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.

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 Experimental Rotordynamic Characterization of Annular Seals: Facility and Methodology

1998 ◽  
Author(s):  
J. Mark Darden ◽  
Eric M. Earhart ◽  
George T. Flowers
Keyword(s):  
High Speed ◽  
Quality Data ◽  
Test Rig ◽  
Stability Margins ◽  
Rotordynamic Coefficients ◽  
Annular Seal ◽  
Theoretical Predictions ◽  
High Reynolds ◽  
Annular Seals

Annular seals are known to enhance rotordynamic stability margins and minimize vibration response levels in high-speed rotating machinery. Theoretical predictions for the rotordynamic characteristics of annular seals exist but additional experimental data is needed to properly anchor these results. NASA’s Marshall Space Flight Center (MSFC) has developed an annular seal test rig and facility to experimentally characterize axially-fed annular seals. The objective of MSFC’s annular seal test rig is to obtain the rotordynamic coefficients (direct and cross-coupled stiffness, damping, and added mass) for a variety of high Reynolds number annular seals. The MSFC test rig supports centered-seal testing with inlet pressures up to 138 bars (2000 psi) and flow rates of over 946 liters per minute (250 gpm). The rig’s shaft is powered by a 186 kilowatt (250 horsepower) steam turbine capable of rotational speeds of over 20,000 revolutions per minute (rpm). A description of the identification process used to obtain rotordynamic coefficients is given as well as procedures for ensuring quality data. Experimental results for a smooth annular seal with an L/D = 0.5 is presented. Excellent agreement between experimental and theoretical results is obtained.

Experimental Rotordynamic Characterization of Annular Seals: Facility and Methodology

1999 ◽  
Vol 121 (2) ◽  
pp. 349-354 ◽  
Author(s):  
J. M. Darden ◽  
E. M. Earhart ◽  
G. T. Flowers
Keyword(s):  
High Speed ◽  
Quality Data ◽  
Test Rig ◽  
Stability Margins ◽  
Rotordynamic Coefficients ◽  
Annular Seal ◽  
Theoretical Predictions ◽  
High Reynolds ◽  
Annular Seals

Annular seals are known to enhance rotordynamic stability margins and minimize vibration response levels in high-speed rotating machinery. Theoretical predictions for the rotordynamic characteristics of annular seals exist but additional experimental data is needed to properly anchor these results. NASA’s Marshall Space Flight Center (MSFC) has developed an annular seal test rig and facility to experimentally characterize axially fed annular seals. The objective of MSFC’s annular seal test rig is to obtain the rotordynamic coefficients (direct and cross-coupled stiffness, damping, and added mass) for a variety of high Reynolds number annular seals. The MSFC test rig supports centered-seal testing with inlet pressures up to 138 bars (2000 psi) and flow rates of over 946 liters per minute (250 gpm). The rig’s shaft is powered by a 186 kilowatt (250 horsepower) steam turbine capable of rotational speeds of over 20,000 revolutions per minute (rpm). A description of the identification process used to obtain rotordynamic coefficients is given as well as procedures for ensuring quality data. Experimental results for a smooth annular seal with an L/D =0.5 is presented. Excellent agreement between experimental and theoretical results is obtained.

A Novel Hybrid Seal: Design and Experimental Validation on a High Pressure Rotordynamic Test Rig

2021 ◽  
Author(s):  
Giuseppe Vannini ◽  
Benjamin Defoy ◽  
Manjush Ganiger ◽  
Carlo Mazzali
Keyword(s):  
High Pressure ◽  
Pressure Ratio ◽  
Test Rig ◽  
Rotordynamic Coefficients ◽  
Experimental Activity ◽  
Seal Design ◽  
Piston Seal ◽  
Delivery Pressure ◽  
Inlet Swirl ◽  
Primary Focus

Abstract The design and experimental activity presented in this paper is related to a novel hybrid seal which is intended to work as a balance piston seal in an AMBs levitated high-pressure (about 300 bar delivery pressure) motor-compressor. The typical solution adopted for balance piston application is a damper seal (e.g. honeycomb seal), as the rotordynamic stability is a primary focus. However, due to interactions between the AMB controller and seal high stiffness level, the aforementioned selection is not so straightforward. After a review of the state of the art it was found that a combination of some conventional geometries (e.g. labyrinth and honeycomb) can be adopted to achieve the desired target. The design was done using a novel tool combining the validated bulk flow codes for each geometry. Moreover, a CFD analysis, based on some literature references, was carried out as a final verification of the design. The experimental activity was then performed at the Authors’ internal seal test rig. As in typical rotordynamic seal testing activity, the operating parameters leveraged to explore performance sensitivity are rotational speed, inlet pressure, pressure ratio and inlet swirl level. The outcome was satisfactory both in terms of leakage and rotordynamic coefficients.

Interrelated Rotordynamic Effects of Cylindrical and Conical Whirl of Annular Seal Rotors

1991 ◽  
Vol 113 (3) ◽  
pp. 470-480 ◽  
Author(s):  
E. A. Baskharone ◽  
S. J. Hensel
Keyword(s):  
Finite Element ◽  
Flow Model ◽  
Computational Procedure ◽  
Rotordynamic Coefficients ◽  
Conical Whirl ◽  
Conical Rotor ◽  
Annular Seal ◽  
Rotor Surface ◽  
Flow Variables ◽  
Sample Case

A comprehensive approach for computing the dynamic coefficients of an annular seal is presented. The coefficients are partly those associated with a uniform lateral eccentricity mode of the rotor (known as the cylindrical whirl mode) and with an angular eccentricity (which gives rise to a conical whirl type). The rotor excitation effects in both cases are treated as interrelated by recognizing the fluid-exerted moments resulting from the lateral eccentricity and the net fluid force resulting from the angular eccentricity. In all cases, the rotor is assumed to undergo a whirling motion around the housing centerline. The computational procedure is a finite-element perturbation model in which the zeroth-order undisplaced-rotor flow solution in the clearance gap is obtained through a Petrov-Galerkin approach. Next, the rotor translational and angular eccentricities, considered to be infinitesimally small, are perceived to cause virtual distortions of varied magnitudes in the finite element assembly which occupies the clearance gap. Perturbations in the flow variables including, in particular, the rotor surface pressure, are then obtained by expanding the finite-element equations in terms of the rotor eccentricity components. The fluid-exerted forces and moments are in this case computed by integration over the rotor surface, and the full matrix of rotordynamic coefficients, in the end, obtained. The computational model is verified against a bulk-flow model for a sample case involving a straight annular seal. Choice of this sample model for validation was made on the basis that no other existing model has yet been expanded to account for the mutual interaction between the cylindrical and conical rotor whirl, which is under focus in this study.

Understanding Friction Factor Behavior in Liquid Annular Seals With Deliberately Roughened Surfaces: Roughness Geometric Characteristics Defining Flow Resistance

2006 ◽  
Author(s):  
L. A. Villasmil ◽  
D. W. Childs ◽  
H. C. Chen
Keyword(s):  
Friction Factor ◽  
Flow Behavior ◽  
Round Hole ◽  
Centrifugal Pumps ◽  
Typical Application ◽  
Geometric Characteristics ◽  
Seal Design ◽  
Annular Seal ◽  
Leakage Characteristics ◽  
Annular Seals

Multistage centrifugal pumps and compressors are among the most widely used pieces of rotating machinery in industry. A typical application demands the arrangement of several impellers mounted on a shaft that spin within a stationary case. Annular seals are the most common sealing devices used in this type of machinery. The annular seal design affects both (i) machinery performance in terms of energy conversion efficiency, and (ii) stability due to the interaction within the rotor and the stator through the fluid flow within the seals. Extensive numerical research of several liquid annular seal experiments is in progress, focusing on the patterns that experimentally and numerically provide larger resistance to flow, hexagonal cells (honeycomb) and equilateral triangular cells (isogrid), both constant depths. In the present paper, the geometric characteristics that define the leakage resistance of roughened seals are explored. First, the results of a parametric analysis are discussed, which include previous 2-D predictions and new simulations of multiple rectangular grooved seal geometries. The analysis is limited to the original clearance in the experiments, 0.175 mm. The results indicate that roughened surface to total area ratio, and the depth-to-length ratio are the primary parameters defining the leakage characteristics of these surfaces. Secondly, the effect of the roughness orientation on the friction factor characteristics of these surfaces is addressed. Previous numerical tests have shown that solving the flow up to the laminar sub-layer better captures the behavior of the friction-factor-to-clearance proportionality. Resolving this layer is demanding. Recent numerical studies show promise in reducing computational efforts by employing a simplified empirical model with extended wall functions, indeed avoiding including each roughness in the numerical domain. These studies evaluated the flow behavior in round-hole seals, a perfectly symmetric pattern. Contrary to round holes, nonsymmetric patterns; knurls, honeycombs, or isogrids, consistently provide larger friction factor values. The numerical evaluation of the leakage characteristics in the last two patterns indicates a non-negligible sensitivity to the pattern orientation in one of them.

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.

Modelling and simulation for cooling processes in television panel manufacture

2007 ◽  
Vol 221 (10) ◽  
pp. 1579-1583 ◽  
Author(s):  
H Zhou ◽  
S Cui ◽  
Z Huang
Keyword(s):  
Transient Analysis ◽  
Thickness Direction ◽  
Cooling Process ◽  
One Dimensional ◽  
Part Quality ◽  
Cooling Design ◽  
Simulation Results ◽  
The Finite Difference Method ◽  
Good Agreement ◽  
Impinging Cooling

Cooling design in the forming operation of the television (TV) panel is important because it significantly affects the part quality associated with residual stresses and productivity. A mathematical model and numerical simulation for the cooling process of the panel has been developed. The renormalization group turbulence model is applied for the jet impinging cooling, and a local one-dimensional transient analysis in the thickness direction is adopted for the part, which employs the finite difference method. The experimental verification shows a good agreement with the simulation results.

scholarly journals Comparison of the Dynamic Characteristics of Smooth Annular Seals and Damping Seals

1999 ◽  
Author(s):  
J. Mark Darden ◽  
Eric M. Earhart ◽  
George T. Flowers
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Rocket Engine ◽  
Rotating Machinery ◽  
Test Rig ◽  
Stability Margins ◽  
Annular Seal ◽  
Theoretical Predictions ◽  
High Fluid ◽  
Annular Seals

Annular seals are known to enhance rotordynamic stability margins and minimize vibration response levels in high-speed rotating machinery. Theoretical predictions for the rotordynamic characteristics of annular seals exist but additional experimental data is needed to properly anchor these results. NASA’s Marshall Space Flight Center (MSFC) has developed an annular seal test rig and facility to experimentally characterize axially-fed annular seals. Annular seals with deliberately roughened stators (i.e. damping seals) have been shown analyticalty to increase stability margins of rocket engine turbomachinery by reducing the seal’s whirl frequency ratio. The capabilities of MSFC’s annular seal test rig have been enhanced to allow high fluid inlet preswirl testing that is more representative of actual turbopump seal bounder conditions. The purpose of this paper is to describe the effect of this realistic preswirl on the stabilizing capability of both damping and smooth seals. Centered seal results are presented for both a smooth annular seal and a damping seal. These results were obtained for a range of seal pressure differentials, shaft rotational speeds, and two levels of inlet fluid preswirl.

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