多场作用下颗粒物在涡轮叶片表面的沉积机理研究

It is necessary to obtain the deposition mechanism of particulate matter on the surface of turbine blade in order to estimate the remaining life of turbine blade under the environment of smog or volcanic ash, and to support the decision of operation and maintenance. But the deposition process is governed by multiple fields, including flow velocity, temperature and particulate concentration. Meanwhile, the whole process is getting more complicated in turbine cascade with the introduce of rotationary force and also the surface shear force which is induced by coolant injection and the secondary flow. Therefore, it becomes an active research topic to estimate the delivery and sticking mechanism of particle in turbine cascade. In this study, three test configurations including flat plate, half cylinder and turbine cascade will be constructed to model the corresponding areas of turbine blade and the deposition process will be simulated on the basic test facility. The experimental data including covering area, deposition rate, surface roughness and temperature will be obtained under different surface conditions, paricle characteristics, test durations, particle loading rates and mainstream temperatures. With these date, the computation and analysis tools will be validated including sticking model, turbulence model, conjugate heat transfer and transient deposition process. At last, numerical simulations will be conducted to analyze the effect of following parameters on deposition: (1)flowing parameters including mainstream Reynolds number, rotational speed, coolant blowing ratio; (2) particle parameters including diameter distribution and mass concentration; (3) structure parameters including blade area, jet hole configuration and arrangement. After that, with the analysis of the effect of basic parameters, including force and heat, the deposition mechanism can be obtained.

为估算雾霾和火山灰环境影响下的涡轮叶片剩余寿命，支持运行和维修决策，需得到颗粒物在涡轮叶片表面的沉积机理。而沉积过程受到气体流场、温度场及颗粒物浓度场的多场作用，同时，涡轮叶栅内的旋转力场、冷却射流和二次流诱发的近壁剪切力场会使得颗粒物的动力和换热特性更为复杂，导致涡轮叶栅内的粒子输运和粘附机制成为研究的热点。本研究通过构建简化的平板、半圆柱及叶栅通道试验件，在基础实验台上分别模拟实际涡轮叶片对应部位处的粒子沉积过程，得到不同表面状况、粒子特性、试验阶段、粒子加载率、主流温度下的沉积区域、沉积率、表面粗糙度和温度的实验数据，进而验证粘附模型、湍流模型、流固耦合及瞬态沉积过程的计算分析工具；最后，数值分析包括主流雷诺数、旋转速度、射流吹风比在内的流动参数，粒径分布和质量浓度等粒子参数，以及叶片区域、射流孔形状和布置在内的结构参数对沉积过程的影响，分析力、热基本参数的作用规律，得出沉积机理。

随着航空运输业的发展，航空发动机越来越多暴露在可见的空气和地面颗粒浓度都很高的地区，发动机内部的颗粒物损伤问题，尤其是存在大量熔融状态颗粒的涡轮叶片表面区域所受的沉积损伤，成为了研究的新的关注点。计算涡轮叶片剩余寿命，进行叶片的维修更换，优化叶片的气膜冷却结构设计需要将颗粒物在涡轮叶片表面的沉积情况作为新的参考因素进行考虑。因而，迫切需要对受到温度场、流场及颗粒物浓度场等多场作用下颗粒物沉积机理进行研究。本研究通过相似参数计算建立了低速低温沉积实验与高温发动机状态之间的联系，基于开式风洞石蜡颗粒沉积实验平台，研究了简化的平板、半圆柱及涡轮叶片等试验件表面的沉积状况和沉积积累过程，得到了不同几何结构、主流温度、气膜孔射流角度、气膜孔径、表面粗糙度等因素对颗粒物沉积厚度及沉积分布的影响规律。并结合红外热像仪测试的温度场信息和气膜冷却效率测试结果，分析了气膜冷却效果对沉积的影响。此外，研究中建立了考虑颗粒剥离的颗粒物沉积模型和非稳态沉积数值模拟计算工具，其运算结果经实验数据验证，具有一定的可行性和实用价值。最终基于该工具，数值模拟了包括主流温度，湍流强度在内的流动参数，粒径大小和质量浓度等粒子参数，以及叶片区域、射流孔形状和孔径在内的结构参数对沉积过程的影响，分析了局部速度场、颗粒法向撞击速度，颗粒撞击时的粘度等基本参数的对沉积概率的影响，揭示了发动机中颗粒沉积的过程实则是多场作用下颗粒撞击，粘附，剥离概率共同决定的，动态平衡的过程。