Numerical Benchmarking of Tip Numerical Benchmarking of Tip Vortex Breakdown in Axial TurbinesVortex Breakdown in Axial Turbines

Eunice Allen-BradleyEunice Allen-Bradley

March 18, 2009March 18, 2009

TVB Cascade Tip Vortex – TVB Cascade Tip Vortex – Overview & IntroductionOverview & Introduction

• Tip leakage losses have been studied since the 1950s:– Rains (1954) was the first to experimentally measure tip vortex in compressor cascade test;– Further studies focused on tip leakage losses in compressor and fan cascades in the 1960s,

1970s, & 1980s;• Lakshminarayana et al. (1962), Lewis et al. (1977), Pandya et al. (1983), Inoue et al. (1989).

– Tip leakage loss studies in turbine cascades conducted in 1980s,1990s, & 2000s;• Booth et al. (1982), Sjolander et al. (1987), Moore et al. (1988), Morphis et al. (1988), Yamamoto

(1989), Dishart et al. (1990), Yaras et al. (1992), Chan et al. (1994), Govardhan et al. (1994), Sondak et al. (1999)

– Tip desensitization studies in turbine & compressor cascades conducted in 1990s & 2000s.• Hamik et al. (2000), Schabowski et al. (2007), Shavalikul et al. (2008), Van Ness et al. (2008).

• Tip vortex breakdown studies (published) have been limited to external body applications:

– Delta wing tip vortex formation, unsteady effects, far field wake effects, flow visualization techniques

• El-Ramly (1972), find some more…

• Studies are lacking in which the event of tip vortex breakdown occurs in turbomachines:

– Is it possible to adequately predict tip vortex breakdown in turbomachines with the current computational tools available?

– Current study will focus on prediction capability in axial turbines, using RANS CFD.

TVB Tip Vortex Methodology & Procedure –TVB Tip Vortex Methodology & Procedure –Design of ExperimentsDesign of Experiments

• Using the geometry and boundary conditions of an existing cascade facility, model tip leakage with RANS CFD.

• Alter boundary conditions until tip vortex breakdown is predicted;– Tip clearance, exit Mach number, inlet flow angle.

• Confirm results with several turbulence models for benchmarking and possible cascade testing for validation.

TVB Cascade Design Conditions

Cascade Span (H) 2.4”

Axial Chord (BX) 1.0”

Inlet flow angle (1) 63o

Exit flow angle (2) 26o

Exit Mach number (M2) 0.8

TVB Cascade Tip Vortex – TVB Cascade Tip Vortex – Benchmarking ConditionsBenchmarking Conditions

ON - Tip CLR = 0.010”; MON - Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 53 = 53oo OFF - Tip CLR = 0.010”; MOFF - Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 63 = 63oo

• Recall that the axial chord of the TVB cascade is 1.0”:– The size of potential measurement probes may be larger than

the core of the predicted tip vortex;– Furthermore, the presence of potential measurement probes

may artificially induce tip vortex to breakdown.– An alternate method for confirmation of tip vortex breakdown is

needed.

The suction side streamlines of the TVB cascade serve as further The suction side streamlines of the TVB cascade serve as further visual confirmation of predicted tip vortex breakdown.visual confirmation of predicted tip vortex breakdown.

ON - Tip CLR = 0.010”; MON - Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 53 = 53oo OFF - Tip CLR = 0.010”; MOFF - Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 63 = 63oo

Direction of Flow

The performance comparison of The performance comparison of loss for the various models run loss for the various models run to date suggest solid confirmation of tip vortex breakdown to date suggest solid confirmation of tip vortex breakdown

prediction .prediction .

Performance Comparison -- Mass Averaged Results

0.34%

0.36%

0.38%

0.40%

0.42%

0.44%

0.46%

Baldwin-Lomax kw Fully Turbulent kw Transitional

Simulation Model

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ff)

Average Average Loss Loss between 3 modelsbetween 3 models

Tip vortex breakdown prediction is maintained for all three models shown Tip vortex breakdown prediction is maintained for all three models shown above.above.

The The Loss generation plots between the three models show the Loss generation plots between the three models show the same trend through the cascade passage.same trend through the cascade passage.

ON - Tip CLR = 0.010”; MON - Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 53 = 53oo OFF - Tip CLR = 0.010”; MOFF - Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 63 = 63oo

Loss Generation

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Axial Location

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Off

Loss Generation

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Axial Location

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Baldwin-Lomax fully turbulentBaldwin-Lomax fully turbulent

kw transitionalkw transitional

kw fully turbulentkw fully turbulent

Loss Generation

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Axial Location

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Off

TVB Cascade Tip VortexTVB Cascade Tip VortexON - Tip CLR = 0.010”; MON - Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 53 = 53oo OFF -- Tip CLR = 0.010”; MOFF -- Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 63 = 63oo

Contour of TKEContour of TKE

Axial Location = 0.75*BxAxial Location = 0.75*Bx

Contour of Total PressureContour of Total Pressure

TVB Cascade Tip VortexTVB Cascade Tip VortexON - Tip CLR = 0.010”; MON - Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 53 = 53oo OFF -- Tip CLR = 0.010”; MOFF -- Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 63 = 63oo

Contour of TKEContour of TKE

Axial Location = 0.95*BxAxial Location = 0.95*Bx

Contour of Total PressureContour of Total Pressure

TVB Cascade Tip VortexTVB Cascade Tip VortexON - Tip CLR = 0.010”; MON - Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 53 = 53oo OFF -- Tip CLR = 0.010”; MOFF -- Tip CLR = 0.010”; M22 = 0.8; = 0.8; 11 = 63 = 63oo

Contour of TKEContour of TKEAxial Location = 1.05*BxAxial Location = 1.05*Bx

Contour of Total PressureContour of Total Pressure

TVB Cascade Tip VortexTVB Cascade Tip VortexContour of Total PressureContour of Total Pressure

Axial Location = 1.50*BxAxial Location = 1.50*Bx

ON ON OFF OFF

Spanwise Loss Plot*Spanwise Loss Plot*

*Mass averaged results from k*Mass averaged results from k transitional model transitional model

Future WorkFuture Work

• Further confirmation of performance results with alternate turbulence models to compare against each other;– Loss generation, spanwise loss, computational flow

visualizations.

• Application of tip leakage correlations developed by previous authors to the current predictions.

• TVB cascade testing for prediction validation.• Explore influence of relative rotation of outer endwall.