Stratified flows and associated shear instabilities modelling over an inclined plan

2020 ◽  
Vol 136 ◽  
pp. 169-181
Author(s):  
Raphael R.C. Santos ◽  
Sávio S.V. Vianna
Keyword(s):  
Stratified Flows ◽  
Shear Instabilities

Mathematical modeling of steady stratified flows

2003 ◽  
Vol 3 ◽  
pp. 195-207
Author(s):  
A.M. Ilyasov ◽  
V.N. Kireev ◽  
S.F. Urmancheev ◽  
I.Sh. Akhatov
Keyword(s):  
Stokes Equations ◽  
Approximate Model ◽  
Immiscible Liquid ◽  
Stratified Flows ◽  
Navier Stokes ◽  
Flat Channel ◽  
Navier Stokes Equations ◽  
Two Fluids ◽  
Flow Parameters ◽  
Direct Numerical Solution

The work is devoted to the analysis of the flow of immiscible liquid in a flat channel and the creation of calculation schemes for determining the flow parameters. A critical analysis of the well-known Two Fluids Model was carried out and a new scheme for the determination of wall and interfacial friction, called the hydraulic approximation in the theory of stratified flows, was proposed. Verification of the proposed approximate model was carried out on the basis of a direct numerical solution of the Navier–Stokes equations for each fluid by a finite-difference method with phase-boundary tracking by the VOF (Volume of Fluid) method. The graphical dependencies illustrating the change in the interfase boundaries of liquids and the averaged over the occupied area of the phase velocities along the flat channel are presented. The results of comparative calculations for two-fluid models are also given, according to the developed model in the hydraulic approximation and direct modeling. It is shown that the calculations in accordance with the hydraulic approximation are more consistent with the simulation results. Thus, the model of hydraulic approximation is the most preferred method for calculating stratified flows, especially in cases of variable volumetric content of liquids.

Instabilities of Jets and Fronts and their Nonlinear Evolution

2018 ◽  
Author(s):  
Vladimir Zeitlin
Keyword(s):  
Nonlinear Evolution ◽  
Baroclinic Instability ◽  
Trapped Modes ◽  
Nonlinear Saturation ◽  
Parallel Flows ◽  
Inertial Instability ◽  
Shear Instabilities ◽  
Linear And Nonlinear ◽  
Flow Configurations ◽  
Characteristic Features

Notions of linear and nonlinear hydrodynamic (in)stability are explained and criteria of instability of plane-parallel flows are presented. Instabilities of jets are investigated by direct pseudospectral collocation method in various flow configurations, starting from the classical barotropic and baroclinic instabilities. Characteristic features of instabilities are displayed, as well as typical patterns of their nonlinear saturation. It is shown that in the Phillips model of Chapter 5, new ageostrophic Rossby–Kelvin and shear instabilities appear at finite Rossby numbers. These instabilities are interpreted in terms of resonances among waves counter-propagating in the flow. It is demonstrated that the classical inertial instability is a specific case of ageostrophic baroclinic instability. At the equator it appears also in the barotropic configuration, and is related to resonances of Yanai waves. The nature of the inertial instability in terms of trapped modes is established. A variety of instabilities of density fronts is displayed.

Latitudinal Shear Instabilities during Type I X‐Ray Bursts

2005 ◽  
Vol 630 (1) ◽  
pp. 441-453 ◽  
Author(s):  
Andrew Cumming
Keyword(s):  
Type I ◽  
X Ray ◽  
Shear Instabilities

scholarly journals Turbulent fluxes of entropy and internal energy in temperature stratified flows

2015 ◽  
Vol 81 (5) ◽  
Author(s):  
I. Rogachevskii ◽  
N. Kleeorin
Keyword(s):  
Mach Number ◽  
Internal Energy ◽  
Turbulent Flux ◽  
Stratified Flows ◽  
Fluid Temperature ◽  
Stratified Turbulence ◽  
Convective Flux ◽  
Low Mach Number ◽  
Linear Approach ◽  
The Mean

We derive equations for the mean entropy and the mean internal energy in low-Mach-number temperature stratified turbulence (i.e. for turbulent convection or stably stratified turbulence), and show that turbulent flux of entropy is given by$\boldsymbol{F}_{s}=\overline{{\it\rho}}\,\overline{\boldsymbol{u}s}$, where$\overline{{\it\rho}}$is the mean fluid density,$s$is fluctuation of entropy and overbars denote averaging over an ensemble of turbulent velocity fields,$\boldsymbol{u}$. We demonstrate that the turbulent flux of entropy is different from the turbulent convective flux,$\boldsymbol{F}_{c}=\overline{T}\,\overline{{\it\rho}}\,\overline{\boldsymbol{u}s}$, of the fluid internal energy, where$\overline{T}$is the mean fluid temperature. This turbulent convective flux is well-known in the astrophysical and geophysical literature, and it cannot be used as a turbulent flux in the equation for the mean entropy. This result is exact for low-Mach-number temperature stratified turbulence and is independent of the model used. We also derive equations for the velocity–entropy correlation,$\overline{\boldsymbol{u}s}$, in the limits of small and large Péclet numbers, using the quasi-linear approach and the spectral${\it\tau}$approximation, respectively. This study is important in view of different applications to astrophysical and geophysical temperature stratified turbulence.

Instabilities developed in stratified flows over pronounced obstacles

2007 ◽  
Vol 386 (2) ◽  
pp. 681-685 ◽  
Author(s):  
J. Varela ◽  
M. Araújo ◽  
I. Bove ◽  
C. Cabeza ◽  
G. Usera ◽  
...  
Keyword(s):  
Stratified Flows

Stratified flows in axially rotating pipes

2018 ◽  
Vol 3 (7) ◽  
Author(s):  
S. Lyu ◽  
S. M. Taghavi
Keyword(s):  
Stratified Flows
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