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

• Applicant: Professor Dr.-Ing. Peter F. Pelz
• Subject Area: Hydraulic and Turbo Engines and Piston Engines
• Term: from 2014 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257095842

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.

• DFG Programme: Research Grants