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Numerical Benchmarking of Tip Vortex Breakdown in Axial Turbines

Numerical Benchmarking of Tip Vortex Breakdown in Axial Turbines. Eunice Allen-Bradley March 18, 2009. TVB Cascade Tip Vortex – Overview & Introduction. Tip leakage losses have been studied since the 1950s:

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Numerical Benchmarking of Tip Vortex Breakdown in Axial Turbines

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  1. Numerical Benchmarking of Tip Vortex Breakdown in Axial Turbines Eunice Allen-Bradley March 18, 2009

  2. TVB Cascade Tip Vortex – Overview & 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.

  3. TVB Tip Vortex Methodology & Procedure –Design 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.

  4. TVB Cascade Tip Vortex – Benchmarking Conditions ON - Tip CLR = 0.010”; M2 = 0.8; b1 = 53o OFF - Tip CLR = 0.010”; M2 = 0.8; b1 = 63o • 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.

  5. The suction side streamlines of the TVB cascade serve as further visual confirmation of predicted tip vortex breakdown. ON - Tip CLR = 0.010”; M2 = 0.8; b1 = 53o OFF - Tip CLR = 0.010”; M2 = 0.8; b1 = 63o Direction of Flow

  6. The performance comparison of Dloss for the various models run to date suggest solid confirmation of tip vortex breakdown prediction . Average D Loss between 3 models Tip vortex breakdown prediction is maintained for all three models shown above.

  7. The DLoss generation plots between the three models show the same trend through the cascade passage. ON - Tip CLR = 0.010”; M2 = 0.8; b1 = 53o OFF - Tip CLR = 0.010”; M2 = 0.8; b1 = 63o Baldwin-Lomax fully turbulent kw fully turbulent kw transitional

  8. TVB Cascade Tip Vortex ON - Tip CLR = 0.010”; M2 = 0.8; b1 = 53o OFF -- Tip CLR = 0.010”; M2 = 0.8; b1 = 63o Axial Location = 0.75*Bx Contour of TKE Contour of Total Pressure

  9. TVB Cascade Tip Vortex ON - Tip CLR = 0.010”; M2 = 0.8; b1 = 53o OFF -- Tip CLR = 0.010”; M2 = 0.8; b1 = 63o Axial Location = 0.95*Bx Contour of TKE Contour of Total Pressure

  10. TVB Cascade Tip Vortex ON - Tip CLR = 0.010”; M2 = 0.8; b1 = 53o OFF -- Tip CLR = 0.010”; M2 = 0.8; b1 = 63o Axial Location = 1.05*Bx Contour of TKE Contour of Total Pressure

  11. TVB Cascade Tip VortexContour of Total Pressure Axial Location = 1.50*Bx Spanwise Loss Plot* ON OFF *Mass averaged results from kw transitional model

  12. Future 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.

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