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

流体系统的耗电量占整个行业耗电量的35%以上，因此，流体系统具有很高的经济意义。因此，有必要提高流体系统的效率，以降低运行成本，减少电力生产的二氧化碳排放。涡轮机械是流体系统的一部分，由于要求灵活性，通常在部分负载下运行，而不是在效率达到最大的设计点。当部分负荷为小流量时，出现汽蚀、旋转失速、部分负荷再循环等损失现象。与设计点相比，这些流动现象降低了涡轮机器的效率和运行安全性。采用涡轮机械的通用模型，对涡轮机械的部分负荷再循环进行了实验和分析研究。一般模型是一种流过非旋转管和旋转管的交点的流体。通过这样做，在一个非常明确的流动情况下，研究了漩涡的演变，离心力和轴向力矩的相互关系，以预测流动分离。旋转壁面附近的涡流是由粘度产生的，与轴向动量边界层类似，它负责流动分离，例如部分载荷再循环。为了系统地研究涡轮机械并扩展参数场，本项目分析了加速和去加速流动对旋流演化和流动分离的影响。这对应于涡轮和泵的系统方法，而涡流分别由加速和去加速流动产生的运动学原因。而泵的功能是增加压力，这是由扩散器完成的示意图，涡轮是喷嘴。管道半径随轴向坐标不断变化，以加速或减速旋转管道内的流动。与本项目的进一步研究相一致，采用实验和分析方法来提高对部分载荷再循环的物理认识和理解。研究项目和所得知识可用于涡轮机械，特别是带冠涡轮机械和涡轮二次气流通道的设计。

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.