An experimental and computational study of tip clearance effects on a transonic turbine stage

Jackson, Adam; Wheeler, Andrew P. S.; Ainsworth, R. W.

doi:10.1016/j.ijheatfluidflow.2015.09.001

Cited by 19 publications

(6 citation statements)

References 47 publications

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“…The solid boundary on the 'casing' was treated as a slip wall since simulation of the boundarylayer on the casing was not part of this investigation; the influence of the casing with relative motion between blade tip and casing wall is a subject for future investigation. The effect of casing shear on the tip flow was the subject of a recent experimental investigation in a rotating transonic high-pressure turbine by Jackson et al (2015). In the study of Jackson et al (2015), experimental results were compared with computational simulations where a no-slip wall and a slip-wall were imposed on the casing.…”

Section: Numerical Set-up Of An Engine Scale Tip Flowmentioning

confidence: 99%

“…The effect of casing shear on the tip flow was the subject of a recent experimental investigation in a rotating transonic high-pressure turbine by Jackson et al (2015). In the study of Jackson et al (2015), experimental results were compared with computational simulations where a no-slip wall and a slip-wall were imposed on the casing. The effect of casing shear was to change the tip-surface adiabatic wall temperature due to the effect of casing shear on the relative total temperature in the tip gap.…”

Section: Numerical Set-up Of An Engine Scale Tip Flowmentioning

confidence: 99%

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Numerical investigation of the flow over a model transonic turbine blade tip

Wheeler

Sandberg

2016

J. Fluid Mech.

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Direct numerical simulations are used to investigate the unsteady flow over a model turbine blade tip at engine scale Reynolds and Mach numbers. The DNS are performed with an in-house multi-block structured compressible Navier-Stokes solver. The particular case of a transonic tip flow is studied since previous work has suggested compressibility has an important effect on the turbulent nature of the separation bubble at the inlet to the tip-casing gap and subsequent flow reattachment. The flow is simulated over an idealized tip geometry where the tip gap is represented by a constant area channel with a sharp inlet corner to represent the pressure side edge of the turbine blade. The effects of free-stream disturbances, cross-flow and pressure-side boundary-layer on the tip flow aerodynamics and heat transfer are studied. For 'clean' in-flow cases we find that even at engine scale Reynolds numbers the tip flow is intermittent in nature, i.e. neither laminar nor fully turbulent. The breakdown to turbulence occurs through the development of spanwise streaks with wavelengths around 15 − 20% of the gap height. Multi-dimensional linear stability analysis confirms the two-dimensional base state to be most unstable with respect to spanwise wavelengths of 25% of the gap height. The linear stability analysis also shows that addition of cross-flows with 25% of the streamwise gap exit velocity increase the stability of the tip flow. This is confirmed by the DNS which also show that the turbulence production is significantly reduced in the separation bubble. For the case when free-stream disturbances are added to the inlet flow, viscous dissipation and the rapid acceleration of the flow at the inlet to the tip-casing gap causes significant distortion of the vorticity field and reductions of turbulence intensity as the flow enters the tip gap. The DNS results also suggest that the assumption of the Reynolds analogy and a constant recovery factor are not accurate, in particular in regions where the skin friction approaches zero while significant temperature gradients remain, such as in the vicinity of flow reattachment.

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Section: Numerical Set-up Of An Engine Scale Tip Flowmentioning

confidence: 99%

Section: Numerical Set-up Of An Engine Scale Tip Flowmentioning

confidence: 99%

Numerical investigation of the flow over a model transonic turbine blade tip

Wheeler

Sandberg

2016

J. Fluid Mech.

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“…In incompressible flow, the loss associated with the tip-leakage flow typically accounts for one third of the overall loss of a turbine stage [2]. Additionally, tip-leakage flows can lead to enhanced heat transfer in the tip-clearance, reducing the turbine blade life in high-temperature gas turbines [3][4][5]. Consequently, a comprehensive body of literature exists on low speed tip-leakage flows.…”

Section: Introductionmentioning

confidence: 99%

Focusing Schlieren Visualization of Transonic Turbine Tip-Leakage Flows

Passmann

Wiesche

Joos

2020

IJTPP

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This paper presents a focusing schlieren system designed for the investigation of transonic turbine tip-leakage flows. In the first part, the functional principle and the design of the system are presented. Major design considerations and necessary trade-offs are discussed. The key optical properties, e.g., depth of focus, are verified by means of a simple bench test. In the second part, results of an idealized tip-clearance model as well as linear cascade tests at engine representative Reynolds and Mach numbers are presented and discussed. The focusing schlieren system, designed for minimum depth of focus, has been found to be well suited for the investigation of three-dimensional transonic flow fields in turbomachinery applications. The schlieren images show the origin and growth of the tip-leakage vortex on the blade suction side. A complex shock system was observed in the tip region, and the tip-leakage vortex was found to interact with the suction side part of the trailing edge shock system. The results indicate that transonic vortex shedding is suppressed in the tip region at an exit Mach number around M 2 , i s = 0.8.

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“…As for the transonic tip, Gao et al (2016) numerically studied the effect of tip clearance variation on transonic tip aerothermal characteristics. Zhang et al (2011) and Jackson et al (2015) performed closely combined experimental and numerical studies on transonic blade tips independently, and both concluded that changes in tip clearance have different influences on the aerothermal performance of the tip frontal region and the trailing edge due to different flow structures. Maesschalck et al (2014) also numerically investigated the aerothermal characteristics Aerothermal performance under tight tip clearances less than 0.5 per cent of the blade span, and the results showed that the aerothermal performance of the overtip region has a novel change, which provides new physical insights.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigations of unsteady passing wake effects on turbine blade tip aerothermal performance with different tip clearances

Zhang

Qiang

et al. 2019

HFF

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Purpose The purpose of this paper is to numerically investigate the effect of guide vane unsteady passing wake on the rotor blade tip aerothermal performance with different tip clearances. Design/methodology/approach The geometry and flow conditions of the first stage of GE-E3 high-pressure turbine have been used to obtain the blade tip three-dimensional heat transfer characteristics. The first stage of GE-E3 high-pressure turbine has 46 guide vanes and 76 rotor blades, and the ratio of the vane to the blade is simplified to 38:76 to compromise the computational resources and accuracy. Namely, each computational domain comprises of one guide vane passage and two rotor blade passages. The investigations are conducted at three different tip gaps of 1.0, 1.5 and 2.0 per cent of the average blade span. Findings The results show that the overall discrepancy of the heat transfer coefficient between steady results and unsteady time-averaged results is quite small, but the dramatic growth of the instantaneous heat transfer coefficient along the pressure side is in excess of 20 per cent. The change of the aerothermal performance is mainly driven by turbulence-level fluctuations of the unsteady flow field within gap regions. In addition, the gap size expansion has a marginal impact on the variation ratio of tip unsteady aerothermal performances, even though it has a huge influence on the leakage flow state within the tip region. Originality/value This paper emphasizes the change ratio of unsteady instantaneous heat transfer characteristics and detailed the mechanism of blade tip unsteady heat transfer coefficient fluctuations, which provide some guidance for the future blade tip design and optimization.

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An experimental and computational study of tip clearance effects on a transonic turbine stage

Cited by 19 publications

References 47 publications

Numerical investigation of the flow over a model transonic turbine blade tip

Numerical investigation of the flow over a model transonic turbine blade tip

Focusing Schlieren Visualization of Transonic Turbine Tip-Leakage Flows

Numerical investigations of unsteady passing wake effects on turbine blade tip aerothermal performance with different tip clearances

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