IMECH-IR  > 高温气体动力学国家重点实验室
发动机冷却结构优化设计方法研究
Alternative TitleOptimal design method for engine cooling structure
李轩
Thesis Advisor范学军
2020-05-29
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline流体力学
Keyword火箭发动机,再生冷却,优化,变分
Abstract

高超声速飞行器是未来飞行器发展的重要方向之一,新一代高超声速飞行器对热防护系统提出了更高的要求,对于发展高超声速飞行器技术而言,多目标权衡和约束下,更合理更轻更经济的热防护结构是工程师们不懈追求的目标,如何快速而有效地给出热防护系统以提高飞行器的工作时间和工作次数对设计带来了巨大的挑战,以专家经验为主的设计模式在应对热防护系统优化设计方面已不能很好的满足需求。本论文主要围绕可重复使用火箭推力室的热防护结构多目标优化设计为应用背景,提出了一套可大幅降低人工参与的自适应冷却结构优化设计方法。使用这套方法,基于推力室热环境和几何特征,采用变分的思想,面向优化目标函数组合,能较为智能的给出冷却结构优化设计结果,降低了优化的盲目性和任意性。

本文首先发展完善了主动冷却火箭发动机稳态传热计算程序,不用依赖任何试验数据。程序针对燃烧室内燃气的流动与传热、冷却通道内燃料的流动与传热与冷却结构的热传导等三个传热子过程编写了不同的计算模块,其中在燃烧室内燃气的流动与传热模块,提出了两种燃气与燃烧室壁面间的传热模型:一种是采用高速平板边界层对流换热关系式以及参考焓值法计算,另一种是采用管内湍流换热关联式以及参考焓值法计算。通过和实验数据做对比分析,得到这两种方法的适用范围。

基于发展的发动机主动冷却稳态传热分析计算方法,设计了两种小流量再生冷却火箭发动机,发现仅采用再生冷却无法满足要求,需要配合膜冷却使得壁温保持在材料的许用范围内,因此对再生冷却配合膜冷却进行了计算。再生冷却配合膜冷却可以对发动机提供很好的热防护,并对其进行了具体分析。

发展了基于等水力直径和等壁温的两种常规冷却优化设计方式,使用这两种方法对冷却结构进行设计,并分析了这两种方法的优缺点,为发动机热防护的设计提供解决方案。

重点发展了基于变分法的冷却结构优化设计方法,该方法以冷却结构的平均温度,温度不均匀度和冷却剂流动压力损失为目标函数,基于变分法生成优化分布的冷却通道,该通道可以根据当地的边界条件而自适应地调整。随后对冷却结构进行流固耦合传热的数值计算,得到冷却结构的温度分布,冷却剂的压力损失,冷却剂出口温度等参数。基于变分法的冷却结构优化设计方法可以根据当地边界条件生成优化的冷却通道;对于不同的优化方案,存在各自对应的最佳通道个数和冷却通道分布使目标函数最优。该方法的适用范围很广,优化的冷却通道既可以随几何条件而变化,又可以随热边界条件而变化,还可以同时受几何条件和热边界条件而变化。分析了在相同的冷却通道分布下,改变冷却通道的高度,平均壁温,温度不均匀度和压降随冷却通道高度的变化规律;改变冷却通道的流量,平均温度,温度不均匀度,压降随流量的变化规律。

在新发展的基于变分法的冷却结构优化设计方法基础上,接下来可以对异型冷却通道进行进一步的设计,拓展冷却结构优化设计的范围,并分析其效果。

Other Abstract

Hypersonic aircraft is one of the important directions for the development of future aircraft. The new generation of hypersonic aircraft puts forward higher requirements for thermal protection systems. For the development of hypersonic aircraft technology, the more reasonable, more economic and lighter thermal protection structure under multi-target trade-offs and constraints is the goal that engineers are relentlessly pursuing. How to quickly provide a more effective thermal protection system to improve the working time and working times of the aircraft has brought great challenges to the design. The design mode based on expert experience has been unable to meet the needs of the optimal design of thermal protection system. This paper focuses on the multi-objective optimization design of the thermal protection structure of the reusable rocket thrust chamber as the application background, and proposes a set of adaptive cooling structure optimization design methods that can greatly reduce manual participation. Using this method, based on the thermal environment and geometric characteristics of the thrust chamber, the idea of variation is used, and the combination of optimization objective functions is oriented. The results of the optimal design of the cooling structure can be given more intelligently, reducing the blindness and arbitrariness of optimization.

This paper first develops and improves the steady-state heat transfer calculation program of the active cooling rocket engine without relying on any data. The program compiles different calculation modules for three heat transfer sub-processes such as gas flow and heat transfer in the combustion chamber, fuel flow and heat transfer in the cooling channel and heat transfer of the cooling structure. Among the gas flow and heat transfer module in the combustion chamber, two heat transfer models between gas and combustion chamber wall are proposed: one is to use the high-speed plate boundary layer convection heat transfer relationship and the reference enthalpy value method, the other is to use the turbulent heat transfer correlation in the tube and the reference enthalpy value calculation. And through comparative analysis with experimental data, the scope of application of these two methods is obtained.

Based on the developed engine active cooling steady-state heat transfer analysis and calculation method, two small-flow regenerative cooling rocket engines were designed. It is found that only regenerative cooling could not meet the requirements. It is necessary to cooperate with film cooling to keep the wall temperature within the required range of materials. Therefore, regenerative cooling and film cooling were calculated. The regenerative cooling combined with film cooling can provide good thermal protection for the engine, and it is specifically analyzed.

Developed two conventional cooling optimization design methods based on equal hydraulic diameter and equal wall temperature. These two methods were used to design the cooling structure, and analyzed the advantages and disadvantages of these two methods, providing solutions for the design of engine thermal protection.

Focused on the development of the cooling structure optimization design method based on the variation method, which takes the average temperature of the cooling structure, temperature unevenness and coolant flow pressure loss as the objective functions, and generated an optimally distributed cooling channel based on the variation method. It can be adjusted adaptively according to local boundary conditions. Then the numerical calculation of the fluid-structure coupling heat transfer of the cooling structure was carried out to obtain the temperature distribution of the cooling structure, the pressure loss of the coolant, the temperature of the coolant outlet and other parameters. The optimization design method of the cooling structure based on the variational method can generate optimized cooling channels according to local boundary conditions; for different optimization schemes, there are corresponding optimal number of channels and cooling channel distribution to optimize the objective function. The method has a wide range of applications: the optimized cooling channel can vary with geometric conditions, thermal boundary conditions, and both geometric and thermal boundary conditions. The change of cooling channel height, average wall temperature, temperature uneveness and pressure drop with different height of the cooling channel under the same cooling channel distribution is analyzed; changing the flow rate of the cooling channel, the average temperature, temperature unevenness, pressure of drop with flow can be obtained.

On the basis of the newly developed cooling structure optimization design method based on variation method, we can further design the special-shaped cooling channel, expand the scope of cooling structure optimization design, and analyze its effect.

Call NumberPhd2020-003
Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/81937
Collection高温气体动力学国家重点实验室
Corresponding Author李轩
Recommended Citation
GB/T 7714
李轩. 发动机冷却结构优化设计方法研究[D]. 北京. 中国科学院大学,2020.
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