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Research Papers: Gas Turbines: Structures and Dynamics

On the Thermodynamic Process in the Bulk-Flow Model for the Estimation of the Dynamic Coefficients of Labyrinth Seals

[+] Author and Article Information
Filippo Cangioli

Department of Mechanical Engineering,
Politecnico di Milano,
Via La Masa 1,
Milan 20156, Italy
e-mail: filippo.cangioli@polimi.it

Paolo Pennacchi

Department of Mechanical Engineering,
Politecnico di Milano,
Via La Masa 1,
Milan 20156, Italy
e-mail: paolo.pennacchi@polimi.it

Giuseppe Vannini

General Electric Oil&Gas,
Via Felice Matteucci 2,
Florence 50127, Italy
e-mail: giuseppe.vannini@ge.com

Lorenzo Ciuchicchi

General Electric Oil&Gas,
480 Allée Gustave Eiffel,
Le Creusot 71200, France
e-mail: lorenzo.ciuchicchi@ge.com

Andrea Vania

Department of Mechanical Engineering,
Politecnico di Milano,
Via La Masa 1,
Milan 20156, Italy
e-mail: andrea.vania@polimi.it

Steven Chatterton

Department of Mechanical Engineering,
Politecnico di Milano,
Via La Masa 1,
Milan 20156, Italy
e-mail: steven.chatterton@polimi.it

Phuoc Vinh Dang

Department of Mechanical Engineering,
The University of Danang—Danang University
of Science and Technology,
Nguyen Luong Bang Road, 54.,
Da Nang 55000, Vietnam
e-mail: dpvinh@dut.udn.vn

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 4, 2017; final manuscript received July 26, 2017; published online October 17, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(3), 032502 (Oct 17, 2017) (10 pages) Paper No: GTP-17-1277; doi: 10.1115/1.4037919 History: Received July 04, 2017; Revised July 26, 2017

The impact of sealing equipment on the stability of turbomachineries is a crucial topic because the power generation market is continuously requiring high rotational speed and high performance, leading to the clearance reduction in the seals. The accurate characterization of the rotordynamic coefficients generated by the seals is pivotal to mitigate instability issues. In the paper, the authors propose an improvement of the state-of-the-art one-control volume (1CV) bulk-flow model (Childs and Scharrer, 1986, “An Iwatsubo-Based Solution for Labyrinth Seals: Comparison to Experimental Results,” ASME J. Eng. Gas Turbines Power, 108(2), pp. 325–331) by considering the energy equation in the steady-state problem. Thus, real gas properties can be evaluated in a more accurate way because the enthalpy variation, expected through the seal cavities, is evaluated in the model. The authors assume that the enthalpy is not a function of the clearance perturbation; therefore, the energy equation is considered only in the steady-state problem. The results of experimental tests of a 14 teeth-on-stator (TOS) labyrinth seal, performed in the high-pressure seal test rig owned by GE Oil&Gas, are presented in the paper. Positive and negative preswirl ratios are used in the experimental tests to investigate the effect of the preswirl on the rotordynamic coefficients. Overall, by considering the energy equation, a better numerical estimation of the rotordynamic coefficients for the tests with the negative preswirl ratio has been obtained (as it results from the comparison with the experiments). Finally, the numerical results are compared with a reference bulk-flow model proposed by Thorat and Childs (2010, “Predicted Rotordynamic Behavior of a Labyrinth Seal as Rotor Surface Speed Approaches Mach 1,” ASME J. Eng. Gas Turbines Power, 132(11), p. 112504), highlighting the improvement obtained.

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References

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Figures

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Fig. 1

Control volume and bulk-flow variables used in the model

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Fig. 2

Circular orbit of the rotor within the labyrinth seal

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Fig. 3

Relative error between the Blasius and the Colebrook correlation (dashed line) and the Swamee–Jain and Colebrook correlation (solid line) as a function of the Reynolds number. Absolute roughness equal to 3.2 μm.

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Fig. 4

High-pressure seal test rig owned by General Electric Oil&Gas

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Fig. 5

Direct stiffness coefficients as a function of the whirling speeds for the positive preswirl ratio (on the right) and negative preswirl ratio (on the left): comparison of the authors' model with and without the energy equation with the experimental results

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Fig. 6

Cross-coupled and direct damping coefficients for the positive preswirl test: comparison of the authors' model with and without the energy equation with the experimental results

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Fig. 7

Cross-coupled and direct damping coefficients for the negative preswirl test: comparison of the authors' model with and without the energy equation with the experimental results

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Fig. 8

Leakage mass flowrate: numerical prediction and experimental measurements

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Fig. 9

Bar graph of the steady pressure difference between the adiabatic model and the isenthalpic model

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Fig. 10

Cross-coupled and direct damping coefficients for the positive preswirl test: comparison of the authors' model with the energy equation with the model developed in Ref. [14] and with the experimental results

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Fig. 11

Cross-coupled and direct damping coefficients for the negative preswirl test: comparison of the authors' model with the energy equation with the model developed in Ref. [14] and with the experimental results

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