A Design to Improve the Effective Damping Characteristics of Hole-Pattern-Stator Annular Gas Seals

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Dara W. Childs ◽  
Yoon-Shik Shin ◽  
Brent Seifert
Keyword(s):  
Friction Factor ◽  
Flow Path ◽  
Crossover Frequency ◽  
Test Results ◽  
Static Stiffness ◽  
Jump Phenomenon ◽  
Hole Depth ◽  
Negative Test ◽  
Damping Characteristics ◽  
Gas Seals

Predictions are presented for hole-pattern-stator seals for which the hole depth is varied axially, showing that various depth patterns can significantly improve damping performance in terms of both increasing the seal’s effective damping and reducing its crossover frequency—the frequency at which effective damping changes from positive to negative. Test results are presented for the seal with the best variable hole depth (VHD) pattern showing an increase in peak damping by a factor of 1.6 over a constant hole depth (CHD) design versus predictions of 2.7. The crossover frequency is reduced by approximately 40%. The VHD seal has a significant negative static stiffness that probably arises from a friction-factor-jump phenomenon, not flow path divergence. The VHD seal leaks less than a comparable CHD design.

A Design to Improve the Effective Damping Characteristics of Hole-Pattern-Stator Annular Gas Seals

2006 ◽  
Author(s):  
Dara W. Childs ◽  
Yoon-Shik Shin ◽  
Brent Seifert
Keyword(s):  
Friction Factor ◽  
Flow Path ◽  
Test Results ◽  
Static Stiffness ◽  
Hole Depth ◽  
Negative Test ◽  
Damping Characteristics ◽  
Jump Phenomena ◽  
The Cross ◽  
Gas Seals

Predictions are presented for hole pattern seals for which the hole depth is varied axially, showing that various depth patterns can significantly improve damping performance in terms of both increasing the seal’s effective damping and reducing its cross-over frequency — the frequency at which effective damping changes from positive to negative. Test results are presented for the seal with the best variable hole depth (VHD) pattern showing an increase in peak damping by a factor of 1.6 over a constant hole depth (CHD) design, versus predictions of 2.7. The cross over frequency is reduced by approximately 40%. The VHD seal has a significant negative static stiffness that probably arises from a friction-factor jump phenomena, not flow path divergence. The VHD seal leaks less than a comparable CHD design.

The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals

2013 ◽  
Author(s):  
Dara W. Childs ◽  
Stephen Arthur ◽  
Naitik J. Mehta
Keyword(s):  
Performance Improvement ◽  
Test Data ◽  
Hole Diameter ◽  
Test Results ◽  
Hole Depth ◽  
Test Variable ◽  
Leakage Characteristics ◽  
Gas Seals ◽  
The Impact ◽  
Annular Seals

Test results are presented for rotordynamic characteristics of hole-pattern-stator annular gas seals at a 70 bar supply pressures running at 20200 rpm. Leakage results are presented for these conditions and the additional speeds: 10200, 15300 rpm. Hole-depth is the principal test variable of interest. Most published annular test data for these seals have a hole diameter of 3.175mm and a hole depth of 3.302mm. For this work, with the 3.175mm hole diameter, additional results are presented for shallow (1.905 mm) and deep (6.604 mm) hole depths. Test results show a pronounced dependence of leakage and rotordynamic behavior on hole depth. Test results show much better leakage performance for the shallow-hole-depth seal in both leakage and rotordynamic performance. Compressor manufacturers and users will need to decide whether this observed performance improvement is worth trying in real machines.

A Design to Increase the Static Stiffness of Hole Pattern Stator Gas Seals

2006 ◽  
Author(s):  
Dara W. Childs ◽  
Yoon-Shik Shin ◽  
John Wade
Keyword(s):  
Axial Length ◽  
Test Results ◽  
Static Stiffness ◽  
Deep Groove ◽  
Gas Seals

An analysis is presented which shows that a deep groove located at about 60% along the axial length from the inlet will approximately double the static stiffness of a hole-pattern-stator, annular gas seal. Test results for a seal using this geometry generally confirm the correctness of this prediction. The groove also produces an increase in leakage by about 4% and a modest decrease in effective damping.

The Impact of Hole Depth on the Rotordynamic and Leakage Characteristics of Hole-Pattern-Stator Gas Annular Seals

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Dara W. Childs ◽  
Stephen Arthur ◽  
Naitik J. Mehta
Keyword(s):  
Performance Improvement ◽  
Test Data ◽  
Hole Diameter ◽  
Test Results ◽  
Running Speed ◽  
Hole Depth ◽  
Test Variable ◽  
Leakage Characteristics ◽  
Gas Seals ◽  
The Impact

Test results are presented for rotordynamic characteristics of hole-pattern-stator annular gas seals at a 70 bar supply pressures with a running speed of 20,200 rpm. Leakage results are presented for these conditions and the additional speeds: 10,200 and 15,300 rpm. Hole-depth is the principal test variable of interest. Most published annular test data for these seals have a hole diameter of 3.175 mm and a hole depth of 3.302 mm. For this work, with the 3.175 mm hole diameter, additional results are presented for shallow (1.905 mm) and deep (6.604 mm) hole depths. Test results show a pronounced dependence of leakage and rotordynamic behavior on hole depth. Test results show much better leakage performance for the shallow-hole-depth seal in both leakage and rotordynamic performance. Compressor manufacturers and users will need to decide whether this observed performance improvement is worth trying in real machines.

Friction-Factor Characteristics for Narrow Channels With Honeycomb Surfaces

1992 ◽  
Vol 114 (4) ◽  
pp. 714-721 ◽  
Author(s):  
T. W. Ha ◽  
G. L. Morrison ◽  
D. W. Childs
Keyword(s):  
Reynolds Number ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Narrow Channel ◽  
Test Results ◽  
Jump Phenomenon ◽  
Narrow Channels ◽  
Friction Factors ◽  
Factor Data

The experimental determination of friction-factors for the flow of air in a narrow channel lined with various honeycomb geometries has been carried out. Test results show that, generally, the friction-factor is nearly constant or slightly decreases as the Reynolds number increases, a characteristic common to turbulent flow in pipes. However, in some test geometries this trend is remarkably different. The friction factor dramatically drops and then rises as the Reynolds number increases. This phenomenon can be characterized as a “friction-factor jump.” Further investigations of the acoustic spectrum and friction-factor measurements for a broad range of Reynolds numbers indicate that the “friction-factor jump” phenomenon is accompanied by an onset of a normal mode resonance excited coherent flow fluctuation structure, which occurs at Reynolds number of the order of 104. The purpose of this paper is not to present the friction-factor data but to explain the friction-factor-jump phenomenon and friction-factor characteristics.

scholarly journals Diagnostic accuracy of clinical tests for cam or pincer morphology in individuals with suspected FAI syndrome: a systematic review

2020 ◽  
Vol 6 (1) ◽  
pp. e000772 ◽  
Author(s):  
Rahel Caliesch ◽  
Martin Sattelmayer ◽  
Stephan Reichenbach ◽  
Marcel Zwahlen ◽  
Roger Hilfiker
Keyword(s):  
Systematic Review ◽  
Diagnostic Accuracy ◽  
Index Test ◽  
Test Results ◽  
Clinical Tests ◽  
Negative Test ◽  
Post Test ◽  
Pincer Morphology ◽  
Fai Syndrome ◽  
Quality Evidence

ObjectivesTo determine the diagnostic accuracy of clinical tests for cam or pincer morphology in individuals with suspected femoroacetabular impingement (FAI) syndrome and to evaluate their clinical utility.DesignA systematic review of studies investigating the diagnostic accuracy of clinical tests for cam and pincer morphology.Data sourcesPubMed, Embase, CINAHL and SPORTDiscus.Eligibility criteria for selecting studiesStudies investigating the diagnostic accuracy of clinical tests for cam, pincer or mixed morphology in symptomatic patients. Patients had to undergo an index test and a reference test able to identify cam or pincer morphology. Study results have to allow the calculation of true or false positives and/or negatives to calculate sensitivity, specificity, likelihood ratios (LR) and post-test probabilities.ResultsEight studies were included, investigating 17 tests and two test combinations. The studies reported a low specificity for all tests, ranging from 0.11 to 0.56. Sensitivity ranged from 0.11 to 1.00, with high sensitivities for the flexion-adduction-internal rotation (FADIR), foot progression angle walking (FPAW) and maximal squat tests. We estimated that negative test results on all of these three tests would result in a negative LR of 0.15. However, we judged the studies to provide low-quality evidence.ConclusionThere is low-quality evidence that negative test results reduce the post-test probability of cam or mixed morphologies and that consecutive testing with the FADIR, FPAW and maximal squat tests might be used as a clinical test combination. We would not recommend their use to confirm the diagnosis of FAI syndrome.PROSPERO registration numberCRD42018079116.

Numerical Investigation on the Leakage and Static Stability Characteristics of Pocket Damper Seals at High Eccentricity Ratios

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Zhigang Li ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Static Stability ◽  
Operating Conditions ◽  
Eccentricity Ratio ◽  
Static Stiffness ◽  
Flow Conditions ◽  
Experiment Data ◽  
High Eccentricity ◽  
Stiffness Coefficients ◽  
Direct Stiffness ◽  
Gas Seals

Annular gas seals for compressors and turbines are designed to operate in a nominally centered position in which the rotor and stator are at concentric condition, but due to the rotor–stator misalignment or flexible rotor deflection, many seals usually are suffering from high eccentricity. The centering force (represented by static stiffness) of an annular gas seal at eccentricity plays a pronounced effect on the rotordynamic and static stability behavior of rotating machines. The paper deals with the leakage and static stability behavior of a fully partitioned pocket damper seal (FPDS) at high eccentricity ratios. The present work introduces a novel mesh generation method for the full 360 deg mesh of annular gas seals with eccentric rotor, based on the mesh deformation technique. The leakage flow rates, static fluid-induced response forces, and static stiffness coefficients were solved for the FPDS at high eccentricity ratios, using the steady Reynolds-averaged Navier–Stokes solution approach. The calculations were performed at typical operating conditions including seven rotor eccentricity ratios up to 0.9 for four rotational speeds (0 rpm, 7000 rpm, 11,000 rpm, and 15,000 rpm) including the nonrotating condition, three pressure ratios (0.17, 0.35, and 0.50) including the choked exit flow condition, two inlet preswirl velocities (0 m/s, 60 m/s). The numerical method was validated by comparisons to the experiment data of static stiffness coefficients at choked exit flow conditions. The static direct and cross-coupling stiffness coefficients are in reasonable agreement with the experiment data. An interesting observation stemming from these numerical results is that the FPDS has a positive direct stiffness as long as it operates at subsonic exit flow conditions; no matter the eccentricity ratio and rotational speed are high or low. For the choked exit condition, the FPDS shows negative direct stiffness at low eccentricity ratio and then crosses over to positive value at the crossover eccentricity ratio (0.5–0.7) following a trend indicative of a parabola. Therefore, the negative static direct stiffness is limited to the specific operating conditions: choked exit flow condition and low eccentricity ratio less than the crossover eccentricity ratio, where the pocket damper seal (PDS) would be statically unstable.

Nonlinear Isolator Optimization Using RMS Cost Function

2004 ◽  
Author(s):  
A. Narimani ◽  
M. F. Golnaraghi
Keyword(s):  
Closed Form Solution ◽  
Optimization Method ◽  
Relative Displacement ◽  
Form Solution ◽  
Jump Phenomenon ◽  
Nonlinear Parameters ◽  
Strongly Nonlinear ◽  
Damping Characteristics ◽  
Stiffness And Damping ◽  
Boundary Limits

In this paper using a modified averaging method the frequency response of a general nonlinear isolator is obtained. Stiffness and damping characteristics are considered cubic functions of displacement and velocity through the isolator. Analytical results are compared with those obtained by numerical integration in order to validate the closed form solution for strongly nonlinear isolator. While increasing the nonlinearity in the system improves the response of the isolator, stability and jump avoidance conditions set boundary limits for the parameters. The effects of nonlinear parameters to avoid jump phenomenon are discussed in detail. The set of parameters where the system behaves regularly are found and the nonlinear isolator is optimized based on RMS optimization method. Using this method the RMS function of absolute acceleration of the sprung mass is minimized versus the RMS function of relative displacement.

Incidence and Recovery of Salmonellae and Other Bacteria from Commercially Processed Poultry Carcasses at Selected Pre- and Post-Evisceration Steps

1989 ◽  
Vol 52 (2) ◽  
pp. 88-91 ◽  
Author(s):  
H. S. LILLARD
Keyword(s):  
False Negative ◽  
Aerobic Bacteria ◽  
Processing Plant ◽  
Test Results ◽  
Negative Test ◽  
Commercial Plant ◽  
Sampling Points ◽  
Processing Line ◽  
False Negative Test ◽  
Progressive Sampling

This study was undertaken to determine whether bacteria are already attached to poultry skin when birds arrive at the processing plant. Multiple rinses were performed on breast skin and whole carcasses taken from five processing points in a commercial plant: Before scalding, after scalding, after picking, after the final washer, and from the exit end of the chiller. Aerobic bacteria and Enterobacteriaceae were recovered from carcasses in up to 40 consecutive whole carcass rinses with a difference of only about one log for Enterobacteriaceae, and 1 to 2 logs for aerobes from the first to the last rinse of carcasses taken from the beginning and the end of the processing line. Data from rinses prior to scalding indicated that bacteria were firmly attached to poultry carcasses when they first arrived in the plant. Not all bacteria were removed during processing; however, there were fewer aerobes and Enterobacteriaceae at progressive sampling points. Attached salmonellae were not always recovered in the first whole carcass rinse, but were sometimes recovered in 3rd, 5th, and 10th rinses. These data show that a single whole carcass rinse can result in false negative test results for salmonellae. Because of the small number of positive samples in this study, the probability of recovering salmonellae with a single whole carcass rinse could not be estimated accurately.

Sign in / Sign up

Export Citation Format

Share Document