Towards Successful Start of International Journal of Fluid Machinery and Systems

Yoshinobu TSUJIMOTO 한국유체기계학회 2008 한국유체기계학회 논문집 Vol.11 No.3

Cavitation Instabilities in Turbopump Inducers

Tsujimoto, Yoshinobu,Horiguchi, Hironori,Yonezawa, Koichi 한국유체기계학회 2010 International journal of fluid machinery and syste Vol.3 No.2

Stability analyses of 1-3 dimensional cavitating flow through turbopump inducers are reviewed with a special focus on the cause of cavitation instabilities. In one-dimensional analysis, cavitation is modeled with the cavitation compliance, defined as the decrease of cavity volume due to the increase of inlet pressure, and the mass flow gain factor, defined as the decrease of cavity volume due to the increase of flow rate. It was shown that the positive mass flow gain factor is the cause of cavitation surge and rotating cavitation. In two-dimensional stability analysis, the blade surface cavity is modeled by a free streamline with a constant pressure. It is shown that various modes of cavitation instabilities start to occur when the cavity length becomes about 65% of the blade spacing. It was found that there is a region near the cavity trailing edge in which the incidence angle to the next blade is decreased. This flow occurs to satisfy the continuity equation near the cavity closure. The cavitation instabilities start to occur when this region starts to interact with the leading edge of the next blade. In three-dimensional real flows, cavitation occurs mostly near the tip. Cavitation instabilities are simulated by three dimensional unsteady cavitating CFD. By separating out the disturbance caused by cavitation, it was found that there exists a flow component towards the trailing edge of tip cavities to fill up the volume of collapsing bubbles. This disturbance flow has an effect to reduce the incidence angle to the next blade. It was found that cavitation instabilities start to occur when this disturbance flow starts to interact with the leading edge of the next blade. So, it was found that the steady cavity length at the tip is the most important parameter in three dimensional real flow. Thus, it was found that the continuity equation plays the most important role in the mechanism of cavitation instabilities in 1-3 dimensional flows.

Effects of Acoustic Resonance and Volute Geometry on Phase Resonance in a Centrifugal Fan

Yoshinobu Tsujimoto,Koichi Yonezawa,Hiroshi Tanaka,Peter Doerfler,Takayuki Suzuki,Keisuke Makikawa 한국유체기계학회 2013 International journal of fluid machinery and syste Vol.6 No.2

The effects of acoustic resonance and volute geometry on phase resonance are studied theoretically and experimentally using a centrifugal fan. One dimensional theoretical model is developed taking account of the reflection from the discharge pipe end. It was found that the phase resonance occurs, even with the effects of acoustic resonance, when the rotational speed of rotor-stator interaction pattern agrees with the sound velocity. This was confirmed by experiments with and without a silencer at the discharge pipe exit. The pressure wave measurements showed that there are certain effects of the cross-sectional area change of the volute which is neglected in the one dimensional model. To clarify the effects of area change, experiments were carried out by using a ring volute with a constant area. It was demonstrated that the phase resonance occurs for both interaction modes travelling towards/away from the volute. The amplitude of travelling wave grows towards the volute exit for the modes rotating towards the volute exit, in the same direction as the impeller. However, a standing wave is developed in the volute for the modes rotating away from the volute exit in the opposite direction as the impeller, as a result of the interaction of a growing wave while travelling towards the tongue and a reflected wave away from the tongue.

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.

Effects of Acoustic Resonance and Volute Geometry on Phase Resonance in a Centrifugal Fan

Tsujimoto, Yoshinobu,Tanaka, Hiroshi,Doerfler, Peter,Yonezawa, Koichi,Suzuki, Takayuki,Makikawa, Keisuke Korean Society for Fluid machinery 2013 International journal of fluid machinery and syste Vol.6 No.2

The effects of acoustic resonance and volute geometry on phase resonance are studied theoretically and experimentally using a centrifugal fan. One dimensional theoretical model is developed taking account of the reflection from the discharge pipe end. It was found that the phase resonance occurs, even with the effects of acoustic resonance, when the rotational speed of rotor-stator interaction pattern agrees with the sound velocity. This was confirmed by experiments with and without a silencer at the discharge pipe exit. The pressure wave measurements showed that there are certain effects of the cross-sectional area change of the volute which is neglected in the one dimensional model. To clarify the effects of area change, experiments were carried out by using a ring volute with a constant area. It was demonstrated that the phase resonance occurs for both interaction modes travelling towards/away from the volute. The amplitude of travelling wave grows towards the volute exit for the modes rotating towards the volute exit, in the same direction as the impeller. However, a standing wave is developed in the volute for the modes rotating away from the volute exit in the opposite direction as the impeller, as a result of the interaction of a growing wave while travelling towards the tongue and a reflected wave away from the tongue.

Moment Whirl due to Leakage Flow in the Back Shroud Clearance of a Rotor

Tsujimoto, Yoshinobu,Ma, Zhenyue,Song, Bing-Wei,Horiguchi, Hironori Korean Society for Fluid machinery 2010 International journal of fluid machinery and syste Vol.3 No.3

Recent studies on the moment whirl due to leakage flow in the back shroud clearance of hydro-turbine runners or centrifugal pump impellers are summarized. First, destabilizing effect of leakage flow is discussed for lateral vibrations using simplified models. Then it is extended to the case of whirling motion of an overhung rotor and the criterion for the instability is obtained. The fluid moment caused by a leakage clearance flow between a rotating disk and a stationary casing was obtained by model tests under whirling and precession motion of the disk. It is shown that the whirl moment always destabilizes the whirl motion of the overhung rotor while the precession moment destabilizes the precession only when the precession speed is less than half the rotor speed. Then vibration analyses considering both whirl and precession are made by using the hydrodynamic moments determined by the model tests. For larger overhung rotors, the whirl moment is more important and cause whirl instability at all rotor speed. On the other hand, for smaller overhung rotors, the precession moment is more important and cancels the destabilizing effect of the whirl moment.

Cavitation Instabilities of Hydrofoils and Cascades

Tsujimoto, Yoshinobu,Watanabe, Satoshi,Horiguchi, Hironori Korean Society for Fluid machinery 2008 International journal of fluid machinery and syste Vol.1 No.1

Studies on cavitation instabilities of hydrofoils and cascades are reviewed to obtain fundamental understandings of the instabilities observed in turbopump inducers. Most of them are based on the stability analysis of two-dimensional inviscid cavitating flow. The most important finding of the analysis is that the cavitation instabilities depend only on the mean cavity length. For a hydrofoil, the characteristic length is the chord length and partial/transitional cavity oscillation occurs with shorter/longer cavity than 75% of the chord length. For cascades, the characteristic length is the blade spacing and various modes of instabilities are predicted when the mean cavity is longer than 65% of the spacing. In the last part, rotating choke is shown to occur when the cavity becomes longer than the spacing.

Genesis of Researches on Surges in Pumping Systems in Japan

Nobuyuki Yamaguchi,Yoshinobu Tsujimoto 한국유체기계학회 2016 International journal of fluid machinery and syste Vol.9 No.1

Researches on the mechanism of surging and the surge behaviors in the systems of pumps, or fans or compressors, and the effects of flow-paths had been initiated and had made a great progress in Japan in the decades from the nineteen-forties to the nineteen-sixties. In 1947, the essential cause of the surges, i.e., self-excited oscillation nature of the flow-system, was discovered analytically by Professor Sumiji Fujii of Tokyo University, and most of the characteristic behaviors of the phenomena had been explained clearly. Successive studies by many other Japanese researchers continued to prove experimentally the mechanism, to extend the analytical studies, and to attempt preventing surge occurrence, etc. in the following two decades. The historical information on the early surge studies could be helpful to some concerned people. At the same time, the basic and plain ways of discussions and reasoning about the phenomena in the pioneering researches could give us much to be learned even in the present time of high-power computing systems. Regrettably, many of the original research works have been published only in Japanese. The present review introduces very briefly the situations in memories of the pioneering researchers and engineers.

Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

Yamamoto, Kazuyoshi,Tsujimoto, Yoshinobu Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.1

Cavitation instabilities in turbo-machinery such as cavitation surge and rotating cavitation are usually explained by the quasi-steady characteristics of cavitation, mass flow gain factor and cavitation compliance. However, there are certain cases when it is required to take account of unsteady characteristics. As an example of such cases, cavitation surge in industrial centrifugal pump caused by backflow vortex cavitation is presented and the importance of the phase delay of backflow vortex cavitation is clarified. First, fundamental characteristics of backflow vortex structure is shown followed by detailed discussions on the energy transfer under cavitation surge in the centrifugal pump. Then, the dynamics of backflow is discussed to explain a large phase lag observed in the experiments with the centrifugal pump.

Genesis of Researches on Surges in Pumping Systems in Japan

Yamaguchi, Nobuyuki,Tsujimoto, Yoshinobu Korean Society for Fluid machinery 2016 International journal of fluid machinery and syste Vol.9 No.1

Researches on the mechanism of surging and the surge behaviors in the systems of pumps, or fans or compressors, and the effects of flow-paths had been initiated and had made a great progress in Japan in the decades from the nineteen-forties to the nineteen-sixties. In 1947, the essential cause of the surges, i.e., self-excited oscillation nature of the flow-system, was discovered analytically by Professor Sumiji Fujii of Tokyo University, and most of the characteristic behaviors of the phenomena had been explained clearly. Successive studies by many other Japanese researchers continued to prove experimentally the mechanism, to extend the analytical studies, and to attempt preventing surge occurrence, etc. in the following two decades. The historical information on the early surge studies could be helpful to some concerned people. At the same time, the basic and plain ways of discussions and reasoning about the phenomena in the pioneering researches could give us much to be learned even in the present time of high-power computing systems. Regrettably, many of the original research works have been published only in Japanese. The present review introduces very briefly the situations in memories of the pioneering researchers and engineers.