Numerical Simulation of Oscillations in a Continuous Optical Discharge

1987 ◽  
Vol 11 (4) ◽  
pp. 201-214
Author(s):  
A.H. Makomaski
Keyword(s):  
Numerical Simulation ◽  
Thermal Wave ◽  
Room Temperature ◽  
Quantitative Agreement ◽  
Oscillatory Behaviour ◽  
Optical Discharge ◽  
Laminar Boundary Layers ◽  
Aerodynamic Instability ◽  
Tollmien Schlichting ◽  
Continuous Optical Discharge

A numerical method based on the assumptions of Forester and Emery is used to study the oscillatory behaviour of the plume and of the thermal wave associated with a point plasma, sustained by continuous optical discharge of a c.w. laser. Computations are carried out to simulate conditions in argon at 4 atm and initially at room temperature. The numerical results explain or confirm many experimental features and generally quantitative agreement with experiment is good. Application of Kimura’s stability theory to the plume suggests aerodynamic instability as the origin of the oscillations. As for flames, these oscillations are associated with waves analogous to the Tollmien-Schlichting waves in laminar boundary layers.

Theoretical model for a continuous optical discharge

Physica B+C ◽  
1982 ◽  
Vol 112 (2) ◽  
pp. 259-270 ◽  
Author(s):  
S. Müller ◽  
J. Uhlenbusch
Keyword(s):  
Theoretical Model ◽  
Optical Discharge ◽  
Continuous Optical Discharge

scholarly journals Linear stability of boundary layers under solitary waves

2014 ◽  
Vol 761 ◽  
pp. 62-104 ◽  
Author(s):  
Joris C. G. Verschaeve ◽  
Geir K. Pedersen
Keyword(s):  
Linear Stability ◽  
Solitary Waves ◽  
Reynolds Numbers ◽  
Quantitative Agreement ◽  
Linear Instability ◽  
Navier Stokes ◽  
Acceleration Region ◽  
Critical Reynolds Numbers ◽  
Tollmien Schlichting ◽  
The Stability

AbstractIn the present treatise, the stability of the boundary layer under solitary waves is analysed by means of the parabolized stability equation. We investigate both surface solitary waves and internal solitary waves. The main result is that the stability of the flow is not of parametric nature as has been assumed in the literature so far. Not only does linear stability analysis highlight this misunderstanding, it also gives an explanation why Sumer et al. (J. Fluid Mech., vol. 646, 2010, pp. 207–231), Vittori & Blondeaux (Coastal Engng, vol. 58, 2011, pp. 206–213) and Ozdemir et al. (J. Fluid Mech., vol. 731, 2013, pp. 545–578) each obtained different critical Reynolds numbers in their experiments and simulations. We find that linear instability is possible in the acceleration region of the flow, leading to the question of how this relates to the observation of transition in the acceleration region in the experiments by Sumer et al. or to the conjecture of a nonlinear instability mechanism in this region by Ozdemir et al. The key concept for assessment of instabilities is the integrated amplification which has not been employed for this kind of flow before. In addition, the present analysis is not based on a uniformization of the flow but instead uses a fully nonlinear description including non-parallel effects, weakly or fully. This allows for an analysis of the sensitivity with respect to these effects. Thanks to this thorough analysis, quantitative agreement between model results and direct numerical simulation has been obtained for the problem in question. The use of a high-order accurate Navier–Stokes solver is primordial in order to obtain agreement for the accumulated amplifications of the Tollmien–Schlichting waves as revealed in this analysis. An elaborate discussion on the effects of amplitudes and water depths on the stability of the flow is presented.

scholarly journals Numerical Simulation of the Solar Granulation

1980 ◽  
Vol 58 ◽  
pp. 293-299
Author(s):  
Lawrence D. Cloutman
Keyword(s):  
Numerical Simulation ◽  
Numerical Solution ◽  
Stokes Equations ◽  
Solar Physics ◽  
Quantitative Agreement ◽  
Time Dependent ◽  
Navier Stokes ◽  
Vortex Rings ◽  
Solar Granulation ◽  
Navier Stokes Equations

AbstractThe solar granulation has been simulated by numerical solution of the multidimensional, time-dependent, nonlinear Navier-Stokes equations applied to the solar atmosphere. Granules may be explained as buoyantly rising bubbles created at the level where T = 8000 K, and which have collapsed into vortex rings. The calculation is in quantitative agreement with observations and has a number of implications for solar physics and convection theory.

scholarly journals Predicting delayed instabilities in viscoelastic solids

2020 ◽  
Vol 6 (36) ◽  
pp. eabb2948
Author(s):  
Erez Y. Urbach ◽  
Efi Efrati
Keyword(s):  
Numerical Simulation ◽  
Predictive Power ◽  
Quantitative Agreement ◽  
Viscoelastic Solids ◽  
Predictive Tools ◽  
Viscoelastic Structure ◽  
The Stability ◽  
Elastic Strains

Determining the stability of a viscoelastic structure is a difficult task. Seemingly stable conformations of viscoelastic structures may gradually creep until their stability is lost, while a discernible creeping in viscoelastic solids does not necessarily lead to instability. In lieu of theoretical predictive tools for viscoelastic instabilities, we are presently limited to numerical simulation to predict future stability. In this work, we describe viscoelastic solids through a temporally evolving instantaneous reference metric with respect to which elastic strains are measured. We show that for incompressible viscoelastic solids, this transparent and intuitive description allows to reduce the question of future stability to static calculations. We demonstrate the predictive power of the approach by elucidating the subtle mechanism of delayed instability in thin elastomeric shells, showing quantitative agreement with experiments.

A new interpretation of the Acidic and Basic structures in Carbons. II. The Chromene-carbonium ion couple in Carbon

1957 ◽  
Vol 10 (3) ◽  
pp. 309 ◽  
Author(s):  
VA Garten ◽  
DE Weiss ◽  
JB Willis
Keyword(s):  
Ferrous Iron ◽  
Room Temperature ◽  
Electrochemical Behaviour ◽  
Quantitative Agreement ◽  
Theoretical Interpretation ◽  
Carbon Electrode ◽  
Partial Pressure Of Oxygen ◽  
Carbonium Ion ◽  
Observed Behaviour ◽  
New Interpretation

The conflicting views of Frumkin, Shilov, and Steenberg on the chemical and adsorptive behaviour of sugar carbons activated at 800 �C (H-carbons) can be reconciled by postulating that the carbons contain chromene structures. The same is true of certain carbon blacks. The chromene system is readily oxidized at room temperature in the presence of acid to the corresponding benzopyrylium (carbonium) system, with the adsorption of the anion of the acid and the liberation of hydrogen peroxide. This reaction accounts for the dependence on the partial pressure of oxygen of adsorption of acid from dilute solutions, for the formation of peroxide from carbon with acids, and for the linear relationship between the potential of an H-carbon electrode and pH. A theoretical interpretation of the electrochemical behaviour of the chromene-carbonium ion couple is in good quantitative agreement with the observed behaviour of a cathodically polarized carbon electrode in acid solution. The ability of H-carbons to catalyse the oxidation of ferrous iron by molecular oxygen can also be accounted for by this couple, the concept of which is in agreement with the observed kinetic behaviour of the reaction.

Numerical simulation of the evolution of Tollmien–Schlichting waves over finite compliant panels

1997 ◽  
Vol 335 ◽  
pp. 361-392 ◽  
Author(s):  
CHRISTOPHER DAVIES ◽  
PETER W. CARPENTER
Keyword(s):  
Numerical Simulation ◽  
Laminar Flow ◽  
Stokes Equations ◽  
Plane Channel ◽  
Solution Procedure ◽  
Good Prospect ◽  
Flow Perturbation ◽  
Compliant Wall ◽  
Compliant Walls ◽  
Tollmien Schlichting

The evolution of two-dimensional Tollmien–Schlichting waves propagating along a wall shear layer as it passes over a compliant panel of finite length is investigated by means of numerical simulation. It is shown that the interaction of such waves with the edges of the panel can lead to complex patterns of behaviour. The behaviour of the Tollmien–Schlichting waves in this situation, particularly the effect on their growth rate, is pertinent to the practical application of compliant walls for the delay of laminar–turbulent transition. If compliant panels could be made sufficiently short whilst retaining the capability to stabilize Tollmien–Schlichting waves, there is a good prospect that multiple-panel compliant walls could be used to maintain laminar flow at indefinitely high Reynolds numbers.We consider a model problem whereby a section of a plane channel is replaced with a compliant panel. A growing Tollmien–Schlichting wave is then introduced into the plane, rigid-walled, channel flow upstream of the compliant panel. The results obtained are very encouraging from the viewpoint of laminar-flow control. They indicate that compliant panels as short as a single Tollmien–Schlichting wavelength can have a strong stabilizing effect. In some cases the passage of the Tollmien–Schlichting wave over the panel edges leads to the excitation of stable flow-induced surface waves. The presence of these additional waves does not appear to be associated with any adverse effect on the stability of the Tollmien–Schlichting waves. Except very near the panel edges the panel response and flow perturbation can be represented by a superposition of the Tollmien–Schlichting wave and two other eigenmodes of the coupled Orr–Sommerfeld/compliant-wall eigensystem.The numerical scheme employed for the simulations is derived from a novel vorticity–velocity formulation of the linearized Navier–Stokes equations and uses a mixed finite-difference/spectral spatial discretization. This approach facilitated the development of a highly efficient solution procedure. Problems with numerical stability were overcome by combining the inertias of the compliant wall and fluid when imposing the boundary conditions. This allowed the interactively coupled fluid and wall motions to be computed without any prior restriction on the form taken by the disturbances.

Experimental and theoretical investigation of laser rocket engine characteristics based on a continuous optical discharge

2010 ◽  
Vol 53 (4) ◽  
pp. 427-435 ◽  
Author(s):  
A. F. Dregalin ◽  
A. S. Cherenkov ◽  
A. G. Sattarov ◽  
A. R. Bikmuchev ◽  
S. N. Pislegin
Keyword(s):  
Theoretical Investigation ◽  
Rocket Engine ◽  
Optical Discharge ◽  
Continuous Optical Discharge
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