Generic Investigations of the Phenomenon of Part Load Recirculations in Turbo-Machines

流体系统消耗的电能占工业总耗电量的35%以上，因此，流体系统具有很高的经济相关性。因此，有必要提高流体系统的效率，以降低运行成本，减少电力生产过程中的二氧化碳排放。透平机械是流体系统的一部分，由于对灵活性的要求，经常在部分负荷下运行，而不是在效率达到最大的设计点。在小流量部分负荷时，会出现汽蚀、旋转失速、部分负荷回流等损失现象，这些流动现象降低了叶轮机械的效率和运行安全性。本文用叶轮机械通用模型对部分负荷再循环进行了实验和分析研究。一般的模型是非旋转管道和旋转管道的交汇处的流动，并带有一个常数。通过这样做，可以通过一个非常清晰的流动状况来研究涡流的演变、离心力和轴向力矩的相互依赖，以预测流动分离。旋转壁附近的漩涡是由粘性产生的，其方式与轴向动量边界层相似，并负责流动分离，例如部分负荷再循环。为了系统地研究叶轮机械和扩展参数场，本项目分析了加速和减速流动对涡流演变和流动分离的影响。这对应于涡轮机和泵的系统特性，而涡流是由运动原因分别由加速和减速流动产生的。而泵的功能是增加压力，这是由扩散器实现的原理图，而对于涡轮机来说，这是一个喷嘴。管道半径随着轴向坐标的变化而不断变化，以加速或减速旋转管道内的流动。结合本课题的进一步研究，采用实验和分析相结合的方法，提高了对部分负荷再循环的物理认识和理解。该研究方案和所获得的知识可用于叶轮机械，特别是带冠叶轮机械和叶轮二次风流道的设计。

Fluid systems exhaust more than 35 % of the electric energyconsumed by the industry and therefore, fluid systems have a higheconomical relevance. Thus, it is necessary to improve the efficiencyof fluid systems to reduce the operating costs and to reduce the CO2emission by the electricity production. Turbomachines, a part of fluidsystems, often operate at part load due to the claim of flexibility andnot at the design point where the efficiency reaches its maximum. Atpart load for small flow numbers, losses causing phenomena such ascavitation, rotating stall, part load recirculation and so on appear.These flow phenomena reduce the efficiency and the operationalsafety of a turbomachine compared to the design point. A genericmodel of a turbomachine is used to investigate part load recirculationexperimentally and analytically. The generic model is a flow throughintersection of a non-rotating and a rotating pipe with a constantradius. By doing so, the evolution of swirl, the interdependence ofcentrifugal force and axial moment is investigated by a very clear flowsituation to predict flow separation. The swirl near the rotating wall isproduced by viscosity in a similar manner to the axial momentumboundary layer and is responsible for the flow separation, e.g. partload recirculation. For a systematic approach to a turbomachine andto expand the parameter field, the influence of an accelerated anddeaccelerated flow on the evolution of the swirl and on the flowseparation is analysed by this project. This corresponds to systematicapproach to a turbine and a pump, whereas the swirl is produced bykinematic reason by an accelerated and a deaccelerated flow,respectively. Whereas the function of a pump is to increase thepressure and this is schematic fulfilled by a diffusor and for turbine itis a nozzle. The pipe radius changes constantly depending on theaxial coordinate, to accelerate or deaccelerate the flow within therotating pipe. Consistent to the further investigations by this project,experimental and analytical methods are applied to improve thephysical knowledge and understanding of part load recirculation. Theresearch project and the gained knowledge is employable for thedesign of a turbomachine, especially a shrouded turbomachine andflow channels of secondary air flow of a gasturbine.