Research Papers: Gas Turbines: Structures and Dynamics

Experimental and Analytical Assessment of Cavity Modes in a Gas Turbine Wheelspace

[+] Author and Article Information
Rachel A. Berg, C. S. Tan

MIT Gas Turbine Laboratory,
Cambridge, MA 02139

Zhongman Ding

GE Power,
Greenville, SC 29615

Gregory Laskowski

GE Aviation,
Lynn, MA 01905

Pepe Palafox, Rinaldo Miorini

Niskayuna, NY 12309

1Present address: GE Aviation, Lynn, MA 01905.

2Corresponding author.

3Present address: GE Aviation, Evendale, OH 45215.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 3, 2017; final manuscript received September 5, 2017; published online January 17, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(6), 062502 (Jan 17, 2018) (11 pages) Paper No: GTP-17-1432; doi: 10.1115/1.4038474 History: Received August 03, 2017; Revised September 05, 2017

Fast response pressure data acquired in a high-speed 1.5-stage turbine hot gas ingestion rig (HGIR) show the existence of pressure oscillation modes in the rim-seal-wheelspace cavity of a high pressure gas turbine stage with purge flow. The experimental results and observations are complemented by computational assessments of pressure oscillation modes associated with the flow in canonical cavity configurations. The cavity modes identified include shallow cavity modes and Helmholtz resonance. The response of the cavity modes to variation in design and operating parameters are assessed. These parameters include cavity aspect ratio (AR), purge flow ratio, and flow direction defined by the ratio of primary tangential to axial velocity. Scaling the cavity modal response based on computational results and available experimental data in terms of the appropriate reduced frequencies appears to indicate the potential presence of a deep cavity mode as well. While the role of cavity modes on hot gas ingestion cannot be clarified based on the current set of data, the unsteady pressure field associated with turbine rim cavity modal response can be expected to drive ingress/egress.

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Grahic Jump Location
Fig. 1

Wheelspace coolant path and nomenclature for wheelspace between turbine disk and stator

Grahic Jump Location
Fig. 2

(a) Canonical Helmholtz resonator and equivalent spring-mass system and (b) turbine rim buffer cavity with corresponding parameter cavity volume V, neck area A (seal clearance), and physical neck length L (tip size of angel wing body) for determining Helmholtz resonance frequency given in Eq. (2)

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Fig. 7

Kulite locations on HGIR rotor surface. There are a total of 30 dynamic Kulites in the trench cavity, five dynamic Kulites in the buffer cavity, and two static Kulites in the inner wheelspace. Ten of the Kulites in the trench cavity are located on the stator side of the trench cavity at the same radial location [13].

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Fig. 6

Summary of stator side instrumentation at radial and circumferential locations with respect to engine centerline and NGV trailing edge

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Fig. 5

Static pressure tap locations on HGIR stator surface. Pss1–Pss3 indicate the static pressure taps located behind the NGV TE and in the trench cavity and are currently used for assessing the circumferential pressure variation [13].

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Fig. 4

Meridional section of HGIR turbine with main auxiliary components adapted from Ref. [13]

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Fig. 10

Hypothesized Helmholtz response is measured at 0.305 of blade passing frequency for configuration 1: blue line is measured response while broken red line is nonrunning rig response

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Fig. 11

Helmholtz response is absent for configuration 3, as hypothesized: blue line is measured response while broken red line is nonrunning rig response

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Fig. 12

Configurations for assessing cavity mode response: configuration 2 has a trench cavity width equal to half that of configuration 1, hence an expected shift in shallow cavity mode response

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Fig. 13

Hypothesized shallow cavity modes 1 and 2 response measured at 0.74 and 1.17 of blade passing frequency compared to corresponding computed response range for configuration 1: blue line is measured response, vertical red bar is computed response range while broken red line is nonrunning rig response

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Fig. 8

Representative responses from a set of kulites at various circumferential locations within rim cavity; the different color lines refer to response from kulite at each corresponding circumferential location. The overlapping of all responses implies axisymmetry of modal response.

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Fig. 17

Cavity-depth-based reduced frequency variation with cavity AR: computational results compared to data [15,17] for shallow and deep cavity modes

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Fig. 3

Geometrical parameters in turbine rim-cavity system

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Fig. 9

Configurations for assessing Helmholtz mode response: configuration 2 has a narrower buffer cavity than configuration 1, and configuration3 has a shorter buffer cavity that eliminates the distinct volume apparent in configurations 1 and 2

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Fig. 14

Computational model setup with BL trip

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Fig. 15

Selected parametric values for computational assessment of cavity mode response

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Fig. 16

Cavity-width-based reduced frequency variation with cavity AR: computational results compared to data [15,17] for shallow and deep cavity modes

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Fig. 18

Effect of cavity purge flow on flow field in cavity. Streamlines are presented along with contours of the pressure coefficient, C−p=(Ps−Ps∞)/((1/2)ρ∞U∞2)). The single vortex in the cavity is visibly being pushed out of the cavity when purge flow is added with a BR of 0.35. At higher BRs, the flow exiting the cavity does not allow a vortex to form. The unsteadiness in the shear layer continues to be present.

Grahic Jump Location
Fig. 19

Effect of flow angle on flow field in cavity. Streamlines are presented along with contours of the pressure coefficient, C−p=(Ps−Ps∞)/((1/2)ρ∞U∞2)). The single vortex expands lengthwise in the cavity as flow angle is increased, with no detectable unsteady response for 60 deg.



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