and local peak heat flux. Therefore, it is urgent to develop efficient cooling methods to ensure that materials and structures are in the safe operating temperature range. At present, the most common cooling method used in scramjet is regenerative cooling. Aviation hydrocarbon fuel is used as coolant and introduced into the cooling channel to absorb structural heat based on principle of convection heat transfer. However, the traditional convection heat transfer method is limited by the fuel flow flux and the size of cooling structure, so the convection heat transfer performance cannot meet the thermal protection requirements of the local high temperature and high heat flux zone of the engine. As an efficient cooling method, impingement jet cooling can efficiently transfer heat of the wall surface that needs cooling by forming high speed jets and vortex structures through impingement holes. Previous studies on impinged jet cooling mainly focus on simple media such as air and water, while there are few studies on complex hydrocarbon fuel impinged jet cooling. Hydrocarbon fuels, such as aviation kerosene, have complex thermal and physical properties and multi-state change processes. Therefore, it is very necessary to study the impingement jet flow and heat transfer characteristics of aviation kerosene and reveal the flow mechanism.

    This paper experimentally studies the heat transfer effect and the change law of pressure difference loss of aviation kerosene impingement jet under different impingement structures and flow parameters. The mica electric heating method is used to provide the thermal load for the test piece. By measuring the temperature difference between the inlet and outlet of the test piece, the pressure drop and the temperature of the impingement cooling wall, the average heat transfer coefficient and the pressure difference coefficient of the kerosene impingement jets are obtained based on the energy and momentum conservation analysis. The experimental results show that the kerosene impingement jets get a significant heat transfer gain of more than 100% compared with the fully developed convective heat transfer in the pipeline. At the same time, the pressure loss of impingement jets is very small compared with the working pressure of kerosene. The effects of Reynolds number Re, impingement height H, opening rate A_f and other parameters on heat transfer coefficient and pressure loss were studied experimentally, and the relationship between Nusselt number and differential pressure coefficient and flow and structural parameters was obtained. Based on the enhancement efficiency factor index, the heat transfer effect and pressure loss of impingement jets were compared comprehensively, and the optimal structural parameters of impingement jet were determined.

    Combined with the numerical method, the flow mechanism of heat transfer enhancement by impinging jets is revealed. The flow and heat transfer characteristics of impingement jets under different working conditions were studied numerically by using the Reynolds average method combined with the SST K-ω turbulence model and the 10-component kerosene substitution model. The numerical results show that the kerosene impinges on the cooling surface through the impingement holes, forming typical counter-rotating vortexes structure in the downstream zone of the holes, and significantly enhancing the turbulent kinetic energy, resulting in a strong heat transfer effect on the impingement cooling surface. At the same time, the interaction between multiple impinging jets further promotes the heat transfer effect. The influence mechanism of Reynolds number, impingement height, hole ratio and inlet temperature on kerosene impingement jets flow and heat transfer was studied numerically. It is found that the impinging jets enter the self-similarity region under the condition of high Reynolds number, the flow field parameters are similar, and the pressure difference coefficient does not change with Reynolds number. By comparing the effects of impingement height, the length of potential flow core of impingement jet was determined, and the flow and heat transfer performance under different impingement height were analyzed. The effect of opening ratio is also studied numerically. With the same flow rate, the velocity and turbulent kinetic energy of the impingent jet decrease continuously with the increase of the opening rate, thus reducing the heat transfer coefficient and the pressure difference between inlet and outlet. In addition, by studying the flow and heat transfer characteristics of high temperature kerosene impinged jets, the flow mechanism of the secondary peak of heat transfer coefficient was determined.

    Based on the detached eddy simulation method, the pulsation phenomenon caused by the shear effect of the impinging jet is found, and the characteristic frequency of the pulsation is obtained. It is found that the heat transfer coefficient and friction on the impinging cooling surface are affected by the flow near the wall, and the fluctuation frequency was basically consistent with that of impinging jet.