Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals—Part II: Smooth and Honeycomb Geometries

2002 ◽  
Vol 124 (4) ◽  
pp. 963-970 ◽  
Author(s):  
M. P. Dawson ◽  
D. W. Childs
Keyword(s):  
Control Volume ◽  
Test Facility ◽  
Radial Clearance ◽  
Cell Width ◽  
Volume Model ◽  
Numerical Predictions ◽  
Dynamic Impedance ◽  
Honeycomb Seals ◽  
Gas Seals ◽  
Honeycomb Cell

Results are presented from tests conducted using an experimental test facility to measure the leakage and dynamic impedance of smooth and honeycomb straight-bore annular gas seals. The test seals had a 114.3 mm (4.500 in.) bore with a length-to-diameter ratio of 0.75 and a nominal radial clearance of 0.19 mm (0.0075 in.). The honeycomb cell depth for both seals was 3.10 mm (0.122 in.), and the cell width was 0.79 mm (0.031 in.). Dynamic impedance and leakage measurements are reported using air at three supply pressures out to 1.72 Mpa (250 psi), three speeds out to 20,200 rpm, and exit-to-inlet pressure ratios of 40% and 50%. Comparisons to the predictions from the two-control-volume model of Kleynhans and Childs [1] are of particular interest. This model predicts that honeycomb seals do not fit the conventional frequency independent model for smooth annular gas seals. The experimental results verify this new theory. Numerical predictions from a computer program incorporating the new two-control-volume model of Kleynhans and Childs [1] correlate well with both measured seal leakage and dynamic impedances for the honeycomb seals.

Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals: Part 2 — Smooth and Honeycomb Geometries

2001 ◽  
Author(s):  
Matthew P. Dawson ◽  
Dara W. Childs
Keyword(s):  
Control Volume ◽  
Test Facility ◽  
Radial Clearance ◽  
Cell Width ◽  
Volume Model ◽  
Numerical Predictions ◽  
Dynamic Impedance ◽  
Honeycomb Seals ◽  
Gas Seals ◽  
Honeycomb Cell

Results are presented from tests conducted using an experimental test facility to measure the leakage and dynamic impedance of smooth and honeycomb straight-bore annular gas seals. The test seals had a 114.3 mm bore with a length-to-diameter ratio of 0.75 and a nominal radial clearance of 0.19 mm. The honeycomb cell depth for both seals was 3.1 mm, and the cell width was 0.79 mm. Dynamic impedance and leakage measurements are reported using air at three supply pressures out to 1.72 MPa, three speeds out to 20,200 rpm, and exit-to-inlet pressure ratios of 40% and 50%. Comparisons to the predictions from the two-control-volume model of Kleynhans and Childs [1] are of particular interest. This model predicts that honeycomb seals do not fit the conventional frequency independent model for smooth annular gas seals. The experimental results verify this new theory. Numerical predictions from a computer program incorporating the new two-control-volume model of Kleynhans and Childs [1] correlate well with both measured seal leakage and dynamic impedances for the honeycomb seals.

Experimental Versus Theoretical Characteristics of a High-Speed Hybrid (Combination Hydrostatic and Hydrodynamic) Bearing

1993 ◽  
Vol 115 (1) ◽  
pp. 160-168 ◽  
Author(s):  
K. Alan Kurtin ◽  
D. Childs ◽  
Luis San Andres ◽  
K. Hale
Keyword(s):  
High Speed ◽  
Load Capacity ◽  
Test Facility ◽  
Navier Stokes ◽  
Radial Clearance ◽  
Hydrodynamic Bearing ◽  
Speed Test ◽  
Discharge Coefficients ◽  
Hybrid Combination ◽  
Numerical Predictions

The high-speed test facility designed and installed at Texas A&M to study water lubricated journal bearings has been successfully used to test statically an orifice compensated five-recess-hybrid (combination hydrostatic and hydrodynamic) bearing for two radial clearance configurations. Measurements of relative-bearing position, torque, recess pressure, flow rate, and temperature were made at speeds from 10,000 to 25,000 rpm and supply pressures of 6.89 MPa (1,000 psi), 5.52 MPa (800 psi), and 4.14 MPa (600 psi). For speeds of 10,000 and 17,500 rpm, the bearing load capacity was also investigated. A pitching instability of the bearing limited the number of test cases. A 2-dimensional, bulk-flow, Navier-Stokes numerical analysis program was used for all theoretical performance predictions. Orifice discharge coefficients used in the program were calculated from measured flow and pressure data. Reynolds numbers for flow within the bearing lands due to shaft rotation and recess pressurization ranged from 6700 to 16,500. Predictions sensitivity to ±10 percent changes in the input parameters was investigated. Results showed that performance prediction sensitivities are high for changes in discharge coefficients and negligible for changes in relative roughness. The numerical predictions of relative bearing position, recess pressure, flowrate, and torque are very accurate, provided the selected orifice discharge coefficients are correct.

Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals: Part 1 — Test Facility and Apparatus

2001 ◽  
Author(s):  
Matthew P. Dawson ◽  
Dara W. Childs ◽  
Christopher G. Holt ◽  
Stephen G. Phillips
Keyword(s):  
Random Excitation ◽  
Supply System ◽  
Test Facility ◽  
Experimental Facility ◽  
Frequency Range ◽  
Labyrinth Seals ◽  
Dynamic Impedance ◽  
Air Supply ◽  
Gas Seals ◽  
Excitation Waveform

An experimental facility and apparatus are described for measuring the dynamic impedance and leakage characteristics of annular gas seals. The apparatus currently has a top speed of 29,800 rpm and can accommodate seal diameters up to 114.3 mm. The air-supply system can provide up to 13.79 MPa (2,000 psi) of pressure at the seal inlet. Test seals are configured in a back-to-back arrangement inside the stator and air enters a central inlet annulus at two opposed radial positions. Labyrinth seals and bleed ports located outboard of each test seal are used to control the pressure drop across the test seals. Two orthogonal, external hydraulic shakers are used to excite the test stator at frequencies up to 400 Hz. At a given operating condition, the apparatus can measure the rotordynamic impedance of a pair of identical seals over a broad frequency range using a single pseudo-random excitation waveform. Measurements are also made of seal leakage rates and upstream and downstream temperatures and pressures.

Theory Versus Experiment for the Rotordynamic Coefficient of Labyrinth Gas Seals: Part II—A Comparison to Experiment

1988 ◽  
Vol 110 (3) ◽  
pp. 281-287 ◽  
Author(s):  
D. W. Childs ◽  
J. K. Scharrer
Keyword(s):  
Experimental Test ◽  
Damping Coefficient ◽  
Test Facility ◽  
Radial Clearance ◽  
Test Results ◽  
Rotordynamic Coefficients ◽  
Theory Versus ◽  
Gas Seals ◽  
Predicted Values ◽  
Rotordynamic Coefficient

An experimental test facility is used to measure the leakage and rotordynamic coefficients of teeth-on-rotor and teeth-on-stator labyrinth gas seals. The test results are presented along with the theoretically predicted values for the two seal configurations at three different radial clearances and shaft speeds to 16,000 cpm. The test results show that the theory accurately predicts the cross-coupled stiffness for both seal configurations and shows improvement in the prediction of the direct damping for the teeth-on-rotor seal. The theory fails to predict a decrease in the direct damping coefficient for an increase in the radial clearance for the teeth-on-stator seal.

Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals—Part I: Test Facility and Apparatus

2002 ◽  
Vol 124 (4) ◽  
pp. 958-962 ◽  
Author(s):  
M. P. Dawson ◽  
D. W. Childs ◽  
C. G. Holt ◽  
S. G. Phillips
Keyword(s):  
Random Excitation ◽  
Supply System ◽  
Test Facility ◽  
Experimental Facility ◽  
Frequency Range ◽  
Labyrinth Seals ◽  
Dynamic Impedance ◽  
Air Supply ◽  
Gas Seals ◽  
Excitation Waveform

An experimental facility and apparatus are described for measuring the dynamic impedance and leakage characteristics of annular gas seals. The apparatus currently has a top speed of 29,800 rpm and can accommodate seal diameters up to 114.3 mm. The air-supply system can provide up to 13.79 MPa (2000 psi) of pressure at the seal inlet. Test seals are configured in a back-to-back arrangement inside the stator and air enters a central inlet annulus at two opposed radial positions. Labyrinth seals and bleed ports located outboard of each test seal are used to control the pressure drop across the test seals. Two orthogonal, external hydraulic shakers are used to excite the test stator at frequencies up to 400 Hz. At a given operating condition, the apparatus can measure the rotordynamic impedance of a pair of identical seals over a broad frequency range using a single pseudo-random excitation waveform. Measurements are also made of seal leakage rates and upstream and downstream temperatures and pressures.

A Bulk Flow Model for Off-Centered Honeycomb Gas Seals

2002 ◽  
Vol 129 (1) ◽  
pp. 185-194 ◽  
Author(s):  
Thomas Soulas ◽  
Luis San Andres
Keyword(s):  
Gas Turbines ◽  
Flow Model ◽  
Control Volume ◽  
Bulk Flow ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Honeycomb Seal ◽  
Rotor Eccentricity ◽  
Honeycomb Seals ◽  
Gas Seals

A computational analysis for prediction of the static and dynamic forced performance of gas honeycomb seals at off-centered rotor conditions follows. The bulk-flow analysis, similar to the two-control volume flow model of Kleynhans and Childs (1997, “The Acoustic Influence of Cell Depth on the Rotordynamic Characteristics of Smooth-Rotor/Honeycomb-Stator Annular Gas Seals,” ASME J. Eng. Gas Turbines Power, 119, pp. 949–957), is brought without loss of generality into a single-control volume model, thus simplifying the computational process. The formulation accommodates the honeycomb effective cell depth, and existing software for annular pressure seals and is easily upgraded for damper seal analysis. An analytical perturbation method for derivation of zeroth- and first-order flow fields renders the seal equilibrium response and frequency-dependent dynamic force impedances, respectively. Numerical predictions for a centered straight-bore honeycomb gas seal shows good agreement with experimentally identified impedances, hence validating the model and confirming the paramount influence of excitation frequency on the rotordynamic force coefficients of honeycomb seals. The effect of rotor eccentricity on the static and dynamic forced response of a smooth annular seal and a honeycomb seal is evaluated for characteristic pressure differentials and rotor speeds. Leakage for the two seal types increases slightly as the rotor eccentricity increases. Rotor off-centering has a pronounced nonlinear effect on the predicted (and experimentally verified) dynamic force coefficients for smooth seals. However, in honeycomb gas seals, even large rotor center excursions do not sensibly affect the effective local film thickness, maintaining the flow azimuthal symmetry. The current model and predictions thus increase confidence in honeycomb seal design, operating performance, and reliability in actual applications.

A Bulk Flow Model for Off-Centered Honeycomb Gas Seals

2002 ◽  
Author(s):  
Thomas Soulas ◽  
Luis San Andres
Keyword(s):  
Flow Model ◽  
Control Volume ◽  
Forced Response ◽  
Bulk Flow ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Honeycomb Seal ◽  
Rotor Eccentricity ◽  
Honeycomb Seals ◽  
Gas Seals

A computational analysis for prediction of the static and dynamic forced performance of gas honeycomb seals at off-centered rotor conditions follows. The bulk-flow analysis, similar to the two-control volume flow model of Kleynhans and Childs [1], is brought without loss of generality into a single-control volume model, thus simplifying the computational process. The formulation accommodates the honeycomb effective cell depth, and existing software for annular pressure seals is easily upgraded for damper seal analysis. An analytical perturbation method for derivation of zeroth- and first-order flow fields renders the seal equilibrium response and frequency-dependent dynamic force impedances, respectively. Numerical predictions for a centered straight-bore honeycomb gas seal show good agreement with experimentally identified impedances, hence validating the model and confirming the paramount influence of excitation frequency on the rotordynamic force coefficients of honeycomb seals. The effect of rotor eccentricity on the static and dynamic forced response of a smooth annular seal and a honeycomb seal is evaluated for characteristic pressure differentials and rotor speeds. Leakage for the two seal types increases slightly as the rotor eccentricity increases. Rotor off-centering does have a pronounced non-linear effect on the predicted (and experimentally verified) dynamic force coefficients for smooth seals. However, in honeycomb gas seals, even large rotor center excursions do not sensibly affect the effective local film thickness, maintaining the flow azimuthal symmetry. The current model and predictions thus increase confidence in honeycomb seal design, operating performance and reliability in actual applications.

Theory Versus Experiment for the Rotordynamic Coefficients of Labyrinth Gas Seals: Part I—A Two Control Volume Model

1988 ◽  
Vol 110 (3) ◽  
pp. 270-280 ◽  
Author(s):  
Joseph K. Scharrer
Keyword(s):  
Pressure Distribution ◽  
Control Volume ◽  
Reaction Force ◽  
Labyrinth Seal ◽  
Wall Friction ◽  
Small Motion ◽  
First Order ◽  
Rotordynamic Coefficients ◽  
Volume Model ◽  
Gas Seals

The basic equations are derived for a two-control-volume model for compressible flow in a labyrinth seal. The recirculation velocity in the cavity is incorporated into the model for the first time. The flow is assumed to be completely turbulent and isoenergetic. The wall friction factors are determined using the Blasius formula. Jet flow theory is used for the calculation of the recirculation velocity in the cavity. Linearized zeroth and first-order perturbation equations are developed for small motion about a centered position by an expansion in the eccentricity ratio. The zeroth-order pressure distribution is found by satisfying the leakage equation while the circumferential velocity distribution is determined by satisfying the momentum equations. The first-order equations are solved by a separation of variable solution. Integration of the resultant pressure distribution along and around the seal defines the reaction force developed by the seal and the corresponding dynamic coefficients.

Measurements and Modeling of Ingress in a New 1.5-Stage Turbine Research Facility

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Marios Patinios ◽  
James A. Scobie ◽  
Carl M. Sangan ◽  
J. Michael Owen ◽  
Gary D. Lock
Keyword(s):  
Theoretical Model ◽  
Gas Turbines ◽  
Test Facility ◽  
Radial Clearance ◽  
Operating Life ◽  
The Core ◽  
Wide Range ◽  
Purge Flow ◽  
Rotor Disk ◽  
Engine Components

In gas turbines, hot mainstream flow can be ingested into the wheel-space formed between stator and rotor disks as a result of the circumferential pressure asymmetry in the annulus; this ingress can significantly affect the operating life, performance, and integrity of highly stressed, vulnerable engine components. Rim seals, fitted at the periphery of the disks, are used to minimize ingress and therefore reduce the amount of purge flow required to seal the wheel-space and cool the disks. This paper presents experimental results from a new 1.5-stage test facility designed to investigate ingress into the wheel-spaces upstream and downstream of a rotor disk. The fluid-dynamically scaled rig operates at incompressible flow conditions, far removed from the harsh environment of the engine which is not conducive to experimental measurements. The test facility features interchangeable rim-seal components, offering significant flexibility and expediency in terms of data collection over a wide range of sealing flow rates. The rig was specifically designed to enable an efficient method of ranking and quantifying the performance of generic and engine-specific seal geometries. The radial variation of CO2 gas concentration, pressure, and swirl is measured to explore, for the first time, the flow structure in both the upstream and downstream wheel-spaces. The measurements show that the concentration in the core is equal to that on the stator walls and that both distributions are virtually invariant with radius. These measurements confirm that mixing between ingress and egress is essentially complete immediately after the ingested fluid enters the wheel-space and that the fluid from the boundary layer on the stator is the source of that in the core. The swirl in the core is shown to determine the radial distribution of pressure in the wheel-space. The performance of a double radial-clearance seal is evaluated in terms of the variation of effectiveness with sealing flow rate for both the upstream and the downstream wheel-spaces and is found to be independent of rotational Reynolds number. A simple theoretical orifice model was fitted to the experimental data showing good agreement between theory and experiment for all cases. This observation is of great significance as it demonstrates that the theoretical model can accurately predict ingress even when it is driven by the complex unsteady pressure field in the annulus upstream and downstream of the rotor. The combination of the theoretical model and the new test rig with its flexibility and capability for detailed measurements provides a powerful tool for the engine rim-seal designer.

Numerical Characterization of Hot Gas Ingestion Through Turbine Rim Seals

2016 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Carl M. Sangan ◽  
James A. Scobie ◽  
Gary D. Lock
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Axial Flow ◽  
Radial Clearance ◽  
Buffering Effect ◽  
Hot Gas ◽  
Numerical Predictions ◽  
Wide Range ◽  
Thermal Buffering

This paper deals with a numerical study aimed at the characterization of hot gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations. With the radial-seal clearance configuration, CFD steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: for a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement. When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations display a distinct kink. It was found that the “kink phenomenon” can be ascribed to an over-estimation of the egress spoiling effects due to turbulence modelling limitations. Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.

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