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

流体系统消耗的电能占工业消耗电能的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，减少发电过程中的CO2排放。叶轮机械是流体系统的一部分，由于要求具有柔性，所以常常在部分负荷下工作，而不是在效率达到最大值的设计点上工作。在小流量的部分负荷下，会出现空泡、旋转失速、部分负荷回流等现象，这些流动现象降低了发动机的效率和运行安全性。本文用一个通用的发动机模型对部分负荷再循环进行了实验和分析研究。通用模型是一个通过一个非旋转和一个旋转的管道与constantradius交叉流。通过这种方法，可以在一个非常清晰的流动情况下研究旋流的演化、离心力和轴向力矩的相互依赖关系，从而预测流动分离。旋转壁面附近的涡流是由粘性以类似于轴向动量边界层的方式产生的，并且是造成流动分离的原因，例如部分负荷再循环。为了系统地研究旋流和扩大参数场，本项目分析了加速流和减速流对旋流发展和流动分离的影响。这对应于涡轮机和泵的系统方法，而涡流分别由加速和减速流的运动学原因产生。而泵的功能是增加压力，这是由扩散器和涡轮机的喷嘴来实现的。管道半径根据轴向坐标不断变化，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负荷再循环的物理知识和理解。本课题的研究成果和所获得的知识对发动机的设计，特别是燃气轮机闭式发动机和二次风流道的设计具有一定的参考价值。

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.