Numerical Study of Unsteady Cavitating Flow in an Inducer with Omega Vortex Identification

Abstract To accurately capture the behaviors of cavitation and reveal the unsteady cavitating flow mechanism, a condensate pump inducer is numerically analyzed in a separate numerical experiment with LES at critical cavitation number sind,c under the design point. Based on the new Omega vortex identification method, the correction between the flow structures and cavities is clearly illustrated. Besides, the pressure fluctuations around the inducer are analyzed. Special emphasis is put on the analysis of the interactions between the cavities, turbulent fluctuations, and vortical flow structures. The Omega vortex identification method could give an overall picture of the whole cavitating flow structures to present a clear correlation between the vortices and cavities. The results show that the shear cavitation dominant the cavitation characteristics under the design point. The pure rigid rotation region mainly concentrates at the edge of the cavities while the other sheet-like cavities near the casing walls are characterized by strong turbulence fluctuations. Besides, based on the analysis of the correlation between the cavities and flow structures, the rotating cavitation under the design point may mainly attribute to the interaction between the tip leakage vortex cavitation and the next blade.

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Vortical structures in the cavitating flow in the Francis-99 draft tube cone under off-design conditions with the new omega vortex identification method

Journal of Physics Conference Series ◽

10.1088/1742-6596/1296/1/012011 ◽

2019 ◽

Vol 1296 ◽

pp. 012011

Author(s):

Cong Trieu Tran ◽

Xinping Long ◽

Bin Ji

Keyword(s):

Draft Tube ◽

Cavitating Flow ◽

Vortex Identification ◽

Vortical Structures ◽

Identification Method

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Investigation of the Surge Phenomena in a Centrifugal Compressor Using Large Eddy Simulation

Volume 7A: Fluids Engineering Systems and Technologies ◽

10.1115/imece2013-66301 ◽

2013 ◽

Cited By ~ 7

Author(s):

Bernhard Semlitsch ◽

V. Jyothishkumar ◽

Mihai Mihaescu ◽

Laszlo Fuchs ◽

Ephraim J. Gutmark

Keyword(s):

Mass Flow ◽

Centrifugal Compressor ◽

Numerical Study ◽

Pressure Fluctuations ◽

Operating Regime ◽

Rotating Stall ◽

Operating Conditions ◽

Flow Structures ◽

Compressor Wheel ◽

Large Eddy

The flow through a ported shroud compressor of an automobile turbocharger is simulated using Large Eddy Simulations. Generally, the compressor is subjected to work within certain range of the mass-flow conditions. Reduction of the operation mass-flow below a certain minimum limit, leads to breakdown of the complete compressor operability. Flow reversal occurs in the compressor wheel, which results in amplification of velocity and pressure fluctuations. Consequentially, large vibratory stresses are induced into the blades under off-design condition and thereby affect the blade life duration detrimentally. The aim of this study is to understand the generation of flow-structures during extreme operable conditions (surge condition) in a centrifugal compressor. The investigation of the appearing flow-structures with the surge phenomenon is essential to explore new methods that improve the stability or the flow-operating regime of the compressor. The complete 360° compressor geometry is utilized in the computational simulations. Further, the transient sliding mesh technique is applied to account for an accurate prediction of the mesh motion and thus, the geometrical interaction between the impeller and the stationary diffuser. The numerical results are compared with available experimental measurements obtained under the same operating conditions (design and near-surge condition). The rotating stall instability is predicted using FFT data analysis. Furthermore, the numerical study captures the low frequency peak characterizing the global instability of the surge condition.

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Experimental and Numerical Study of the Cavitating Flow on a Hydrofoil

Volume 2: Symposia, Parts A, B, and C ◽

10.1115/fedsm2003-45005 ◽

2003 ◽

Cited By ~ 2

Author(s):

O. Coutier-Delgosha ◽

J.-F. Devillers

Keyword(s):

Void Ratio ◽

Numerical Study ◽

Oscillatory Behavior ◽

Cavitating Flow ◽

Vapor Cavity ◽

First Results ◽

Recent Developments ◽

Flow Configurations ◽

Good Agreement ◽

Unsteady Cavitating Flow

The unsteady cavitating flow field on a 2D hydrofoil is investigated by experimental means and numerical calculations. The self-oscillatory behavior of the cavitation sheet observed experimentally is correctly simulated by the numerical model. A particularly good agreement is obtained concerning the frequency of the phenomenon in various flow configurations. To confirm the low void ratio predicted by the model in the main part of the liquid/vapor cavity a new experimental device is applied: it is based on an endoscopic visualization of the interior of the mixture. Recent developments of the method are presented, and some first results are analysed.

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Visualization and analysis of flow structures in an open cavity

Modern Physics Letters B ◽

10.1142/s0217984918400109 ◽

2018 ◽

Vol 32 (12n13) ◽

pp. 1840010

Author(s):

Jun Liu ◽

Jinsheng Cai ◽

Dangguo Yang ◽

Junqiang Wu ◽

Xiansheng Wang

Keyword(s):

Numerical Study ◽

Pressure Fluctuations ◽

Leading Edge ◽

Open Cavity ◽

Flow Structures ◽

Sustained Oscillation ◽

Multi Scale ◽

Numerical Visualization ◽

New Type ◽

Attached Vortex

A numerical study is performed on the supersonic flow over an open cavity at Mach number of 1.5. A newly developed visualization method is employed to visualize the complicated flow structures, which provide an insight into major flow physics. Four types of shock/compressive waves which existed in experimental schlieren are observed in numerical visualization results. Furthermore, other flow structures such as multi-scale vortices are also obtained in the numerical results. And a new type of shocklet which is beneath large vortices is found. The shocklet beneath the vortex originates from leading edge, then, is strengthened by successive interactions between feedback compressive waves and its attached vortex. Finally, it collides against the trailing surface and generates a large number of feedback compressive waves and intensive pressure fluctuations. It is suggested that the shocklets beneath vortex play an important role of cavity self-sustained oscillation.

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Numerical Study on the Mechanism of Wind Noise Generation About a Car-Like Body

Journal of Fluids Engineering ◽

10.1115/1.2910294 ◽

1994 ◽

Vol 116 (3) ◽

pp. 424-432 ◽

Cited By ~ 3

Author(s):

Ming Zhu ◽

Yuji Hanaoka ◽

Hideaki Miyata

Keyword(s):

Surface Pressure ◽

Flow Separation ◽

Numerical Study ◽

Pressure Fluctuations ◽

Strong Relationship ◽

Vortical Flow ◽

Noise Generation ◽

Front Side ◽

Wind Noise ◽

Side Window

Three-dimensional flow separation about the sharp-edged front-pillar of a car-like body at high cruising speed is numerically studied. A time-dependent and full Navier-Stokes simulation is carried out for the understanding of mechanism of wind noise generation due to the vortical flow motions. The surface pressure fluctuations on the front-side window are examined in terms of wind noise, based on a simplified Lighthill-Curle’s equation. The simulated results are validated regarding the numerical grid resolution and assessed by comparison with the conventional acoustic theory. The analyses of the simulated flow-field data indicate that there is a strong relationship between the vortical motions associated with the flow separation and the surface pressure fluctuations on the front-side window. The bifurcations of flow geometry, such as the breakdown of a separated vortex as well as the vortex-vortex interaction, seem to be most strongly related to the production of surface pressure fluctuations.

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Numerical investigation of the generation and growth of coherent flow structures in a triggered turbulent spot

Journal of Fluid Mechanics ◽

10.1017/jfm.2014.538 ◽

2014 ◽

Vol 759 ◽

pp. 257-294 ◽

Cited By ~ 12

Author(s):

Joshua R. Brinkerhoff ◽

Metin I. Yaras

Keyword(s):

Boundary Layer ◽

Numerical Study ◽

Quantitative Description ◽

Shear Layers ◽

Vortical Flow ◽

Flow Structures ◽

Test Surface ◽

Turbulent Spot ◽

Hairpin Vortices ◽

Coherent Flow Structures

AbstractMultiple mechanisms for the regeneration of hairpin-like coherent flow structures in transitional and turbulent boundary layers have been proposed in the published literature, but a complete understanding of the typical topologies of coherent structures observed in the literature has not yet been achieved. To contribute to this understanding, a numerical study is performed of a turbulent spot triggered in a zero-pressure-gradient laminar boundary layer by a pulsed, transverse jet. Two direct numerical simulations (DNS) capture the growth of the spot into a mature turbulent region containing a large number of coherent vortical flow structures. The boundary-layer Reynolds number based on the test-surface streamwise length is $\mathit{Re}_{L}=309\,200$. The internal structure of the spot is characterized by densely spaced packets of hairpin vortices. Lateral growth of the spot occurs as new hairpin vortices form along the spanwise edges of the spot. The formation of these hairpin vortices is attributed to unstable shear layers that develop in the streamwise–spanwise plane due to the wall-normal motions induced by the streamwise oriented legs of hairpin vortices within the spot. Results are presented that highlight the mechanism by which the instability of such shear layers forms wavepackets of hairpin vortices; how the formation of these vortices produces a flow environment that promotes the creation of new hairpin vortices; and how the newly created hairpin vortices impact the production of turbulence kinetic energy in the flow region surrounding the spot. A quantitative description of the hairpin-vortex regeneration mechanism based on the transport of the instantaneous vorticity vector is presented to illustrate how the velocity and vorticity fields interact with the local strain rates to promote the growth of coherent vortical structures. The simulation results also shed light on a mechanism that seems to have a dominant influence on the formation of the calmed region in the wake of the turbulent spot.

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Experimental and Numerical Study of the Cloud Cavitating Flow Around a Slender Cylinder With a Petals-Shaped Section

Volume 2, Fora: Cavitation and Multiphase Flow; Advances in Fluids Engineering Education ◽

10.1115/fedsm2017-69296 ◽

2017 ◽

Author(s):

Yiwei Wang ◽

Jian Huang ◽

Chang Xu ◽

Chao Yu ◽

Chenguang Huang ◽

...

Keyword(s):

High Speed ◽

Numerical Study ◽

Three Dimensional ◽

Tangential Direction ◽

Cavitating Flow ◽

Flow Structures ◽

Eddy Simulation ◽

Inner Region ◽

Gradient Variation ◽

Shaped Section

Three-dimensional flow structures of sheet-to-cloud transition have attracted a lot of attentions in the past years. Cloud cavitating flow around a slender cylinder with the petals shaped section was investigated by experimental and numerical methods. The experiment was performed in a launching system on the basis of the SHPB technology with a high-speed camera. The numerical method was established with large-eddy simulation (LES) and volume of fraction (VOF) approach. Numerical results agree well with experimental data. Interesting phenomena of three-dimensional evolution are observed, especially in which the U-type shedding of cavities are generated repeatedly in the channels along the inner region. Analysis of the unsteady evolution of cavitating flow is performed, and emphasis is placed on the study of the relationship between flow structures around the ridges and channels. Results demonstrate that the pressure gradient variation in the tangential direction of the cylinder is essential for the unsteady development of the cavity including re-entry jet and local shedding. Interactions between the cavity and vortex are also analyzed, which indicates that the U-type cavity/vortex shedding is jointly induced by the re-entry jet and tangential vortex.

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