A Numerical Study on the Influence of Hole Depth on the Static and Dynamic Performance of Hole-Pattern Seals

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Patrick J. Migliorini ◽  
Alexandrina Untaroiu ◽  
Houston G. Wood
Keyword(s):  
Steady State ◽  
Turbulence Model ◽  
Gas Turbines ◽  
Numerical Study ◽  
Bulk Flow ◽  
Hole Depth ◽  
Rotordynamic Coefficients ◽  
The Impact ◽  
Good Agreement ◽  
Annular Seals

Annular seals serve an important role in the dynamics of turbomachinery by reducing leakage of a process fluid while also contributing potentially destabilizing forces to the rotor system. Hole-pattern seals have been the focus of many investigations, but recent experimental studies have shown that there are still many phenomena that require exploration. One such phenomenon is the influence of hole depth on the static and dynamic characteristics of the seal. In this paper, a hybrid computational fluid dynamics (CFD)/bulk-flow method is employed to investigate the nonmonotonic relationship between hole depth and leakage shown in experimental measurements of a hole-pattern seal by Childs et al. (2014, “The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals,” ASME J. Eng. Gas Turbines Power, 136(4), p. 042501). Three hole depths (1.905 mm, 3.302 mm, and 6.604 mm) and three running speeds (10,200 rpm, 15,350 rpm, and 20,200 rpm) are considered. For the steady-state flow, the 3D Reynolds-Averaged-Navier-Stokes (RANS) equations are solved with the k-ϵ turbulence model for a circumferentially periodic sector of the full seal geometry. The steady-state results are input into the first-order equations of a bulk-flow model to predict rotordynamic coefficients. Results of the hybrid method are compared to experimental data. CFD predicted leakage showed good agreement (within 5%) for the 3.302 mm and 6.604 mm hole depth configurations. For the 1.905 mm hole depth seal, agreement was within 17%. An additional set of calculations performed with the shear stress transport (SST) turbulence model produced worse agreement. Examination of streamlines along the seal show that the hole depth controls the shape of the vortex that forms in the hole, driving the resistance experienced by the jet flow in the clearance region. For the rotordynamic coefficients, good agreement is shown between predictions and experiment for most excitation frequencies.

A Numerical Study on the Influence of Hole Aspect Ratio on the Performance Characteristics of a Hole-Pattern Seal

2014 ◽  
Author(s):  
Patrick J. Migliorini ◽  
Alexandrina Untaroiu ◽  
Houston G. Wood
Keyword(s):  
Aspect Ratio ◽  
Friction Factor ◽  
Numerical Study ◽  
Vortex Formation ◽  
Experimental Studies ◽  
Jet Flow ◽  
Bulk Flow ◽  
Hole Depth ◽  
Friction Factors ◽  
Annular Seals

In turbomachinery, annular seals are used to reduce leakage between regions of high and low pressure. Many configurations of annular seals have been developed and studied in the literature including plain, labyrinth, pocket-damper, honeycomb, and hole-pattern. In machines experiencing stability issues, honeycomb and hole-pattern type seals have been used to replace labyrinth seals. Bulk-flow models are typically used to predict the leakage and dynamic coefficients of hole-pattern seals, relying on empirically derived friction factor coefficients. Previous experimental studies have shown that, for hole-pattern seals, the leakage and stator friction factor are strongly influenced by hole-depth. However, this behavior is not a monotonic function of hole-depth, a fact that might reduce confidence in future bulk-flow model predictions if not properly accounted for. A recent numerical study has highlighted the role of vortex formation in the holes which has a strong influence on the flow in the clearance region. Depending on the shape of the vortex, the flow in the hole can act much like a pinch valve, reducing the effective clearance of the jet flow. In this paper, computational fluid dynamics simulations of several hole-pattern seal configurations have been performed to study the effect of hole-aspect ratio (depth versus diameter) on the leakage and friction factors. The Reynolds Averaged Navier Stokes (RANS) equations with k-ε turbulence model were solved using ANSYS CFX. It was found that the shape of the hole influences the vortex formation within the hole, effecting the jet flow in the clearance region and the seal leakage. The results show that the leakage is heavily dependent on the hole diameter in addition to the hole depth. The relationship between the friction factors and the geometry of the seal was found to be non-monotonic. It is therefore difficult to develop a friction factor model that will accurately encompass all configurations and it is recommended that friction factor data be interpolated from experimental or numerical results.

Life Prediction of Power Turbine Components for High Exhaust Back Pressure Applications: Part I — Disks

2015 ◽  
Author(s):  
Dipankar Dua ◽  
Brahmaji Vasantharao
Keyword(s):  
Steady State ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Life Prediction ◽  
Creep Damage ◽  
Back Pressure ◽  
System Level ◽  
Cyclic Life ◽  
Power Turbine ◽  
The Impact

Industrial and aeroderivative gas turbines when used in CHP and CCPP applications typically experience an increased exhaust back pressure due to pressure losses from the downstream balance-of-plant systems. This increased back pressure on the power turbine results not only in decreased thermodynamic performance but also changes power turbine secondary flow characteristics thus impacting lives of rotating and stationary components of the power turbine. This Paper discusses the Impact to Fatigue and Creep life of free power turbine disks subjected to high back pressure applications using Siemens Energy approach. Steady State and Transient stress fields have been calculated using finite element method. New Lifing Correlation [1] Criteria has been used to estimate Predicted Safe Cyclic Life (PSCL) of the disks. Walker Strain Initiation model [1] is utilized to predict cycles to crack initiation and a fracture mechanics based approach is used to estimate propagation life. Hyperbolic Tangent Model [2] has been used to estimate creep damage of the disks. Steady state and transient temperature fields in the disks are highly dependent on the secondary air flows and cavity dynamics thus directly impacting the Predicted Safe Cyclic Life and Overall Creep Damage. A System-level power turbine secondary flow analyses was carried out with and without high back pressure. In addition, numerical simulations were performed to understand the cavity flow dynamics. These results have been used to perform a sensitivity study on disk temperature distribution and understand the impact of various back pressure levels on turbine disk lives. The Steady Sate and Transient Thermal predictions were validated using full-scale engine test and have been found to correlate well with the test results. The Life Prediction Study shows that the impact on PSCL and Overall Creep damage for high back pressure applications meets the product design standards.

Eccentricity Effects on the Rotordynamic Coefficients of Plain Annular Seals: Theory Versus Experiment

1997 ◽  
Vol 119 (3) ◽  
pp. 443-447 ◽  
Author(s):  
O. R. Marquette ◽  
D. W. Childs ◽  
L. San Andres
Keyword(s):  
High Speed ◽  
Small Motion ◽  
Rotordynamic Coefficients ◽  
Annular Seal ◽  
Theory Versus ◽  
High Speed Data ◽  
Static Eccentricity ◽  
Good Signal ◽  
Good Agreement ◽  
Annular Seals

Reliable high-speed data are presented for leakage and rotordynamic coefficients of a plain annular seal at centered and eccentric positions. A seal with L/D = 0.45 was tested, and measured results have good signal-to-noise ratios. The influence on rotordynamic coefficients of pressure drop, running speed, and static eccentricity was investigated. There is an excellent agreement between experimental and theoretical results in the centered position, even for direct inertia terms, which have not shown good agreement with predictions in past studies. However, the rotordynamic coefficients are more sensitive to changes in eccentricity than predicted. These results suggest that, in some cases, annular seals for pumps may need to be treated more like hydrodynamic bearings, with rotordynamic coefficients which are valid for small motion about a static equilibrium position versus the present eccentricity-independent coefficients.

scholarly journals VATEMP: The Variable Area Turbine Engine Matching Program

1990 ◽  
Author(s):  
J. E. A. Roy-Aikins ◽  
J. R. Palmer
Keyword(s):  
Steady State ◽  
Gas Turbines ◽  
Variable Geometry ◽  
Aircraft Engines ◽  
Flow Temperature ◽  
Turbine Engine ◽  
Path Component ◽  
The Impact ◽  
Engine Cycle ◽  
Steady State Performance

Variable geometry in key gas turbine components offers the advantage of either improving the internal performance of a component or of re-matching the engine cycle to alter the flow-temperature-pressure relationships. Future gas turbines are expected to use variable geometry components extensively if they are to overcome some of the problems encountered by present day engines at off-design conditions in order to give much more advanced performance. Greater attention is also being paid to the impact of installation losses on the performance of aircraft engines. A computer program called VATEMP, herein described, has been developed capable of simulating the steady-state performance of arbitrary gas turbines with or without variable geometry in almost any gas path component. Results obtained from the program led to the conclusion that variable geometry components have the potential to improve significantly the off-design performance of gas turbines.

Numerical Study of the Heat Transfer in Micro Gas Turbines

2006 ◽  
Vol 129 (4) ◽  
pp. 835-841 ◽  
Author(s):  
T. Verstraete ◽  
Z. Alsalihi ◽  
R. A. Van den Braembussche
Keyword(s):  
Heat Transfer ◽  
Gas Turbines ◽  
Numerical Study ◽  
Three Dimensional ◽  
High Heat ◽  
Large Temperature ◽  
Radial Compressor ◽  
Micro Gas Turbine ◽  
High Heat Transfer ◽  
The Impact

This paper presents a numerical investigation of the heat transfer inside a micro gas turbine and its impact on the performance. The large temperature difference between turbine and compressor in combination with the small dimensions results in a high heat transfer causing a drop in efficiency of both components. Present study aims to quantify this heat transfer and to reveal the different mechanisms that contribute to it. A conjugate heat transfer solver has been developed for this purpose. It combines a three-dimensional (3D) conduction calculation inside the rotor and the stator with a 3D flow calculation in the radial compressor, turbine and gap between stator and rotor. The results for micro gas turbines of different size and shape and different material characteristics are presented and the impact on performance is evaluated.

scholarly journals Thermomechanical Modelling of a Steel Plate Impacted by a Shot and Experimental Validation

2006 ◽  
Vol 524-525 ◽  
pp. 167-172 ◽  
Author(s):  
Sébastien Rouquette ◽  
Emmanuelle Rouhaud ◽  
Hervé Pron ◽  
Manuel François ◽  
Christian Bissieux ◽  
...  
Keyword(s):  
Temperature Rise ◽  
Experimental Validation ◽  
Steel Plate ◽  
Numerical Study ◽  
Infrared Camera ◽  
Metallic Plate ◽  
Mechanical Problem ◽  
The Impact ◽  
Compressive Residual Stresses ◽  
Good Agreement

This work presents an experimental and numerical study of the thermo-mechanical problem of a steel plate impacted by a shot. The temperature rise is estimated and its effect on the compressive residual stress is analyzed. The simulations show that the value of the compressive residual stresses at the surface of the plate is modified when thermo-mechanical effects are included in the model as compared with simulation including hardening effects only. To validate this numerical study, an experimental device has been developed to measure the temperature rise after the impact. The experiment consists of the impact of a shot on a metallic plate. The temperature measurement is performed by an infrared camera located on the side of the plate opposite to the impact. Comparison between these experimental measurements and the numerical solution gives good agreement (to within 5%).

Incompressible Navier-Stokes Computation of the NREL Airfoils Using a Symmetric Total Variational Diminishing Scheme

1994 ◽  
Vol 116 (4) ◽  
pp. 174-182 ◽  
Author(s):  
S. L. Yang ◽  
Y. L. Chang ◽  
O. Arici
Keyword(s):  
Turbulence Model ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Wind Tunnel Test ◽  
Factorization Method ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Approximate Factorization ◽  
Two Dimensional Flow ◽  
Good Agreement

The purpose of this paper is to present a numerical study of flow fields for the NREL S805 and S809 airfoils using a spatially second-order symmetric total variational diminishing scheme. The steady two-dimensional flow is modeled as turbulent, viscous, and incompressible and is formulated in the pseudo-compressible form. The turbulent flow is closed by the Baldwin-Lomax algebraic turbulence model. Numerical solutions are obtained by the implicit approximate-factorization method. The accuracy of the numerical results is compared with the Delft two-dimensional wind tunnel test data. For comparison, the Eppler code results are also included. Numerical solutions of pressure and lift coefficients show good agreement with the experimental data, but not the drag coefficients. To properly simulate the post-stall flow field, a better turbulence model should be used.

Numerical Modeling of Rotordynamic Coefficients for Deliberately Roughened Stator Gas Annular Seals

2006 ◽  
Vol 129 (2) ◽  
pp. 424-429 ◽  
Author(s):  
Gocha Chochua ◽  
Thomas A. Soulas
Keyword(s):  
Transient Analysis ◽  
Test Rig ◽  
One Dimensional ◽  
Design And Optimization ◽  
Rotordynamic Coefficients ◽  
Seal Design ◽  
Annular Seal ◽  
Rotor Surface ◽  
Good Agreement ◽  
Annular Seals

A method is proposed for computations of rotordynamic coefficients of deliberately roughened stator gas annular seals using computational fluid dynamics. The method is based on a transient analysis with deforming mesh. Frequency-dependent direct and cross-coupled rotordynamic coefficients are determined as a response to an assigned rotor surface periodic motion. The obtained numerical results are found to be in good agreement with the available test data and one-dimensional tool predictions. The method can be used as a research tool or as a virtual annular seal test rig for seal design and optimization.

Study of the Vortex Breakdown in a Conical Swirler Using LDV, LES and POD

2007 ◽  
Author(s):  
Christophe Duwig ◽  
Laszlo Fuchs ◽  
Arnaud Lacarelle ◽  
Matthias Beutke ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Pattern ◽  
Coherent Structures ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Numerical Study ◽  
Flame Stabilization ◽  
Turbulent Fluctuation ◽  
Characteristic Frequencies ◽  
The Impact ◽  
Good Agreement

Modeling and understanding the vortex breakdown is a key issue of modern Lean Premixed Combustors. The main difficulty of the problem is the unsteady behavior of this type of flow: Large structures resulting from vortex breakdown and the swirling shear-layers, affect directly the flame stabilization leading to heat-release fluctuations and combustion instabilities. Consequently, one needs to capture and understand turbulent coherent structures dynamics for designing efficient burners. This task is particularly challenging since it deals with capturing coherent motions within a chaotic system and should be done using state-of-the art numerical and experimental techniques. The present work focuses on the experimental and numerical study of iso-thermal vortex breakdown in a conical swirler. Experimental investigations were performed with 2D Laser Doppler Velocimetry (LDV) and Hotwire Anemometry at the outlet of the combustor model. Averaged velocity fields and RMS values are showing a strong central recirculation zone. In addition, characteristic frequencies of the flow have been exhibited showing the strong influence of large scale turbulent fluctuation on the flow pattern. These measurements showed also the impact of different outlet geometries on the strength and position of the coherent structures of the flow. Further, Large Eddy Simulation (LES) has been used to obtain a 4D description of the flow. Comparison with LDV profiles showed a good agreement, indicating that the LES tool captures accurately the flow. The LES results were then processed for capturing and identifying the coherent structures. Firstly, characteristic frequencies were analyzed. Here also a good agreement with the experimental data was achieved. Secondly the cores of the vortices were visualized providing a good insight into the unsteady flow pattern. Finally, Proper Orthogonal Decomposition (POD) was applied to the 4D field in order to identify the contribution of different large scale fluctuation modes. The presence of the Precessing Vortex Core (PVC) corresponding to a pair of helical structures was captured.

Numerical Investigations on Rotordynamic Characteristic of Hole-Pattern Seals With Two Different Hole-Diameters

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Xin Yan ◽  
Kun He ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Total Energy ◽  
Constant Temperature ◽  
Turbulence Model ◽  
Ideal Gas ◽  
Hole Diameter ◽  
Bulk Flow ◽  
Numerical Accuracy ◽  
Flow Method ◽  
Rotordynamic Coefficients ◽  
Diameter Hole

The rotordynamic characteristic of the hole-pattern seals with two different hole-diameters was investigated using the unsteady Reynolds-averaged Navier–Stokes (URANS) equations solutions and bulk flow methods. The mesh deformation method combined with elliptical orbit model was adopted to numerically solve the transient flow fields. By integrating the transient reaction forces on the rotor surface, the rotordynamic coefficients of the hole-pattern seals at a set of excitation frequencies were obtained with the reaction-force/motion model. The effects of mesh density, constant temperature assumption, and turbulence model on the numerical accuracy were analyzed for both large hole-diameter hole-pattern (LDHP) and small hole-diameter hole-pattern (SDHP) seals. The comparisons between the two bulk flow methods (i.e., the isothermal bulk flow method (ISOTSEAL) and the ideal gas bulk flow method with energy equation (ideal gas bulk flow model)) and transient computational fluid dynamics (CFD) method were performed. It shows that, compared to the experimental data, the isothermal URANS (constant temperature assumption) and total energy URANS (consider the temperature varying) solutions almost have the same accuracy with respect to the rotordynamic coefficients predictions. However, for the direct damping coefficient predictions, the total energy URANS method has a slight advantage over the isothermal URANS for both SDHP and LDHP cases. For the LDHP seal, the predicted rotordynamic coefficients are not sensitive to the selected turbulence models, but as the hole-diameter becomes smaller, the effect of turbulence model on the numerical accuracy becomes pronounced. Among the studied numerical methods, the isothermal URANS solutions with standard k–ε turbulence model have a good performance taking both numerical accuracy and computational time into consideration. For the SDHP seal, the present ideal gas bulk flow method and ISOTSEAL can provide the reasonable predictions of the rotordynamic coefficients. However, for the LDHP seal, both of them show a low accuracy in predicting the rotordynamic coefficients.

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