scholarly journals Inlet effects on roll-wave development in shallow turbulent open-channel flows

2016 ◽  
Vol 64 (1) ◽  
pp. 45-55 ◽  
Author(s):  
Francesca Campomaggiore ◽  
Cristiana Di Cristo ◽  
Michele Iervolino ◽  
Andrea Vacca
Keyword(s):  
Statistical Characteristics ◽  
Finite Volume Scheme ◽  
Flow Profile ◽  
Spatial Evolution ◽  
Inlet Condition ◽  
Spatial Growth ◽  
Roll Waves ◽  
Saint Venant Equations ◽  
Wave Development ◽  
Wave Trains

Abstract The present work investigates the effect of the flow profile induced by an inlet condition on the roll-wave evolution in turbulent clear-water flows. The study employs theoretical and numerical analyses. Firstly, the influence of the inlet condition on the spatial evolution of a single perturbation in a hypercritical flow is examined through the expansion near a wavefront analysis. The results show that an accelerated unperturbed profile reduces the disturbance spatial growth. A decelerated profile causes an increase. The effect of the flow profile on the spatial evolution of roll-wave trains is then numerically investigated solving the Saint Venant equations with a second-order Runge-Kutta Total Variation Diminishing (TVD) Finite Volume scheme. The numerical simulations comply with the analytical results for the initial and transition phases of the roll-wave development. The unperturbed profile influences even the roll-waves statistical characteristics in the final stage, with a more evident effect in case of accelerated profiles. The influence of the flow profile should be therefore accounted for in the formulation of predictive criteria for roll-waves appearance based on the estimation of the disturbance spatial growth rate.

A dynamical systems view of granular flow: from monoclinal flood waves to roll waves

2019 ◽  
Vol 869 ◽  
pp. 143-181
Author(s):  
Dimitrios Razis ◽  
Giorgos Kanellopoulos ◽  
Ko van der Weele
Keyword(s):  
Granular Flow ◽  
Granular Matter ◽  
Uniform Flow ◽  
Constant Thickness ◽  
Undular Bore ◽  
Formula One ◽  
Chute Flow ◽  
Roll Waves ◽  
Saint Venant Equations ◽  
Systems View

On the basis of the Saint-Venant equations for flowing granular matter, we study the various travelling waveforms that are encountered in chute flow for growing Froude number. Generally, for $Fr<2/3$ one finds either a uniform flow of constant thickness or a monoclinal flood wave, i.e. a shock structure monotonically connecting a thick region upstream to a shallower region downstream. For $Fr>2/3$ both the uniform flow and the monoclinal wave cease to be stable; the flow now organizes itself in the form of a train of roll waves. From the governing Saint-Venant equations we derive a dynamical system that elucidates the transition from monoclinal waves to roll waves. It is found that this transition involves several intermediate stages, including an undular bore that had hitherto not been reported for granular flows.

scholarly journals ROLL-WAVES IN BI-LAYER FLOWS

2012 ◽  
Vol 22 (06) ◽  
pp. 1250006 ◽  
Author(s):  
MARC BOUTOUNET ◽  
PASCAL NOBLE ◽  
JEAN-PAUL VILA
Keyword(s):  
Spectral Analysis ◽  
Shallow Water ◽  
Shallow Water Equations ◽  
Low Frequency ◽  
Newtonian Fluids ◽  
Hydrodynamic Instabilities ◽  
Steady Flows ◽  
Long Wavelength ◽  
Roll Waves ◽  
Saint Venant Equations

We derive consistent shallow water equations (so-called Saint Venant equations) for the superposition of two Newtonian fluids flowing down a ramp. We carry out a complete spectral analysis of steady flows in the low frequency/long wavelength regime and show the occurrence of hydrodynamic instabilities, so-called roll-waves, when steady flows are unstable.

scholarly journals On the applicability of minimum channel length criterion for roll-waves in mud-flows

2013 ◽  
Vol 61 (4) ◽  
pp. 286-292 ◽  
Author(s):  
Cristiana Di Cristo ◽  
Michele Iervolino ◽  
Andrea Vacca
Keyword(s):  
Flow Model ◽  
Laboratory Data ◽  
Channel Length ◽  
Clear Water ◽  
Spatial Growth ◽  
Roll Waves

Abstract The paper addresses the prediction of roll-waves occurrence in mud-flows. The spatial growth of a point-wise disturbance is analytically described, based on the linearized flow model of a Herschel and Bulkley fluid, in the neighborhood of an initial uniform base condition. The theoretical achievements allow to generalize to mud-flows the minimum channel criterion commonly used for the prediction of roll-waves in clear-water. The applicability of the criterion is discussed through the comparison with literature laboratory data concerning unstable flows without rollwaves.

scholarly journals NOTES ON THE GENERATION AND GROWTH OF OCEAN WAVES UNDER WIND ACTION

2000 ◽  
Vol 1 (3) ◽  
pp. 7
Author(s):  
Gerhard Neumann
Keyword(s):  
Energy Dissipation ◽  
Energy Supply ◽  
Basic Problem ◽  
Ocean Waves ◽  
Wind Action ◽  
Wave Development ◽  
Component Wave ◽  
Wave Trains ◽  
Physical Laws ◽  
The Waves

The basic problem of forecasting wind-generated waves is the development of equations which express the energy budget between wind and waves, and the derivation of physical laws governing the growth of the component wave trains. The waves can grow only in the case where the supply of energy by wind exceeds the loss of energy by friction and turbulence. Thus any attempt to calculate the growth of ocean waves under wind action requires a knowledge of the energy supply and the energy dissipation in every phase of wave development.

Influence of Relative Roughness and Reynolds Number on the Roll-Waves Spatial Evolution

2010 ◽  
Vol 136 (1) ◽  
pp. 24-33 ◽  
Author(s):  
Cristiana Di Cristo ◽  
Michele Iervolino ◽  
Andrea Vacca ◽  
Barbara Zanuttigh
Keyword(s):  
Reynolds Number ◽  
Spatial Evolution ◽  
Relative Roughness ◽  
Roll Waves

Space and Time Distribution of Hard X-Ray Emission in a Loop at the Beginning of a Flare

1994 ◽  
Vol 144 ◽  
pp. 275-277
Author(s):  
M. Karlický ◽  
J. C. Hénoux
Keyword(s):  
Time Distribution ◽  
Electron Bombardment ◽  
Spatial Evolution ◽  
Superthermal Electrons ◽  
Flare Loop ◽  
X Ray ◽  
Superthermal Electron ◽  
Flare Loops ◽  
Chromospheric Evaporation ◽  
Temporal And Spatial

AbstractUsing a new ID hybrid model of the electron bombardment in flare loops, we study not only the evolution of densities, plasma velocities and temperatures in the loop, but also the temporal and spatial evolution of hard X-ray emission. In the present paper a continuous bombardment by electrons isotropically accelerated at the top of flare loop with a power-law injection distribution function is considered. The computations include the effects of the return-current that reduces significantly the depth of the chromospheric layer which is evaporated. The present modelling is made with superthermal electron parameters corresponding to the classical resistivity regime for an input energy flux of superthermal electrons of 109erg cm−2s−1. It was found that due to the electron bombardment the two chromospheric evaporation waves are generated at both feet of the loop and they propagate up to the top, where they collide and cause temporary density and hard X-ray enhancements.

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