Comparison Between Numerical and Experimental Dynamic Coefficients of a Hybrid Aerostatic Bearing

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Mohamed Amine Hassini ◽  
Mihai Arghir ◽  
Manuel Frocot
Keyword(s):  
Experimental Data ◽  
Theoretical Models ◽  
Bulk Flow ◽  
Major Influence ◽  
Aerostatic Bearing ◽  
Complex Flow ◽  
Flow Equations ◽  
Dynamic Coefficients ◽  
Equivalent Area ◽  
Feeding Pressure

Hybrid journal bearings have been considered for many years as a possible replacement for ball bearings in turbopumps used by the aerospace industry. Due to flow regimes dominated by inertia and due to the nature of the lubricant (cryogenic fluids), the prediction of the linearized dynamic coefficients in these bearings must be based on the compressible bulk-flow equations. Theoretical models based on these equations were validated for hybrid bearings working with water or for liquid or gas annular seals. Validations for hybrid compressible bearings are missing. Experimental data obtained for an air lubricated hybrid aerostatic bearing designed with shallow pockets were recently presented; the data consist of linearized dynamic coefficients obtained for rotation speeds up to 50 krpm and up to 7 bars feeding pressure. The present work introduces a consolidated numerical approach for predicting static and linearized dynamic characteristics. Theoretical predictions are based on bulk flow equations in conjunction with CFD analysis. It was found that, for a given feeding pressure, the value of the pressure downstream the orifice has a major influence on all results. Special care was then taken to describe the complex flow in the feeding system and the orifice. Three dimensional CFD was employed because the bulk-flow equations are inappropriate in this part of the bearing. The pressure downstream the orifice stemming from CFD results and the feeding pressure were next imposed in the bulk flow model and the equivalent area of the orifice was obtained from the numerical solution of the steady flow in the bearing. Since the pockets of the hybrid bearing are shallow, this equivalent area is considered as being the harmonic average of the orifice cross section area and of the cylindrical curtain area located between the orifice and the rotor. The comparisons between theoretical dynamic coefficients and experimental data validated this approach of the equivalent area of the orifice.

Comparison Between Numerical and Experimental Dynamic Coefficients of a Hybrid Aerostatic Bearing

2012 ◽  
Author(s):  
Mohamed Amine Hassini ◽  
Mihai Arghir ◽  
Manuel Frocot
Keyword(s):  
Experimental Data ◽  
Theoretical Models ◽  
Bulk Flow ◽  
Major Influence ◽  
Aerostatic Bearing ◽  
Complex Flow ◽  
Flow Equations ◽  
Dynamic Coefficients ◽  
Equivalent Area ◽  
Feeding Pressure

Hybrid journal bearings are considered since many years as a possible replacement for ball bearings in turbo-pumps used by the aerospace industry. Due to flow regimes dominated by inertia and due to the nature of the lubricant (cryogenic fluids), the prediction of the linearized dynamic coefficients in these bearings must be based on the compressible bulk-flow equations. Theoretical models based on these equations were validated for hybrid bearings working with water or for liquid or gas annular seals. Validations for hybrid compressible bearings are missing. Experimental data obtained for an air lubricated hybrid aerostatic bearing designed with shallow pockets were recently presented; the data consist of linearized dynamic coefficients obtained for rotation speeds up to 50 krpm and up to 7 bar feeding pressure. The present work introduces a consolidated numerical approach for predicting static and linearized dynamic characteristics. Theoretical predictions are based on bulk flow equations in conjunction with CFD analysis. It was found that for a given feeding pressure, the value of the pressure downstream the orifice has a major influence on all results. Special care was then taken for describing the complex flow in the feeding system and the orifice. Three dimensional CFD was employed because the bulk-flow equations are inappropriate in this part of the bearing. The pressure downstream the orifice stemming from CFD results and the feeding pressure were next imposed in the bulk flow model and the equivalent area of the orifice was obtained from the numerical solution of the steady flow in the bearing. Since the pockets of the hybrid bearing are shallow, this equivalent area is considered as being the harmonic average of the orifice cross section area and of the cylindrical curtain area located between the orifice and the rotor. The comparisons between theoretical dynamic coefficients and experimental data validated this approach of the equivalent area of the orifice.

Computational Modeling and Experimental Investigation of Static Straight-Through Labyrinth Seals

2008 ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Christopher P. Goyne ◽  
Costin D. Untaroiu ◽  
Houston G. Wood ◽  
Robert Rockwell ◽  
...  
Keyword(s):  
Experimental Data ◽  
Flow Behavior ◽  
Optimization Techniques ◽  
Bulk Flow ◽  
Numerical Code ◽  
Cfd Modeling ◽  
Leakage Flow ◽  
Dynamic Coefficients ◽  
Seal Design ◽  
Flow Parameters

To design highly efficient and stable turbomachines, engineers require accurate methods to model seal flows and calculate clearance-excitation forces generated by the eccentric position of the rotor. One of the most widely used methods to predict leakage flow and dynamic coefficients is the use of computer codes developed based on bulk flow theory. In recent years, computational fluid dynamics (CFD) modeling is increasingly being recognized as an accurate assessment tool for flow parameters and dynamic coefficients evaluation as compared to the bulk flow codes. This paper presents computational and experimental investigations that were carried out to calculate flow parameters in a stationary straight-through model labyrinth seal. The main objective of this study is to explore the capabilities of Ansys-CFX, a commercially available state of the art 3D numerical code, to accurately model compressible flow through the seals. The flow behavior is analyzed using CFD and the flow parameters calculated by CFD are validated against experimental data taken for the same seal configuration. The integrated values of leakage flow rates estimated from the computational results agree with the experimental data within 7.6%. This study serves as a benchmark case that supports further efforts in applying CFD analysis in conjunction with automatic design optimization techniques for seals used for compressible media. It was shown that optimization algorithms combined with CFD simulations have good potential for improving seal design.

On the Dynamic Properties of Pump Liquid Seals

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Alexandrina Untaroiu ◽  
Vahe Hayrapetian ◽  
Costin D. Untaroiu ◽  
Houston G. Wood ◽  
Bruno Schiavello ◽  
...  
Keyword(s):  
Complex Geometry ◽  
Dynamic Properties ◽  
Bulk Flow ◽  
Damping Factor ◽  
Steam Turbines ◽  
Fluid Inertia ◽  
Flow Equations ◽  
Dynamic Coefficients ◽  
Aspect Ratios ◽  
Rotor Dynamic

Rotordynamic instability due to fluid flow in seals is a well known phenomenon that can occur in pumps as well as in steam turbines and air compressors. While analysis methods using bulk-flow equations are computationally efficient and can predict dynamic properties fairly well for short seals, they often lack accuracy in cases of seals with complex geometry or with large aspect ratios (L/D above 1.0). This paper presents the linearized rotordynamic coefficients for a liquid seal with large aspect ratio subjected to incompressible turbulent flow. The fluid-induced forces acting on the rotor are calculated by means of a three-dimensional computational fluid dynamics (3D-CFD) analysis, and are then expressed in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients. For comparison, the seal dynamic coefficients were calculated using two other codes: one developed with the bulk flow method and one based on the finite difference method. The three sets of dynamic coefficients calculated in this study were used then to predict the rotor dynamic behavior of an industrial pump. These estimations were then compared to the vibration characteristic measured during the pump shop test, results indicating that the closest agreement was achieved utilizing the CFD generated coefficients. The results of rotor dynamic analysis using the coefficients derived from CFD approach, improved the prediction of both damped natural frequency and damping factor for the first mode, showing substantially smaller damping factor which is consistent with the experimentally observed instability of the rotor-bearing system. As result of continuously increasing computational power, it is believed that the CFD approach for calculating fluid excitation forces will become the standard in industry.

Static and Dynamic Analysis of Annular Seals

2006 ◽  
Author(s):  
Mihai Arghir ◽  
Jean Frene
Keyword(s):  
Static Problem ◽  
Bulk Flow ◽  
Friction Coefficients ◽  
Flow Equations ◽  
Static And Dynamic Analysis ◽  
Dynamic Coefficients ◽  
Theoretical Approaches ◽  
Eccentric Rotor ◽  
Inertia Forces ◽  
Annular Seals

This work is an overview of theoretical approaches used for estimating the characteristics of straight or grooved annular seals. The flow in annular seals is dominated by inertia forces. The goal of the static analysis is to describe the relation between the pressure difference across the seal and the (mass) flow rate. The presentation introduces different approaches of the static problem (analytic, simplified–“bulk flow” and CFD) and underlines the main difficulties in analysing annular seals. The forces on an eccentric rotor are described as a superposition between three effects (Lomakin, viscous and Bernoulli forces). This approach is then used to describe the dynamic characteristics of the seal for a rotor whirling around its centred position. The specific aspects that compressibility adds to gas annular seals analysis are next discussed, with its most important consequence, the flow choking in the exit section. Finally, some recent findings concerning the analysis of textured stator annular seals are presented. The results show that the presence of textures engenders stator and rotor friction coefficients obeying different laws. The use of these new friction coefficients in the bulk-flow equations enables to match the values of the experimental dynamic coefficients. A discussion about the further needs (development and research) in annular seals analysis is carried out at the end of this work.

Modeling Maximum Droplet Size In Gas-Liquid Annular Flow and Liquid–Liquid Dispersed Flow

2021 ◽  
Author(s):  
Kanat Karatayev ◽  
Yilin Fan
Keyword(s):  
Experimental Data ◽  
Open Source ◽  
Droplet Size ◽  
Annular Flow ◽  
Flow Behavior ◽  
Droplet Size Distribution ◽  
Theoretical Models ◽  
Dispersed Phase ◽  
Complex Flow ◽  
Dispersed Flow

Abstract Hydrocarbon production is commonly associated as the dispersed flow of two and more immiscible phases starting from porous media to surface facilities. In the dispersed flow, one phase is usually dispersed into another dominating phase in terms of droplets. Accurate prediction of the droplet size distribution of a dispersed phase is critical in characterizing complex flow behavior in pipe flows. In the first part of this paper, we provide the analyses of open-source experimental data on the maximum droplet size in gas-liquid annular flow and evaluate the existing theoretical models and suggest an improvement based on the experimental data analyses to predict the maximum droplet size of the entrained liquid droplets in gas-liquid annular flow. In the second part of this paper, we cover the experimental results from the open-source literature data and in-house experimental data to give the general understanding on droplet formation concepts and evaluate the existing predictive models and present a new modeling approach to determine a maximum stable droplet size of the dispersed phase in the liquid-liquid dispersed flow under turbulent flow conditions.

TEMPERATURE DEPENDENCE BEHAVIOR OF ELECTRICAL RESISTIVITY IN NOBLE METALS AT LOW TEMPERATURES

2014 ◽  
Vol 5 (3) ◽  
pp. 982-992 ◽  
Author(s):  
M AL-Jalali
Keyword(s):  
Experimental Data ◽  
Electrical Resistivity ◽  
Temperature Dependence ◽  
Concentration Dependence ◽  
Low Temperatures ◽  
Noble Metals ◽  
Phonon Scattering ◽  
Theoretical Models ◽  
Residual Resistivity ◽  
Electron Phonon Scattering

Resistivity temperature – dependence and residual resistivity concentration-dependence in pure noble metals(Cu, Ag, Au) have been studied at low temperatures. Dominations of electron – dislocation and impurity, electron-electron, and electron-phonon scattering were analyzed, contribution of these mechanisms to resistivity were discussed, taking into consideration existing theoretical models and available experimental data, where some new results and ideas were investigated.

Simple theoretical models of elimination reactions on polar catalysts; Dehydration reactivity of secondary alcohols on acidic and basic catalysts

1985 ◽  
Vol 50 (4) ◽  
pp. 920-929 ◽  
Author(s):  
Jiří Sedláček
Keyword(s):  
Experimental Data ◽  
Quantum Chemical ◽  
Theoretical Models ◽  
Aliphatic Alcohols ◽  
Secondary Alcohols ◽  
Carbonium Ion ◽  
Dehydration Reactions ◽  
Aromatic Alcohols ◽  
Basic Catalysts ◽  
Simple Models

CNDO/2 calculations for simple models of adsorption and dehydration reactions of secondary aliphatic and aromatic alcohols on polar catalysts are presented. The models involve selected stages of elimination mechanisms of various types (E1, E2 and E1cB elimination). Calculated quantum chemical quantities were correlated with reported experimental data. It is shown that reactivities for the series of substituted phenylethanols correlate very well with the ease of carbonium ion formation. In the case of aliphatic alcohols, calculated quantities correlate generally with the reactivities on SiO2 and are in anticorrelation with the reactivities on Al2O3.NaOH.

Initiation and Statistical Evolution of Horizontal Slug Flow With a Two-Fluid Model

2013 ◽  
Vol 135 (12) ◽  
Author(s):  
A. O. Nieckele ◽  
J. N. E. Carneiro ◽  
R. C. Chucuya ◽  
J. H. P. Azevedo
Keyword(s):  
Experimental Data ◽  
Slug Flow ◽  
Fluid Model ◽  
Subsequent Development ◽  
Complex Flow ◽  
Horizontal Pipes ◽  
Dimensional Version ◽  
Two Fluid Model ◽  
Log Normal ◽  
Two Fluid

In the present work, the onset and subsequent development of slug flow in horizontal pipes is investigated by solving the transient one-dimensional version of the two-fluid model in a high resolution mesh using a finite volume technique. The methodology (named slug-capturing) was proposed before in the literature and the present work represents a confirmation of its applicability in predicting this very complex flow regime. Further, different configurations are analyzed here and comparisons are performed against different sets of experimental data. Predictions for mean slug variables were in good agreement with experimental data. Additionally, focus is given to the statistical properties of slug flows such as shapes of probability density functions of slug lengths (which were represented by gamma and log-normal distributions) as well as the evolution of the first statistical moments, which were shown to be well reproduced by the methodology.

Hybrid Analysis of Gas Annular Seals With Energy Equation

2013 ◽  
Author(s):  
Patrick J. Migliorini ◽  
Alexandrina Untaroiu ◽  
William C. Witt ◽  
Neal R. Morgan ◽  
Houston G. Wood
Keyword(s):  
Experimental Data ◽  
Hybrid Method ◽  
Energy Equation ◽  
Flow Analysis ◽  
Experimental Studies ◽  
Rotor System ◽  
Bulk Flow ◽  
Outlet Temperature ◽  
Cfd Analysis ◽  
Annular Seals

Annular seals are used in turbomachinery to reduce secondary flow between regions of high and low pressure. In a vibrating rotor system, the non-axisymmetric pressure field developed in the small clearance between the rotor and the seal generate reactionary forces that can affect the stability of the entire rotor system. Traditionally, two analyses have been used to study the fluid flow in seals, bulk-flow analysis and computational fluid dynamics (CFD). Bulk-flow methods are computational inexpensive, but solve simplified equations that rely on empirically derived coefficients and are moderately accurate. CFD analyses generally provide more accurate results than bulk-flow codes, but solution time can vary between days and weeks. For gas damper seals, these analyses have been developed with the assumption that the flow can be treated as isothermal. Some experimental studies show that the difference between the inlet and outlet temperature temperatures is less than 5% but initial CFD studies show that there can be a significant temperature change which can have an effect on the density field. Thus, a comprehensive analysis requires the solution of an energy equation. Recently, a new hybrid method that employs a CFD analysis for the base state, unperturbed flow and a bulk-flow analysis for the first order, perturbed flow has been developed. This method has shown to compare well with full CFD analysis and experimental data while being computationally efficient. In this study, the previously developed hybrid method is extended to include the effects of non-isothermal flow. The hybrid method with energy equation is then compared with the isothermal hybrid method and experimental data for several test cases of hole-pattern seals and the importance of the use of energy equation is studied.

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