存在剥离条件下颗粒物沉积过程的数值研究和实验验证

Experimental Validation and Numerical Simulation ofParticles Depositional Processes with Detachment

关键词:  涡轮  叶片  沉积过程  剥离模型  颗粒  气膜冷却

Key words:  Turbine  Blade  Depositional processes  Detachment model  Particles  Film cooling

摘要:

为了更加准确地模拟涡轮叶片表面颗粒物沉积的增长过程和分布状况，研究颗粒物沉积过程中粘附、剥离直至稳定平衡的规律，在经改进的颗粒粘附模型基础上考虑两种剥离形式，利用Fluent的User Defined Function (UDF)功能和网格重构技术，最终实现了熔融石蜡颗粒于带有气膜冷却的平板上沉积动态增长的过程。通过与相同条件下所得实验结果的对比，验证了所用模型的有效性和合理性。随后研究了是否加入剥离模型、气膜冷却吹风比、气膜孔射流角度等因素对沉积效果的影响。计算结果表明，考虑颗粒的剥离效应将减少颗粒物沉积的总量，尤其是在气膜孔后较短区域内；此外，吹风比的增加将使颗粒不易撞击壁面，已粘附的颗粒也更容易剥离从而降低沉积的厚度和质量；射流角度不断增大则使气膜覆盖效果变差，壁面温度升高，颗粒更易达到熔融状态沉积下来。研究发现该数值方法有助于更加精确地仿真沉积增长的过程，证实了吹风比和射流角度对沉积的分布和厚度有很大影响。当射流角度处于35°~40°时，可在一定程度上减少沉积。

Abstract:

In order to simulate the growth process and distribution of particles deposition on the surface of turbine blades more accurately and study the rules of sticking, detachment and developing stably during the process of particles deposition, the User Defined Function (UDF) in FLUENT and mesh reconstruction technology was used to perform the dynamic growth of molten wax particles deposition on the surface of plate with film cooling, which was based on a new particle sticking model and two kinds of detachment methods. The validity and rationality of the model were guaranteed by comparison with the experimental results obtained under the same conditions. Subsequently, the effects of the detachment model, the blow ratios, and the jet angle of film holes were investigated in detail. The calculation results show that considering the detachment of the particles reduces the total amount of particulate deposits, especially in the area behind of the film holes. In addition, the increase of the blowing ratio makes the particles less likely to impact on the wall surface, and the adhered particles are also more easily peeled off, thus reducing the thickness and mass of the deposition. What’s more, the increasing jet angle not only reduces the cooling effectiveness of the film holes, but increases the wall surface temperature, and the particles are more easily deposited in molten state. It is found that this study is helpful to simulate the process of deposition growth more accurately, and it is proved that the blowing ratio and jet angle have great influence on the deposition distribution and thickness. When the jet angle is between 35°~40°, it may reduce deposition to some extent.