The role of secondary instabilities in the stabilization of a nonpremixed lifted jet flame

2001 ◽  
Vol 13 (9) ◽  
pp. 2662-2670 ◽  
Author(s):  
David Demare ◽  
Françoise Baillot
Keyword(s):  
Jet Flame ◽  
Secondary Instabilities

Equilibrium transport in double-diffusive convection

2011 ◽  
Vol 692 ◽  
pp. 5-27 ◽  
Author(s):  
Timour Radko ◽  
D. Paul Smith
Keyword(s):  
Linear Growth ◽  
Density Ratio ◽  
Molecular Characteristics ◽  
Diffusive Transport ◽  
Salt Fingers ◽  
Diffusive Convection ◽  
Wide Range ◽  
Secondary Instabilities ◽  
Double Diffusive

AbstractA theoretical model for the equilibrium double-diffusive transport is presented which emphasizes the role of secondary instabilities of salt fingers in saturation of their linear growth. Theory assumes that the fully developed equilibrium state is characterized by the comparable growth rates of primary and secondary instabilities. This assumption makes it possible to formulate an efficient algorithm for computing diffusivities of heat and salt as a function of the background property gradients and molecular parameters. The model predicts that the double-diffusive transport of heat and salt rapidly intensifies with decreasing density ratio. Fluxes are less sensitive to molecular characteristics, mildly increasing with Prandtl number $(\mathit{Pr})$ and decreasing with diffusivity ratio $(\tau )$. Theory is successfully tested by a series of direct numerical simulations which span a wide range of $\mathit{Pr}$ and $\tau $.

Surface quasi-geostrophic dynamics

1995 ◽  
Vol 282 ◽  
pp. 1-20 ◽  
Author(s):  
Isaac M. Held ◽  
Raymond T. Pierrehumbert ◽  
Stephen T. Garner ◽  
Kyle L. Swanson
Keyword(s):  
Potential Temperature ◽  
Edge Wave ◽  
Distinctive Features ◽  
Wave Characteristics ◽  
Inverse Energy Cascade ◽  
System A ◽  
Start Up ◽  
Two Dimensional Flow ◽  
Secondary Instabilities

The dynamics of quasi-geostrophic flow with uniform potential vorticity reduces to the evolution of buoyancy, or potential temperature, on horizontal boundaries. There is a formal resemblance to two-dimensional flow, with surface temperature playing the role of vorticity, but a different relationship between the flow and the advected scalar creates several distinctive features. A series of examples are described which highlight some of these features: the evolution of an elliptical vortex; the start-up vortex shed by flow over a mountain; the instability of temperature filaments; the ‘edge wave’ critical layer; and mixing in an overturning edge wave. Characteristics of the direct cascade of the tracer variance to small scales in homogeneous turbulence, as well as the inverse energy cascade, are also described. In addition to its geophysical relevance, the ubiquitous generation of secondary instabilities and the possibility of finite-time collapse make this system a potentially important, numerically tractable, testbed for turbulence theories.

scholarly journals Nonlinear saturation of Rayleigh-Taylor instability and generation of shear flow in equatorial spread-F plasma

2001 ◽  
Vol 8 (3) ◽  
pp. 181-190
Author(s):  
N. Chakrabarti ◽  
G. S. Lakhina
Keyword(s):  
Shear Flow ◽  
Mode Coupling ◽  
Nonlinear Behaviour ◽  
Coupling Equations ◽  
Spread F ◽  
Rayleigh Taylor Instability ◽  
Secondary Instabilities ◽  
Rt Instability ◽  
Collisional Regime

Abstract. An analysis of low order mode coupling equations is used to describe the nonlinear behaviour of the Rayleigh-Taylor (RT) instability in the equatorial ionosphere. The nonlinear evolution of RT instability leads to the development of shear flow. It is found that there is an interplay between the nonlinearity and the shear flow which compete with each other and saturate the RT mode, both in the collisionless and collisional regime. However, the nonlinearly saturated state, normally known as vortices or bubbles, may not be stable. Under certain condition these bubbles are shown to be unstable to short scale secondary instabilities that are driven by the large gradients which develop within these structures. Some understanding of the role of collisional nonlinearity in the  shear flow generations is also discussed.

Symmetry, sidewalls, and the transition to chaos in baroclinic systems

1995 ◽  
Vol 300 ◽  
pp. 311-338 ◽  
Author(s):  
Michael D. Mundt ◽  
John E. Hart ◽  
Daniel R. Ohlsen
Keyword(s):  
Plane Channel ◽  
Cylinder Wall ◽  
Horizontal Shear ◽  
Onset Of Chaos ◽  
Spatial Modes ◽  
Route To Chaos ◽  
Baroclinic Flow ◽  
Secondary Instabilities ◽  
Rectilinear Channel

A high-resolution, quasi-geostrophic numerical model is utilized to examine two-layer baroclinic flow in a cylinder. Particular attention is given to the role of horizontal shear of the basic state induced by viscosity near the cylinder wall, and to the desymmetrization brought about by the cylindrical geometry, in the transition to baroclinic chaos. Solutions are computed for both f-plane and β-plane situations, and the results are compared to previous laboratory experiments. Agreement in the former case is found to be good, although the onset of chaos occurs at slightly lower forcing in the laboratory when its basic flow is prograde, and at higher forcing amplitude when the experimental basic azimuthal currents are retrograde. This suggests that the modest discrepancies may be attributable to computationally neglected ageostrophic effects in the interior fluid and Ekman boundary layers. When β ≠ 0, the numerical and laboratory results are in excellent agreement. The computational simulations indicate that the viscous sidewall boundary layer plays a pivotal role in the dynamics. Moreover, in contrast to previous studies performed in a periodic, rectilinear channel, the route to chaos is largely temporal and involves relatively few spatial modes. The reduction in symmetries upon going from f-plane channel to either f-plane or β-plane cylinder models leads to fewer secondary instabilities and fewer spatial modes that are active in the dynamics.

Blowout Limits of a Jet Diffusion Flame in the Presence of Small Surrounding Jet Pilot Flames

1996 ◽  
Vol 118 (2) ◽  
pp. 140-144
Author(s):  
M. G. Kibrya ◽  
G. A. Karim
Keyword(s):  
Flow Rate ◽  
Diffusion Flame ◽  
Operating Parameters ◽  
Jet Flames ◽  
Jet Flame ◽  
Flowing Stream

The blowout limit of a methane jet diffusion flame is examined in the presence of a number of much smaller pilot jet flames of different fuels arranged within an experimental burner assembly in a co-flowing stream of air. It is shown that the blowout limit of the central jet flame can be extended very appreciably by increasing the flow rate through the smaller pilot jets. The basis for this extension to the blowout limit and the role of some changes in the operating parameters are discussed. It is suggested that the extension to the blowout limit observed is due mainly to the thermal contribution of the pilot jet flames.

Role of dactinomycin in the improved survival of children with Wilms' tumor

JAMA ◽  
1966 ◽  
Vol 195 (12) ◽  
pp. 1005-1009 ◽  
Author(s):  
D. J. Fernbach
Keyword(s):  
Wilms Tumor

Role of the allergist in diagnosis and management of patients with uveitis

JAMA ◽  
1966 ◽  
Vol 195 (3) ◽  
pp. 167-172 ◽  
Author(s):  
T. E. Van Metre
Keyword(s):  
Diagnosis And Management
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