POF Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter iResearch App Facebook

Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Jun 2012

Volume 24, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Phys. Fluids 24, 063302 (2012); http://dx.doi.org/10.1063/1.4729453 (18 pages)

Wenbo Tang, Brent Knutson, Alex Mahalov, and Reneta Dimitrova
Enlarge Image | Read More
Page 2 of 2 Pages Previous Page | Jump to Page
back to top
RSS Feeds
back to top Turbulent Flows

A compressible wall model for large-eddy simulation with application to prediction of aerothermal quantities

S. Bocquet, P. Sagaut, and J. Jouhaud

Phys. Fluids 24, 065103 (2012); http://dx.doi.org/10.1063/1.4729614 (42 pages) | Cited 1 time

Online Publication Date: 26 June 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Large-eddy simulation (LES) of compressible flow with wall modelling is assessed on a quasi-isothermal and supersonic plane channel. The derivation of a quasi-analytical wall model based on empirical laws appears very difficult for combined physical effects like compressibility with pressure gradient. A wall model based on the compressible thin boundary layer equations constitutes a more general approach toward the simulation of multiphysical wall bounded flows with LES. In this work, such a wall model is derived and solved thanks to a new meshless method. An adequate scaling of the wall distance is introduced in the Van-Driest damping function of the wall model to handle compressibility effects. The choice of the proper wall distance scaling is shown to be crucial as soon as compressibility effects become significant. Additionally, some sources of error inherent to this wall-modelling approach are treated by appropriate corrections, and show non-negligible impact on the results. On a quasi-isothermal plane channel flow, the mean wall fluxes, primitive variable profiles and velocity fluctuations compare well to Direct Numerical Simulation (DNS) and empirical correlations for a wide range of Reynolds number. Then the DNS of supersonic isothermal-wall plane channel of Coleman at Mach = 1.5 and Mach = 3 are used as a more discriminant test case. The results agree well with the DNS data in terms of mean wall friction and wall heat flux. Finally, a specific analysis of the wall model accuracy is performed outside of the LES solver. This analysis allows to discriminate the error due to the wall model itself from the error due to the interaction between the wall model and the LES solver.
Show PACS
47.40.Ki Supersonic and hypersonic flows
47.27.ep Large-eddy simulations
47.27.nb Boundary layer turbulence
47.27.nd Channel flow
47.27.te Turbulent convective heat transfer

A subgrid-scale model for large-eddy simulation based on the physics of interscale energy transfer in turbulence

Brian W. Anderson and J. Andrzej Domaradzki

Phys. Fluids 24, 065104 (2012); http://dx.doi.org/10.1063/1.4729618 (35 pages)

Online Publication Date: 28 June 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The scale-similarity model in large-eddy simulation (LES) leads to an attractive, functionally simple expression for the subgrid-scale (SGS) stress tensor. It is well known, however, that the similarity model fails to accurately predict some of the most fundamental quantities in turbulent flows, perhaps the most important being the global energy transfer and the associated subgrid-scale dissipation. To address this, additional dissipative terms are usually added to the similarity model to improve its performance. In the present paper, considerations of interscale energy transfer have been used to identify sources of the observed deficiencies of the similarity model, specifically its inadequate balancing of terms contributing energy to the smallest scales and its duplication of terms producing effects in the largest scales. These considerations provide guidance in the development of a new model, which shows more favorable characteristics of energy transfer while preserving the functional simplicity of the scale-similarity model. Partial nonlinear terms are used to decompose the nonlinear transfer present in LES and to formulate a model expression capable of balancing small-scale production terms depositing energy near the LES cutoff. The proposed model is formulated in the same vein as the scale-similarity model, consisting of test filtered velocities and their products, but offers clear improvements in predictions of mean flow quantities and the global energy flux from the resolved to subgrid scales without the need for additional terms to augment subgrid-scale energy dissipation. The application of the new interscale transfer model in LES of wall-bounded flows leads to predictions of mean and RMS flow quantities comparable to those obtained for other, established SGS models.
Show PACS
47.27.nb Boundary layer turbulence
47.11.-j Computational methods in fluid dynamics
47.27.ep Large-eddy simulations
back to top Compressible Flows

Dynamic mode decomposition analysis of detonation waves

L. Massa, R. Kumar, and P. Ravindran

Phys. Fluids 24, 066101 (2012); http://dx.doi.org/10.1063/1.4727715 (22 pages)

Online Publication Date: 11 June 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Dynamic mode decomposition is applied to study the self-excited fluctuations supported by transversely unstable detonations. The focus of this study is on the stability of the limit cycle solutions and their response to forcing. Floquet analysis of the unforced conditions reveals that the least stable perturbations are almost subharmonic with ratio between global mode and fundamental frequency λi/ωf = 0.47. This suggests the emergence of period doubling modes as the route to chaos observed in larger systems. The response to forcing is analyzed in terms of the coherency of the four fundamental energy modes: acoustic, entropic, kinetic, and chemical. Results of the modal decomposition suggest that the self-excited oscillations are quite insensitive to vortical forcing, and maintain their coherency up to a forcing turbulent Mach number of 0.3.
Show PACS
47.40.Rs Detonation waves
47.20.-k Flow instabilities
47.52.+j Chaos in fluid dynamics
47.27.-i Turbulent flows

Numerical estimates for the bulk viscosity of ideal gases

M. S. Cramer

Phys. Fluids 24, 066102 (2012); http://dx.doi.org/10.1063/1.4729611 (23 pages)

Online Publication Date: 28 June 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We estimate the bulk viscosity of a selection of well known ideal gases. A relatively simple formula is combined with published values of rotational and vibrational relaxation times. It is shown that the bulk viscosity can take on a wide variety of numerical values and variations with temperature. Several fluids, including common diatomic gases, are seen to have bulk viscosities which are hundreds or thousands of times larger than their shear viscosities. We have also provided new estimates for the bulk viscosity of water vapor in the range 380–1000 K. We conjecture that the variation of bulk viscosity with temperature will have a local maximum for most fluids. The Lambert-Salter correlation is used to argue that the vibrational contribution to the bulk viscosities of a sequence of fluids having a similar number of hydrogen atoms at a fixed temperature will increase with the characteristic temperature of the lowest vibrational mode.
Show PACS
47.40.-x Compressible flows; shock waves
51.10.+y Kinetic and transport theory of gases
51.20.+d Viscosity, diffusion, and thermal conductivity
51.30.+i Thermodynamic properties, equations of state
47.11.-j Computational methods in fluid dynamics
back to top Geophysical Flows

Finite Rossby radius effects on vortex motion near a gap

R. S. Nilawar, E. R. Johnson, and N. R. McDonald

Phys. Fluids 24, 066601 (2012); http://dx.doi.org/10.1063/1.4721432 (18 pages) | Cited 1 time

Online Publication Date: 5 June 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This work investigates the effect of the Rossby radius of deformation on the motion of a vortex near a gap in an infinitely long barrier. A key parameter determining the behaviour of the vortex is a, the ratio of the Rossby radius of deformation to the width of the gap. Assuming quasi-geostrophic dynamics for a single-layer, reduced-gravity fluid, an integral equation is derived whose solution gives the velocity at any point in the fluid. The integral equation is solved numerically and the velocity field is integrated to give the trajectories of point vortices. Combined with the method of contour dynamics, the method can be used to compute the evolution of finite area patches of constant vorticity. The trajectories of point vortices and vortex patches are compared. The patches are initially circular and the centroids of those vortex patches that remain close to circular follow the trajectory and speed of their equivalent point vortices when appropriately normalised. The critical point vortex trajectory (the separatrix) which divides vortices that leap across the gap and those that pass through, is computed for various a. Decreasing the Rossby radius of deformation increases the tendency of vortices to pass through the gap. The effect of various background flows on both point vortex and vortex patch motion is also described.
Show PACS
47.32.cb Vortex interactions
47.60.-i Flow phenomena in quasi-one-dimensional systems
02.30.Rz Integral equations
02.60.Nm Integral and integrodifferential equations

Structure and stability of the finite-area von Kármán street

Paolo Luzzatto-Fegiz and Charles H. K. Williamson

Phys. Fluids 24, 066602 (2012); http://dx.doi.org/10.1063/1.4724307 (25 pages) | Cited 2 times

Online Publication Date: 8 June 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
By using a recently developed numerical method, we explore in detail the possible inviscid equilibrium flows for a Kármán street comprising uniform, large-area vortices. In order to determine stability, we make use of an energy-based stability argument (originally proposed by Lord Kelvin), whose previous implementation had been unsuccessful in determining stability for the Kármán street [P. G. Saffman and J. C. Schatzman, “Stability of a vortex street of finite vortices,” J. Fluid Mech. 117, 171–186 (1982)10.1017/S0022112082001578]. We discuss in detail the issues affecting this interpretation of Kelvin's ideas, and show that this energy-based argument cannot detect subharmonic instabilities. To find superharmonic instabilities, we employ a recently introduced approach, which constitutes a reliable implementation of Kelvin's stability ideas [P. Luzzatto-Fegiz and C. H. K. Williamson, “Stability of conservative flows and new steady fluid solutions from bifurcation diagrams exploiting a variational argument,” Phys. Rev. Lett. 104, 044504 (2010)10.1103/PhysRevLett.104.044504]. For periodic flows, this leads us to organize solutions into families with fixed impulse I, and to construct diagrams involving the flow energy E and horizontal spacing (i.e., wavelength) L. Families of large-I vortex streets exhibit a turning point in L, and terminate with “cat's eyes” vortices (as also suggested by previous investigators). However, for low-I streets, the solution families display a multitude of turning points (leading to multiple possible streets, for given L), and terminate with teardrop-shaped vortices. This is radically different from previous suggestions in the literature. These two qualitatively different limiting states are connected by a special street, whereby vortices from opposite rows touch, such that each vortex boundary exhibits three corners. Furthermore, by following the family of I = 0 streets to small L, we gain access to a large, hitherto unexplored flow regime, involving streets with L significantly smaller than previously believed possible. To elucidate in detail the possible solution regimes, we introduce a map of spacing L, versus impulse I, which we construct by numerically computing a large number of steady vortex configurations. For each constant-impulse family of steady vortices, our stability approach also reveals a single superharmonic bifurcation, leading to new families of vortex streets, which exhibit lower symmetry.
Show PACS
47.32.cd Vortex stability and breakdown
02.60.-x Numerical approximation and analysis
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking
47.32.ck Vortex streets

Role of fluid density in shaping eruption currents driven by frontal particle blow-out

C. S. Carroll, B. Turnbull, and M. Y. Louge

Phys. Fluids 24, 066603 (2012); http://dx.doi.org/10.1063/1.4725538 (20 pages)

Online Publication Date: 8 June 2012

Full Text: Read Online (HTML) | Download PDF

multimedia

Show Abstract
We study the role of suspension density in eruption currents, a regime of gravity-driven flow that is sustained by massive, localized blow-out of particles acting as a steady source of heavier fluid injected into a uniform flow at high Reynolds number. Inspired by the potential flow solution of Saffman and Yuen [“Finite-amplitude interfacial waves in the presence of a current,” J. Fluid Mech. 123, 459–476 (1982)10.1017/S0022112082003152], we show that the relative density difference between the two fluids swells the size of the current's head without changing its shape, while inducing a velocity jump at the interface. We test this inviscid theory against inviscid and large-eddy-simulations. We also conduct experiments in a water flume, where a line source of fluorescent brines of various densities is injected in a cross-stream and visualized with a narrow sheet of light. Simulations and experiments reveal that, with isotropic velocity distribution on a finite source, eruption currents expand further and develop interface oscillations, but the inviscid theory still captures relative swelling induced by density. We compare predictions to the static pressure data of McElwaine and Turnbull [“Air pressure data from the Vallee de la Sionne avalanches of 2004,” J. Geophys. Res. 110, F03010, doi:10.1029/2004JF000237 (2005)] in powder snow avalanches.
Show PACS
47.57.E- Suspensions
47.27.Jv High-Reynolds-number turbulence
47.27.ep Large-eddy simulations
47.80.Jk Flow visualization and imaging
47.55.Kf Particle-laden flows
47.35.Bb Gravity waves

On the necessary conditions for bursts of convection within the rapidly rotating cylindrical annulus

Robert J. Teed, Chris A. Jones, and Rainer Hollerbach

Phys. Fluids 24, 066604 (2012); http://dx.doi.org/10.1063/1.4711398 (21 pages) | Cited 1 time

Online Publication Date: 8 June 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Zonal flows are often found in rotating convective systems. Not only are these jet-flows driven by the convection, they can also have a profound effect on the nature of the convection. In this work the cylindrical annulus geometry is exploited in order to perform nonlinear simulations seeking to produce strong zonal flows and multiple jets. The parameter regime is extended to Prandtl numbers that are not unity. Multiple jets are found to be spaced according to a Rhines scaling based on the zonal flow speed, not the convective velocity speed. Under certain conditions the nonlinear convection appears in quasi-periodic bursts. A mean field stability analysis is performed around a basic state containing both the zonal flow and the mean temperature gradient found from the nonlinear simulations. The convective growth rates are found to fluctuate with both of these mean quantities suggesting that both are necessary in order for the bursting phenomenon to occur.
Show PACS
47.32.Ef Rotating and swirling flows
47.20.-k Flow instabilities
47.10.-g General theory in fluid dynamics
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Light attenuation experiments on double diffusive plumes and fountains

Bruce R. Sutherland, Brace Lee, and Joseph K. Ansong

Phys. Fluids 24, 066605 (2012); http://dx.doi.org/10.1063/1.4730431 (20 pages)

Online Publication Date: 29 June 2012

Full Text: Read Online (HTML) | Download PDF

Show Abstract
By adapting the method of light attenuation to the study of axisymmetric disturbances, we examine the structure of forced plumes and fountains whose buoyancy is set by salinity and/or temperature differences between the turbulent flow and the otherwise stationary ambient. The attenuation measurements are used to infer the statistically steady-state density as a function of radius and height. These compare well with in situ measurements of density taken from a conductivity-temperature probe that repeatedly traversed the centreline of the plume. The theory for forced plumes also agrees well with the centreline density profile. The radial structure of plumes and fountains near the source is found to correspond well to a Gaussian profile, although the standard deviation is found to increase moderately faster with height than spreading rates reported in the existing literature. This is attributed in part to averaging biases resulting from light attenuating through transient eddies. In most experiments, hot and salty fountains reached a steady state height consistent with existing semi-empirical theories for fountains with just one diffusive component. However, if the density of the hot and salty fluid near the source is close to, but moderately larger than, that of the ambient, over time, the fountain is observed to increase progressively in height. This occurs presumably as a consequence of heat diffusion at the top of the fountain making the ambient above it increasingly buoyant relative to the negative buoyancy associated with less diffusive salt.
Show PACS
47.27.tb Turbulent diffusion
47.80.-v Instrumentation and measurement methods in fluid dynamics
68.08.Bc Wetting
back to top Others

Aeroacoustic power generated by multiple compact axisymmetric cavities: Effect of hydrodynamic interference on the sound production

G. Nakiboğlu and A. Hirschberg

Phys. Fluids 24, 067101 (2012); http://dx.doi.org/10.1063/1.4718726 (18 pages)

Online Publication Date: 11 June 2012

Full Text: Read Online (HTML) | Download PDF

multimedia

Show Abstract
Aeroacoustic sound generation due to self-sustained oscillations by a series of compact axisymmetric cavities exposed to a grazing flow is studied both experimentally and numerically. The driving feedback is produced by the velocity fluctuations resulting from a coupling of vortex sheddings at the upstream cavity edges with acoustic standing waves in the coaxial pipe. When the cavities are separated sufficiently from each other, the whistling behavior of the complete system can be determined from the individual contribution of each cavity. When the cavities are placed close to each other there is a strong hydrodynamic interference between the cavities which affects both the peak amplitude attained during whistling and the corresponding Strouhal number. This hydrodynamic interference is captured successfully by the proposed numerical method.
Show PACS
47.40.-x Compressible flows; shock waves
02.60.-x Numerical approximation and analysis
47.11.-j Computational methods in fluid dynamics
47.32.-y Vortex dynamics; rotating fluids
47.35.Rs Sound waves
47.60.Dx Flows in ducts and channels
back to top
RSS Feeds
FREE

Retraction: “A unified probability density function formulation to model turbulence modification in two-phase flow” [Phys. Fluids 21, 105101 (2009)]

Gaurav Anand and Patrick Jenny

Phys. Fluids 24, 069901 (2012); http://dx.doi.org/10.1063/1.4729616 (1 page)

Online Publication Date: 22 June 2012

Full Text: Read Online (HTML) | Download PDF

Abstract Unavailable
Show PACS
99.10.Ln Retraction
47.27.E- Turbulence simulation and modeling
47.55.-t Multiphase and stratified flows
Page 2 of 2 Pages Previous Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close