Theoretical Solution as a Boundary Value Problem for Externally Pressurized Porous Gas-Bearings

1965 ◽  
Vol 87 (3) ◽  
pp. 622-630 ◽  
Author(s):  
H. Mori ◽  
H. Yabe ◽  
T. Shibayama
Keyword(s):  
Porous Media ◽  
Boundary Value ◽  
Three Dimensional ◽  
Flow In Porous Media ◽  
Gas Bearings ◽  
Bearing Clearance ◽  
Reasonable Prediction ◽  
Gas Bearing ◽  
Theoretical Results ◽  
Theoretical Standpoint

In this paper, an analytical solution is obtained and discussed for externally pressurized porous gas-bearings from a theoretical standpoint in which the flowing condition in bearing clearance is taken into consideration as a boundary value of the three-dimensional flow in porous media. This approach makes it possible to investigate the characteristics of various bearing configurations with consideration of anisotropy of porous material. And it is assumed that the flow in bearing clearance is laminar and fully viscous while the flow in porous media is characterized by Darcy’s law. The theoretical results are found to give more reasonable prediction of porous gas-bearing performance than those in the previous paper [1].

Estimation of the Rotordynamic Coefficients of a Compressor Mounted on Gas Bearings Using the Phase Diagram and the Unbalance Response

2015 ◽  
Author(s):  
Claudia Aide González ◽  
Juan Carlos Jáuregui ◽  
Oscar De Santiago ◽  
Víctor Solórzano
Keyword(s):  
Phase Diagram ◽  
Three Dimensional ◽  
Dynamic Parameters ◽  
Gas Bearings ◽  
Force Coefficients ◽  
Rotordynamic Coefficients ◽  
Dynamic Coefficients ◽  
Unidentified Source ◽  
Spring System ◽  
Gas Bearing

This paper presents a novel method for identifying the dynamic parameters of a gas bearing, whose force coefficients are strong functions of frequency. The method is based on the analysis of the phase diagram with the model assuming a mass-damper-spring system with time-dependent force coefficients. Usually, it is necessary a controlled mechanism to find the transfer function, this condition limits the application of the method. On the other hand, estimation of the damping and stiffness parameters under real loading is very cumbersome and requires a special care on identifying the excitation forces. One of the main difficulties is the isolation of noise and those vibration signals with an unidentified source. In this work, the excitation force was taken from the unbalance loading of a rotor test. Therefore, there is no need for a special test rig. The dynamic parameters can be estimated analyzing data from the actual rotor mounted on the gas bearings. Identifying the parameters that cause gas bearing instabilities is a big challenge. The gas properties are very sensitive to temperature and pressure changes, and, as a consequence the bearing rotor-dynamic coefficients change drastically and the rotor behaves chaotically, which means that the dynamic parameters are nonlinear. In this research a methodology based on the phase diagram construction to identify nonlinear instabilities of gas bearings is presented. The results show the method capability to estimate the dynamic coefficients by the analysis of the energy variation. Among nonparametric methods, the phase diagram or phase space is in use to identify nonlinearities in dynamic systems. The identification is conducted through the analysis of the energy variations. The energy variations can be represented as a three dimensional function E(x,v,t). In this way the phase diagram can be related to the frequency and the dynamic parameters of the system. According to Taken’s theorem, a dynamic system can be obtained by reconstructing the phase diagram. Then, using this method, the damping and stiffness coefficients are estimated.

Three-dimensional imaging of multiphase flow in porous media

2004 ◽  
Vol 339 (1-2) ◽  
pp. 166-172 ◽  
Author(s):  
M.L. Turner ◽  
L. Knüfing ◽  
C.H. Arns ◽  
A. Sakellariou ◽  
T.J. Senden ◽  
...  
Keyword(s):  
Porous Media ◽  
Multiphase Flow ◽  
Three Dimensional ◽  
Flow In Porous Media ◽  
Three Dimensional Imaging

Sudden and Smooth Transitions to Weak Turbulence in Porous Media Convection

2003 ◽  
Author(s):  
Johnathan J. Vadasz ◽  
Joseph E. A. Roy-Aikins
Keyword(s):  
Porous Media ◽  
Three Dimensional ◽  
Flow In Porous Media ◽  
Lorenz Attractor ◽  
Weak Turbulence ◽  
Periodic Regime ◽  
Linear Interaction ◽  
Isothermal System ◽  
Smooth Transitions ◽  
Convection In Porous Media

The fundamental understanding of the transition from laminar to turbulent convection in porous media is far from being conclusive. In isothermal flow in porous media no experiments identifying the three dimensional nature of a transition from the Darcy regime, via an inertia dominated regime, towards turbulence are available. In particular this detailed description of turbulence is missing in the problem of porous media convection where an additional non-linear interaction appears as a result of the coupling between the equations governing the fluid flow and the energy equation. The latter can typically cause a transition to a non-steady and non-periodic regime (referred to as weak turbulent) at much lower values of the parameter controlling the flow, when compared to the corresponding isothermal system. The present paper identifies the conditions for sudden and smooth transitions. In addition it attempts to address the question related to the reason for the subcritical transition to weak turbulence and the existence of a range of values of the porous media Rayleigh number over which the transition occurs, i.e. the Lorenz attractor.

scholarly journals Stretching and folding sustain microscale chemical gradients in porous media

2020 ◽  
Vol 117 (24) ◽  
pp. 13359-13365 ◽  
Author(s):  
Joris Heyman ◽  
Daniel R. Lester ◽  
Régis Turuban ◽  
Yves Méheust ◽  
Tanguy Le Borgne
Keyword(s):  
Porous Media ◽  
Reactive Transport ◽  
Granular Matter ◽  
Kinematic Model ◽  
Three Dimensional ◽  
Transport Processes ◽  
Flow In Porous Media ◽  
Chaotic Mixing ◽  
Pore Scale ◽  
Chemical Gradients

Fluid flow in porous media drives the transport, mixing, and reaction of molecules, particles, and microorganisms across a wide spectrum of natural and industrial processes. Current macroscopic models that average pore-scale fluctuations into an effective dispersion coefficient have shown significant limitations in the prediction of many important chemical and biological processes. Yet, it is unclear how three-dimensional flow in porous structures govern the microscale chemical gradients controlling these processes. Here, we obtain high-resolution experimental images of microscale mixing patterns in three-dimensional porous media and uncover an unexpected and general mixing mechanism that strongly enhances concentration gradients at pore-scale. Our experiments reveal that systematic stretching and folding of fluid elements are produced in the pore space by grain contacts, through a mechanism that leads to efficient microscale chaotic mixing. These insights form the basis for a general kinematic model linking chaotic-mixing rates in the fluid phase to the generic structural properties of granular matter. The model successfully predicts the resulting enhancement of pore-scale chemical gradients, which appear to be orders of magnitude larger than predicted by dispersive approaches. These findings offer perspectives for predicting and controlling the vast diversity of reactive transport processes in natural and synthetic porous materials, beyond the current dispersion paradigm.

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