Large-eddy simulation analysis of mechanisms for viscous losses in a turbomachinery tip-clearance flow

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

doi:10.1017/s0022112007006842

Cited by 170 publications

(81 citation statements)

References 43 publications

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“…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). He concludes that the velocity gradients are the major source for viscous losses in the cascade endwall region, and an approach which can alleviate the viscous losses through changing the direction of the tip-leakage flow was proposed.…”

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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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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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“…At the same region, the most intensive pressure fluctuations These complicated vortexes have a remarkable influence on the flow pattern. Studies on the mechanisms of viscous losses [39][40][41] show that the TLV and leakage flow can lead to violent turbulence intensity, which increases the viscous losses near the tip clearance. Using the results from numerical simulation, You et al proposed strategies to improve the engineering design, such as optimizing the direction of leakage flow by changing the tip shape.…”

Section: Vortex Types and Corresponding Characteristicsmentioning

confidence: 99%

A Review of Tip Clearance in Propeller, Pump and Turbine

2018

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Propellers, pumps, and turbines are widely applied in marine equipment, water systems, and hydropower stations. With the increasing demand for energy conservation and environmental protection, the high efficiency and the stable operation of pumps and turbine have been drawing great attention in recent decades. However, the tip clearance between the rotating impeller and the stationary shroud can induce leakage flow and interact with the main stream, introducing complex vortex structures. Consequently, the energy performance and the operation stability of pumps and turbines deteriorate considerably. Constant efforts are exerted to investigate the flow mechanism of tip-clearance flow and its induced influence on performance. However, due to various pump and turbine types and the complexity of tip-clearance flow, previous works are usually focused on a specific issue. Therefore, a systematic review that synthesizes the related research is necessary and meaningful. This review investigates related research in the recent two decades in the perspectives from fundamental physics to engineering applications. Results reveal the vortex types, trajectory, evolution, and cavitation behaviors induced by tip-clearance flow. It is concluded that the influence characteristics of tip clearance on energy performance are closely related to the machinery type. Tip-clearance size and tip shape are found to be crucial parameters for tip-leakage vortex (TLV). The proposed optimization schemes are also demonstrated to provide inspiration for future research. Overall, this review article provides a coherent insight into the characteristics of tip-clearance flow and the associated engineering-design applications. On the basis of these understandings, comments on conducted research and ideas on future research are proposed.

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“…Therefore, the flow field near the rotor blade is emphatically analyzed as follows. You et al [2007] found that the tip vortex structure of ducted propeller is formed by three parts: the tip-separation vortex, the tip-leakage vortex and the induced vortex. The tip-leakage vortex is caused by the pressure difference between the pressure and the suction side.…”

Section: Effects Of Different Tip Clearances On the Open Water Performentioning

confidence: 99%

Numerical Investigation of Different Tip Clearances Effect on the Hydrodynamic Performance of Pumpjet Propulsor

Qin

Pan

Huang

et al. 2018

Int. J. Comput. Methods

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Previous studies show that the tip clearance loss limits the improvement of turbomachinery performance, and it is roughly in close relation with the gap size. In this study, a pumpjet propulsor (PJP) with different sizes of tip clearances (δ = 0.2, 0.5, 1, 2, 3 mm) has been presented to investigate the influence of tip clearances on PJP. This analysis is based on computational fluid dynamic (CFD) method, and the SST k-ω turbulence model is applied. Calculations are carried out with a worldwide employed ducted propeller (the Ka4-70 propeller in 19A duct) to verify the numerical simulation. And the grid independence validation is discussed. The numerical simulation of PJP flow with different tip clearances is carried out. Results show that the open water efficiency decreases gradually with the increase of tip clearance. The efficiency decreasing is caused by the tip flow loss. The shape of tip vortex of PJP which consisted of tip-separation vortex and tip-leakage vortex is presented. Furthermore, the formation and spread process of tip vortex at different tip clearances are discussed. Then, the effect of different tip clearances on the pressure field of rotor blade is investigated. The main pressure area affected by different tip clearances is mainly concentrated in the area above 0.9 spanwise of the suction side of rotor blade. Beyond that, the effects of different tip clearances on the velocity field of PJP has been studied.

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Large-eddy simulation analysis of mechanisms for viscous losses in a turbomachinery tip-clearance flow

Cited by 170 publications

References 43 publications

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

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

A Review of Tip Clearance in Propeller, Pump and Turbine

Numerical Investigation of Different Tip Clearances Effect on the Hydrodynamic Performance of Pumpjet Propulsor

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