Measurements of Rotordynamic Force Coefficients of Metallic Type Brush Seals

2018 ◽  
pp. 335-346
Author(s):  
Pascal Jolly ◽  
Olivier Bonneau ◽  
Mihai Arghir ◽  
Florent Cochain ◽  
Jérôme Dehouve
Keyword(s):  
Force Coefficients ◽  
Brush Seals

Analysis of Performance and Rotordynamic Force Coefficients of Brush Seals With Reverse Rotation Ability

2004 ◽  
Author(s):  
Adolfo Delgado ◽  
Luis San Andre´s ◽  
John F. Justak
Keyword(s):  
Pressure Ratio ◽  
Nonlinear Partial Differential Equation ◽  
Forced Response ◽  
Operating Conditions ◽  
Partial Differential ◽  
Force Coefficients ◽  
Brush Seal ◽  
Brush Seals ◽  
Discharge Pressure ◽  
Stiffness And Damping

Multiple-shoed brush seals represent an alternative to resolve poor reliability resulting from bristle tip wear while also allowing for reverse rotation operation. The novel configuration incorporates pads contacting the shaft, and which under rotor spinning; lift off due to the generation of hydrodynamic pressures. The ensuing gas film prevents intermittent contact; thus lowering the operating temperature and thermal distortions, and even eliminating bristles’ wear. A computational analysis for the equilibrium and dynamic forced response of a brush seal with reverse rotation capability is presented. Small amplitude rotor motions about an equilibrium position lead to a nonlinear partial differential equation for the static pressure field, and a set of first order linear partial differential equations to determine the rotordynamic force coefficients, stiffness and damping, as function of the excitation frequency and other operating conditions. Predictions for the stiffness and damping coefficients of a 20 shoe-brush seal configuration operating over a range of rotor speeds are detailed. The parametric study varies the nominal gas film thickness, the supply to discharge pressure ratio, and the bristle bed structural loss (damping) coefficient. The results show that the film clearance and supply to discharge pressure ratio do not affect the shoed-brush seal force coefficients. On the other hand, the direct stiffness drops rapidly as the operating speed increases. The shoed-brush seal offers whirl frequency ratios much lower than 0.50 due to the (structural) damping arising from friction among the brush seal bristles.

scholarly journals Determination of Force Coefficients for a Submerged Rigid Breakwater under the Action of Solitary Waves

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 315
Author(s):  
Francesco Aristodemo ◽  
Giuseppe Tripepi ◽  
Luana Gurnari ◽  
Pasquale Filianoti
Keyword(s):  
Solitary Waves ◽  
Pressure Sensors ◽  
Wave Forces ◽  
Wave Loads ◽  
Force Coefficients ◽  
Wave Flume ◽  
Physical Tests ◽  
The Difference ◽  
The University ◽  
Semi Empirical

We present an analysis related to the evaluation of Morison and transverse force coefficients in the case of a submerged square barrier subject to the action of solitary waves. To this purpose, two-dimensional experimental research was undertaken in the wave flume of the University of Calabria, in which a rigid square barrier was provided by a discrete battery of pressure sensors to determine the horizontal and vertical hydrodynamic forces. A total set of 18 laboratory tests was carried out by varying the motion law of a piston-type paddle. Owing to the low Keulegan–Carpenter numbers of the tests, the force regime of the physical tests was defined by the dominance of the inertia loads in the horizontal direction and of the lift loads in the vertical one. Through the use of the time series of wave forces and the undisturbed kinematics, drag, horizontal inertia, lift, and vertical inertia coefficients in the Morison and transverse semi-empirical schemes were calculated using time-domain approaches, adopting the WLS1 method for the minimization of the difference between the maximum forces and the linked phase shifts by comparing laboratory and calculated wave loads. Practical equations to calculate these coefficients as a function of the wave non-linearity were introduced. The obtained results highlighted the prevalence of the horizontal forces in comparison with the vertical ones which, however, prove to be fundamental for stability purposes of the barrier. An overall good agreement between the experimental forces and those calculated by the calibrated semi-empirical schemes was found, particularly for the positive horizontal and vertical loads. The analysis of the hydrodynamic coefficients showed a decreasing trend for the drag, horizontal inertia, and lift coefficients as a function of the wave non-linearity, while the vertical inertia coefficient underlined an initial increasing trend and a successive slight decreasing trend.

scholarly journals Buoyancy Effect on the Flow Pattern and the Thermal Performance of an Array of Circular Cylinders

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Francesco Fornarelli ◽  
Antonio Lippolis ◽  
Paolo Oresta
Keyword(s):  
Nusselt Number ◽  
Flow Pattern ◽  
Richardson Number ◽  
Near Field ◽  
Circular Cylinders ◽  
Momentum Exchange ◽  
Force Coefficients ◽  
The Earth ◽  
Spacing Ratio ◽  
Oscillatory Character

In this paper, we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are isothermal and they are aligned with the earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between −1 and 1. Two values of center-to-center spacing (s = 3.6d–4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found, and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri=−1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard deviation of the force coefficients and heat flux. In fact, the transition occurs due to rearrangement of the near-field flow in a more ordered wake pattern. Therefore, attention is focused on the influence of geometrical and buoyancy parameters on the heat and momentum exchange and their fluctuations. The available heat exchange models for cylinders array provide a not accurate prediction of the Nusselt number in the cases here studied.

scholarly journals Flow Visualization in a Simulated Brush Seal

1990 ◽  
Author(s):  
M. J. Braun ◽  
R. C. Hendricks ◽  
V. Canacci
Keyword(s):  
Flow Visualization ◽  
Flow Fields ◽  
Inlet Pressure ◽  
Complex Flow ◽  
Axial Pressure ◽  
Interface Motion ◽  
Pressure Profiles ◽  
Brush Seal ◽  
Brush Seals

A method to visualize and characterize the complex flow fields in simulated brush seals is presented. The brush seal configuration was tested in a water and then in an oil tunnel. The visualization procedure revealed typical regions that are rivering, jetting, vortical or lateral flows and exist upstream, downstream or within the seal. Such flows are engendered by variations in fiber void that are spatial and temporal and affect changes in seal leakage and stability. While the effects of interface motion for linear or cylindrical configurations have not been considered herein, it is believed that the observed flow fields characterize flow phenomenology in both circular and linear brush seals. The axial pressure profiles upstream, across and downstream of the brush in the oil tunnel have been measured under a variety of inlet pressure conditions and the ensuing pressure maps are presented and discussed.

Effect of Air Fraction on Force Coefficients in Oscillatory Flow

2021 ◽  
Author(s):  
Malene Hovgaard Vested ◽  
Erik Damgaard Christensen
Keyword(s):  
High Speed ◽  
Offshore Structures ◽  
Air Injection ◽  
Wave Loads ◽  
Morison Equation ◽  
Force Coefficients ◽  
Air Content ◽  
Set Up ◽  
High Level ◽  
Spilling Breakers

Abstract The forces on marine and offshore structures are often affected by spilling breakers. The spilling breaker is characterized by a roller of mixed air and water with a forward speed approximately equal to the wave celerity. This high speed in the top of the wave has the potential to induce high wave loads on upper parts of the structures. This study analyzed the effect of the air content on the forces. The analyses used the Morison equation to examine the effect of the percentage of air on the forces. An experimental set-up was developed to include the injection of air into an otherwise calm water body. The air-injection did introduce a high level a turbulence. It was possible to assess the amount of air content in the water for different amounts of air-injection. In the mixture of air and water the force on an oscillating square cylinder was measured for different levels of air-content, — also in the case without air. The measurements indicated that force coefficients for clear water could be use in the Morison equation as long as the density for water was replaced by the density for the mixture of air and water.

A NONHOMOGENEOUS BULK FLOW MODEL FOR GAS IN LIQUID FLOW ANNULAR SEALS: AN EFFORT TO PRODUCE ENGINEERING RESULTS

2021 ◽  
pp. 1-31
Author(s):  
Xueliang Lu ◽  
Luis San Andres ◽  
Jing Yang
Keyword(s):  
Pressure Drop ◽  
Test Data ◽  
Liquid Flow ◽  
Flow Model ◽  
Bulk Flow ◽  
Experimental Results ◽  
Pure Liquid ◽  
Dynamic Force ◽  
Force Coefficients ◽  
Direct Stiffness

Abstract Seals in multiple phase rotordynamic pumps must operate without compromising system efficiency and stability. Both field operation and laboratory experiments show that seals supplied with a gas in liquid mixture (bubbly flow) can produce rotordynamic instability and excessive rotor vibrations. This paper advances a nonhomogeneous bulk flow model (NHBFM) for the prediction of the leakage and dynamic force coefficients of uniform clearance annular seals lubricated with gas in liquid mixtures. Compared to a homogeneous BFM (HBFM), the current model includes diffusion coefficients in the momentum transport equations and a field equation for the transport of the gas volume fraction (GVF). Published experimental leakage and dynamic force coefficients for two seals supplied with an air in oil mixture whose GVF varies from 0 (pure liquid) to 20% serve to validate the novel model as well as to benchmark it against predictions from a HBFM. The first seal withstands a large pressure drop (~ 38 bar) and the shaft speed equals 7.5 krpm. The second seal restricts a small pressure drop (1.6 bar) as the shaft turns at 3.5 krpm. The first seal is typical as a balance piston whereas the second seal is found as a neck-ring seal in an impeller. For the high pressure seal and inlet GVF = 0.1, the flow is mostly homogeneous as the maximum diffusion velocity at the seal exit plane is just ~0.1% of the liquid flow velocity. Thus, both the NHBFM and HBFM predict similar flow fields, leakage (mass flow rate) and drag torque. The difference between the predicted leakage and measurement is less than 5%. The NHBFM direct stiffness (K) agrees with the experimental results and reduces faster with inlet GVF than the HBFM K. Both direct damping (C) and cross-coupled stiffness (k) increase with inlet GVF < 0.1.Compared to the test data, the two models generally under predict C and k by ~ 25%. Both models deliver a whirl frequency ratio (fw) ~ 0.3 for the pure liquid seal, hence closely matching the test data. fw raises to ~0.35 as the GVF approaches 0.1. For the low pressure seal the flow is laminar, the experimental results and both NHBFM and HBFM predict a null direct stiffness (K). At an inlet GVF = 0.2, the NHBFM predicted added mass (M) is ~30 % below the experimental result while the HBFM predicts a null M. C and k predicted by both models are within the uncertainty of the experimental results. For operation with either a pure liquid or a mixture (GVF = 0.2), both models deliver fw = 0.5 and equal to the experimental finding. The comparisons of predictions against experimental data demonstrate the NHBFM offers a marked improvement, in particular for the direct stiffness (K). The predictions reveal the fluid flow maintains the homogeneous character known at the inlet condition.

Closure to “Bridge Piers - Hydrodynamic Force Coefficients”

1969 ◽  
Vol 95 (5) ◽  
pp. 1717-1717
Author(s):  
Colin J. Apelt ◽  
Lewis T. Isaacs
Keyword(s):  
Hydrodynamic Force ◽  
Bridge Piers ◽  
Force Coefficients
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