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 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.

Free surface flow over square bars at different Reynolds numbers

2021 ◽  
Author(s):  
Razieh Jalalabadi ◽  
Thorsten Stoesser ◽  
Pablo Ouro ◽  
Qianyu Luo ◽  
Zhihua Xie
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Reynolds Numbers ◽  
Surface Flow

scholarly journals Photogrammetry for Free Surface Flow Velocity Measurement: From Laboratory to Field Measurements

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1675
Author(s):  
Hang Trieu ◽  
Per Bergström ◽  
Mikael Sjödahl ◽  
J. Gunnar I. Hellström ◽  
Patrik Andreasson ◽  
...  
Keyword(s):  
Free Surface ◽  
Particle Tracking ◽  
Field Measurements ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Hydropower Plant ◽  
Surface Velocity ◽  
Camera System ◽  
Particle Tracking Method ◽  
Calibration Methods

This study describes a multi-camera photogrammetric approach to measure the 3D velocity of free surface flow. The properties of the camera system and particle tracking velocimetry (PTV) algorithm were first investigated in a measurement of a laboratory open channel flow to prepare for field measurements. The in situ camera calibration methods corresponding to the two measurement situations were applied to mitigate the instability of the camera mechanism and camera geometry. There are two photogrammetry-based PTV algorithms presented in this study regarding different types of surface particles employed on the water flow. While the first algorithm uses the particle tracking method applied for individual particles, the second algorithm is based on correlation-based particle clustering tracking applied for clusters of small size particles. In the laboratory, reference data are provided by particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The differences in velocities measured by photogrammetry and PIV, photogrammetry and LDV are 0.1% and 3.6%, respectively. At a natural river, the change of discharges between two measurement times is found to be 15%, and the corresponding value reported regarding mass flow through a nearby hydropower plant is 20%. The outcomes reveal that the method can provide a reliable estimation of 3D surface velocity with sufficient accuracy.

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.

scholarly journals Developed liquid film passing a smoothed and wedge-shaped trailing edge: small-scale analysis and the ‘teapot effect’ at large Reynolds numbers

2021 ◽  
Vol 926 ◽  
Author(s):  
B. Scheichl ◽  
R.I. Bowles ◽  
G. Pasias
Keyword(s):  
Free Surface ◽  
Weber Number ◽  
Free Surface Flow ◽  
Reynolds Numbers ◽  
Surface Flow ◽  
Small Scale ◽  
Scale Analysis ◽  
Trailing Edge ◽  
Plate Edge ◽  
Wetting Properties

Recently, the authors considered a thin steady developed viscous free-surface flow passing the sharp trailing edge of a horizontally aligned flat plate under surface tension and the weak action of gravity, acting vertically, in the asymptotic slender-layer limit (J. Fluid Mech., vol. 850, 2018, pp. 924–953). We revisit the capillarity-driven short-scale viscous–inviscid interaction, on account of the inherent upstream influence, immediately downstream of the edge and scrutinise flow detachment on all smaller scales. We adhere to the assumption of a Froude number so large that choking at the plate edge is insignificant but envisage the variation of the relevant Weber number of $O(1)$ . The main focus, tackled essentially analytically, is the continuation of the structure of the flow towards scales much smaller than the interactive ones and where it no longer can be treated as slender. As a remarkable phenomenon, this analysis predicts harmonic capillary ripples of Rayleigh type, prevalent on the free surface upstream of the trailing edge. They exhibit an increase of both the wavelength and amplitude as the characteristic Weber number decreases. Finally, the theory clarifies the actual detachment process, within a rational description of flow separation. At this stage, the wetting properties of the fluid and the microscopically wedge-shaped edge, viewed as infinitely thin on the larger scales, come into play. As this geometry typically models the exit of a spout, the predicted wetting of the wedge is related to what in the literature is referred to as the teapot effect.

Steady, viscous, free-surface flow on a rotating cylinder

1994 ◽  
Vol 272 ◽  
pp. 91-108 ◽  
Author(s):  
Erik B. Hansen ◽  
Mark A. Kelmanson
Keyword(s):  
Free Surface ◽  
Stokes Equations ◽  
Fluid Layer ◽  
Free Surface Flow ◽  
Rotating Cylinder ◽  
Surface Flow ◽  
Surface Velocity ◽  
Cylinder Surface ◽  
Stokes Approximation ◽  
Integral Equation Formulation

The commonly observed phenomenon of steady, viscous, free-surface flow on the outer surface of a rotating cylinder is investigated by means of an iterative, integral-equation formulation applied to the Stokes approximation of the Navier-Stokes equations. The method of solution places no restriction on the thickness of the fluid layer residing on the cylinder surface; indeed, results are presented for cases where the layer thickness is of the same order of magnitude as the cylinder radius.Free-surface profiles and free-surface velocity distributions are presented for a range of flow parameters. Where appropriate, comparisons are made with the results of thinfilm theory; excellent agreement is observed.For all film thicknesses and surface tensions, results show a high degree of symmetry about a horizontal axis even though the gravity field is vertical. A proof is presented that, for vanishing surface tension, this is a consequence of the Stokes approximation.

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