Vortex Transport in Separating Flows and Role of Vortical Structures in Reynolds Stress Production and Distribution

2005 ◽  
Author(s):  
Miad Yazdani ◽  
Yasmin Khakpour
Keyword(s):  
Reynolds Stress ◽  
Momentum Equation ◽  
Navier Stokes ◽  
Viscous Effects ◽  
Navier Stokes Equation ◽  
Vortical Structures ◽  
Open Questions ◽  
Production And Distribution ◽  
History Of ◽  
Separating Flows

In this paper we will present some approaches on Reynolds stress production by vortex transport phenomena and nonlinear vorticity generation in momentum equation. First of all we represent a history of recent works to describe how fluid particle motions can be associated with Reynolds stress through either displacement or acceleration terms. In the next section we will describe how vortex stretching causes the Reynolds stress production and what is the dominant effect near and far from the boundary where viscous effects have to be considered. On the other hand, some vortex considered methodologies such as those synthesize boundary layer, as a collection of vortical objects seem to be inappropriate in general flow configuration. Therefore, there must be a moderate consideration in which both vortex and momentum transports come into account as it is done in LES. Furthermore since there exist open questions on Reynolds stress distribution in complex flows such as those with separation, our particular attention is paid to such effects due to vortical structures in separating flows. Further discussions include turbulence development caused by either vortex stretching or gradient terms that is determined by predominant conditions. However, it is seen that at the beginning, vorticity generators in Navier-Stokes equation contribute to dissipation effect. In addition, since such contribution corresponds to vorticity alignment, we investigate maximum vortex aligning and the effects of which causes the deviation of such alignment. The paper provides theoretical and numerical comparisons, where in the former, the vortical structure role is taken into account.

Effects of Particle-Particle Collisions on Particle Concentration in a Turbulent Channel Flow

2006 ◽  
Author(s):  
H. Nasr ◽  
G. Ahmadi ◽  
J. B. McLaughlin
Keyword(s):  
Particle Concentration ◽  
Random Distribution ◽  
Pseudospectral Method ◽  
Time History ◽  
Turbulent Channel Flow ◽  
Navier Stokes ◽  
Particle Collisions ◽  
Navier Stokes Equation ◽  
History Of ◽  
Grid Points

This study is concerned with the effect of inter particle collisions on the particle concentration in turbulent duct flows. The time history of the instantaneous turbulent velocity vector was generated by the two-way coupled direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudospectral method. The particle equation of motion included the Stokes drag, the Saffman lift, and the gravitational forces. The effect of particles on the flow is included in the analysis via a feedback force on the grid points. Several simulations for three classes of particles (28 μm Lycopodia, 50μm glass and 70μm copper) and different mass loadings were performed, and the effect of inter particle collisions on the particle concentration was evaluated and discussed. It was found that the particle-particle collisions reduce the tendency of particles to accumulate near the wall. This might be because collisions decorrelate particles with coherent eddies which are responsible for accumulation of particles near the wall. The spatial distribution of particles at the channel centerplane was compared with the experimental results of Fessler et al. (1994). The simulation results showed that the copper and glass particles had a random distribution while Lycopodium particles showed a non-random distribution with bands of particles that were preferentially concentrated.

Rotational and Quasiviscous Cold Flow Models for Axisymmetric Hybrid Propellant Chambers

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
Joseph Majdalani ◽  
Michel Akiki
Keyword(s):  
Rocket Engine ◽  
Navier Stokes ◽  
Mathematical Treatment ◽  
Hybrid Rocket ◽  
Mean Flow ◽  
Viscous Effects ◽  
Navier Stokes Equation ◽  
Flow Models ◽  
Hybrid Rocket Engine ◽  
Wall Injection

In this work, we present two simple mean flow solutions that mimic the bulk gas motion inside a full-length, cylindrical hybrid rocket engine. Two distinct methods are used. The first is based on steady, axisymmetric, rotational, and incompressible flow conditions. It leads to an Eulerian solution that observes the normal sidewall mass injection condition while assuming a sinusoidal injection profile at the head end wall. The second approach constitutes a slight improvement over the first in its inclusion of viscous effects. At the outset, a first order viscous approximation is constructed using regular perturbations in the reciprocal of the wall injection Reynolds number. The asymptotic approximation is derived from a general similarity reduced Navier–Stokes equation for a viscous tube with regressing porous walls. It is then compared and shown to agree remarkably well with two existing solutions. The resulting formulations enable us to model the streamtubes observed in conventional hybrid engines in which the parallel motion of gaseous oxidizer is coupled with the cross-streamwise (i.e., sidewall) addition of solid fuel. Furthermore, estimates for pressure, velocity, and vorticity distributions in the simulated engine are provided in closed form. Our idealized hybrid engine is modeled as a porous circular-port chamber with head end injection. The mathematical treatment is based on a standard similarity approach that is tailored to permit sinusoidal injection at the head end.

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.

Analysis of Electroosmotic Flow in a Microchannel Packed With Microspheres

2004 ◽  
Author(s):  
Y. J. Kang ◽  
C. Yang ◽  
X. Y. Huang
Keyword(s):  
Stokes Equation ◽  
Electric Fields ◽  
Electroosmotic Flow ◽  
Momentum Equation ◽  
Navier Stokes ◽  
Counter Flow ◽  
Navier Stokes Equation ◽  
Uniform Size ◽  
Capillary Model ◽  
Alternating Electric Fields

The electroosmotic flow in a microchannel packed with microspheres under both direct and alternating electric fields is analyzed. In the case of the steady DC electroosmosis in a packed microchannel, the so-called “capillary model” is used, in which it is assumed that a porous medium is equivalent to a series of intertwined tubules. The interstitial tubular velocity is obtained by analytically solving the Navier-Stokes equation and the complete Poisson-Boltzmann equation. Then using the volume averaging method, the solution for the electroosmotic flow in a single charged cylindrical tubule is applied to estimate the electroosmosis in the overall porous media by introducing the porosity and tortuosity. Assuming uniform porosity, an exact solution accounting for the electrokinetic wall effect is obtained by solving the modified Brinkman momentum equation. For the electroosmotic flow under alternating electric fields in a cylindrical microchannel packed with microspheres of uniform size, two different conditions regarding the openness of channel ends are considered. Based on the capillary model, the time-periodic oscillating electroosmotic flow in an open-end microchannel in response to the application of an alternating electric field is obtained using the Green’s function approach to the Navier-Stokes equation. When the two ends of the channel are closed, a backpressure is induced to generate a counter flow, resulting in a new zero flow rate. Such induced backpressure associated with the counter-flow in a closed-end microchannel is obtained analytically by solving the transient modified Brinkman momentum equation.

SCALING OF FLUID RECOVERY FROM PERCOLATION FRACTALS

Fractals ◽  
1994 ◽  
Vol 02 (02) ◽  
pp. 269-272 ◽  
Author(s):  
IAN D WEDGWOOD ◽  
DONALD M MONRO
Keyword(s):  
Stokes Equations ◽  
Petroleum Reservoirs ◽  
Finite Difference Approximation ◽  
Navier Stokes ◽  
Difference Approximation ◽  
Viscous Effects ◽  
Navier Stokes Equation ◽  
Navier Stokes Equations ◽  
Reservoir Models ◽  
Wide Range

We report on the recovery of fluid driven through percolation lattices across a range of scales using a finite difference approximation to the Navier-Stokes equation. This is important in the study of recovery from petroleum reservoirs, in which flow occurs over a wide range of scales, from the microscopic pores right up to the full reservoir. This variation of scale presents difficulties, since flow at the pore level is subject to predominantly viscous effects, whereas at the larger scales the viscous effects may become negligible in comparison with inertial effects. The Navier-Stokes equations may differ greatly with scale. Theoretical rock structures are created using percolation lattices and the flow properties of identical rock structures are then examined as a function of scale. The resultant recovery rates exhibit similarity across scale which would simplify the study of geological reservoir models.

Computational simulation of turbulent flows around a marine propeller by solving the partially averaged Navier–Stokes equation

2019 ◽  
Vol 233 (18) ◽  
pp. 6357-6366
Author(s):  
Woochan Seok ◽  
Sang Bong Lee ◽  
Shin Hyung Rhee
Keyword(s):  
Turbulent Flow ◽  
Reynolds Stress ◽  
Stokes Equation ◽  
Leading Edge ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Stress Model ◽  
Navier Stokes Equation ◽  
Local Flow ◽  
Reynolds Averaged Navier Stokes

This study concerns the characteristics of the partially averaged Navier–Stokes method for local flow analysis around a rotating propeller. Partially averaged Navier–Stokes, resolving crucial large-scale structures of turbulent flow at a given computational grid resolution, is a bridging turbulence closure model between the Reynolds-averaged Navier–Stokes equation and the direct numerical simulation. A detailed comparison between partially averaged Navier–Stokes and Reynolds-averaged Navier–Stokes models is made to achieve a better understanding of partially averaged Navier–Stokes characteristics for predicting the coherent structures in turbulent flow. The two-equation k-ω shear stress transport model and the seven-equation Reynolds stress model are selected for Reynolds-averaged Navier–Stokes computations. The problem of interest is the flow around a rotating KP505 propeller in open water conditions at an advance ratio of 0.7. Near the leading edge, the partially averaged Navier–Stokes results are similar to those of Reynolds stress model in terms of the vortical structures. Vorticity predicted by different turbulence models, however, shows significant differences. For a more detailed analysis, the velocity gradient constituting the vorticity is identified at the leading edge. It is proven that partially averaged Navier–Stokes is able to capture the anisotropic characteristics of the flow at the leading edge, where both the geometric and flow characteristics change abruptly.

Dynamics of vortical structures in a homogeneous shear flow

1994 ◽  
Vol 274 ◽  
pp. 43-68 ◽  
Author(s):  
Shigeo Kida ◽  
Mitsuru Tanaka
Keyword(s):  
Longitudinal Vortex ◽  
Navier Stokes ◽  
Spanwise Direction ◽  
Vorticity Field ◽  
Navier Stokes Equation ◽  
Vortical Structures ◽  
Homogeneous Shear ◽  
The Mean ◽  
Spanwise Vorticity ◽  
Vortex Tubes

The mechanism of generation, development and interaction of vortical structures, extracted as concentrated-vorticity regions, in homogeneous shear turbulence is investigated by the use of the results of a direct numerical simulation of the Navier-Stokes equation with 1283 grid points. Among others, a few of typical vortical structures are identified as important dynamical elements, namely longitudinal and lateral vortex tubes and vortex layers. They interact strongly with each other. Longitudinal vortex tubes are generated from a random fluctuating vorticity field through stretching of fluid elements caused by the mean linear shear. They are inclined toward the streamwise direction by rotational motion due to the mean shear. There is a small (about 10°) deviation in direction between the longitudinal vortex tubes and vorticity vectors therein, which makes the vorticity vectors turn toward the spanwise direction (against the mean vorticity) until the spanwise components of the fluctuating vorticity become comparable in magnitude with the mean vorticity. These longitudinal vortex tubes induce straining flows perpendicular to themselves which generate vortex layers with spanwise vorticity in planes spanned by the tubes and the spanwise axis. These vortex layers are unstable, and roll up into lateral vortex tubes with concentrated spanwise vorticity through the Kelvin-Helmholtz instability. All of these vortical structures, through strong mutual interactions, break down into a complicated smallscale random vorticity field. Throughout the simulated period an oblique stripe structure dominates the whole flow field: initially it is inclined at about 45° to the downstream and, as the flow develops, the inclination angle decreases but eventually stays at around 10°–20°.

Nashville Cats

2020 ◽  
Author(s):  
Travis D. Stimeling
Keyword(s):  
Music History ◽  
Country Music ◽  
Primary Sources ◽  
Recording Industry ◽  
Global View ◽  
Production And Distribution ◽  
History Of ◽  
The 1950S ◽  
Hall Of Fame ◽  
The City

Nashville Cats: Record Production in Music City, 1945–1975 is the first history of record production during country music’s so-called Nashville Sound era. This period of country music history produced some of the genre’s most celebrated recording artists, including Country Music Hall of Fame inductees Patsy Cline, Jim Reeves, and Floyd Cramer, and marked the establishment of a recording industry that has come to define Nashville in the national and international consciousness. Yet, despite country music’s overwhelming popularity during this period and the continued legacy of the studios that were built in Nashville during the 1950s and 1960s, little attention has been given to the ways in which recording engineers, session musicians, and record producers shaped the sounds of country music during the time. Drawing upon a rich array of previously unexplored primary sources, Nashville Cats: Record Production in Music City, 1945–1975 is the first book to take a global view of record production in Nashville during the three decades that the city’s musicians established the city as the leading center for the production and distribution of country music.

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