深低温氦透平膨胀机的设计理论与自耦匹配特性研究

In the helium cryogenic system, turbo-expander is the crucial unit which provides most of the cooling. The cooling capacity can be significantly increased if the saturation state is achieved at the expander outlet, which is of great importance for improving system feasibility and economical efficiency. In order to resolve the critical issues of the fundamental theory of the large-ratio expansion in the cryogenic helium turbo-expander, both theoretical and experimental work will be performed to study the cooling-down characteristics and the mechanism of energy transport during the transcritical expansion of helium near the saturation temperature. The numerical model for the unsteady viscous compressible flow will be developed to describe the transonic flow of low-temperature helium in the incomplete Laval nozzles, revealing the mechanisms of helium expansion and internal energy conversion. The coupling between fluid-solid slip and distribution of flow and temperature field and the interaction between gap flow and main stream will be analyzed in detail, and the effects of size, boundary, three-dimension flow and fluid properties on the performance of the turbo-expander can be obtained. The matching characteristics will be investigated for the interaction between the expansion cooling and the compression break, the interaction between thermodynamics and aerodynamics, and the relations between mechanical performances. Finally, this study is aimed to develop the design and modulation theory and realize the modeling and simulation of the dynamic characteristics of expander-compressor system, providing guidelines and support for the application of large cryogenic system and the development of the great science projects.

在低温系统中,氦透平膨胀机是主要的冷量来源和核心部件。氦透平深低温运行出口达到饱和状态可提供更多的冷量，提高整套低温装置的可行性与经济性。针对深低温氦透平膨胀机大膨胀比膨胀的核心问题，拟开展膨胀机内近饱和氦气跨临界膨胀过程中的降温特性和能量迁移规律的基础理论和关键技术研究，建立非定常粘性可压缩流动模型，描述深低温氦气在不完全拉法尔喷嘴中的跨音速流动，揭示高速旋转扭曲狭窄流道内氦气膨胀与内能转换机理，分析气-固界面间滑移与流场、温度场的耦合以及间隙流动与主流的相互作用机制，获得尺度效应、边界效应、三元流与工质特性对透平性能的影响。开展深低温透平膨胀降温与压缩制动，非平衡热力学与气动、机械性能间的自耦与匹配特性研究，构建大膨胀比深低温氦透平膨胀机的基础设计理论和调控方法，实现氦透平膨胀机-制动压缩机系统特性的动态模拟与仿真正反两方面命题求解，为大型低温系统的应用和大科学工程的实现提供保障。

针对深低温氦透平膨胀机的设计理论与自耦匹配特性的核心基础问题，本项目目标要求的研究内容为：1.研究深低温氦透平膨胀机跨临界近饱和膨胀机理；2.研究高速流道内工质跨音速流动与能量迁移的内在联系，掌握深低温氦透平膨胀机的基础设计理论；3.研究深低温氦透平膨胀机系统向心膨胀-离心压缩自耦匹配特性。由于在大膨胀比下可以获得深低温氦透平膨胀机的大冷量、减少系统复杂性，本项目还着重对深低温氦透平膨胀机大膨胀比膨胀特性进行了研究。.本项目针对深低温氦透平膨胀机膨胀的基础问题研究，基于不可逆过程热力学和非定常理论，揭示了狭长扭曲流道内受静-动界面影响的二次流、扰流和边界层脱离现象；获得深低温氦气特殊物性和高速离心力及科里奥利力对跨临界向心膨胀过程的影响；建立了深低温氦透平膨胀机跨音速膨胀三元流动数学模型，分析了近马赫数流体在叶轮中的内流机理以及跨音速膨胀降温特性，揭示高速流道内工质流场-壁面相互作用与能量迁移的内在联系，提出膨胀段与压缩段不同工况特性的固定流道与扭曲叶型型线的设计方法；基于改进一元流动 及三元流动分布参数动态传输模型，解决了高速透平各通流单元的数学建模问题并进行耦合分析，揭示了高速流道内跨音速、跨临界、近饱和膨胀及同轴制动匹配的机理，并建立了耦合热力学、流体气动力学和转子动力学的性能评估理论；在理论分析和数值模拟工作的基础上，对氦透平膨胀机进行了常温和 80K 温区的测试和定量分析，获得了氦透平膨胀机膨胀段与压缩制动端的热力学特性和气动性能，进一步在 EAST 4.5K 氦低温系统实验平台进行深低温氦透平膨胀机的运行测试，提出适合于大型低温系统降温要求的调控机制。最终通过对实验结果的分析与归纳，验证理论研究的正确性，并对理论模型和仿真预测方法进行改进，设计出低温膨胀叶轮和高效制动压缩叶轮；开展了大膨胀比深低温氦透平膨胀机的实验测试，掌握了深低温氦透平膨胀机的基础理论和关键技术。