超临界压力下纳米流体对流传热的数值模拟研究

To develop hypersonic flight vehicle is one of the most challenging topics in aerospace engineering. Scramjet engines, which are the hearts of hypersonic flight vehicles, encounter severe thermal management issues because of the significant heat release from combustion and aerodynamic heating. At high hypersonic flight speeds, the temperature of scramjet engines is too high to be cooled by convective heat transfer of traditional hydrocarbon fuels, so it is necessary to improve the thermal performance of hydrocarbon fuels..This numerical study focuses on the heat transfer enhancement of hydrocarbon fuels containing nanoparticles at supercritical pressures in the regenerative cooling system of hypersonic flight vehicles. The prediction method for hydrocarbon fuel thermophysical properties at supercritical pressures is to be developed based on classic solid-liquid two phases suspension theory and the effects of nanoparticles’ micromovement. Then, computational method and numerical model for convective heat transfer of nanofluids at supercritical pressures are to be established. Systematic numerical studies on supercritical flow and heat transfer characteristics of nanofluids will be conducted, and enhancement mechanism of supercritical heat transfer will be discussed. This work can provide foundational basis for the design and optimization of regenerative cooling system.

高超声速飞行器的研发是航天工程中极具挑战性的研究课题，而超燃冲压发动机是有动力高超声速飞行器的心脏，目前面临最关键的问题是燃烧室的冷却问题。随着高超声速飞行器飞行马赫数的增加，迫切需要提高碳氢燃料的传热性能，以满足发动机主动再生冷却需求。. 本项目以高超声速飞行器主动再生冷却系统为研究对象，开展该系统中纳米粒子强化碳氢燃料超临界传热的数值研究。本项目拟基于经典固液两相悬浮液理论和纳米粒子微运动作用，并考虑压力影响，建立超临界压力下纳米流体的物性计算方法；在此基础上，建立纳米流体超临界压力对流传热的模拟方法和数值模型，研究纳米流体在超临界压力下的流动和传热特性，探索超临界传热的强化机理，为主动再生冷却系统的优化设计奠定理论基础。

随着纳米科技的发展及其在传热领域的应用，使用纳米流体来强化对流传热成为了当前的重要研究课题。本项目开展了超临界压力下碳氢燃料基纳米流体湍流传热的数值模拟研究，分析了纳米颗粒对主动冷却通道内湍流传热的影响，包括强化超临界传热、延迟和减弱传热恶化等；对影响纳米流体传热性能的关键参数进行分析，探索纳米粒子对碳氢燃料超临界压力下湍流传热的强化机理。数值模拟结果表明：CuO、Cu纳米颗粒能显著提高低温甲烷、正癸烷基液的湍流传热性能。纳米流体强化湍流传热归因于加入纳米颗粒降低了近壁面湍流区内流体的运动粘度而提升了它的湍流导热系数，而且加热纳米颗粒减小近壁面粘性底层的厚度，最终达到强化湍流传热的效果。研究揭示了碳氢燃料基纳米流体作为冷却剂在主动冷却系统的应用前景。