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

Flickr Twitter UniPHY Group iResearch App Facebook

Search Issue | RSS Feeds RSS
Previous Issue Next Issue

Apr 1998

Volume 10, Issue 4, pp. 757-1046

Page 1 of 2 Pages Next Page | Jump to Page
back to top
RSS Feeds

The generation of the first visible wind waves

G. Caulliez, N. Ricci, and R. Dupont

Phys. Fluids 10, 757 (1998); http://dx.doi.org/10.1063/1.869600 (3 pages) | Cited 6 times

Full Text: | Download PDF

Show Abstract
In this paper we report the results of the first laboratory study on the relationship between the initial growth of the short wind waves and the simultaneous development of the wind-induced drift current. The phenomenon of the first visible ripples appearing “suddenly” on the water surface and forming V-shaped streaks aligned with the wind is explained. We show that the laminar–turbulent transition of the near surface water flow causes an explosive growth of the initial wind-generated ripples. The grown ripples become visible and thus mark the surface of the well-localized V-shaped turbulent zones forming the streaks. © 1998 American Institute of Physics.
Show PACS
92.10.Hm Ocean waves and oscillations
92.10.Kp Sea-air energy exchange processes
92.60.Gn Winds and their effects
92.10.Lq Turbulence, diffusion, and mixing processes in oceanography
47.35.-i Hydrodynamic waves
47.27.Cn Transition to turbulence
47.15.Fe Stability of laminar flows
back to top
RSS Feeds

Hydrodynamics of a compound drop with application to leukocyte modeling

Heng-Chuan Kan, H. S. Udaykumar, Wei Shyy, and Roger Tran-Son-Tay

Phys. Fluids 10, 760 (1998); http://dx.doi.org/10.1063/1.869601 (15 pages) | Cited 21 times

Full Text: | Download PDF

Show Abstract
We study the dynamics of a compound liquid drop which is comprised of an outer membrane surface, a shell layer, and a core. The deformation due to an imposed extensional flow and the subsequent recovery are investigated computationally employing a combined Eulerian–Lagrangian technique. The numerical method allows for large viscosity and capillarity differences between layers. The present study reports several findings which provide direct insight into developing a dynamic model for leukocytes. A compound drop behaves like a homogeneous, simple liquid drop if the core is sufficiently deformed and the time scale of the core, related to the combination of its viscosity and capillarity, is comparable to that of the shell layer. Disparate time scales between the core and shell layer result in a rapid initial recoil of the drop during which the shell fluid is the primary participant in the hydrodynamics, followed by a slower relaxation period during which the core and shell layer interact with each other. Consequently, the apparent viscosity of the drop depends not only on the rheological properties of the drop, but also on the flow dynamics surrounding it. The findings obtained with the three-layer compound drop model can explain several main characteristics of leukocytes reported in the literature. Furthermore, our study suggests that unless the presence and possible deformation of the nucleus are explicitly accounted for, neither Newtonian nor non-Newtonian models for leukocytes can adequately predict the hydrodynamics of leukocytes. © 1998 American Institute of Physics.
Show PACS
47.55.D- Drops and bubbles
87.19.U- Hemodynamics
87.19.Wx Pneumodyamics, respiration

A numerical study of chemical front propagation in a Hele-Shaw flow under buoyancy effects

Jingyi Zhu

Phys. Fluids 10, 775 (1998); http://dx.doi.org/10.1063/1.869602 (14 pages) | Cited 8 times

Full Text: | Download PDF

Show Abstract
We consider the propagation of chemical fronts in a Hele-Shaw flow where the front is assumed to propagate with a curvature dependent velocity. The motivation is to model some recent experiments that employ aqueous autocatalytic chemical reactions in such a device. The density change across the front in such experiments is quite small so the Boussinesq approximation can be used, and the flow field generated is exclusively due to buoyancy effects. We derive a free boundary formulation based on Darcy’s law and potential theory, and describe the evolution in terms of the θ−L formulation, in which the tangent angle and the perimeter of the closed front are followed in time. Numerical solutions are obtained for this formulation with a rising and expanding bubble. As observed in the experiments, a fingering phenomenon which is different from the surface tension associated phenomenon appears in our calculations. The mechanisms that control the wavelength selection of the fingers, and a comparison with the result of a linear stability analysis for flat fronts are discussed. © 1998 American Institute of Physics.
Show PACS
47.70.Fw Chemically reactive flows
82.33.Vx Reactions in flames, combustion, and explosions
47.55.D- Drops and bubbles
47.20.Bp Buoyancy-driven instabilities (e.g., Rayleigh-Benard)
82.30.Vy Homogeneous catalysis in solution, polymers and zeolites
47.56.+r Flows through porous media
02.60.-x Numerical approximation and analysis
47.27.T- Turbulent transport processes

Experimental and numerical investigations of the interface profile close to a moving contact line

Chonghui Shen and Douglas W. Ruth

Phys. Fluids 10, 789 (1998); http://dx.doi.org/10.1063/1.869603 (11 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
For the problem of one fluid displacing another on a solid surface, Dussan V. et al. (1991) proposed a one-parameter analytical solution (the DRG solution) to describe the dynamic interface shape in the overlap region of the intermediate and the outer regions, for small capillary numbers. In the present study we examined the validity of the DRG solution with both experimental and numerical approaches. Our experiments consisted of displacing air with paraffin oil in parallel (Hele–Shaw) glass cells. The slope of the air–oil interface was measured at distances from the contact line, ranging between 5 and 200 μm. The displacement speeds corresponded to capillary numbers ranging between 4.7×10−6 and 2.6×10−4. Excellent agreement was obtained among the DRG solution, the numerical, and the experimental results in the region >10 μm from the contact line, but systematic deviation was observed in the region close to the contact line. This deviation was confirmed by the numerical simulations that used the finite element method. The measured dynamic contact angle increases with the displacing speed and can be correlated with a power law in Ca, which is similar to Tanner’s law. © 1998 American Institute of Physics.
Show PACS
68.03.Cd Surface tension and related phenomena
68.15.+e Liquid thin films
68.08.Bc Wetting
47.55.Hd Stratified flows
47.80.-v Instrumentation and measurement methods in fluid dynamics
07.60.Ly Interferometers
02.70.Dh Finite-element and Galerkin methods

Hamilton’s principle for quasigeostrophic motion

Darryl D. Holm and Vladimir Zeitlin

Phys. Fluids 10, 800 (1998); http://dx.doi.org/10.1063/1.869623 (7 pages) | Cited 1 time

Full Text: | Download PDF

Show Abstract
We show that the equation of quasigeostrophic (QG) potential vorticity conservation in geophysical fluid dynamics follows from Hamilton’s principle for stationary variations of an action for geodesic motion in the f-plane case or its prolongation in the β-plane case. This implies a new momentum equation and an associated Kelvin circulation theorem for QG motion. We treat the barotropic and two-layer baroclinic cases, as well as the continuously stratified case. © 1998 American Institute of Physics.
Show PACS
47.32.C- Vortex dynamics
47.55.Hd Stratified flows
02.30.Xx Calculus of variations
02.30.Yy Control theory

Thermoacoustics: Transient regimes and singular temperature profiles

Luc Bauwens

Phys. Fluids 10, 807 (1998); http://dx.doi.org/10.1063/1.869604 (12 pages) | Cited 3 times

Full Text: | Download PDF

Show Abstract
The stationary, periodic solution to the problem of oscillating flow of a conducting fluid, in a duct closed at one end and with periodical mass flow rate at the other end, is known to exhibit a singularity in the mean temperature at the closed end when transverse conduction in the fluid and the duct wall is taken into account, but longitudinal conduction is neglected. For instance, a solution of that type was originally suggested by Gifford and Longsworth as a prototype for pulse-tube refrigeration. Whether these stationary singular solutions are physical or mere theoretical curiosities depend upon the existence of a scenario leading to such a limit cycle. To address that question, a transient theory is formulated, using the narrow duct approximation. The results show that at least for constant fluid thermal conductivity, all singular profiles generated by the mechanism under study are linearly stable. For round tubes, the temperature profile is shown to evolve, from an arbitrary initial value, toward an equilibrium profile which results in balanced energy fluxes. © 1998 American Institute of Physics.
Show PACS
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
47.35.-i Hydrodynamic waves
47.60.-i Flow phenomena in quasi-one-dimensional systems

Thermohaline convection with nonlinear salt profiles

N. J. Balmforth, A. R. R. Casti, and K. A. Julien

Phys. Fluids 10, 819 (1998); http://dx.doi.org/10.1063/1.869605 (10 pages) | Cited 1 time

Full Text: | Download PDF

Show Abstract
We study the linear stability of a fluid to double-diffusive convection in the case for which the background temperature field is linear, but the mean salt distribution is a nonlinear function. A variety of idealized limits amenable to perturbative treatment are examined, and a detailed numerical study of a hyperbolic tangent profile is presented. It is shown that nonlinearity in the background salinity profile leads to pronounced competition and interaction between the linear normal modes. © 1998 American Institute of Physics.  
Show PACS
47.27.T- Turbulent transport processes
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking
47.55.Hd Stratified flows
47.20.Bp Buoyancy-driven instabilities (e.g., Rayleigh-Benard)
47.35.-i Hydrodynamic waves

Non-linear spirals in the Taylor–Couette problem

J. Antonijoan, F. Marquès, and J. Sánchez

Phys. Fluids 10, 829 (1998); http://dx.doi.org/10.1063/1.869606 (10 pages) | Cited 7 times

Full Text: | Download PDF

Show Abstract
We examine non-linear spiral flow in the Taylor–Couette problem for a wide gap with axially periodic conditions. We present a highly efficient computational method adapted to this problem, based on continuation methods applied to a pseudospectral discretization of the Navier–Stokes equations in a rotating frame of reference. The spiral flow is computed in a wide range of parameters, and different features are explored in detail: domain of existence of the flow, behavior for high Reynolds number, appearance of axial flows, dependency on parameters, and stability against helical disturbances. A first integral is obtained and used to describe the particle trajectories in the fluid. This description shows that the axial and radial motion of the particles is mainly confined within an internal boundary layer. © 1998 American Institute of Physics.
Show PACS
47.32.-y Vortex dynamics; rotating fluids
47.20.-k Flow instabilities
47.15.-x Laminar flows
05.45.-a Nonlinear dynamics and chaos
47.60.-i Flow phenomena in quasi-one-dimensional systems

Elliptic instability in two-dimensional flattened Taylor–Green vortices

D. Sipp and L. Jacquin

Phys. Fluids 10, 839 (1998); http://dx.doi.org/10.1063/1.869607 (11 pages) | Cited 21 times

Full Text: | Download PDF

Show Abstract
The aim of the present paper is to study three-dimensional elliptic instability in two-dimensional flattened Taylor–Green vortices, which constitutes a model problem for the topics of wake vortex dynamics. Shortwave asymptotics and classical linear stability theory are developed. Both approaches show that the flow is unstable. In particular, the structure of the most amplified growing mode is the same as that obtained in unbounded elliptical flows. The limits of the linear regime and the effects of the nonlinear interactions are characterized by means of a spectral Direct Numerical Simulation (DNS). © 1998 American Institute of Physics.
Show PACS
47.32.C- Vortex dynamics
47.20.-k Flow instabilities

Bifurcation analysis of double-diffusive convection with opposing horizontal thermal and solutal gradients

Shihe Xin, Patrick Le Quéré, and Laurette S. Tuckerman

Phys. Fluids 10, 850 (1998); http://dx.doi.org/10.1063/1.869608 (9 pages) | Cited 21 times

Full Text: | Download PDF

Show Abstract
The onset of convection in double diffusion with equal and opposite thermal and solutal buoyancy forces is studied. Numerical linear stability analyses and integration of the full Boussinesq equations are performed in an infinite vertical fluid layer and in closed rectangular cavities bounded by rigid walls. Detailed study of the subsequent nonlinear evolution is carried out for Le = 1.2 and Pr = 1. In the infinite vertical layer, the onset of convection is found to correspond to a subcritical circle pitchfork bifurcation. The finite-amplitude branch of steady states in turn loses stability to traveling waves via a supercritical drift pitchfork bifurcation. In a square cavity the bifurcation is transcritical and the full branch of stable and unstable solutions is constructed. With increasing cavity aspect-ratio, we observe alternating transcritical and pitchfork bifurcations, depending on the symmetry of the most unstable eigenvector. © 1998 American Institute of Physics.
Show PACS
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking
47.27.T- Turbulent transport processes
47.35.-i Hydrodynamic waves
47.60.-i Flow phenomena in quasi-one-dimensional systems

Experimental study of the kinematic mixing of two fluids in a 2D enclosure

Olusegun J. Ilegbusi and Mahmut D. Mat

Phys. Fluids 10, 859 (1998); http://dx.doi.org/10.1063/1.869609 (10 pages) | Cited 1 time

Full Text: | Download PDF

Show Abstract
A simple experiment is described to investigate the buoyancy driven mixing of two fluids separated by a valve in a 2D (two-dimension) enclosure. The experiment is performed for a range of Grashof numbers, Gr ranging from 1 to 3.7×105 and a valve speed of Vval = 0.05 m/s. Three distinct flow regimes are investigated within the parametric range considered, depending on the Grashof number: Chaotic (Gr ≥ 3.7×105), convective (1<Gr<3.7×105) and diffusive (Gr<1). A novel image processing technique is used to measure the mix fraction, interface elongation, and mixing width. The technique is based on the analysis of the color intensity of images obtained from the video recording. Mixing is quantified by analysis of the interface length and mixing width, from which the molecular mixing rate and Lyapunov exponents are deduced. The chaotic regime is found to be efficiently mixed compared with the convective and diffusive regimes. © 1998 American Institute of Physics.
Show PACS
47.80.-v Instrumentation and measurement methods in fluid dynamics
64.75.-g Phase equilibria
47.52.+j Chaos in fluid dynamics
42.30.Sy Pattern recognition
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.27.T- Turbulent transport processes
07.05.Pj Image processing
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

Numerical simulation of the flow behind a rotary oscillating circular cylinder

Seung-Jin Baek and Hyung Jin Sung

Phys. Fluids 10, 869 (1998); http://dx.doi.org/10.1063/1.869610 (8 pages) | Cited 33 times

Full Text: | Download PDF

Show Abstract
A numerical study was made of flow behind a circular cylinder in a uniform flow, where the cylinder was rotationally oscillated in time. The temporal behavior of vortex formation was scrutinized over broad ranges of the two externally specified parameters, i.e., the dimensionless rotary oscillating frequency (0.110 ⩽ Sf ⩽ 0.220) and the maximum angular amplitude of rotation (θmax = 15°, 30°, and 60°). The Reynolds number (Re = U∞D/ν) was fixed at Re=110. A fractional-step method was utilized to solve the Navier–Stokes equations with a generalized coordinate system. The main emphasis was placed on the initial vortex formations by varying Sf and θmax. Instantaneous streamlines and pressure distributions were displayed to show the vortex formation patterns. The oscillatory forcing was in the vicinity of the lock-on range, which can be applied to flow feedback control afterwards. The vortex formation modes and relevant phase changes were characterized by measuring the lift coefficient (CL) and the time of negative maximum CL (t−CLmax) with variable forcing conditions. © 1998 American Institute of Physics.
Show PACS
47.32.C- Vortex dynamics
47.35.-i Hydrodynamic waves
47.11.-j Computational methods in fluid dynamics

Cyclic flow oscillations in a system of repeatedly branching channels

Ch. Brücker and M. L. Riethmuller

Phys. Fluids 10, 877 (1998); http://dx.doi.org/10.1063/1.869611 (9 pages) | Cited 6 times

Full Text: | Download PDF

Show Abstract
The unsteady nature of the flow within a cascade of bifurcating branches was investigated for Reynolds numbers of 900 and 2700 in the mother branch. The cascade consists of three generations of planar symmetric bifurcations with a fixed branching angle and ratio of branch length to width. Chronological flow field measurements were carried out using digital-particle-image-velocimetry (DPIV) to determine the time-dependent velocity distribution within the branches. Though the flow input was steady, low-frequency flow oscillations were found within the branches which were coupled with the dynamics of the separation regions and the cross-talk between the communicating daughter branches. The toggling flip-flop character of the flow was explained by means of a feedback loop in which the cyclic growth, wash-out and re-generation of the separation regions is assumed to be the inner motor for the periodic continuation. These local excitation mechanisms were suggested to be similar to those causing the generation of low-frequency oscillations in shear-layers impinging on edges like in a rectangular cavity. The results demonstrate that unsteady effects and excited oscillations play an additional role in uneven flow partitioning in flow bifurcation cascades, however, they do not favor any flow partitioning in a preferential pathway constant in time © 1998 American Institute of Physics.
Show PACS
47.35.-i Hydrodynamic waves
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.20.Ky Nonlinearity, bifurcation, and symmetry breaking
47.80.-v Instrumentation and measurement methods in fluid dynamics
06.30.Gv Velocity, acceleration, and rotation
47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)
47.32.Ff Separated flows

Ultrasound scattering by a swirling jet

M. Oljaca, X. Gu, A. Glezer, M. Baffico, and F. Lund

Phys. Fluids 10, 886 (1998); http://dx.doi.org/10.1063/1.869612 (13 pages) | Cited 15 times

Full Text: | Download PDF

Show Abstract
Recent analytical work has shown that when an acoustic plane wave propagates through a rotational flow field there is a linear relationship between the Fourier component of the scattered acoustic pressure and the Fourier transform in space and time of the vorticity component that is normal to the plane defined by the wave vectors of the incident and scattered acoustic waves. Hence, ultrasound scattering can be used as a non-intrusive spectral probe of vorticity and potentially as a tool for direct measurements of vorticity distributions. Some aspects of this technique have been tested in a swirling air jet emanating from a 2.54 cm diameter nozzle where the swirl is generated upstream of the jet nozzle by a rotating paddle. For a given exit volume flow rate, swirl numbers up to 0.4 are realized. Radial distributions of the streamwise and tangential velocity components downstream of the jet exit plane are measured using two-component hot-wire anemometry and the corresponding distributions of streamwise vorticity are computed. A nominally plane ultrasonic wave field is generated normal to the jet axis by a transmitter having a 16 cm square aperture. The scattered ultrasound in the radial direction is measured at a number of streamwise and azimuthal stations. In accord with the theory, the normalized amplitude of the scattered acoustic wave is a linear function of the magnitude of the centerline vorticity at the exit plane of the jet, and is independent of the intensity of the incident wave field. Fourier components of the vorticity distribution are directly measured by varying the scattering angle and are in good agreement with theoretical predictions. © 1998 American Institute of Physics.
Show PACS
47.32.-y Vortex dynamics; rotating fluids
43.25.-x Nonlinear acoustics
47.27.-i Turbulent flows
47.32.C- Vortex dynamics

A numerical investigation on the effect of the inflow conditions on the self-similar region of a round jet

B. J. Boersma, G. Brethouwer, and F. T. M. Nieuwstadt

Phys. Fluids 10, 899 (1998); http://dx.doi.org/10.1063/1.869626 (11 pages) | Cited 71 times

Full Text: | Download PDF

Show Abstract
In this paper we consider the direct numerical simulation (DNS) of a spatially developing free round jet at low Reynolds numbers. Simulation of a spatially evolving flow such as the jet requires boundary conditions, which allow entrainment into the turbulent flow across the lateral boundaries of the computational domain. The boundary conditions which satisfy this requirement are so-called traction free boundary conditions. After showing that these boundary conditions lead to a correct behavior of the velocity near the lateral boundary of the jet, we will consider the DNS of the jet flow at a Reynolds number of 2.4×103 and compare the results with experimental data obtained by Hussein et al. [J. Fluid Mech. 258, 31 (1994)] and by Panchapakesan and Lumley [J. Fluid Mech. 246, 197 (1993)]. The results of our numerical simulations agree very well with the experimental data. Next we use the DNS to investigate the influence of the shape of the velocity profile at the jet orifice on the self-similarity scaling for the far-field velocity and shear stress profile. Evidence is presented in support of the suggestion by George [Advances in Turbulence (Springer, New York, 1989)] that the details of self-similarity depend on the initial conditions. This fact implies that there may exist no universally valid similarity scaling for the free jet. © 1998 American Institute of Physics.
Show PACS
47.27.wg Turbulent jets
47.11.-j Computational methods in fluid dynamics

Intermittency and Reynolds number

H. Kahalerras, Y. Malécot, Y. Gagne, and B. Castaing

Phys. Fluids 10, 910 (1998); http://dx.doi.org/10.1063/1.869613 (12 pages) | Cited 17 times

Full Text: | Download PDF

Show Abstract
Hot wire measurements of longitudinal and transverse increments are performed in three different types of flows on a large range of Reynolds numbers (100≲Rλ≲3000). An improved technique based on cumulant expansion of velocity structure functions is used to estimate the spreading of the pdfs and to study their scaling properties in the inertial range. Thus, the rate of intermittency depth through the scales of flow, called here β(Rλ), is experimentally introduced, and it is shown that β(Rλ) has a universal behavior on a very large Reynolds numbers range. © 1998 American Institute of Physics.
Show PACS
47.27.-i Turbulent flows

Conditional methods in application for Lagrangian modeling

A. Y. Klimenko

Phys. Fluids 10, 922 (1998); http://dx.doi.org/10.1063/1.869614 (6 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
The exact unclosed equation for the phase-space density function (or corresponding Lagrangian pdf) in turbulent flows is obtained using conditional techniques. The equation has direct implications for stochastic Lagrangian models based on the assumption of similarity with a Markov process. The problem of random particle sources is examined and the appropriate correcting term is suggested. © 1998 American Institute of Physics.  
Show PACS
47.27.E- Turbulence simulation and modeling
02.50.Ey Stochastic processes
02.50.Ga Markov processes

Intermittency and relative scaling of subgrid-scale energy dissipation in isotropic turbulence

Stefano Cerutti and Charles Meneveau

Phys. Fluids 10, 928 (1998); http://dx.doi.org/10.1063/1.869615 (10 pages) | Cited 25 times

Full Text: | Download PDF

Show Abstract
The rate at which large-scale kinetic energy in turbulent flows is transferred to, or from, unresolved scales (smaller than a filter scale Δ) is given by Π(x,t) = −τijmathij, where τij is the subgrid stress, and mathij is the resolved strain-rate tensor. The spatial distribution of Π(x,t) is computed from DNS of isotropic turbulence, and is found to be highly intermittent with increasing levels of intermittency as the filter size decreases. Relative scaling exponents of high-order moments of Π are measured using extended self-similarity, and are compared to those of longitudinal velocity structure functions. Reasonably good agreement is found, both sets of exponents clearly departing from the Kolmogorov (1941) theory. Relative scaling exponents of the SGS dissipation as predicted by several models are measured a priori from the DNS, and are compared to those of the true dissipation. We find the constant and spectral eddy viscosity models to be significantly less intermittent, and the local dynamic model to be much more intermittent than the true SGS dissipation field. The traditional and volume-averaged dynamic Smagorinsky models, together with the similarity model, yield more realistic levels of intermittency. © 1998 American Institute of Physics.
Show PACS
47.27.Gs Isotropic turbulence; homogeneous turbulence
47.27.E- Turbulence simulation and modeling
47.11.-j Computational methods in fluid dynamics

Scalar dissipation rate modelling in variable density turbulent axisymmetric jets and diffusion flames

J. P. H. Sanders and I. Gökalp

Phys. Fluids 10, 938 (1998); http://dx.doi.org/10.1063/1.869616 (11 pages) | Cited 10 times

Full Text: | Download PDF

Show Abstract
In recent years several transport equation models for the scalar dissipation rate have been proposed to replace the well known algebraic expression based on equality of mechanical and scalar turbulent time scales. In this study various transport equation models are compared with each other and the model equation of Yoshizawa [J. Fluid Mech. 195, 541 (1988)] is given special attention. The latter is shown to allow an algebraic solution that is different from the classical “equal-scales” algebraic model. The constants that appear in this equation are assigned values based on similarity behavior in turbulent jets and based on studies of homogeneous isotropic turbulence. Both algebraic models and the transport equation models are compared and applied to isothermal variable density jets and jet diffusion flames. It is found that general features, such as the behavior of scalar fluctuation intensities of variable density turbulent jets are relatively well predicted by all the models. Differences between the models exist regarding the predicted time scale ratios. © 1998 American Institute of Physics.
Show PACS
47.27.wg Turbulent jets
47.27.tb Turbulent diffusion
47.70.Fw Chemically reactive flows
82.33.Vx Reactions in flames, combustion, and explosions
02.10.-v Logic, set theory, and algebra
47.27.Gs Isotropic turbulence; homogeneous turbulence

Convection velocities in a turbulent boundary layer

P.-Å. Krogstad, J. H. Kaspersen, and S. Rimestad

Phys. Fluids 10, 949 (1998); http://dx.doi.org/10.1063/1.869617 (9 pages) | Cited 21 times

Full Text: | Download PDF

Show Abstract
The convection velocities of ejections, sweeps, and shear layers have been studied in a turbulent boundary layer at Reθ = 1409 by means of two-point correlations. Except in the buffer layer, where the convection velocities are reasonably constant, considerable variations in Uc are observed, both with respect to the distance from the wall and the scale of the event. The largest-scale motions (of the order of the boundary layer thickness) are convected at velocities close to the local mean. However, the velocities drop significantly as the scales are reduced for all types of events studied. Hence, the concept of a unique structure convection velocity does not appear to be very useful, since it must depend on the state of evolution of the structure. The propagation velocity also appears to be different for different parts of the event. It is found that for all scales and positions, the convection velocity for ejections is distinctly lower than that for sweeps, suggesting that the mechanisms responsible for the two types of events are quite different. © 1998 American Institute of Physics.
Show PACS
47.27.T- Turbulent transport processes
47.27.nb Boundary layer turbulence

Time scales of stratified turbulent flows and relations between second-order closure parameters and flow numbers

Stefan Heinz

Phys. Fluids 10, 958 (1998); http://dx.doi.org/10.1063/1.869618 (16 pages) | Cited 5 times

Full Text: | Download PDF

Show Abstract
The description of turbulent mixing and chemical reactions by Lagrangian probability density function methods offers some significant advantages over other methods, mainly due to the simulation of mixing processes and the exact treatment of chemical transformations. A key problem of such methods is the information on the time scales of processes, because they determine the dynamics and intensity of mixing. This question is considered for stratified flow. Different models are presented for the development of these time scales in time and their stationary spatial patterns in dependence on shear and stratification. The model predictions are shown to be in agreement with large-eddy simulations of stratified homogeneous shear flow. Two further applications of these models are considered: the description of transitions between flow regimes (characterized by different scaling quantities) in the stationary atmospheric surface layer and, second, the simulation of buoyant plume rise. It is shown that the predictions of the stationary frequency model agree with measured data. The consideration of limit cases of this model leads to connections between second-order closure parameters and (critical) flow numbers that characterize these transitions. These relationships are shown to be very advantageous for the application of closure models. A new flow number that characterizes the transition to free convective flow under unstable stratification is introduced here in analogy to the critical gradient Richardson number, which characterizes the onset of turbulence in stably stratified flow. The second application provides a new theory for buoyant plume rise. Two parameters that describe the turbulent mixing in the entrainment and extrainment stages of plume rise are explained as ratios of the relevant time scales. The two-thirds power law of buoyant plume rise, which is observed for nonturbulent and neutrally stratified flow, is obtained without having to make ad hoc assumptions. For turbulent flow, the plume’s leveling-off is calculated in accord with measurements. © 1998 American Institute of Physics.
Show PACS
47.55.Hd Stratified flows
47.70.Fw Chemically reactive flows
47.27.nb Boundary layer turbulence
47.27.T- Turbulent transport processes

A numerical study of Richtmyer–Meshkov instability driven by cylindrical shocks

Qiang Zhang and Mary Jane Graham

Phys. Fluids 10, 974 (1998); http://dx.doi.org/10.1063/1.869624 (19 pages) | Cited 17 times

Full Text: | Download PDF

Show Abstract
As an incident shock wave hits a material interface between two fluids of different densities, the interface becomes unstable. Small disturbances at the interface start to grow. This interfacial instability is known as a Richtmyer–Meshkov (RM) instability. It plays an important role in the studies of inertial confinement fusion and supernova. The majority of studies of the RM instability were in plane geometry—namely, plane shocks in Cartesian coordinates. We present a systematic numerical study of the RM instability driven by cylindrical shocks for both the imploding and exploding cases. The imploding (exploding) case refers to a cylindrical shock colliding with the material interface from the outside in (inside out). The phenomenon of reshock caused by the waves reflected from the origin is also studied. A qualitative understanding of this system has been achieved. Detailed studies of the growth rate of the fingers at the unstable interface are presented. © 1998 American Institute of Physics.
Show PACS
47.20.Ma Interfacial instabilities (e.g., Rayleigh-Taylor)
47.11.-j Computational methods in fluid dynamics

The structure of the compressible reacting mixing layer: Insights from linear stability analysis

M. J. Day, W. C. Reynolds, and N. N. Mansour

Phys. Fluids 10, 993 (1998); http://dx.doi.org/10.1063/1.869619 (15 pages) | Cited 18 times

Full Text: | Download PDF

Show Abstract
Previous investigations have demonstrated that a compressible reacting mixing layer can develop two instability modes in addition to the more common central mode that exists unaccompanied in incompressible nonreacting flows. These two additional modes are termed “outer” because of their association with the fast and slow free streams. Numerical simulations have shown that mixing layers dominated by outer modes have a lower global reaction rate in comparison to a flow structure governed by the central mode. Therefore, the presence of these modes has important consequences for applications in supersonic combustion. Results are presented from a parametric study of the compressible reacting mixing layer’s regime space using linear stability analysis. The focus of our work is to develop a better understanding for the combined effects of compressibility, heat release and the ratios of density, equivalence, and velocity on the instability characteristics of each mode and on the structure predicted to result in a turbulent reacting mixing layer. © 1998 American Institute of Physics.
Show PACS
47.70.Fw Chemically reactive flows
47.40.-x Compressible flows; shock waves
82.33.Vx Reactions in flames, combustion, and explosions
47.20.-k Flow instabilities

Mixing enhancement in compressible shear layers via sub-boundary layer disturbances

T. C. Island, W. D. Urban, and M. G. Mungal

Phys. Fluids 10, 1008 (1998); http://dx.doi.org/10.1063/1.869620 (13 pages) | Cited 8 times

Full Text: | Download PDF

Show Abstract
Mixing enhancement results are presented for compressible (convective Mach number 0.63) planar shear layers perturbed by 2D and 3D disturbances located within the supersonic-side splitter tip boundary layer. The disturbances were parametrically varied in shape, spacing, and thickness, and for each geometry time-resolved end-, side-, and plan-view visualizations of mixed fluid were obtained. The mixing layer thickness and growth rate are measured directly from the averaged images. As an indicator of the pressure loss induced by each disturbance geometry, the streamwise static pressure distribution is also recorded. The visualizations reveal that discrete 3D disturbances induce appreciable spanwise convolution, streamwise structure, and thickening of the mixing layer with disturbances as thin as 5% of the boundary layer displacement thickness. The optimal disturbance appears to have an angle of 30° to the streamwise direction and be located at the splitter tip, rather than upstream. Panoramic side-views show that the far-field growth rate increases (45% in one case) for certain discrete 3D disturbances but not 2D disturbances, despite equivalent area blockage. For the most promising geometry, quantitative measurements of the mixing layer thickness, probability of mixed fluid, and mixing efficiency were made using cold chemistry planar laser-induced fluorescence. The perturbed layer shows a slight improvement (7%) in mixing efficiency and a large increase (48%) in layer thickness, indicating that gains in the total amount of mixed fluid occur primarily by layer thickening. © 1998 American Institute of Physics.
Show PACS
47.40.Ki Supersonic and hypersonic flows
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.27.nb Boundary layer turbulence
47.80.-v Instrumentation and measurement methods in fluid dynamics

Nonlinear Poiseuille flow in a gas

Mohamed Tij, Mohamed Sabbane, and Andrés Santos

Phys. Fluids 10, 1021 (1998); http://dx.doi.org/10.1063/1.869621 (7 pages) | Cited 12 times

Full Text: | Download PDF

Show Abstract
The nonlinear Boltzmann equation for the steady planar Poiseuille flow generated by an external field g is exactly solved through order g2. It is shown that the pressure and temperature profiles, as well as the momentum and heat fluxes, are in qualitative disagreement with the Navier–Stokes predictions. For instance, the temperature has a local minimum at the middle layer instead of a maximum. Also, a longitudinal component of the heat flux exists in the absence of gradients along that direction and normal stress differences appear although the flow is incompressible. To account for these g2-order effects, which are relevant when the hydrodynamic quantities change over a characteristic length of the order of the mean free path, it is shown that the Chapman–Enskog expansion should be carried out three steps beyond the Navier–Stokes level. © 1998 American Institute of Physics.
Show PACS
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.27.T- Turbulent transport processes
47.10.-g General theory in fluid dynamics
51.10.+y Kinetic and transport theory of gases
Page 1 of 2 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Discontinuous behavior of liquids between parallel and tilted plates
  2. Dynamics of spontaneous spreading with evaporation on a deep fluid layer
  3. Transport processes in random arrays of cylinders. I. Thermal conduction
  4. A nonlocal theory for the heat transport in composites containing highly conducting fibrous inclusions
  5. The effect of hydrodynamic interactions on the orientation of axisymmetric particles flowing through a fixed bed of spheres or fibers
Go to AIP Home
Copyright © American Institute of Physics
close