On the Leakage and Dynamic Force Coefficients of a Novel Stepped Shaft Pocket Damper Seal: Experimental and Numerical Verification

2020 ◽  
Author(s):  
Jing Yang ◽  
Luis San Andres ◽  
Xueliang Lu
Keyword(s):  
High Performance ◽  
System Stability ◽  
Damping Coefficient ◽  
Dynamic Force ◽  
Numerical Verification ◽  
Labyrinth Seals ◽  
Stepped Shaft ◽  
Blade Tip ◽  
Rotor Surface ◽  
Computational Fluid Dynamics Cfd

Abstract High performance turbomachinery favors annular seals with a large damping coefficient to ensure rotor system stability. Pocket damper seals (PDSs), a variation of labyrinth seals with axial blades (ribs) and adding circumferential partition walls (ridges), produce a favorable damping performance. To further enhance the damping characteristic, a novel stepped shaft PDS is hereby introduced. The invention has a unique arrangement of steps on the rotor, each facing an upstream rib in a pocket. The step and a blade tip form a tight clearance (c1), while the rotor surface and the downstream blade tip make a larger clearance (c2). To validate the invention performance, a stepped shaft PDS (c1/c2 = 0.5) with four ribs and eight pockets is built and tested. For supply pressure (Ps) = 1.1 bar to 3.2 bar, the measured leakage for the stepped shaft PDS is 50% of that for an identical PDS with a smooth rotor surface (c1/c2 = 1, i.e., a uniform clearance PDS). Computational fluid dynamics (CFD) and bulk flow model predicted leakages agree well with the measurements. For Ps = 2.3 bar, the test damping coefficient for the stepped shaft PDS is ~ 1.5 times greater than that for the uniform clearance PDS. With an increase in Ps to 3.2 bar, the stepped shaft PDS shows a 2.5 times increase in damping coefficient. Both the test data and CFD predictions demonstrate the superior damping performance of the invention, thus providing a novel alternative seal configuration for turbomachinery usage.

On the Leakage and Dynamic Force Coefficients of a Novel Stepped Shaft Pocket Damper Seal: Experimental and Numerical Verification

2020 ◽  
Author(s):  
Jing Yang ◽  
Luis San Andrés ◽  
Xueliang Lu
Keyword(s):  
Test Data ◽  
Flow Direction ◽  
System Stability ◽  
Damping Coefficient ◽  
Dynamic Force ◽  
Numerical Verification ◽  
Force Coefficients ◽  
Stepped Shaft ◽  
Blade Tip ◽  
Rotor Surface

Abstract High performance turbomachinery favors annular seals with a large damping coefficient to ensure rotor system stability. Pocket damper seals (PDSs), a variation of labyrinth seals with axial blades (ribs) and adding circumferential partition walls (ridges), produce a favorable damping performance. To further enhance the damping characteristic and reduce leakage, a novel stepped shaft PDS is hereby introduced. The invention has a unique arrangement of steps on the rotor surface, each facing an upstream rib in a pocket row. Thus, the step and a blade tip form a tight clearance (c1), while the rotor surface and the downstream blade tip make a larger clearance (c2). The convergence-divergence variation of cross-section areas along the flow direction increases the PDS damping coefficient. To validate the performance of the novel design, a stepped shaft PDS (c1/c2 = 0.5) with four axial ribs and eight circumferential pockets is built and tested. A comprehensive investigation, experimental and computational, produces the seal leakage and dynamic force coefficients for the stepped shaft PDS, as well as similar performance characteristics for an identical PDS with a smooth rotor surface (c1/c2 = 1, i.e., a uniform clearance PDS). The stepped shaft PDS operates with air at supply pressure (PS) ranging from 1.1 bar to 3.2 bar. The measured leakage for the stepped shaft PDS is 50% of that for the uniform clearance PDS. Computational fluid dynamics (CFD) and bulk flow model (BFM) predictions of leakage agree well with the test data. For PS = 2.3 bar, the test damping coefficient (C) for the stepped shaft PDS is ∼ 1.5 times greater than the one for the uniform clearance PDS. With an increase in PS to 3.2 bar, the stepped shaft PDS shows a two and one half increase in damping coefficient. In comparison to the test data, a CFD model over estimates C by 29% for operation at PS = 3.2 bar, though capturing the variation trend versus whirl frequency. The BFM largely under predicts C for the stepped shaft PDS and is abandoned for future work. Both the test data and CFD predictions demonstrate the superior damping performance of the stepped shaft PDS, thus providing a novel alternative seal configuration for turbomachinery usage.

Effect of Straight Through Labyrinth Seals on Rotordynamics

1993 ◽  
Author(s):  
John M. Vance ◽  
J. J. Zierer ◽  
E. M. Conway
Keyword(s):  
Critical Speed ◽  
Tip Clearance ◽  
Damping Coefficient ◽  
Inlet Pressure ◽  
Labyrinth Seals ◽  
Worst Case ◽  
Blade Tip ◽  
Gas Seals ◽  
Range Of Values ◽  
Blade Tip Clearance

Abstract Experimental measurements have been made to evaluate the rotordynamic performance of straight-through labyrinth seals under conditions that are realistic for many turbomachines. Both teeth-on-rotor and teeth-on-stator gas seals were tested, each with twelve blades, 173 mm (6.8″) blade diameter, and 102 mm (4″) total length. The nominal blade tip clearance was 0.5 mm (20 mils). The teeth-on-stator seal was tested with the blade tip clearances diverging (in the direction of the flow), uniform, and converging. The teeth-on-rotor seal was tested with uniform clearances. The inlet air pressure to the seals was varied from 1.7 bar to 14.6 bar (25 psi to 200 psig) with the last blade exhausting to the atmosphere. Coastdown tests of all the seals were performed on a rotordynamic test rig to show their effect on synchronous response to imbalance when passing through a 3700 rpm critical speed. For the teeth-on-rotor seal, rap tests at 4500 rpm were also conducted to measure the effective damping coefficient for subsynchronous vibration. The synchronous response to imbalance was generally increased by all the seals at inlet pressures up to about 11.2 bar (150 psig). The worst case was for the teeth-on-rotor seal at about 2.7 bar (35–45 psi) inlet pressure where the rotor whirl amplitude was increased from .1 mm (3.75 mils, peak to peak) to over .13 mm (5 mils). In most cases the rotor whirl amplitude was slightly decreased at inlet pressures above 13 bar (176 psig). The teeth-on-rotor seal provided a small amount of damping to attenuate the 61 Hz subsynchronous vibration with the rotor running at 4500 rpm. A computer model which includes both the rotor and housing dynamics was developed to evaluate the possible range of values of the rotordynamic seal coefficients. Simulations show that the effective subsynchronous damping coefficient of the teeth-on-rotor seal ranges from 175 N-s/m at 5.1 bar inlet pressure (1 lb-s/in at 75 psi) to 876 N-s/m at 10.2 bar (5 lb-s/in at 150 psi). This corresponds to a range of 0.3% to 1.4% of critical damping added by the seal for subsynchronous vibration, even though the seal increased the synchronous response at the critical speed. It is shown that the orbit conditions for the synchronous and subsynchronous tests were radically different, as they likely will be in most turbomachines.

scholarly journals Numerical Analysis of Flow across Brush Elements Based on a 2-D Staggered Tube Banks Model

Aerospace ◽  
2021 ◽  
Vol 8 (1) ◽  
pp. 19
Author(s):  
Xiaolei Song ◽  
Meihong Liu ◽  
Xiangping Hu ◽  
Xueliang Wang ◽  
Taohong Liao ◽  
...  
Keyword(s):  
Euler Number ◽  
Dynamic Pressure ◽  
Labyrinth Seals ◽  
System A ◽  
Brush Seal ◽  
Back Plate ◽  
Computational Fluid Dynamics Cfd ◽  
Secondary Air ◽  
Tube Banks ◽  
Gas Expansion

In order to improve efficiency in turbomachinery, brush seal replaces labyrinth seals widely in the secondary air system. A 2-d staggered tube bank model is adopted to simulate the gas states and the pressure character in brush seal, and computational fluid dynamics (CFD) is used to solve the model in this paper. According to the simulation results, the corrected formula of the Euler number and dimensionless pressure are given. The results show that gas expands when flow through the bristle pack, and the gas expansion closes to an isotherm process. The dynamic pressure increases with decreasing static pressure. The Euler number can reflect the seal performance of brush seals in leakage characteristics. Compared with increasing the number of rows, the reduction of the gap is a higher-efficiency method to increase the Euler number. The Euler number continually increases as the gap decreases. However, with the differential pressure increasing, Euler number first increases and then decreases as the number of rows increases. Finally, the pressure distribution on the surface of end rows is asymmetric, and it may increase the friction between the bristles and the back plate.

Research on CFD Simulation of the Cement Slurry Mixer

2012 ◽  
Vol 621 ◽  
pp. 196-199
Author(s):  
Shui Ping LI ◽  
Ya Li Yuan ◽  
Lu Gang Shi
Keyword(s):  
Flow Field ◽  
High Performance ◽  
Cfd Simulation ◽  
Structural Parameters ◽  
Internal Flow ◽  
Simulation Method ◽  
Cement Slurry ◽  
Fluid Machinery ◽  
Computational Fluid Dynamics Cfd ◽  
Machinery Design

Numerical simulation method of the internal flow field of fluid machinery has become an important technology in the study of fluid machinery design. In order to obtain a high-performance cement slurry mixer, computational fluid dynamics (CFD) techniques are used to simulate the flow field in the mixer, and the simulation results are studied. According to the analysis results, the structural parameters of the mixer are modified. The results show the mixer under the revised parameters meet the design requirements well. So CFD analysis method can shorten design period and provide valuable theoretical guidance for the design of fluid machinery.

Impact of Frequency Dependence of Gas Labyrinth Seal Rotordynamic Coefficients on Centrifugal Compressor Stability

2010 ◽  
Author(s):  
Giuseppe Vannini ◽  
Manish R. Thorat ◽  
Dara W. Childs ◽  
Mirko Libraschi
Keyword(s):  
Molecular Weight ◽  
Numerical Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Labyrinth Seals ◽  
Frequency Dependent ◽  
Rotordynamic Coefficients ◽  
Frequency Independent ◽  
Rotor Surface ◽  
Independent Model

A numerical model developed by Thorat & Childs [1] has indicated that the conventional frequency independent model for labyrinth seals is invalid for rotor surface velocities reaching a significant fraction of Mach 1. A theoretical one-control-volume (1CV) model based on a leakage equation that yields a reasonably good comparison with experimental results is considered in the present analysis. The numerical model yields frequency-dependent rotordynamic coefficients for the seal. Three real centrifugal compressors are analyzed to compare stability predictions with and without frequency-dependent labyrinth seal model. Three different compressor services are selected to have a comprehensive scenario in terms of pressure and molecular weight (MW). The molecular weight is very important for Mach number calculation and consequently for the frequency dependent nature of the coefficients. A hydrogen recycle application with MW around 8, a natural gas application with MW around 18, and finally a propane application with molecular weight around 44 are selected for this comparison. Useful indications on the applicability range of frequency dependent coefficients are given.

CFD Leakage Predictions of Unworn and Worn Labyrinth Seals With and Without Tooth Axial Offset

2017 ◽  
Author(s):  
Hasham H. Chougule ◽  
Alexander Mirzamoghadam
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Numerical Modeling ◽  
Steady State ◽  
Flow Field ◽  
Labyrinth Seals ◽  
Small Clearance ◽  
Total Leakage ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Deflection

The objective of this study is to develop a Computational Fluid Dynamics (CFD) based methodology for analyzing and predicting leakage of worn or rub-intended labyrinth seals during operation. The simulations include intended tooth axial offset and numerical modeling of the flow field. The purpose is to predict total leakage through the seal when an axial tooth offset is provided after the intended/unintended rub. Results indicate that as expected, the leakage for the in-line worn land case (i.e. tooth under rub) is higher compared to unworn. Furthermore, the intended rotor/teeth forward axial offset/shift with respect to the rubbed land reduces the seal leakage. The overall leakage of a rubbed seal with axial tooth offset is observed to be considerably reduced, and it can become even less than a small clearance seal designed not to rub. The reduced leakage during steady state is due to a targeted smaller running gap because of tooth offset under the intended/worn land groove shape, higher blockages, higher turbulence and flow deflection as compared to worn seal model without axial tooth offset.

On the Extraction of Milling Tools Out of Shrink Fit Chucks

2012 ◽  
Vol 523-524 ◽  
pp. 445-450 ◽  
Author(s):  
Berend Denkena ◽  
Dennis Heinisch
Keyword(s):  
High Performance ◽  
Experimental Investigations ◽  
Process Conditions ◽  
Geometrical Parameters ◽  
Dynamic Force ◽  
Unique Type ◽  
Milling Operations ◽  
Torque Transmission ◽  
Shrink Fit ◽  
Milling Tools

Thermal shrink fit chucks are widely used in high performance machining where excellent concentricity and high torque transmission are required. It was reported that in those milling operations, severe damage of tools, workpieces, and also machine tools occurs due to an extraction of the milling tool out of the shrink fit chuck during the process. Although, theoretically the interference fit assembly should withstand certain process forces, milling tools are apparently pulled out under special process conditions. The resulting increase of the cutting depth often leads to tool overload and breakage. So far, the phenomenon of tool extraction could not be explained. This paper presents an experimental approach of the investigation of the phenomenon of axial tool extraction. Therefore, a unique type of test rig for main spindles and tool interfaces is used. Experimental investigations on dynamic force and torque combinations leading to tool extraction are described. Results show, that the holding force is not only affected by geometrical parameters of the shrink fit chuck, but also by the applied dynamic load.

scholarly journals Enhanced Central System of the Traversing Rod for High-Performance Rotor Spinning Machines

2017 ◽  
Vol 17 (1) ◽  
pp. 27-34 ◽  
Author(s):  
Jan Valtera ◽  
Petr Žabka ◽  
Jaroslav Beran
Keyword(s):  
Mathematical Model ◽  
High Performance ◽  
Mechanical Energy ◽  
Optimal Number ◽  
Dynamic Force ◽  
Rectilinear Motion ◽  
Central System ◽  
Rotor Spinning ◽  
New System

Abstract The paper deals with the improvement of central traversing system on rotor spinning machines, where rectilinear motion with variable stroke is used. A new system of traversing rod with implemented set of magnetic-mechanical energy accumulators is described. Mathematical model of this system is analysed in the MSC. Software Adams/View and verified by an experimental measurement on a real-length testing rig. Analysis results prove the enhancement of devised traversing system, where the overall dynamic force is reduced considerably. At the same time, the precision of the traversing movement over the machine length is increased. This enables to increase machine operating speed while satisfying both the maximal tensile strength of the traversing rod and also output bobbin size standards. The usage of the developed mathematical model for determination of the optimal number and distribution of accumulators over the traversing rod of optional parameters is proved. The potential of the devised system for high-performance rotor spinning machines with longer traversing rod is also discussed.

scholarly journals Return Flight

1999 ◽  
Vol 121 (12) ◽  
pp. 62-64 ◽  
Author(s):  
Peggy Chalmers
Keyword(s):  
Flight Control ◽  
High Performance ◽  
Development Work ◽  
Flight Control System ◽  
Complex Interactions ◽  
System A ◽  
Physical Testing ◽  
Fluid Properties ◽  
Computational Fluid Dynamics Cfd ◽  
Thrust Control

This article focuses on the fact that using computational fluid dynamics (CFD) and design of experiments (DOE) software, researchers are in pursuit of aircraft fluidics thrust control without moving component parts. Fluidics’ performance is dictated by complex interactions among approximately two dozen geometric and fluid properties. These complex interactions probably proved overwhelming to early researchers seeking a stable, reliable rocket flight control system. A major advantage of DOE is that it allows all the parameters to vary simultaneously. A single permutation, on the other hand, varies one parameter at a time and cannot deal with interactions among the fixed parameters. There is still more development work to be done, but indications are that CFD and DOE are leading Lockheed Martin to a promising design. Physical testing reinforces the belief that a fluidic nozzle can achieve the performance levels required. The technology that never got off the ground in the early rocket era may find itself flying high in the next generation of high-performance tactical aircraft.

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