scholarly journals Early-time free-surface flow driven by a deforming boundary

2015 ◽  
Vol 767 ◽  
pp. 811-841 ◽  
Author(s):  
C. Frederik Brasz ◽  
Craig B. Arnold ◽  
Howard A. Stone ◽  
John R. Lister
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Liquid Layer ◽  
Early Time ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Solid Boundary ◽  
Jet Formation ◽  
Domain Perturbation ◽  
Quiescent Liquid

AbstractWhen a solid boundary deforms rapidly into a quiescent liquid layer, a flow is induced that can lead to jet formation. An asymptotic analytical solution is presented for this flow, driven by a solid boundary deforming with dimensionless vertical velocity $V_{b}(x,t)={\it\epsilon}(1+\cos x)\,f(t)$, where the amplitude ${\it\epsilon}$ is small relative to the wavelength and the time dependence $f(t)$ approaches 0 for large $t$. Initially, the flow is directed outwards from the crest of the deformation and slows with the slowing of the boundary motion. A domain-perturbation method is used to reveal that, when the boundary stops moving, nonlinear interactions with the free surface leave a remnant momentum directed back towards the crest, and this momentum can be a precursor to jet formation. This scenario arises in a laser-induced printing technique in which an expanding blister imparts momentum into a liquid film to form a jet. The analysis provides insight into the physics underlying the interaction between the deforming boundary and free surface, in particular, the dependence of the remnant flow on the thickness of the liquid layer and the deformation amplitude and wavelength. Numerical simulations are used to show the range of validity of the analytical results, and the domain-perturbation solution is extended to an axisymmetric domain with a Gaussian boundary deformation to compare with previous numerical simulations of blister-actuated laser-induced forward transfer.

scholarly journals Channelized free-surface flow of cohesionless granular avalanches in a chute with shallow lateral curvature

1999 ◽  
Vol 392 ◽  
pp. 73-100 ◽  
Author(s):  
M. WIELAND ◽  
J. M. N. T. GRAY ◽  
K. HUTTER
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Laboratory Experiments ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Smooth Transition ◽  
Lateral Confinement ◽  
Lateral Curvature ◽  
Granular Deposit ◽  
Good Agreement

A series of laboratory experiments and numerical simulations have been performed to investigate the rapid fluid-like flow of a finite mass of granular material down a chute with partial lateral confinement. The chute consists of a section inclined at 40° to the horizontal, which is connected to a plane run-out zone by a smooth transition. The flow is confined on the inclined section by a shallow parabolic cross-slope profile. Photogrammetric techniques have been used to determine the position of the evolving boundary during the flow, and the free-surface height of the stationary granular deposit in the run-out zone. The results of three experiments with different granular materials are presented and shown to be in very good agreement with numerical simulations based on the Savage–Hutter theory for granular avalanches. The basal topography over which the avalanche flows has a strong channelizing effect on the inclined section of the chute. As the avalanche reaches the run-out zone, where the lateral confinement ceases, the head spreads out to give the avalanche a characteristic ‘tadpole’ shape. Sharp gradients in the avalanche thickness and velocity began to develop at the interface between the nose and tail of the avalanche as it came to rest, indicating that a shock wave develops close to the end of the experiments.

Role of rigid boundary on the decay of turbulence generated by passive-grid for free surface flow

2020 ◽  
pp. 095440622094256 ◽  
Author(s):  
Pankaj Kumar Raushan ◽  
Santosh Kumar Singh ◽  
Koustuv Debnath
Keyword(s):  
Free Surface ◽  
Near Field ◽  
Flow Characteristics ◽  
Joint Probability ◽  
Mesh Size ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Solid Boundary ◽  
Joint Probability Distribution ◽  
Rigid Boundary

The present study aims to investigate the flow characteristics of grid-generated turbulence under the consideration of solid boundary in free surface flow. To understand the nature of isotropy and anisotropy in the flow, the turbulent intensity is evaluated at the downstream of the grid for different mesh sizes. The energy spectrums based on the Fast Fourier and marginal Hilbert–Huang transform are presented to understand the decay of energy in the associated spectral frequency domain. It is observed that the peak of energy associated with the Fourier spectrum decreases in the near-field region of the grid with the increase in mesh size of the grid. Further, to characterise the concentrated velocity fluctuations, the paper strives to analyse the joint probability distribution function and the local intermittency measure in the close and far stream of the grid. The autocorrelation functions and the magnitude of integral length scale of the stream-wise fluctuating velocity components are also presented at two different vertical levels from the solid boundary. The normalised Shannon entropy is also evaluated to characterise the degree of the orderness or disorderness in the flow due to the interaction of grid and rigid boundary.

Upstream influence and the form of standing hydraulic jumps in liquid-layer flows on favourable slopes

1995 ◽  
Vol 284 ◽  
pp. 63-96 ◽  
Author(s):  
Robert I. Bowles
Keyword(s):  
Free Surface ◽  
Liquid Layer ◽  
Numerical Solutions ◽  
Free Surface Flow ◽  
Quantitative Agreement ◽  
Surface Flow ◽  
Hydraulic Jumps ◽  
Sloping Surface ◽  
Free Interaction ◽  
Limiting Case

Steady planar flow of a liquid layer over an obstacle is studied for favourable slopes. First, half-plane Poiseuille flow is found to be a non-unique solution on a uniformly sloping surface since eigensolutions exist which are initially exponentially small far upstream. These have their origin in a viscous–inviscid interaction between the retarding action of viscosity and the hydrostatic pressure from the free surface. The cross-stream pressure gradient caused by the curvature of the streamlines also comes into play as the slope increases. As the interaction becomes nonlinear, separation of the liquid layer can occur, of a breakaway type if the slope is sufficiently large. The breakaway represents a hydraulic jump in the sense of a localized relatively short-scaled increase in layer thickness, e.g. far upstream of a large obstacle. The solution properties give predictions for the shape and structure of hydraulic jumps on various slopes. Secondly, the possibility of standing waves downstream of the jump is addressed for various slope magnitudes. A limiting case of small gradient, governed by lubrication theory, allows the downstream boundary condition to be included explicitly. Numerical solutions showing the free-surface flow over an obstacle confirm the analytical conclusions. In addition the predictions are compared with the experimental and computational results of Pritchardet al.(1992), yielding good qualitative and quantitative agreement. The effects of surface tension on the jump are also discussed and in particular the free interaction on small slopes is examined for large Bond numbers.

Measurements of the Free Surface Flow Structure Under an Impinging, Free Liquid Jet

1992 ◽  
Vol 114 (1) ◽  
pp. 79-84 ◽  
Author(s):  
J. Stevens ◽  
B. W. Webb
Keyword(s):  
Free Surface ◽  
Flow Structure ◽  
Liquid Layer ◽  
Free Surface Flow ◽  
Reynolds Numbers ◽  
Surface Flow ◽  
Surface Velocity ◽  
Liquid Jet ◽  
Radial Coordinate ◽  
Measured Velocity

The objective of this research was to characterize the flow structure under an impinging liquid jet striking a flat, normally oriented surface. The approach was the measurement of the free surface velocities of the jet prior to impingement and the surface velocities of the radially spreading liquid layer. A novel laser-Doppler velocimetry technique was used. The LDV system was configured such that the measurement volume would span the time-dependent fluctuations of the free surface, with the surface velocity being measured. The mean and fluctuating components of a single direction of the velocity vector were measured. It was found that the radial liquid layer data collapsed well over the range of jet Reynolds numbers 16,000 < Re < 47,000 if plotted in dimensionless coordinates, where the measured velocity was normalized by the average jet exit velocity and the radial coordinate was normalized by the nozzle diameter. Mean liquid layer depths were inferred from the velocity measurements by assuming a velocity profile across the layer, and were reported. Pre-impingement jet measurements suggest that the flow development is nearly complete two diameters from the nozzle exit.

scholarly journals Gravity-driven granular free-surface flow around a circular cylinder

2013 ◽  
Vol 720 ◽  
pp. 314-337 ◽  
Author(s):  
X. Cui ◽  
J. M. N. T. Gray
Keyword(s):  
Free Surface ◽  
Circular Cylinder ◽  
Numerical Simulations ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Pyroclastic Flows ◽  
Small Scale ◽  
Shallow Water Flows ◽  
Free Region ◽  
Gravity Driven

AbstractSnow avalanches and other hazardous geophysical granular flows, such as debris flows, lahars and pyroclastic flows, often impact on obstacles as they flow down a slope, generating rapid changes in the flow height and velocity in their vicinity. It is important to understand how a granular material flows around such obstacles to improve the design of deflecting and catching dams, and to correctly interpret field observations. In this paper small-scale experiments and numerical simulations are used to investigate the supercritical gravity-driven free-surface flow of a granular avalanche around a circular cylinder. Our experiments show that a very sharp bow shock wave and a stagnation point are generated in front of the cylinder. The shock standoff distance is accurately reproduced by shock-capturing numerical simulations and is approximately equal to the reciprocal of the Froude number, consistent with previous approximate results for shallow-water flows. As the grains move around the cylinder the flow expands and the pressure gradients rapidly accelerate the particles up to supercritical speeds again. The internal pressure is not strong enough to immediately push the grains into the space behind the cylinder and instead a grain-free region, or granular vacuum, forms on the lee side. For moderate upstream Froude numbers and slope inclinations, the granular vacuum closes up rapidly to form a triangular region, but on steeper slopes both experiments and numerical simulations show that the pinch-off distance moves far downstream.

scholarly journals Laminar free-surface flow into a vertical cylinder

1975 ◽  
Vol 3 (1) ◽  
pp. 51-68 ◽  
Author(s):  
Thomas G. Smith ◽  
J.O. Wilkes
Keyword(s):  
Free Surface ◽  
Vertical Cylinder ◽  
Free Surface Flow ◽  
Surface Flow
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