Analysis of Leakage Flow in a Labyrinth-Sealed Pneumatic Cylinder with Computational Fluid Dynamics

Brush seals are a mature technology that has generated extensive experimental and theoretical work. Theoretical models range from simple correlations with experimental results to advanced numerical approaches coupling the bristles deformation with the flow in the brush. The present work follows this latter path. The bristles of the brush are deformed by the pressure applied by the flow, by the interference with the rotor and with the back plate. The bristles are modeled as linear beams but a nonlinear numerical algorithm deals with the interferences. The brush with its deformed bristles is then considered as an anisotropic porous medium for the leakage flow. Taking into account, the variation of the permeability with the local geometric and flow conditions represents the originality of the present work. The permeability following the principal directions of the bristles is estimated from computational fluid dynamics (CFD) calculations. A representative number of bristles are selected for each principal direction and the CFD analysis domain is delimited by periodicity and symmetry boundary conditions. The parameters of the CFD analysis are the local Reynolds number and the local porosity estimated from the distance between the bristles. The variations of the permeability are thus deduced for each principal direction and for Reynolds numbers and porosities characteristic for brush seal. The leakage flow rates predicted by the present approach are compared with experimental results from the literature. The results depict also the variations of the pressures, of the local Reynolds number, of the permeability, and of the porosity through the entire brush seal.

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Effect of hydraulic and geometric factors upon leakage flow rate in pressurized pipes

RBRH ◽

10.1590/2318-0331.262120210057 ◽

2021 ◽

Vol 26 ◽

Author(s):

Mayara Francisca da Silva ◽

Fábio Veríssimo Gonçalves ◽

Johannes Gérson Janzen

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Flow Rate ◽

Leakage Flow ◽

Cfd Simulations ◽

Mean Velocity ◽

Leakage Flow Rate ◽

Geometric Factors ◽

Leakage Area ◽

Computational Fluid Dynamics Cfd

ABSTRACT Computational Fluid Dynamics (CFD) simulations of a leakage in a pressurized pipe were undertaken to determine the empirical effects of hydraulic and geometric factors on the leakage flow rate. The results showed that pressure, leakage area and leakage form, influenced the leakage flow rate significantly, while pipe thickness and mean velocity did not influence the leakage flow rate. With relation to the interactions, the effect of pressure upon leakage flow rate depends on leakage area, being stronger for great leakage areas; the effects of leakage area and pressure on leakage flow rate is more pronounced for longitudinal leakages than for circular leakages. Finally, our results suggest that the equations that predict leakage flow rate in pressurized pipes may need a revision.

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A Comparison of Static and Rotordynamic Characteristics for Two Types of Liquid Annular Seals With Parallelly Grooved Stator/Rotor

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4048144 ◽

2020 ◽

Vol 142 (9) ◽

Author(s):

Zhigang Li ◽

Zhi Fang ◽

Jun Li

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Leakage Flow ◽

Frequency Range ◽

Flow Rates ◽

Pressure Drops ◽

Force Coefficients ◽

Operation Conditions ◽

Annular Seal ◽

Annular Seals

Abstract Liquid annular seals with parallelly grooved stator or rotor are used as replacements for smooth plain seals in centrifugal pumps to reduce leakage and break up contaminants within the working fluid. Parallelly grooved liquid annular seals have advantages of less leakage and smaller possibility of abrasion when the seal rotor–stator rubs in comparison to smooth plain seals. This paper deals with the static and rotordynamic characteristics of parallelly grooved liquid annular seals, which are limited in the literature. Numerical results of leakage flow rates, drag powers, and rotordynamic force coefficients were presented and compared for a grooved-stator/smooth-rotor (GS-SR) liquid annular seal and a smooth-stator/grooved-rotor (SS-GR) liquid annular seal, utilizing a modified transient computational fluid dynamics-based perturbation approach based on the multiple-frequency elliptical-orbit rotor whirling model. Both liquid annular seals have identical seal axial length, rotor diameter, sealing clearance, groove number, and geometry. The present transient computational fluid dynamics-based perturbation method was adequately validated based on the published experiment data of leakage flow rates and frequency-independent rotordynamic force coefficients for the GS-SR and SS-GR liquid annular seals at various pressure drops with differential inlet preswirl ratios. Simulations were performed at three pressure drops (4.14 bar, 6.21 bar, and 8.27 bar), three rotational speeds (2 krpm, 4 krpm, and 6 krpm) and three inlet preswirl ratios (0, 0.5, and 1.0), applying a wide rotor whirling frequency range up to 200 Hz, to analyze and compare the influences of operation conditions on the static and rotordynamic characteristics for both the GS-SR and SS-GR liquid annular seals. Results show that the present two liquid annular seals possess similar sealing capability, and the SS-GR seal produces a slightly larger (∼2–10%) drag power loss than the GS-SR seal. For small rotor whirling motion around a centered position, both seals have the identical direct force coefficients and the equal-magnitude opposite-sign cross-coupling force coefficients in the orthogonal directions x and y. For all operation conditions, both the GS-SR and SS-GR liquid annular seals possess negative direct stiffness K and positive direct damping C. The GS-SR seal produces purely positive Ceff throughout the whirling frequency range for all operation conditions, while Ceff for the SS-GR seal shows a significant decrease and transitions to negative value at the crossover frequency fco with increasing rotational speed and inlet preswirl. From a rotordynamic viewpoint, the GS-SR liquid annular seal is a better seal concept for pumps.

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Shroud leakage flow models and a multi-dimensional coupling CFD (computational fluid dynamics) method for shrouded turbines

Energy ◽

10.1016/j.energy.2016.02.070 ◽

2016 ◽

Vol 103 ◽

pp. 410-429 ◽

Cited By ~ 8

Author(s):

Zhengping Zou ◽

Jingyuan Liu ◽

Weihao Zhang ◽

Peng Wang

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Leakage Flow ◽

Flow Models ◽

Dimensional Coupling ◽

Dynamics Method

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Analysis of the shroud leakage flow and mainflow interactions in high-pressure turbines using an unsteady computational fluid dynamics approach

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1243/09576509jpe466 ◽

2007 ◽

Vol 221 (6) ◽

pp. 837-848 ◽

Cited By ~ 5

Author(s):

P Adami ◽

F Martelli ◽

S Cecchi

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

High Pressure ◽

Leakage Flow

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One-dimensional modeling for tip clearance leakage vortex trajectory and stall-onset prediction in subsonic centrifugal impellers

Proceedings of the Institution of Mechanical Engineers Part A Journal of Power and Energy ◽

10.1177/0957650919856737 ◽

2019 ◽

Vol 234 (3) ◽

pp. 263-282

Author(s):

Chaowei Zhang ◽

Xuezhi Dong ◽

Xiyang Liu ◽

Qing Gao ◽

Chunqing Tan ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Tip Clearance ◽

Leakage Flow ◽

Tip Leakage Flow ◽

Tip Leakage Vortex ◽

One Dimensional ◽

Tip Leakage ◽

Onset Point ◽

The One

Two one-dimensional models are established for the tip leakage vortex trajectory and rotating stall-onset point prediction respectively for subsonic centrifugal impellers. The goal of modeling is to supply an effective estimation strategy of the stall-onset point for use in the one-dimensional performance prediction stage. The tip leakage vortex trajectory prediction is a critical part of the stall-onset prediction. The proposed one-dimensional model (one-dimensional tip leakage vortex trajectory model) to predict the tip leakage vortex trajectory is based on blade loading, i.e. the velocity difference between the pressure and suction surfaces. The loading function considers the effect of radial rotation, blade turning, and passage width variation. Compared with the computational fluid dynamics results, the current model shows reasonable accuracy, with an average relative error below 12.35%. The one-dimensional prediction model (Model II) is developed to determine the stall-onset point, where the interface between the tip leakage flow and the main flow spills from the blade leading edge. In this model, the momentum balance analysis is applied to identify the position of the interface. The parameter of the tip leakage vortex trajectory in Model II is determined by one-dimensional tip leakage vortex trajectory model. The effective origin of the tip leakage flow is correlated with the rotational speed and tip clearance. The effectiveness of Model II is validated with the experimental and computational fluid dynamics results using three impellers. Compared with the conventional model (Model I), Model II shows better accuracy, with a maximum error of about 7.42%.

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