Response of Backflow to Flow Rate Fluctuations

Qiao, Xiangyu; Horiguchi, Hironori; Tsujimoto, Yoshinobu

doi:10.1115/1.2427081

Cited by 11 publications

(10 citation statements)

References 11 publications

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“…[8] Response of backflow to flow rate fluctuation was discussed from the balance of angular momentum at the inlet. [9] The angular momentum transfer by the backflow was in anti-phase with the flow rate fluctuation. [10] The angular momentum transfer by the normal flow was larger when the angular momentum in the upstream is larger.…”

Section: Methods Of Analysis and Geometrymentioning

confidence: 99%

See 1 more Smart Citation

Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

Yamamoto¹,

Tsujimoto²

2009

International Journal of Fluid Machinery and Systems

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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.Keywords: Cavitation, Instability, Backflow, Cavitation Surge, Inducer, Centrifugal pump, Vortex Backflow Vortex CavitationIndustrial pumps are usually required to operate in a wide range of flow rate with cavitation. In such cases, a system instability caused by cavitation may occur. This is called cavitation surge. Under low flow rates, a backflow occurs at the outer part of pump inlet due to excessive pressure difference across the blades near the leading edge. The backflow has a high tangential velocity due to the angular momentum imparted by the blades. The shear layer between the swirling backflow and straight main flow rolls up and forms a backflow vortex structure as shown in Fig.1. Backflow vortex cavitation occurs at the vortex core, as shown in Fig.2, if the pressure there becomes lower than the vapor pressure due to the centrifugal force on the vortical motion and the increase of the main flow velocity caused by the displacement effect of the backflow.For high speed turbo-pumps such as for rocket engines, an axial stage with high solidity is often attached at the inlet of centrifugal main pump, to improve cavitation performance. This axial stage is called "inducer". Since inducers are usually operated under cavitation, they are designed with a certain incidence angle to secure that the cavitation occurs only on the suction surface to prevent pre-mature head breakdown caused by the cavitation on the pressure surface. From this reason, inducers are operated with certain backflow even at the design point. So, we need to understand fundamental characteristics the backflow at the inlet. Structure of Backflow VorticesTo show the fundamental characteristics of backflow vortex structure, we consider an inducer as shown in Fig.3 with the specifications given in Table 1, which is analogous to the liquid oxygen turbopump inducer for HII rocket. The picture in Fig.2 was taken at the design flow coefficient of φ d =0.078 and the cavitation number σ=0.050 at the rotational speed of N=3,000rpm. Figure 4 shows the profile of vortex filaments projected to meridional plane, measured by using a laser displacement sensor [1]. The upstream end of the vortex is attached to the pipe wall and the downstrea...

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Section: Methods Of Analysis and Geometrymentioning

confidence: 99%

“…Calculations were made by using a commercial code CFXTASCflow based on RANS with the k-ε turbulence model [9]. For the simulation of the backflow vortex structure, it is required to use a LES code [10] and the present calculation could not simulate the vortex structure.…”

Section: Methods Of Analysis and Geometrymentioning

confidence: 99%

Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

Yamamoto¹,

Tsujimoto²

2009

International Journal of Fluid Machinery and Systems

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“…A lot of work has been performed to describe both experimentally and numerically its dynamics (see e.g., Refs. [18][19][20][21][22][23]. The backflow consists in a rotating annular free shear layer in which the diphasic content of the eddies may vary with respect to the inducer inlet cavitation number.…”

Section: A Backgroundmentioning

confidence: 99%

Velocity field analysis in an experimental cavitating mixing layer

2011

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International audienceThe present study was carried out on a 2D shear layer test bed where no wall effect interfered with the flow. The objective was to obtain refined database and informations concerning the behavior of the liquid phase under different cavitation levels. This reference test has provided us a well documented test case to be used for numerical simulations of the complex turbulent two-phase flow and in order to quantify the turbulence-cavitation interactions

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“…Backflow from the inducer has a swirl velocity of about 20-30% of tip velocity and a backflow vortex structure is formed at the shear layer between swirling backflow and straight main flow. Experimental and computational studies of the backflow and backflow vortex of inducer have been reported [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

Large Eddy Simulation of the Dynamic Response of an Inducer to Flow Rate Fluctuations

Kang

Yonezawa

Ueda

et al. 2009

International Journal of Fluid Machinery and Systems

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A Large Eddy Simulation (LES) of the flow in an inducer is carried out under flow rate oscillations. The present study focuses on the dynamic response of the backflow and the unsteady pressure performance to the flow rate fluctuations under non-cavitation conditions. The amplitude of angular momentum fluctuation evaluated by LES is larger than that evaluated by RANS. However, the phase delay of backflow is nearly the same as RANS calculation. The pressure performance curve exhibits a closed curve caused by the inertia effect associated with the flow rate fluctuations. Compared with simplified one dimensional evaluation of the inertia component, the component obtained by LES is smaller. The negative slope of averaged performance curve becomes larger under unsteady conditions. From the conservations of angular momentum and energy, an expression useful for the evaluation of unsteady pressure rise was obtained. The examination of each term of this expression show that the apparent decrease of inertia effects is caused by the response delay of Euler's head and that the increase of negative slope is caused by the delay of inertial term associated with the delay of backflow response. These results are qualitatively confirmed by experiments.

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Response of Backflow to Flow Rate Fluctuations

Cited by 11 publications

References 11 publications

Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

Velocity field analysis in an experimental cavitating mixing layer

Large Eddy Simulation of the Dynamic Response of an Inducer to Flow Rate Fluctuations

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