Vortex Dynamics and Mechanisms for Viscous Losses in the Tip-Clearance Flow

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

doi:10.1115/fedsm2005-77175

Cited by 3 publications

(4 citation statements)

References 26 publications

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“…In the downstream locations from the trailing edge, the endwall vortical structures become highly complicated due to the interaction of the tip-leakage vortex, tip-separation vortices, and blade wake. In parallel with the present study, You et al (2005) performed a detailed analysis of the vortex-shedding frequency in the blade wake and the space-time correlations of the velocity fluctuations in the endwall tip-leakage flow, and suggested that the tip-leakage vortex is subject to a pitchwise low-frequency wandering motion. Similar observations have been reported by other experimental and numerical studies in tip-clearance configurations (Zierke & Straka 1996;Wang & Devenport 2004).…”

Section: Resultsmentioning

confidence: 64%

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

et al. 2007

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The tip-leakage flow in a turbomachinery cascade is studied using large-eddy simulation with particular emphasis on understanding the underlying mechanisms for viscous losses in the vicinity of the tip gap. Systematic and detailed analysis of the mean flow field and turbulence statistics has been made in a linear cascade with a moving endwall. Gross features of the tip-leakage vortex, tip-separation vortices, and blade wake have been revealed by investigating their revolutionary trajectories and mean velocity fields. The tip-leakage vortex is identified by regions of significant streamwise velocity deficit and high streamwise and pitchwise vorticity magnitudes. The tip-leakage vortex and the tip-leakage jet which is generated by the pressure difference between the pressure and suction sides of the blade tip are found to produce significant mean velocity gradients along the spanwise direction, leading to the production of vorticity and turbulent kinetic energy. The velocity gradients are the major causes for viscous losses in the cascade endwall region. The present analysis suggests that the endwall viscous losses can be alleviated by changing the direction of the tip-leakage flow such that the associated spanwise derivatives of the mean streamwise and pitchwise velocity components are reduced.

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Section: Resultsmentioning

confidence: 64%

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

et al. 2007

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“…Analytical studies by Vo [9], Vo et al [13,14], and Jothiprasad et al [15] and cascade studies conducted by Bae et al [16] and Donghyun et al [17] suggest that the optimum location of the actuators is over or slightly downstream of the rotor leading edge to impact the formation of the clearance vortex. As this technology was new for a high-speed compressor, the actuators were not placed directly over the blade tip.…”

Section: Test Setup and Instrumentationmentioning

confidence: 96%

“…Donghyun et al [17] at Stanford University used large-eddy simulation to analyze the energy spectra and space-time correlations of the velocity fluctuations that suggested that the tip leakage vortex is subject to a pitchwise low frequency wandering motion. Measurements by Bae et al [16] in a linear compressor cascade at MIT showed that there exists a peak in the frequency content that is a periodic unsteadiness, which corresponds to the most effective frequency for blockage reduction using a normal synthetic jet.…”

Section: Tip Vortex Dynamics-strouhal Numbermentioning

confidence: 99%

Experimental Investigation of Tip Clearance Flow in a Transonic Compressor With and Without Plasma Actuators

Saddoughi

Bennett

Boespflug

et al. 2014

Journal of Turbomachinery

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Blade tip losses represent a major performance penalty in low aspect ratio transonic compressors. This paper reports on the experimental evaluation of the impact of tip clearance with and without plasma actuator flow control on performance of an U.S. Air Force-designed low aspect ratio, high radius ratio single-stage transonic compressor rig. The detailed stage performance measurements without flow control at three clearance levels, classified as small, medium, and large, are presented. At design-speed, increasing the clearance from small to medium resulted in a stage peak efficiency drop of almost six points with another four point drop in efficiency with the large clearance (LC). Comparison of the speed lines at high-speed show significantly lower pressure rise with increasing tip clearance, the compressor losing 8% stall margin (SM) with medium clearance (MC) and an additional 1% with the LC. Comparison of the stage exit radial profiles of total pressure and adiabatic efficiency at both part-speed and design-speed and with throttling are presented. Tip clearance flow-control was investigated using dielectric barrier discharge (DBD) type plasma actuators. The plasma actuators were placed on the casing wall upstream of the rotor leading edge and the compressor mapped from part-speed to high-speed at three clearances with both axial and skewed configurations at six different frequency levels. The plasma actuators did not impact steady state performance. A maximum SM improvement of 4% was recorded in this test series. The LC configuration benefited the most with the plasma actuators. Increased voltage provided more SM improvement. Plasma actuator power requirements were almost halved going from continuous operation to pulsed plasma. Most of the improvement with the plasma actuators is attributed to the reduction in unsteadiness of the tip clearance vortex near-stall resulting in additional reduction in flow prior to stall.

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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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Vortex Dynamics and Mechanisms for Viscous Losses in the Tip-Clearance Flow

Cited by 3 publications

References 26 publications

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

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

Experimental Investigation of Tip Clearance Flow in a Transonic Compressor With and Without Plasma Actuators

A Review of Tip Clearance in Propeller, Pump and Turbine

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