低压比煤油涡轮数值计算与优化设计

Numerical Simulation and Optimal Design for Kerosene-Based Turbine with Low Pressure Ratio

关键词:  膨胀循环超燃冲压发动机  涡轮  超临界/裂解态煤油  数值计算  优化设计

Key words:  Scramjet with expansion cycle  Turbine  Supercritical/cracking kerosene  Numerical simulation  Optimal design

摘要:

小流量煤油涡轮泵可用于膨胀循环超燃冲压发动机燃料供应系统，针对特定工况提出了超临界/裂解态煤油基低压比涡轮的数值计算方法和优化设计策略。根据液体火箭发动机中典型的涡轮设计方法获得了低压比煤油涡轮的设计方案，采用湍流模拟方法结合煤油的多组分代理模型对25kr/min转速下的涡轮内部超临界态流动进行数值计算，发现设计方案的轴功率超过所需轴功率的120%，不利于涡轮泵系统在设计点工况下的稳定运转。取涡轮轴功率大于所需轴功率为约束条件，选择涡轮结构尺寸为设计变量，以两个目标量(优化方案的轴功率和效率相对于设计方案的变化率)的加权函数值最大为目标，基于响应面模型和多岛遗传算法开展渐进优化，优化过程中采用iSIGHT平台集成了3维参数化建模和流场仿真等C++程序和软件以实现数值计算自动化。利用试验设计方法建立样本数据库，并进行了涡轮轴功率和效率关于设计变量的灵敏度分析，发现二者成合作关系；所得涡轮优化方案的两个目标量分别下降16.5%和2.9%，以较低的效率损失为代价实现了轴功率的良好配合。

Abstract:

Kerosene-based turbo-pump with small flow rate is highly possible to be applied to the fuel supply system of expansion cycle scramjet. A method of numerical simulation and optimal design for supercritical/cracking kerosene-based turbine with low pressure ratio under interested conditions was proposed. Turbine design scheme was obtained according to the classic technology in liquid rocket engines. Turbulence simulation combined with a multi-species kerosene surrogate model was employed to study objective characteristics by simulating supercritical flow inside the turbine at 25kr/min. Shaft power of turbine design scheme is 20% higher than the required value， which has an adverse effect on the stable operation of turbo-pump. Constraint that turbine shaft power must be higher than the required value was employed. Structure parameters of turbine were chosen as design variables. Shaft power and efficiency are the performance parameters for turbine， and the optimization objective is to maximize the given weighted combination of two target variables (the variation of shaft power and efficiency comparing to design scheme). A successive optimization process based on Response Surface Model and Multi-Island Genetic Algorithm was implemented to obtain an optimized turbine scheme. The C++ program and software for 3D parametric modeling and flow field simulation were integrated within iSIGHT platform to realize an automation process for numerical simulation. The sample database was built on a basis of the Design of Experiment method， then parametric sensitivity was analyzed carefully， which indicates that most design variables have same effects on shaft power and efficiency. Comparing with design scheme， shaft power and efficiency of the optimized scheme decrease by 16.5% and 2.9% respectively， where the former one is basically consistent with the required value at a low price of the later.