基于转捩/湍流一体化模式的RANS-LES混合方法研究

When the air-vehicles reentry, such as X-37B and Shenzhou capsules, the flow on the windward side encounter transition and the temperature is very high. It’s a great challenge for the thermal protection system (TPS) design. At the same time, the flows on the leeward side are massive separation, which has an important influence on the designs of aerodynamics and flight control. In fact, both the transition on the windward surface and the massive separation on the leeward side are the two very difficult frontier problems in the field of fluid mechanics. When both of them happen, accurate prediction becomes much more difficult. However, the designers desire to well capture both of transition and massive separation around the space airplanes and capsules at the same time...In this project, on the basis of the three-equation compressible transition and turbulence model proposed by our laboratory members, the new Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) hybrid model, RANS-LES-Tr (DDES-Tr or IDDES-Tr), is constructed, developed and validated. On the windward surface, the transition of the attached flow is mainly simulated by the transition model, including the following transition factors, such as the first, second, crossflow, separation, and so on. On the leeward side, the massive separation is predicted by the RANS-LES hybrid model. To improve the robustness of numerical scheme, the shock wave detector is introduced and optimized in the adaptive dissipation scheme. Three flows with both transition and massive separation, which have been measured with plenty of transition and separated flowfields data, are selected to validate and verify our new RANS-LES-Tr model. The first one is the cylinder at subcritical and critical Reynolds numbers. In this case, only the effects of first mode instability and separation on the transition are considered. The second one is the flow around the 6:1 prolate spheroid at middle and high angles of attack. Here, two effects of the first and crossflow on the transition are considered at the same time. The third case is the Orion capsule at hypersonic speed and at high angle of attack. In this case, the third transition factor of second mode instability is added. Through these three cases, more and more transition factors are gradually introduced, validated and verified. At the same time, the hybrid strategies are also validated and verified through them. Finally, our new RANS-LES-Tr model can be applied to well predict this kind of flow, which contains both the transition on the windward surface and the massive separation on the leeward side. It can be extended to design the TSP, aerodynamics and flight control of space plane and capsule.

X-37B空天飞机、返回舱等再入时，迎风面流动转捩温度极高，挑战热防护设计；背风面大分离，严重影响气动力和飞行控制设计。无论迎风面转捩还是背风面大分离，都是当今尚未完全解决的前沿难题；共存时难度更大，同时准确模拟却势在必行。..拟基于实验室提出的三方程可压缩转捩/湍流一体化模式，构造兼顾计算精度与效率的新型RANS-LES-Tr混合方法（迎风面用计及第一、第二、横流、分离等因素的转捩模式准确模拟层流和转捩；背风面用混合方法解析非定常大分离；系统研究符合物理过程的耦合策略）；引入激波探测器构造高精度自适应耗散格式。通过分析亚/临界Re圆柱、大攻角椭球体、高超声速大攻角猎户座等具有详细实验数据的算例，由少至多验证转捩影响因素（第一，第一和横流，第一、二和横流）和混合方法耦合策略，既准确模拟迎风面附体转捩，又精细预测背风面大范围分离，可推广应用于空天飞机和返回舱热防护、气动力和飞行控制设计。

边界层转捩和大范围分离的非定常流动问题一直都是工程上关注的焦点。特别是对于高超声速飞行器，如返回舱等再入大气层时，迎风面流动转捩温度极高，挑战热防护设计；背风面大分离，严重影响气动力和飞行控制设计。无论迎风面转捩还是背风面大分离，都是当今尚未完全解决的前沿难题；共存时难度更大，同时准确模拟却势在必行。兼顾计算精度和效率的DES类混合方法预测大分离效果不错，但由于目前的DES类混合方法未考虑转捩的影响，预测结果与真实情况存在差异。.本项目基于实验室提出的三方程可压缩转捩/湍流一体化模式，构造了兼顾计算精度与效率的新型RANS-LES-Tr混合方法，迎风面用计及第一、第二、横流模态影响和分离等因素的转捩模式准确模拟层流和转捩，背风面用混合方法解析非定常大分离。通过仅含第一模态转捩的亚临界圆柱绕流、A-Airfoil近失速翼型流动、含第一和横流模态转捩的6:1大攻角椭球体流动，以及含第一、第二和横流模态转捩的高超声速大攻角“猎户座”返回舱流动算例，对比基于转捩模式的混合方法和基于全湍流的混合方法结果，并与实验数据对比，验证了转捩影响因素（第一，第一和横流，第一、二和横流）和混合方法耦合策略，既准确模拟迎风面附体转捩，又精细预测背风面大范围分离，可推广应用于空天飞机和返回舱热防护、气动力和飞行控制设计。

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