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Research Papers

An Investigation of Turbine Wheelspace Cooling Flow Interactions With a Transonic Hot Gas Path—Part II: CFD Simulations

[+] Author and Article Information
G. M. Laskowski

 General Electric Global Research Center, Niskayuna, NY 12309laskowsk@research.ge.com

R. S. Bunker, J. C. Bailey, G. Ledezma

 General Electric Global Research Center, Niskayuna, NY 12309

S. Kapetanovic, G. M. Itzel, M. A. Sullivan, T. R. Farrell

 General Electric Energy, Greenville, SC 29615

J. Turbomach 133(4), 041020 (Apr 25, 2011) (12 pages) doi:10.1115/1.4002410 History: Received August 11, 2009; Revised November 21, 2009; Published April 25, 2011; Online April 25, 2011

A computational model has been developed to study the mechanisms responsible for hot gas ingestion into the wheel-space cavity of a stationary high pressure turbine (HPT) cascade rig. Simulations were undertaken for the stationary rig described by Bunker (2009, “An Investigation of Turbine Wheelspace Cooling Flow Interactions With a Transonic Hot Gas Path—Part I: Experimental Measurements,” ASME Paper No. GT2009-59237) in a companion paper. The rig consists of five vanes, a wheel-space cavity, and five cylinders that represent the blockage due to the leading edge of the rotor airfoils. The experimental program investigated two cylinder diameters and three clocking positions for a nominal coolant flow rate. Comparisons are made between the computed and measured flow-fields for the smaller of the two cylinders. It is demonstrated that the circumferential variation of pressure established by the vane wake and leading edge bow wave results in an unstable shear layer over the rim seal axial gap (trench) that causes hot gases to ingest for a nominal coolant flow. Steady-state computational fluid dynamics (CFD) simulations did not capture this effect and it was determined that an unsteady analysis was required in order to match the experimental data. Favorable agreement is noted between the time-averaged computed and measured pressure distributions in the circumferential direction both upstream and downstream of the trench, as well as within the trench itself. Furthermore, it is noted that time-averaged buffer cavity effectiveness agrees to within 5% of the experimental data for the cases studied. The validated CFD model is then used to simulate the effect of rotation by rotating the cylinders and disk at rotational rate that scales with a typical engine. A sliding mesh interface is utilized to communicate data between the stator and rotor domains. The stationary cases tend to ingest past the first angel-wing for a nominal coolant flow condition, whereas the effect of rotation helps pressurize the cavity and is responsible for preventing hot gas from entering the buffer cavity.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 17

Buffer cavity effectiveness for (a) rotating and (b) stationary cases

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Figure 18

Mean secondary flow structures within buffer cavity for (a) stationary and (b) rotating cases space 1.5 deg apart

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Figure 16

Time-averaged hub wall temperature for different cylinder clocking positions (a) θ=0, (b) θ=−2, (c) θ=−5

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Figure 15

FFT of probe 6 (outer) time history denoting fundamental resonant frequency of Kelvin–Helmholtz instability over trench cavity

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Figure 14

Time history of temperature at outer probe locations for different clocking positions

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Figure 13

Instantaneous (a) hub wall adiabatic temperature and (b) buffer cavity gas temperature for θ=−5 clocking position

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Figure 12

Time-averaged pressure distribution on cylinder (bucket) platform surface

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Figure 11

Time-averaged pressure distribution on vane endwall surface

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Figure 10

Comparison of steady and unsteady pressure variation at (a) vane aft and (b) platform forward locations for clocking position θ=0

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Figure 9

Time and spatially averaged radial buffer cavity effectiveness distribution for different clocking positions

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Figure 8

Steady-state RANS and time-averaged unsteady RANS buffer cavity effectiveness: (a) θ=0, (b) θ=−2, and (c) θ=−5

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Figure 7

Time and spatial averaged effectiveness distribution in buffer cavity for baseline sensitivity study: impact of time step

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Figure 6

Time-averaged vane forward pressure distribution for baseline sensitivity study: impact of time step

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Figure 5

Time-averaged vane forward pressure distribution for baseline sensitivity study: impact of mesh density

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Figure 4

Pressure tap and thermocouple validation metric locations

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Figure 3

Computational domain for the rotating case

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Figure 2

Boundary conditions for the stationary case (aft cooling hole inlets not shown)

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Figure 1

Wheelspace geometry and terminology

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