A Study of Vortex Structure in the Shear Layer between Main Flow and Swirling Backflow

Yokota, Kazuhiko; Mitsuda, Kimihiko; Tsujimoto, Yoshinobu; Kato, Chisachi

doi:10.1299/jsmeb.47.541

Cited by 11 publications

(5 citation statements)

References 2 publications

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“…The role of the impeller is just to supply the angular momentum to the backflow and it does not affect the vortex structure. This was confirmed by an experiment in which swirling back flow from the impeller was simulated by a swirling symmetrical hollow jet [2]. …”

Section: Fig 3 Geometry Of Test Inducermentioning

confidence: 57%

“…[1] For inducers, a backflow vortex structure appears even at design flow rate, as a result of the roll up of shear layer between swirling backflow and axial main flow. [2] As the flow rate decreases, the backflow vortex extends more upstream and moves to inner radial locations. The number of vortices gets smaller as the radial location of the vortices moves inward.…”

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: Fig 3 Geometry Of Test Inducermentioning

confidence: 57%

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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“…[38], the disappearance of the distinct TLV core co-occurs with the formation of "backflow vortices" (BFVs) in the middle of the passage, which extends from the blade SS diagonally upstream. The name is adapted from a related phenomenon occurring in cavitating inducers [52][53][54][55]. Figure 4 shows that BFVs form in all cases at the mid-chord.…”

Section: Resultsmentioning

confidence: 99%

On the Effects of Tip Clearance and Operating Condition on the Flow Structures Within an Axial Turbomachine Rotor Passage

Chen

Tan

et al. 2019

Journal of Turbomachinery

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Effects of tip clearance size and flowrate on the flow around the tip of an axial turbomachine rotor are studied experimentally. Visualizations and stereo-particle image velocimetry (PIV) measurements in a refractive index-matched facility compare the performance, leakage velocity, and the trajectory, growth rate, and strength of the tip leakage vortex (TLV) for gaps of 0.49% and 2.3% of the blade chord, and two flowrates. Enlarging the tip clearance delays the TLV breakup in the aft part of the rotor passage at high flowrates but causes earlier breakup under pre-stall conditions. It also reduces the entrainment of endwall boundary layer vorticity from the separation point where the leakage and passage flows meet. Reducing the flowrate or tip gap shifts the location of the TLV detachment from the blade suction side (SS) upstream to points where the leakage velocity is 70–80% of the tip speed. Once detached, the growth rates of the total shed circulation are similar for all cases, i.e., varying the gap or flowrate mostly shifts the detachment point. The TLV migration away from the SS decreases with an increasing gap but not with the flowrate. Two mechanisms dominate this migration: initially, the leakage jet pushes the TLV away from the blade at 50% of the leakage velocity. Further downstream, the TLV is driven by its image on the other side of the endwall. Differences in migration rate are caused by the smaller distance between the TLV and its image for the narrow gap, and the increase in initial TLV strength with decreasing flowrate and gap.

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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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A Study of Vortex Structure in the Shear Layer between Main Flow and Swirling Backflow

Cited by 11 publications

References 2 publications

Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

Backflow Vortex Cavitation and Its Effects on Cavitation Instabilities

On the Effects of Tip Clearance and Operating Condition on the Flow Structures Within an Axial Turbomachine Rotor Passage

Velocity field analysis in an experimental cavitating mixing layer

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