Identification of Flow Regimes and Self-adaption Simulation of Complex Flow Mechanisms in Multiple Media with Different-Scale Pores and Fractures

2020 ◽  
pp. 261-300
Author(s):  
Qiquan Ran
Keyword(s):  
Flow Regimes ◽  
Complex Flow ◽  
Flow Mechanisms ◽  
Multiple Media

scholarly journals Gas flow mechanisms under the effects of pore structures and permeability characteristics in source rocks of coal measures in Qinshui Basin, China

2017 ◽  
Vol 35 (3) ◽  
pp. 338-355 ◽  
Author(s):  
Xiaowei Hou ◽  
Yanming Zhu ◽  
Shangbin Chen ◽  
Yang Wang
Keyword(s):  
Flow Regime ◽  
Mass Flux ◽  
Gas Flow ◽  
Slip Flow ◽  
Flow Regimes ◽  
Source Rocks ◽  
Cross Sectional ◽  
Direction Parallel ◽  
Permeability Characteristics ◽  
Flow Mechanisms

The gas flow mechanisms in source rocks of coal measures under the effects of the pore structures and permeability characteristics were investigated by field-emission scanning electron microscopy, low-pressure nitrogen gas adsorption, high-pressure mercury intrusion, and pressure pulse decay permeability method. Various flow regimes were distinguished in the pores and fractures of differing scales, and the mass fluxes through the same were calculated using the data obtained by the numerical and experimental investigations. Results indicated that mesopores predominated in shale, while coal contained well-developed mesopores and macropores. In addition, the permeabilities of coal and shale were observed to be significantly anisotropic and highly stress dependent. The cross-sectional area proportions of the pores per unit cross-sectional area of the matrix in the free molecular, transition, and slip flow regimes in shale and coal were determined to be, respectively, 0.2:0.7:0.1 and 0.15:0.6:0.25. In the free molecular and transition flow regimes, the mass flux decreased with increasing reservoir depth, while the reverse was the case in the slip flow regime. Further, in the continuum flow regime, the mass flux was unimodally distributed with respect to the reservoir depth. The total mass flux in coal was greater in the direction perpendicular to the bedding compared to the direction parallel to the bedding, while the reverse was the case in shale. In addition, the continuum flow regime predominated in coal in both the directions perpendicular and parallel to the bedding, but only in the direction parallel to the bedding in shale. This work presents a comprehensive model for the analysis of all the flow regimes in pores and fractures of differing scales, as well as the anisotropy. Findings of the study are meaningful for establishing the coupling accumulation mechanism of the Three Coal Gases and developing a unified exploration and exploitation program.

LARGE-EDDY SIMULATION OF OPPOSING-JET-PERTURBED SUPERSONIC FLOWS PAST A HEMISPHERICAL NOSE

2010 ◽  
Vol 24 (13) ◽  
pp. 1287-1290 ◽  
Author(s):  
LI-WEI CHEN ◽  
CHANG-YUE XU ◽  
XI-YUN LU
Keyword(s):  
Large Eddy Simulation ◽  
Flow Regime ◽  
Cell Structure ◽  
Pressure Ratio ◽  
Flow Regimes ◽  
Bow Shock ◽  
Complex Flow ◽  
Unstable Flow ◽  
Eddy Simulation ◽  
Large Eddy

A supersonic flow past a hemispherical nose with an opposing jet placed on its axis has been investigated using large eddy simulation. We find that the flow behaviors depend mainly on the jet total pressure ratio and can be classified into three typical flow regimes of unstable, stable and transition. The unstable flow regime is characterized by an oscillatory bow shock with a multi-jet-cell structure and the stable flow regime by a steady bow shock with a single jet cell. The transition regime lies between the unstable and stable ones with a complex flow evolution. Turbulence statistics are further analyzed to reveal the relevant turbulent behaviors in the three flow regimes. The results obtained in this study provide a physical insight into the understanding of the mechanisms underlying this complex flow.

Modelling of Buoyancy-Affected Flow in Co-Rotating Disc Cavities

2009 ◽  
Author(s):  
Alistair S. R. Kilfoil ◽  
John W. Chew
Keyword(s):  
Three Dimensional ◽  
Computationally Efficient ◽  
Complex Flow ◽  
Rotating Disc ◽  
Flow Process ◽  
Physical Mechanisms ◽  
Compressor Rotor ◽  
Modelling Method ◽  
Current Design ◽  
Flow Mechanisms

Research in rotational buoyancy-driven flow has shown that the flow within the compressor inter-disc cavities is highly three-dimensional and time dependent. Two approaches in the numerical modelling of the flow have been considered. One is to use 3D, unsteady CFD to model a single inter-disc cavity with axial throughflow. This is very computationally expensive. A second approach, adopted here, is to break down the complex flow process into separate physical mechanisms and introduce approximate but computationally efficient models for these processes. The aim is to produce a method that can be incorporated into current design practice. Two underlying flow mechanisms may be identified for this complex flow; the first associated with the flow within the inter-disc cavities and the second associated with the axial throughflow under the compressor disc bores. Using CFD, the modelling of these two underlying flow mechanisms has been combined and a steady axisymmetric modelling method has been developed. The technique has been applied to both a research compressor rig and to an actual gas turbine HP compressor rotor, and results have been compared to measured data.

On the Energy Transfer in Centrifugal Compressors

1974 ◽  
Author(s):  
K. Bammert ◽  
M. Rautenberg
Keyword(s):  
Energy Transfer ◽  
Energy Conversion ◽  
Complex Flow ◽  
Momentum Exchange ◽  
Centrifugal Compressors ◽  
Stage Design ◽  
Flow Mechanisms ◽  
Rotating Impeller ◽  
Mass Flow Rates

In the layout and calculation of centrifugal compressors there are still considerable uncertainties when it comes to the theoretical determination of energy transfer from the impeller to the flowing medium and to the subsequent energy conversion in the diffuser. These problems arise particularly where compressor stage design with high pressure ratios and mass flow rates are concerned. A solution to these questions can presumably be found only through a physically balanced interpretation of the extremely complex flow mechanisms in the impeller. Since purely theoretical methods have hardly led to any reliable conclusions concerning the criteria of flow separation in the impeller or the secondary character of the impeller flow, there is still little knowledge about the creation of the jet-and-wake zones in the impeller and their decay (associated with large losses) in the connected diffuser. In studying the energy conversion process in the stage as a whole, great attention has to be devoted to the effects of the momentum exchange directly downstream the impeller. Hence the only possible way of solving these problems seems to be specific experimentation. For high flow velocities, this necessitates a special nonsteady measuring technique which also gives information about the relative flow in the rotating impeller.

Secondary Flow Structure Induced by Physiologically Relevant Waveform in a Curved Tube

2009 ◽  
Author(s):  
Chekema N. Prince ◽  
Sean D. Peterson ◽  
Michael W. Plesniak
Keyword(s):  
Secondary Flow ◽  
Blood Vessels ◽  
Complex Geometry ◽  
Vascular System ◽  
Flow Regimes ◽  
Flow Conditions ◽  
Complex Flow ◽  
Curved Tube ◽  
Secondary Flow Structure ◽  
The Impact

The complex geometry of the vascular system can induce the development of complex primary and secondary flow regimes within blood vessels. Recent literature has focused on the impact of these complex flow regimes on endothelial cells (EC), which line blood vessels, and their role on the progression of vascular disease. One such disease, atherosclerosis has been linked to the reaction of ECs to flow conditions. Atherosclerosis is often treated by stent implantation to return the vessel lumen to its native diameter. It is hypothesized that stent struts may alter the development of secondary flow within the vessel and cause re-stenosis and/or thrombosis distal to the stent.

Condensation Flow Mechanisms in Microchannels: Basis for Pressure Drop and Heat Transfer Models

2003 ◽  
Author(s):  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Visualization ◽  
Flow Regime ◽  
Annular Flow ◽  
Flow Regimes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Mechanisms ◽  
Transfer Models

This paper presents an overview of the use of flow visualization in micro- and mini-channel geometries for the development of pressure drop and heat transfer models during condensation of refrigerants. Condensation flow mechanisms for round, square and rectangular tubes with hydraulic diameters in the range 1–5 mm for 0 < x < 1 and 150 kg/m2-s and 750 kg/m2-s were recorded using unique experimental techniques that permit flow visualization during the condensation process. The effect of channel shape and miniaturization on the flow regime transitions was documented. The flow mechanisms were categorized into four different flow regimes: intermittent flow, wavy flow, annular flow, and dispersed flow. These flow regimes were further subdivided into several flow patterns within each regime. It was observed that the intermittent and annular flow regimes become larger as the tube hydraulic diameter is decreased, at the expense of the wavy flow regime. These maps and transition lines can be used to predict the flow regime or pattern that will be established for a given mass flux, quality and tube geometry. These observed flow mechanisms, together with pressure drop measurements, are being used to develop experimentally validated models for pressure drop during condensation in each of these flow regimes for a variety of circular and noncircular channels with 0.4 < Dh < 5 mm. These flow regime-based models yield substantially better pressure drop predictions than the traditionally used correlations that are primarily based on air-water flows for large diameter tubes. Condensation heat transfer coefficients were also measured using a unique thermal amplification technique that simultaneously allows for accurate measurement of the low heat transfer rates over small increments of refrigerant quality and high heat transfer coefficients characteristic of microchannels. Models for these measured heat transfer coefficients are being developed using the documented flow mechanisms and the corresponding pressure drop models as the basis.

The influence of simulated missile warhead fragment damage on the aerodynamic characteristics of two-dimensional wings

2013 ◽  
Vol 117 (1194) ◽  
pp. 823-837 ◽  
Author(s):  
A. J. Irwin ◽  
P. M. Render
Keyword(s):  
Order Approximation ◽  
Aerodynamic Characteristics ◽  
Layer Growth ◽  
Surface Flow ◽  
Flow Visualisation ◽  
Hole Size ◽  
Two Dimensional ◽  
Complex Flow ◽  
Flow Mechanisms ◽  
Lift And Drag

AbstractThe paper describes a method of representing damage on a wing due to multiple warhead fragments, and investigates two of the key variables: fragment impact density and hole diameter. The aerodynamic effects of the damage were quantified by wind-tunnel tests on a two-dimensional wing at a Reynolds number of 5 × 105. The wing was of hollow construction with leading and trailing-edge spars. In all of the cases tested, simulated fragment damage resulted in significant lift losses, drag increases and pitching moment changes. Increasing fragment density or hole size resulted in greater effects. To a first order approximation, both lift and drag increments at a given incidence were related to the percentage wing area removed. Surface flow visualisation showed that low fragment densities and small damage sizes resulted in a complex flow structure on the surface of the wing. This was made up of boundary-layer growth between the damage holes, attached wakes from the forward damage holes and separated surface flow over the rear of the wing. For these cases, individual hole patterns showed similar flow mechanisms to those seen for larger scale gunfire damage cases. Increased fragment density and hole size resulted in upper surface flow separation at the first row of holes. Behind this separation, the flow was attached and consisted of the combined wakes from the forward damage holes. Investigations into the influence of internal model structure indicated that trends in coefficient changes were similar for both hollow and solid wings. However, the magnitudes of the effects were found to be smaller for hollow wings than for solid wings.

Mixing Flow Characteristics in a Vessel Agitated by the Screw Impeller With a Draught Tube

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Yeng-Yung Tsui ◽  
Yu-Chang Hu
Keyword(s):  
Stokes Equations ◽  
Flow Characteristics ◽  
Computational Procedure ◽  
Navier Stokes ◽  
Complex Flow ◽  
Navier Stokes Equations ◽  
Mixing Energy ◽  
Draught Tube ◽  
Flow Mechanisms ◽  
Entire Flow

The circulating flow in a vessel induced by rotating impellers has drawn a lot of interests in industries for mixing different fluids. It used to rely on experiments to correlate the performance with system parameters because of the theoretical difficulty to analyze such a complex flow. The recent development of computational methods makes it possible to obtain the entire flow field via solving the Navier–Stokes equations. In this study, a computational procedure, based on multiple frames of reference and unstructured grid methodology, was used to investigate the flow in a vessel stirred by a screw impeller rotating in a draught tube. The performance of the mixer was characterized by circulation number, power number, and nondimensionalized mixing energy. The effects on these dimensionless parameters were examined by varying the settings of tank diameter, shaft diameter, screw pitch, and the clearance between the impeller and the draught tube. Also investigated was the flow system without the draught tube. The flow mechanisms to cause these effects were delineated in detail.

Beyond dual-porosity modeling for the simulation of complex flow mechanisms in shale reservoirs

2015 ◽  
Vol 20 (1) ◽  
pp. 69-91 ◽  
Author(s):  
Bicheng Yan ◽  
Yuhe Wang ◽  
John E. Killough
Keyword(s):  
Dual Porosity ◽  
Complex Flow ◽  
Flow Mechanisms ◽  
Shale Reservoirs
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