scholarly journals The concept of turbulent «vortex backfill» - models and methods. Power engineering: research, equipment, technology

2019 ◽  
Vol 21 (5) ◽  
pp. 97-109
Author(s):  
L. E. Melamed ◽  
G. A. Filippov
Keyword(s):  
Turbulent Flow ◽  
Numerical Solutions ◽  
Turbulent Viscosity ◽  
Internal Resistance ◽  
Navier Stokes ◽  
Flow Profile ◽  
Navier Stokes Equation ◽  
Engineering Research ◽  
Turbulent Vortex ◽  
Fluctuation Method

Models and methods for studying turbulence based on the concept of turbulent "vortex backfill" are presented. The essence of this concept is that the turbulent flow is considered as laminar, flowing through a "vortex backfill ", which creates internal resistance. This resistance can be considered either as distributed, or as locally concentrated. Based on the first representation, a modified Navier-Stokes equation, its approximate analytical and numerical solutions are obtained. Based on the second concept and the local fluctuation method developed for these purposes, a computer model of the turbulent flow in the pipes is obtained. Using simulation, it is shown that, when a certain system of local viscosity fluctuations is specified, the calculated flow profile corresponds to the profile of the turbulent flow velocity. The magnitude and profile of the turbulent viscosity of the flow are completely determined by the structure and properties of the "vortex backfill ". The results of the work confirm the possibility and efficiency of considering turbulence based on this concept.

Turbulent Flow Velocity Between Rotating Co-Axial Disks of Finite Radius

1989 ◽  
Vol 111 (3) ◽  
pp. 333-340 ◽  
Author(s):  
J. F. Louis ◽  
A. Salhi
Keyword(s):  
Turbulent Flow ◽  
Turbulence Model ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Finite Radius ◽  
Navier Stokes Equations ◽  
Rotating Cavity ◽  
Tangential Wall ◽  
Frictional Forces

The turbulent flow between two rotating co-axial disks is driven by frictional forces. The prediction of the velocity field can be expected to be very sensitive to the turbulence model used to describe the viscosity close to the walls. Numerical solutions of the Navier–Stokes equations, using a k–ε turbulence model derived from Lam and Bremhorst, are presented and compared with experimental results obtained in two different configurations: a rotating cavity and the outflow between a rotating and stationary disk. The comparison shows good overall agreement with the experimental data and substantial improvements over the results of other analyses using the k–ε models. Based on this validation, the model is applied to the flow between counterrotating disks and it gives the dependence of the radial variation of the tangential wall shear stress on Rossby number.

Heat Transfer and Hydraulic Resistance in Turbulent Flow in Vertical Round Tubes At Supercritical Pressures. Part 1. Results From Numerical Simulations Using Algebraic Turbulent Viscosity Models

2020 ◽  
Author(s):  
Georgii Glebovich Yankov ◽  
Vladimir Kurganov ◽  
Yury Zeigarnik ◽  
Irina Maslakova
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Turbulent Flow ◽  
Hydraulic Resistance ◽  
Turbulent Viscosity ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Heating And Cooling ◽  
Prediction Techniques ◽  
Vertical Tubes

Abstract The review of numerical studies on supercritical pressure (SCP) coolants heat transfer and hydraulic resistance in turbulent flow in vertical round tubes based on Reynolds-averaged Navier-Stokes (RANS) equations and different models for turbulent viscosity is presented. The paper is the first part of the general analysis, the works based on using algebraic turbulence models of different complexity are considered in it. The main attention is paid to Petukhov-Medvetskaya and Popov et al. models. They were developed especially for simulating heat transfer in tubes of the coolants with significantly variable properties (droplet liquids, gases, SCP fluids) under heating and cooling conditions. These predictions were verified on the entire reliable experimental data base. It is shown that in the case of turbulent flow in vertical round tubes these models make it possible predicting heat transfer and hydraulic resistance characteristics of SCP flows that agree well with the existed reliable experimental data on normal and certain modes of deteriorated heat transfer, if significant influence of buoyancy and radical flow restructuring are absent. For the more complicated cases than a flow in round vertical tubes, as well as for the case of rather strong buoyancy effect, more sophisticated prediction techniques must be applied. The state-of-the-art of these methods and the problems of their application are considered in the Part II of the analysis.

The Reynolds Stress in Channel Flows From a Lagrangian Treatment of the Turbulence Momentum

2019 ◽  
Author(s):  
T.-W. Lee
Keyword(s):  
Turbulent Flow ◽  
Reynolds Stress ◽  
Current Approach ◽  
Navier Stokes ◽  
Current Transport ◽  
Lagrangian Analysis ◽  
Navier Stokes Equation ◽  
Mechanistic Approach ◽  
Turbulent Momentum

Abstract We have developed a mechanistic approach for determination of the Reynolds stress, using a Lagrangian analysis of turbulent momentum. Analysis and comparison with DNS and experimental data point toward the soundness of this approach (Lee, 2018). von Karman constant, the inner layer thickness and the Reynolds stress itself are all recovered through this approach, in agreement with DNS data. In addition, the turbulent flow profiles can be calculated iteratively using the basic Reynolds-averaged Navier-Stokes equation, in conjunction with the current transport equation for the Reynolds stress. In this work, we explore these and further uses of the current approach in solving turbulent flow dynamics.

A two-dimensional vortex condensate at high Reynolds number

2013 ◽  
Vol 715 ◽  
pp. 359-388 ◽  
Author(s):  
Basile Gallet ◽  
William R. Young
Keyword(s):  
Stokes Equation ◽  
Numerical Solutions ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Finite Limit ◽  
Two Dimensional ◽  
Navier Stokes Equation ◽  
Quasilinear Theory ◽  
Zero Integral ◽  
High Reynolds

AbstractWe investigate solutions of the two-dimensional Navier–Stokes equation in a $\lrm{\pi} \ensuremath{\times} \lrm{\pi} $ square box with stress-free boundary conditions. The flow is steadily forced by the addition of a source $\sin nx\sin ny$ to the vorticity equation; attention is restricted to even $n$ so that the forcing has zero integral. Numerical solutions with $n= 2$ and $6$ show that at high Reynolds numbers the solution is a domain-scale vortex condensate with a strong projection on the gravest mode, $\sin x\sin y$. The sign of the vortex condensate is selected by a symmetry-breaking instability. We show that the amplitude of the vortex condensate has a finite limit as $\nu \ensuremath{\rightarrow} 0$. Using a quasilinear approximation we make an analytic prediction of the amplitude of the condensate and show that the amplitude is determined by viscous selection of a particular solution from a family of solutions to the forced two-dimensional Euler equation. This theory indicates that the condensate amplitude will depend sensitively on the form of the dissipation, even in the undamped limit. This prediction is verified by considering the addition of a drag term to the Navier–Stokes equation and comparing the quasilinear theory with numerical solution.

Cavitation Bubble Collapse in Viscous, Compressible Liquids—Numerical Analysis

1965 ◽  
Vol 87 (4) ◽  
pp. 977-985 ◽  
Author(s):  
R. D. Ivany ◽  
F. G. Hammitt
Keyword(s):  
Surface Tension ◽  
High Pressures ◽  
Numerical Solutions ◽  
Compressible Liquid ◽  
Navier Stokes ◽  
Bubble Collapse ◽  
Navier Stokes Equation ◽  
Scaling Parameters ◽  
Collapse Behavior ◽  
Normalized Solution

Collapse of a spherical bubble in a compressible liquid, including the effects of surface tension, viscosity, and an adiabatic compression of gas within the bubble is investigated by numerical solutions of the hydrodynamic equations. A limiting value of shear viscosity causes the bubble collapse to slow down markedly, for both compressible and incompressible liquids, whereas moderate viscosities have very little effect on the rate of collapse. The inclusion of surface tension and viscosity introduces two scaling parameters into the solution, so that a single normalized solution is no longer sufficient to describe collapse behavior. The magnitude of the density changes calculated for the compressible liquid and the extremely rapid changes with time suggest that the usual Navier-Stokes equation of motion may not be appropriate. The possibility of liquid relaxational phenomenon and its contribution to sonoluminescence is considered. Shock waves or damagingly high pressures are not generated during collapse at a distance in the liquid equal to the initial radius from the center of collapse, although they will appear at such a distance if the bubble rebounds.

Validation of the INS3D-UP Code in the Prediction of Turbulent Flow of Liquid Propellants in a Sharp Bend

1995 ◽  
Author(s):  
M. A. R. Sharif ◽  
J. T. Haskew
Keyword(s):  
Turbulent Flow ◽  
Space Shuttle ◽  
Circular Cross Section ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Sharp Bend ◽  
Flow Problems ◽  
Fortran Code ◽  
Main Engine ◽  
Liquid Propellants

Abstract The capability of the INS3D-UP code in the prediction of turbulent flow in a sharp bend of circular cross-section has been investigated. The code, developed by the NASA Ames Research Center, is being used by the NASA Marshal Space Flight Center to analyze turbulent flow of liquid propellant in vaned pipe bends designed for use in the Space Shuttle Main Engine. The FORTRAN code is based on finite difference method and uses the concept of pseudocompressibility to solve incompressible Navier-Stokes equation. The Baldwin-Barth turbulence model is embedded in the code for turbulence computation. The flow field, at a Reynolds number of 43,000, in a sharp 90° bend has been predicted and compared with measurement. It is found that the agreement between the predicted and measured velocities is very well. The predicted pressures at the bend wall also compares reasonably well with the measurement. It is concluded that the INS3D-UP code is a good computational tool to analyze similar flow problems.

Preliminary Imaging of Red Blood Cells in Turbulent Flow

2012 ◽  
Author(s):  
Mostafa Shakeri ◽  
Iman Khodarahmi ◽  
M. Keith Sharp
Keyword(s):  
Turbulent Flow ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Imaging System ◽  
Navier Stokes ◽  
Viscous Stress ◽  
Damage Potential ◽  
Navier Stokes Equation ◽  
Considerable Uncertainty ◽  
Mathematical Construct

Considerable uncertainty exists about how momentum and energy are transferred to cells in turbulent flow, which has been shown to cause six times more damage to red blood cells (RBC’s) than laminar flow with the same mean wall shear stress [Kameneva, et al. 2004]. Though it is a purely mathematical construct to yield closure of the time-averaged Navier-Stokes equation for a continuum fluid, which is not valid at the scale of the cell, Reynolds stress has been used as an empirical indicator for damage potential [Sallam & Hwang 1984]. Other scales, including local viscous stress [Jones 1995], flow of plasma around inertia cells [Quinlan & Dooley 2007], shear within eddies [Quinlan & Dooley 2007] and shear between rigid cells within an eddy [Antiga & Steinman 2009], have been forwarded. To provide data to validate these models, an imaging system was assembled to directly observe RBC’s in turbulent flow under a microscope.

Analysis of Capillary Flow in Rounded Corners

Volume 1 ◽  
2004 ◽  
Author(s):  
Yongkang Chen ◽  
Mark M. Weislogel
Keyword(s):  
Numerical Solutions ◽  
Flow Problem ◽  
Capillary Flow ◽  
Outer Region ◽  
Cross Flow ◽  
Numerical Data ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Inner Region ◽  
The Impact

The problem of capillary flow in interior corners that are rounded is re-visited analytically in this work. By the appropriate geometric scaling, and through the introduction of a new parameter that features the roundedness of the corner, the Navier-Stokes equation is reduced to a convenient form for both numerical and analytical solution. The scaling and analysis of the problem is expected to significantly reduce the reliance on numerical data for such problems, and the design process can be both shortened and improved as a result. For capillary flows of perfect wetting fluids in the rounded corner with an advancing tip, a finite interfacial curvature related to the corner roundedness results at the tip. Accordingly, an outer and inner region of the flow is suggested based on the impact of the corner roundedness on the flow. In this study, asymptotic solutions of the geometrical ‘cross-flow’ problem for the outer region are sought under several constraints and are expected to narrowly bracket parallel numerical solutions. A complete understanding of the flow will be obtained only after the cross-flow problem for the inner region is solved. However, for the flow in the outer region a similarity solution is obtained and presented that reveals how roundedness retards the flow.

History forces and the unsteady wake of a cylinder

1999 ◽  
Vol 393 ◽  
pp. 99-121 ◽  
Author(s):  
J. R. CHAPLIN
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Stokes Equation ◽  
Oscillatory Flow ◽  
Numerical Solutions ◽  
Asymptotic Properties ◽  
Quantitative Agreement ◽  
Navier Stokes ◽  
Navier Stokes Equation ◽  
Unsteady Wake

History forces on a stationary cylinder in arbitrary unsteady rectilinear flow are calculated by means of a model based on the asymptotic properties of the steady-state wake. The results capture many features found in numerical solutions of the Navier–Stokes equation for the same flows, though quantitative agreement deteriorates as the Reynolds number increases over the range 2 to 40. The cases studied are the impulsive start, stop, and reverse, and oscillatory flow.

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