大调节比径向直叶片气心泵叶轮区气液两相演变机理及控制方法研究

Developed from centrifugal pump, VCP (vapour core pump) is a new type of dynamic pump with its own inlet flow control, fulfilling the function of fuel supply under request. Its unique vapour core regulation and compensation can keep the flow rate approximately constant even under the outlet load disturbances. In fact VCP has been used as augmented fuel pump in many foreign military aero-engines while a prototype has not been developed so far in China. The reason is that the fundamental mechanism of formation, configuration and full envelope evolution of vapour core remains unclear, which prohibites the performance improvement of the pump..In this project, based on the gas-liquid phase transition and the volume fraction of gas phase, the mechanism of the formation and evolution of the vapour core in radial straight blade VCP with wide regulating ratio will be studied by mathematical modeling, CFD simulation and experimentation approaches under the full operation. In order to evaluate the influence on pump performance, the flow regulation characteristics, together with the problem of induced cavitation under low flow rate will be investigated for several typical inlet throttles. A bypass drainage method will be proposed for the second compensating the throttle outlet pressure to inhibitate cavitation. And finally the objective of impeller parameter optimizaiton can be achieved for vapour core stabilization and cavitation inhibitation. As a consequence, the research provides fundations for developing wide regulating ratio VCP and its performance improvement.

气心泵是由离心泵发展而来的一种新型动力式泵，它自带进口节流可应需供油，其特有的气心调节补偿作用可使出口负载干扰时泵的流量保持基本恒定。国外已在多个军用航空发动机上用作加力燃油泵，国内还未成功样机研制。究其原因，主要是对泵内气心的形成、形态及全包线演变机理等关键基础问题尚不清楚，这严重阻碍了对气心泵性能的改进。.本项目拟用数学模型、CFD数值模拟和实验对比等手段，基于叶轮区气液相变和气相体积比研究大调节比径向直叶片气心泵在全工况调节时的气心形成及演变规律；研究几种典型进口节流活门的调节特性，以及小流量时由此诱发的气穴问题，从而获得气心形成机理及对泵性能的影响关系；提出基于旁通引流来二次补偿节流活门出口压力的方法以抑制气穴；最终达到以气心稳定和气穴抑制为目标的叶轮参数优化。项目的研究为大流量调节比气心泵研制和性能改进打下基础。

为新一代航空发动机高性能燃油泵提供设计参考，通过数值模拟和样机试验手段研究大调节比径向直叶片燃油气心泵气液相变机理及对泵的性能影响。根据本项目的计划书内容，具体工作如下：获得了基于RNG k-ε双方程湍流模型与Schnerr-Sauer空化相变模型的数值模拟方法，该方法可满足气心泵工况转变和气心形态的模拟，是气心泵流动机理与性能分析的一种有效手段。典型气心形成过程：一定进口节流活门开度下随转速升高，隔舌附近叶片吸力面根部先出现小块气态区域，随转速增加叶轮中心出现半径较小的气态区域。至气态区域完全充盈叶轮时，气心的半径不再随转速增加发生显著变化；在原有气心半径的基础上提出利用气相体积分数分布和叶轮区空化数共同描述气心，不仅反映其大小，其形态和演变规律的描述与泵的性能也有明显的对应关系；开展了气心泵原理样机性能的静态试验，获得了全调节范围泵的供油特性。提高进口压力可扩大大开度供油范围，节流活门开度调节使其拥有更宽的压头效率特性，尤其是小流量工况供油效率明显优于其它燃油泵。提高转速有助于增大压头，但效率随之减小，大开度工况这一现象更为显著；提出了一种气心泵的叶轮中心补压调节装置，该装置主要由压比控制阀、单向阀等集成。研究表明，叶轮中心压力过低时，该装置可将进口节流活门阀口处的较高压力燃油部分引至叶轮中心，可一定程度抑制气穴的产生和发展；对泵的叶片数进行了优化计算，表明叶片数对气心影响较小，获得了确保气心性能的叶片数及其对压力脉动和泵内流动漩涡的影响；针对气心泵小开度时效率较低，数值研究了一种变叶宽离心泵的流量调节方案。结果表明，转速和进出口压力不变时叶片宽度与供油量正相关。与旁路回油调节流量相比，各工况下效率较高，为发动机供油量主动调节提供了另一种备选方案。