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Compressor-Surge Behaviors Distinguished Between Near-resonant Type and Convective Type
Nobuyuki Yamaguchi,Yutaka Kawata,Yoshinobu Tsujimoto 한국유체기계학회 2021 International journal of fluid machinery and syste Vol.14 No.4
In deep surges in compressors, the behaviors tend to show either a near-resonant one or a convective one, the latter performing emptying and filling actions. However, detailed information on the differences between them have not been obtained so far. In order to understand the situations, surge simulations by a one-dimensional simulation code were conducted with respect to a single-stage centrifugal compressor, paying attention to the effects of changes in the compressor tip speed and in the geometry of the flowpaths. As the results, it has been found that near-resonant surges appear at very low tip speeds and for relatively narrow sectional areas of the delivery flowpath, and they transform to convective surges of emptying and filling actions toward higher speeds and wider sectional areas. The features of the behaviors are generalized in terms of several non-dimensional surge frequency parameters. The results are visualized by several global framework maps showing the relations among the parameters. The obtained results will give deeper understandings on the surge phenomena.
Characteristic Equation and Reflection Models of Air Column Resonant Surge
Yoshinobu Tsujimoto,Yutaka Kawata,Nobuyuki Yamaguchi 한국유체기계학회 2022 International journal of fluid machinery and syste Vol.15 No.1
Fundamental models of air column resonant surge are proposed. It is assumed that the flow in the suction pipe is incompressible but the effects of compressibility and pipe friction are taken into account in the discharge pipe. The characteristic equation is derived and the differences of onset condition and frequency from those of extended Helmholtz resonant surge are discussed. A reflection model considering the wave reflections at the compressor and throttle is also proposed to obtain better understanding. The results of characteristic equation and reflection models agree nicely. The results are validated by comparisons with experiments.
Cause of Cavitation Instabilities in Three Dimensional Inducer
Kang, Dong-Hyuk,Yonezawa, Koichi,Horiguchi, Hironori,Kawata, Yutaka,Tsujimoto, Yoshinobu Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.3
Alternate blade cavitation, rotating cavitation and cavitation surge in rocket turbopump inducers were simulated by a three dimensional commercial CFD code. In order to clarify the cause of cavitation instabilities, the velocity disturbance caused by cavitation was obtained by subtracting the velocity vector under non-cavitating condition from that under cavitating condition. It was found that there exists a disturbance flow towards the trailing edge of the tip cavity. This flow has an axial flow component towards downstream which reduces the incidence angle to the next blade. It was found that all of the cavitation instabilities start to occur when this flow starts to interact with the leading edge of the next blade. The existence of the disturbance flow was validated by experiments.
Choked Surge in a Cavitating Turbopump Inducer
Watanabe, Toshifumi,Kang, Dong-Hyuk,Cervone, Angelo,Kawata, Yutaka,Tsujimoto, Yoshinobu Korean Society for Fluid machinery 2008 International journal of fluid machinery and syste Vol.1 No.1
During an experimental investigation on a 3-bladed and a 4-bladed axial inducer, a severe surge instability was observed in a range of cavitation number where the blade passage is choked and the inducer head is decreased from noncavitating value. The surge was stronger for the 4-bladed inducer as compared with a 3-bladed inducer with the same inlet and outlet blade angles. For the 4-bladed inducer, the head decreases suddenly as the cavitation number is decreased. The surge was observed after the sudden drop of head. This head drop was found to be associated with a rapid extension of tip cavity into the blade passage. The cause of surge is attributed to the decrease of the negative slope of the head-flow rate performance curve due to choke. Assuming that the difference between the 3 and 4-bladed inducers is caused by the difference of the blockage effects of the blade, a test was carried out by thickening the blades of the 3-bladed inducer. However, opposite to the expectations, the head drop became smoother and the instability disappeared on the thickened blade inducer. Examination of the pressure distribution on both inducers could not explain the difference. It was pointed out that two-dimensional cavitating flow analyses predict smaller breakdown cavitation number at higher flow rates, if the incidence angle is smaller than half of the blade angle. This causes the positive slope of the performance curve and suggests that the choked surge as observed in the present study might occur in more general cases.
Rotating Choke and Choked Surge in an Axial Pump Impeller
Watanabe, Toshifumi,Sato, Hideyoshi,Henmi, Yasuhiko,Horiguchi, Hironori,Kawata, Yutaka,Tsujimoto, Yoshinobu Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.3
Unlike usual turbopump inducers, the axial flow pump tested operates very stably at design flow rate without rotating cavitation nor cavitation surge. Flow visualization suggests that this is because the tip cavity smoothly extends into the flow passage without the interaction with the leading edge of the next blade. However, at low flow rate and low cavitation number, choked surge and rotating choke were observed. Their correlation with the performance curve under cavitation is discussed and their instantaneous flow fields are shown.