Boundary Layer Development in Axial Compressors and Turbines: Part 3 of 4— LP Turbines

Halstead, David E.; Wisler, D. C.; Okiishi, T. H.; Walker, G. J.; Hodson, H. P.; Shin, Hyun Wook

doi:10.1115/1.2841105

Cited by 100 publications

(16 citation statements)

References 2 publications

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“…However, the turbulent kinetic energy is a factor of three higher. The fact that the bars generate much higher levels of turbulent kinetic energy is in agreement with the experimental findings of Halstead et al [8] (p. 442). x a and x n denote the axes parallel and perpendicular to the wakes, respectively.…”

Section: Wake Resultssupporting

confidence: 91%

“…The wall shear stress levels on the mid-chord, where the wakes hit the blade surface, seem to be slightly lower for case R 1 . This is consistent with the experimental results of Halstead et al [8], who found increasing levels of wall shear stress for stronger wakes impinging on the blade. However, as already observed in Figure 4, the wakes in case R −1 cause slightly lower stress levels compared to case R 0 in the mid-chord region.…”

Section: Implications For the Turbine Cascadesupporting

confidence: 93%

“…In order to simplify both experiments and simulations, a setup with moving bars upstream of the rotor is commonly used to generate velocity wakes [3][4][5][6], which are also referred to as 'negative jets' as they pass over the blades [7]. In an extensive study, Halstead et al [8] exposed three forms of boundary layer transition on blades in a turbine cascade caused by incoming wakes. Schulte and Hodson [9] found in their experimental investigations that wakes impinging on the blade increase the wall shear stress and thus create more losses.…”

Section: Introductionmentioning

confidence: 99%

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The Influence of Different Wake Profiles on Losses in a Low Pressure Turbine Cascade

Hammer

Sandham

Sandberg

2018

IJTPP

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Large eddy simulations were carried out in order to investigate the influence of unsteady incoming wakes with different profiles on the loss mechanisms of the high lift T106Alinear low-pressure turbine (LPT) cascade. Bars placed upstream of the LPT blade were set into rotation around their axis, thus generating circulation, as well as asymmetrical wake profiles. Three different rotation rates were simulated, yielding different wake parameters that were then compared to an actual turbine blade wake profile. Whereas the commonly-used non-rotating bars generated wakes with turbulent kinetic energy levels several times higher than that of an actual blade wake, the case with counterclockwise rotation led to more rapid wake mixing. All three wakes were able to trigger boundary layer transition and thus intermittently prevent separation on the suction surface. However, the weaker the wakes, the larger and longer lasting the separation bubbles became, and an increase in profile losses could be observed. Interestingly, the configuration with the weakest wake and the largest separation bubble resulted in a reduction of the overall LPT loss.

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Section: Wake Resultssupporting

confidence: 91%

Section: Implications For the Turbine Cascadesupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

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The Influence of Different Wake Profiles on Losses in a Low Pressure Turbine Cascade

Hammer

Sandham

Sandberg

2018

IJTPP

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“…In order to simplify both experiments and simulations, a setup with moving bars upstream of the rotor is commonly used to generate velocity wakes (Ladwig and Fottner, 1993;Engber and Fottner, 1995;Wu et al, 1999;, which are also referred to as 'negative jets' (Meyer, 1958). In an extensive study Halstead et al (1997) exposed three forms of boundary layer transition on blades in a turbine cascade caused by incoming wakes. Hodson and Howell (2005) found in their experimental investigations that wakes impinging on the blade increase the skin-friction and thus create more losses.…”

Section: Introductionmentioning

confidence: 99%

The Influence Of Different Wake Profiles On Losses In A Low Pressure Turbine Cascade

Hammer¹,

Sandham²,

Sandberg³

2017

European Conference on Turbomachinery Fluid Dynamics and Hermodynamics

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Large eddy simulations were carried out in order to investigate the influence of unsteady wakes with different profiles on the loss mechanisms of the T106A linear LPT cascade. The upstream bars were set into rotation around their axis, thus generating circulation as well as asymmetrical wake profiles. Two different rotation rates were simulated yielding different wake parameters that were then compared to an actual turbine blade wake profile. It has been found that the commonly used non-rotating bars generated wakes several times stronger than that of a blade. Both wakes were able to trigger early boundary layer transition and thus intermittently prevent separation on the suction surface. However, the weaker wakes resulted in a larger and longer-lasting separation bubble. Interestingly, the bigger separation bubble, in combination with the weaker wakes, resulted in an overall lower loss.

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“…For example, Halstead et al (1), (2) comprehensively reported on ensembleaveraged quasi-wall shear stress on compressor or turbine blades to elucidate the interaction between upstream wakes-the blade boundary layer using test rigs for compressors and turbines. Cumptsy et al (3) investigated wakeaffected boundary layers containing separation bubble on a compressor cascade.…”

Section: Introductionmentioning

confidence: 99%

Studies on Effects of Periodic Wake Passing upon a Blade Leading Edge Separation Bubble (Suppresion of Separation Bubble Due to Wake Passing)

Funazaki

Yamada

Kato

2004

JSME international journal. Ser. B, Fluids and thermal engineer

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This paper describes an experimental investigation on aerodynamic interaction between incoming periodic wakes from moving bars and separation bubble on a scaled leading edge model. Numerical simulations are also attempted to grasp an idea how the incoming wakes interact with the separation bubble. The model, which consists of a semi-circular leading edge and two flat-plates, is used to simulate the flow field around a compressor or a turbine blade. Cylindrical bars of the wake generator produce the periodic wakes in front of the test model. The study aims at enriching the knowledge on how and to what extent the periodic wake passing suppresses the leading edge separation bubble. Special attention is paid to emergence of wake-induced turbulent spots and subsequent calmed regions. Hot-wire probe measurements are executed under five different flow conditions to examine effects of Reynolds number, Strouhal number, direction of the bar movement and incidence of the test model against the incoming flow. The measurements reveal that the wake moving over the separation bubble does not directly suppress the separation bubble. Instead, wake-induced turbulence spots and the subsequent calmed regions have dominant impacts on the separation bubble suppression for the all test cases.

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Boundary Layer Development in Axial Compressors and Turbines: Part 3 of 4— LP Turbines

Cited by 100 publications

References 2 publications

The Influence of Different Wake Profiles on Losses in a Low Pressure Turbine Cascade

The Influence of Different Wake Profiles on Losses in a Low Pressure Turbine Cascade

The Influence Of Different Wake Profiles On Losses In A Low Pressure Turbine Cascade

Studies on Effects of Periodic Wake Passing upon a Blade Leading Edge Separation Bubble (Suppresion of Separation Bubble Due to Wake Passing)

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