Effects of tip-gap size on the tip-leakage flow in a turbomachinery cascade

You, Donghyun; Wang, Meng; Moin, Parviz; Mittal, Rajat

doi:10.1063/1.2354544

Cited by 119 publications

(54 citation statements)

References 26 publications

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“…On the numerical side, studies have been done with Reynolds averaged Navier-Stokes simulations, as well as with large eddy simulations. 14,15 Many similarities between the two-vortex configuration (wing-tip vortices) and the one-vortex configuration (tip-leakage vortex) have been observed in previous studies. 8,10,16 These similarities were found to be a useful tool for modeling the flow around the blades in a compressor and the loading they experienced.…”

Section: Introductionsupporting

confidence: 57%

Effect of a splitter plate on the dynamics of a vortex pair

2012

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An experimental and numerical study was performed to investigate and compare the behavior of a counter-rotating vortex pair and a single vortex in the vicinity of a wall. This analysis is motivated by the theoretical equivalence, in the inviscid limit, between these two configurations. A wind tunnel with two NACA0012 profiles mounted vertically with an optional splitter plate in the center and a stereoscopic particle image velocimetry system was used to experimentally study these interactions. Many significant differences were found between the two configurations, including the growth of the Crow instability in the two vortex configuration, but not in the one vortex/wall configuration. The numerical results re-enforced the experimental results, and emphasized the fundamental physical differences between the two configurations. While modeling a vortex wall system with an image vortex may give correct integral results for loads experienced by blades, this model does not accurately describe the downstream dynamics of the vortex system.

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Section: Introductionsupporting

confidence: 57%

Effect of a splitter plate on the dynamics of a vortex pair

2012

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“…Thence, the large-eddy simulation provides the most promising and feasible alternative to conventional numerical methods. You et al (2006) investigated the effect of tip-gap size on the tip-leakage vortical structures and velocity and pressure fields using LES computation. Simultaneously, the mechanisms for viscous losses in a turbomachinery tip-leakage flow was revealed by You et al (2007).…”

mentioning

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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“…The smaller the gap, the more intense is the vortex, which eventually gets fade because of the change in leakage flow velocity. This turbulent vortex is formed due to flow rolling during interaction of leakage flow with primary flow, while detaching from guide vane tip [13]. The leading edge downstream is found to have fade turbulence since the leakage induced turbulence vortex is largely dependent on the thickness of the guide vane [14].…”

Section: Nature Of Leakage Flowmentioning

confidence: 99%

Effect of Guide Vane Clearance Gap on Francis Turbine Performance

2016

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Francis turbine guide vanes have pivoted support with external control mechanism, for conversion of pressure to kinetic energy and to direct them to runner vanes. This movement along the support is dependent on variation of load and flow (operating conditions). Small clearance gaps between facing plates and the upper and lower guide vane tips are available to aid this movement, through which leakage flow occurs. This secondary flow disturbs the main flow stream, resulting performance loss. Additionally, these increased horseshoe vortex, in presence of sand, when crosses through the gaps, both the surfaces are eroded. This causes further serious effect on performance and structural property by increasing gaps. This paper discusses the observation of the severity in hydropower plants and effect of clearance gaps on general performance of the Francis turbine through computational methods. It also relates the primary result with the empirical relation for leakage flow prediction. Additionally, a possible method to computationally estimate thickness depletion has also been presented. With increasing clearance gap, leakage increases, which lowers energy conversion and turbine efficiency along with larger secondary vortex.

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Effects of tip-gap size on the tip-leakage flow in a turbomachinery cascade

Cited by 119 publications

References 26 publications

Effect of a splitter plate on the dynamics of a vortex pair

Effect of a splitter plate on the dynamics of a vortex pair

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

Effect of Guide Vane Clearance Gap on Francis Turbine Performance

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