scholarly journals On the convective nature of roll waves instability

2005 ◽  
Vol 2005 (3) ◽  
pp. 259-271 ◽  
Author(s):  
C. Di Cristo ◽  
A. Vacca
Keyword(s):  
Flow Model ◽  
Theoretical Foundation ◽  
Wave Number ◽  
Branch Points ◽  
Periodic Disturbance ◽  
One Dimensional ◽  
Dimensional Flow ◽  
Roll Waves ◽  
The One ◽  
Time Periodic

A theoretical analysis of the Saint-Venant one-dimensional flow model is performed in order to define the nature of its instability. Following the Brigg criterion, the investigation is carried out by examining the branch points singularities of dispersion relation in the complexωandkplanes, whereωandkare the complex pulsation and wave number of the disturbance, respectively. The nature of the linearly unstable conditions of flow is shown to be of convective type, independently of the Froude number value. Starting from this result a linear spatial stability analysis of the one-dimensional flow model is performed, in terms of time asymptotic response to a pointwise time periodic disturbance. The study reveals an influence of the disturbance frequency on the perturbation spatial growth rate, which constitutes the theoretical foundation of semiempirical criteria commonly employed for predicting roll waves occurrence.

An Evaluation of the Average Flow Model [1] for Surface Roughness Effects in Lubrication

1980 ◽  
Vol 102 (3) ◽  
pp. 360-366 ◽  
Author(s):  
J. L. Teale ◽  
A. O. Lebeck
Keyword(s):  
Surface Roughness ◽  
Flow Model ◽  
Two Dimensional ◽  
Roughness Effects ◽  
Important Conclusion ◽  
Average Flow ◽  
One Dimensional ◽  
Dimensional Flow ◽  
Two Dimensional Flow ◽  
Average Flow Model

The average flow model presented by Patir and Cheng [1] is evaluated. First, it is shown that the choice of grid used in the average flow model influences the results. The results presented are different from those given by Patir and Cheng. Second, it is shown that the introduction of two-dimensional flow greatly reduces the effect of roughness on flow. Results based on one-dimensional flow cannot be relied upon for two-dimensional problems. Finally, some average flow factors are given for truncated rough surfaces. These can be applied to partially worn surfaces. The most important conclusion reached is that an even closer examination of the average flow concept is needed before the results can be applied with confidence to lubrication problems.

Numerical Simulation of Supersonic Combustion in Quasi One-Dimensional Flow

1991 ◽  
Author(s):  
T. Gary Yip
Keyword(s):  
Flow Model ◽  
Cone Angle ◽  
Initial Pressure ◽  
Supersonic Combustion ◽  
Propulsion Systems ◽  
One Dimensional ◽  
Hypersonic Propulsion ◽  
Dimensional Flow ◽  
Conical Shock ◽  
Shock System

Abstract Supersonic combustion induced by a two-shock system has been studied using a chemical nonequilibrium, quasi one-dimensional flow model. The combustion of stoichiometric, premixed H2-air is described by a chemistry model which consists of 11 species and 28 reactions. The freestream Mach numbers used in this calculations are 8, 10 and 12. The initial pressure is 0.01 atm and temperature 300 K. The first of the two shocks is a conical shock and the second is its reflection. Supersonic combustion has been predicted to occur at combustor pressures between 0.8 and 2.9 atmospheres, and temperatures between 1500 and 3000 K. The Mach number of the flow in the combustor is between 1.7 and 4. These combustor conditions are typical of the future hypersonic propulsion systems. The results also show the changes in the composition of the flow during the induction and heat release phases. The two-shock system is assumed to be generated by a cone. For Mach 8, 10 and 12, the minimum cone angle for generating a strong enough two-shock system to induce supersonic combustion has also been identified.

Modeling of Wall Friction for Multispecies Solid-Gas Flows

1986 ◽  
Vol 108 (4) ◽  
pp. 486-488 ◽  
Author(s):  
E. D. Doss ◽  
M. G. Srinivasan
Keyword(s):  
Shear Stress ◽  
Flow Model ◽  
Flow Characteristics ◽  
Wall Friction ◽  
Gas Flows ◽  
Two Phase ◽  
One Dimensional ◽  
Friction Models ◽  
Wall Interaction ◽  
The One

The empirical expressions for the equivalent friction factor to simulate the effect of particle-wall interaction with a single solid species have been extended to model the wall shear stress for multispecies solid-gas flows. Expressions representing the equivalent shear stress for solid-gas flows obtained from these wall friction models are included in the one-dimensional two-phase flow model and it can be used to study the effect of particle-wall interaction on the flow characteristics.

scholarly journals Impact of Energy Slope Averaging Methods on Numerical Solution of 1D Steady Gradually Varied Flow

2015 ◽  
Vol 62 (3-4) ◽  
pp. 101-119 ◽  
Author(s):  
Wojciech Artichowicz ◽  
Dzmitry Prybytak
Keyword(s):  
Numerical Methods ◽  
Numerical Solution ◽  
Numerical Integration ◽  
Cross Sections ◽  
Flow Model ◽  
One Dimensional ◽  
Averaging Methods ◽  
Integration Formulas ◽  
Different Types ◽  
The One

AbstractIn this paper, energy slope averaging in the one-dimensional steady gradually varied flow model is considered. For this purpose, different methods of averaging the energy slope between cross-sections are used. The most popular are arithmetic, geometric, harmonic and hydraulic means. However, from the formal viewpoint, the application of different averaging formulas results in different numerical integration formulas. This study examines the basic properties of numerical methods resulting from different types of averaging.

scholarly journals Predicted response of the calving glacier Svartisheibreen, Norway, and outbursts from it, to future changes in climate and lake level

1997 ◽  
Vol 24 ◽  
pp. 16-20 ◽  
Author(s):  
Michael Kennett ◽  
Tron Laumann ◽  
Bjarne Kjøllmoen
Keyword(s):  
Mass Balance ◽  
Lake Level ◽  
Flow Model ◽  
Peak Discharge ◽  
Northern Norway ◽  
One Dimensional ◽  
Dimensional Flow ◽  
Glacier Front

The Svartisheibreen glacier in northern Norway has been investigated since 1988 in connection with a proposed hydropower scheme. The scheme includes regulation of the lake into which the glacier calves. A one-dimensional flow model has been used to estimate the response of the glacier to changes in mass balance and lake level. The model predicts that a net balance, excluding calving, of 0 m a−1 will cause the glacier to retreat approximately 400 m over 50 years if lake level is maintained at 774 m a.s.l., but that the glacier front will not move significantly if lake level is lowered to 720 m a.s.l. In 1989 and 1991, lake outbursts occurred beneath the glacier. The 1991 outburst was monitored, and culminated in a peak discharge of only 3.5 m3 s−1, much less than for other reported outbursts. This outburst can be explained in a model in which the outburst tunnel passes over a subglacial threshold approximately 70 m behind the 1991 calving front. The model shows that outbursts will probably increase dramatically in size if the front retreats beyond this threshold.

scholarly journals The Effect of the Flow Distribution on the Thermal Efficiency of a Solar Collector

1986 ◽  
Vol 39 (6) ◽  
pp. 945 ◽  
Author(s):  
MJ O'Keefe ◽  
JLA Francey
Keyword(s):  
Flat Plate ◽  
Thermal Efficiency ◽  
Solar Collector ◽  
Flow Model ◽  
Flow Distribution ◽  
Isothermal Flow ◽  
One Dimensional ◽  
Dimensional Flow ◽  
Uniform Flow Distribution ◽  
Flat Plate Solar Collector

An isothermal one-dimensional flow model is used to calculate the flow distribution across the manifold of a flat plate solar collector in order to quantify the effect of a non-uniform flow distribution on the thermal efficiency for a variety of manifold geometries. The predictions of this flow model are found to compare favourably with measured isothermal flow distributions.

Verification of a One-Dimensional Two-Phase Flow Model of the Frontal Gap in Electrochemical Machining

1976 ◽  
Vol 98 (2) ◽  
pp. 431-437 ◽  
Author(s):  
F. Fluerenbrock ◽  
R. D. Zerkle ◽  
J. F. Thorpe
Keyword(s):  
Flow Model ◽  
Radial Flow ◽  
Electrochemical Machining ◽  
Equilibrium Conditions ◽  
Two Phase ◽  
One Dimensional ◽  
Supply Pressure ◽  
Theoretical Predictions ◽  
The One ◽  
Experimental Pressure

A set of six equations, which are based on the ECM model developed by Thorpe and Zerkle, can be solved numerically to yield the one-dimensional distributions of pressure, temperature, gas density, gap thickness, void fraction, and electrolyte velocity in the rectilinear ECM frontal gap under equilibrium conditions. The validity of the model, which also applies to radial flow geometries, is confirmed by comparing experimental pressure and gap profiles with theoretical predictions. It is shown that for a given set of operating parameters there is a minimum supply pressure below which no machining is possible. When machining steel with an aqueous NaCl electrolyte the deposition of a black smut (Fe(OH)2) occurs beyond a certain smut-free entrance length, which was experimentally found to be proportional to the inlet gap thickness.

Sign in / Sign up

Export Citation Format

Share Document