Mind the gap: a new insight into the tip leakage vortex using stereo-PIV

Dreyer, Matthieu; Decaix, Jean; Münch-Alligné, Cécile; Farhat, Mohamed

doi:10.1007/s00348-014-1849-7

Cited by 200 publications

(71 citation statements)

References 31 publications

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“…SPIV measurements of Chang et al (2011) and Dreyer et al (2014), similar to the present study, both focused on the effect of the velocity field on vortex cavitation, but no velocities were measured in the presence of cavitation.…”

Section: Introductionmentioning

confidence: 73%

“…The global vortex detection method by Graftieaux et al (2001) and used in Dreyer et al (2014) was also considered. This method is much more robust due to lower susceptibility to noise in the instantaneous vector fields.…”

Section: Page 4 Of 13mentioning

confidence: 99%

“…This was necessary due to vortex center wandering. Similar vortex center identification was used by Graftieaux et al (2001), del Pino et al (2011), Bhagwat and Ramasamy (2012 and Dreyer et al (2014). Second, the original PIV images were grouped according to their vortex center position.…”

Section: Introductionmentioning

confidence: 99%

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Flow field measurement around vortex cavitation

2015

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stage. These involve the smooth transport of vapor into the tip vortex, leading harmful implosions away from the propeller surface. The tip vortex cavity dynamics are not directly related to the propeller rotation rate. The excitation of this cavity often leads to high amplitude broadband pressure fluctuations between the fourth and seventh blade rate frequency (Wijngaarden et al. 2005).To better understand the sound production from vortex cavitation, a model for the waves on a tip vortex cavity was developed and was shown to be able to describe the interface dynamics in detail (Pennings et al. 2015). As a result, a condition could be predicted where a cavity resonance frequency could be amplified to produce high amplitude sound, as reported by Maines and Arndt (1997).The part that remains to be validated is a vortex model for the cavity size and cavity angular velocity. It has been shown that a Lamb-Oseen vortex model poorly estimates the cavity size as a function of cavitation number (Pennings et al. 2015). It is possible that overestimation of the vortex peak azimuthal velocity could have led to an overestimation of the cavity size. The main goal of the present study was to configure a simple low-order vortex model, to serve as an input into a vortex cavity wave dynamics model, to describe the tip vortex resonance frequency. It is based on the following steps.1. Model the tip vortex velocity field without cavitation (further referred to as wetted vortex) 2. Model the cavity size as a function of cavitation number based on wetted vortex properties 3. Show the difference in velocity field around a wetted and cavitating vortex 4. Obtain the cavity angular velocity value that gives the best correlation to the tip vortex cavity resonance frequency Abstract Models for the center frequency of cavitatingvortex induced pressure-fluctuations, in a flow around propellers, require knowledge of the vortex strength and vapor cavity size. For this purpose, stereoscopic particle image velocimetry (PIV) measurements were taken downstream of a fixed half-wing model. A high spatial resolution is required and was obtained via correlation averaging. This reduces the interrogation area size by a factor of 2-8, with respect to conventional PIV measurements. Vortex wandering was accounted for by selecting PIV images for a given vortex position, yielding sufficient data to obtain statistically converged and accurate results, both with and without a vapor-filled vortex core. Based on these results, the loworder Proctor model was applied to describe the tip vortex velocity outside the viscous core, and the cavity size as a function of cavitation number. The flow field around the vortex cavity shows, in comparison with a flow field without cavitation, a region of retarded flow. This layer around the cavity interface is similar to the viscous core of a vortex without cavitation.

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Section: Introductionmentioning

confidence: 73%

Section: Page 4 Of 13mentioning

confidence: 99%

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Flow field measurement around vortex cavitation

2015

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“…Lei Shi, Zhang, Zhao, Weidong Shi and van Esch, Journal of Fluid Science and Technology, Vol.12, No.1 (2017) 7 low pressure in the vortex core (Arndt, 2002;Higashi et al, 2002;Murayama, 2006). Thus, cavitation inception is often coupled with vortex structures, such as tip leakage, trailing and hub vortices as well as turbulent vortex structures developing in regions of flow separation.In the aforementioned research, much attention has been paid to the tip leakage vortex cavitation around the fully-wetted hydrofoils (Boulon et al, 1999;Park et al, 2006;Dreyer et al, 2014). Although many progress has been made in regard to the vortex structures and self-induced cavitation, some important parameters are still missing in actual hydraulic machines, for instance, the body force in rotating frame which can alter the cavitation phenomenon.…”

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confidence: 99%

Visualized observations of trajectory and dynamics of unsteady tip cloud cavitating vortices in axial flow pump

Shi

Zhang

Zhao

et al. 2017

JFST

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A large-scale perpendicular cavitating vortices (PCVs), at the trailing edge of attached cavitation on the blade suction side near the tip region, has been found recently due to the great impact on performance breakdown in an axial waterjet pump. However, the trajectory and dynamics of this structure have been given scant attention. In this study, some visualized experiments were carried out to elucidate the PCVs for different conditions. The high-speed imaging coupled with numerical computations show that the vortical cloud cavitation is induced by the combination of tip leakage vortex (TLV) and radial re-entrant jets from the hub to blade tip. Moreover, the trajectory and intensity of PCVs depend on the operating conditions strongly, whether the other parameters, e.g. blade number and blade geometries, are modified. When taken the blade number into consideration, as a consequence of flow passage width and blade loading distributions, the dynamics and strength of PCVs vary considerably. Furthermore, an optimum clearance geometry is seen to eliminate corner vortex and clearance cavitation when the clearance edge is rounded on the pressure side. However, the more intensive tip leakage vortex cavitation is observed due to the increased amount of leakage flux. Additionally, in the original blade with sharp edges, the PCVs is relative weak and has a loose structure, resulting in the multiple interaction with the next blade. These phenomenon are responsible for the severe performance degradation and flow instabilities in the tip region of an axial-flow pump. Lei Shi, Zhang, Zhao, Weidong Shi and van Esch, Journal of Fluid Science and Technology, Vol.12, No.1 (2017) 7 low pressure in the vortex core (Arndt, 2002;Higashi et al., 2002;Murayama, 2006). Thus, cavitation inception is often coupled with vortex structures, such as tip leakage, trailing and hub vortices as well as turbulent vortex structures developing in regions of flow separation.In the aforementioned research, much attention has been paid to the tip leakage vortex cavitation around the fully-wetted hydrofoils (Boulon et al., 1999;Park et al., 2006;Dreyer et al., 2014). Although many progress has been made in regard to the vortex structures and self-induced cavitation, some important parameters are still missing in actual hydraulic machines, for instance, the body force in rotating frame which can alter the cavitation phenomenon. As a result, for the practical applications, the numerical and experimental investigations have been carried out in many rotating machines, both for single and multiphase flows. Farrell and Billet (1994) measured the important variables for the correlation which predict the vortex minimum pressure in a high Reynolds number axial-flow test rig. Moreover, an optimum tip clearance has been theoretically identified as experiments have shown. Afterwards, a combined study of tip clearance and tip vortex cavitation in an axial flow pump was carried out by Laborde et al. (1997). A conclusion is drawn that cavitation inception is...

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“…Moreover, numerous studies have shown that the re-entrant jet is considered as the main mechanism responsible for the shedding of cavity (Arndt et al 2000, Altimira and Fuchs, 2015, Dreyer et al 2014, Decaix and Goncalvès, 2013, Goncalvès and Charrière, 2014, Roohi et al 2013, Zhang et al 2014and Yu et al 2014.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study of Unsteady Cavitating Flows around a Hydrofoil

Taher

Kanfoudi

Ennouri

et al. 2017

JAFM

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In this paper, we report the results of a numerical investigation on unsteady cavitating flows around a circular leading edge (CLE) hydrofoil. The objective of this study is to properly predict the appearance of cavitation pocket, its development and its detachment causing adverse effects on industrial systems such as microscopic plastic deformations at the solid walls. For this reason it is very important to study the influence of turbulence models on simulation results. We present a closing of the hydrodynamic equation system by a transport equation of an active scalar (volume fraction of the vapor phase) with a source terms. The Computational Fluid Dynamics (CFD) code used is ANSYS CFX. Before comparing the capability of the different turbulent models to predict unsteady behavior of cavitating flow along the hydrofoil, the study of the influence of the mesh resolution was performed in cavitating condition. This investigation was performed, on CLE hydrofoil, by monitoring the influence of for progressively finer meshes on the values of the drag CD and lift CL coefficients. Moreover, a study of the influence of the normal dimensionless distance to the wall (y+) was carried out on the hydrofoil surface. For the unsteady flow, a comparison of different turbulence models with the experiment leads to study the interaction of these models with the vapor pocket (detachment and collapse of vapor pocket). Two turbulence models were tested in this study: modified k-ε model and large eddy simulation (LES). In the present work, the predictions of velocity and pressure evolutions in the vicinity of the hydrofoil are compared to experimental data.

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Mind the gap: a new insight into the tip leakage vortex using stereo-PIV

Cited by 200 publications

References 31 publications

Flow field measurement around vortex cavitation

Flow field measurement around vortex cavitation

Visualized observations of trajectory and dynamics of unsteady tip cloud cavitating vortices in axial flow pump

Numerical Study of Unsteady Cavitating Flows around a Hydrofoil

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