Experimental Visualization of Lagrangian Coherent Structures in Aperiodic Free Surface Flow

2001 ◽  
Author(s):  
Antonis Chrisohoides ◽  
Fotis Sotiropoulos
Keyword(s):  
Free Surface ◽  
Coherent Structures ◽  
Finite Size ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Lagrangian Coherent Structures ◽  
Time Averaging ◽  
Complex Interactions ◽  
Passive Tracers

Abstract We propose a simple experimental technique for visualizing Lagrangian coherent structures (LCS) in turbulent free-surface flows. The technique employs digital photography to record the transport of passive tracers (small paper pieces) introduced manually at the free surface. Coherent eddies are detected by time-averaging the instantaneous light intensity fields on finite-size temporal windows. We demonstrate the potential of the method by applying it to visualize the flow in the vicinity of a surface-piercing rectangular block mounted at one corner of a rectangular open channel. We show that by appropriately selecting the time averaging window, the technique can reveal the presence of organized patterns in the chaotic instantaneous flow and elucidate their complex interactions.

scholarly journals Two infinite-Froude-number cusped free-surface flows due to a submerged line source or sink

1986 ◽  
Vol 28 (2) ◽  
pp. 260-270 ◽  
Author(s):  
I. L. Collings
Keyword(s):  
Free Surface ◽  
Froude Number ◽  
Ideal Fluid ◽  
Line Source ◽  
Steady Motion ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Surface Flows ◽  
Flow Problems

AbstractSolutions are found to two cusp-like free-surface flow problems involving the steady motion of an ideal fluid under the infinite-Froude-number approximation. The flow in each case is due to a submerged line source or sink, in the presence of a solid horizontal base.

scholarly journals Flow from a source above a sloping base

2020 ◽  
Vol 61 ◽  
pp. C75-C88
Author(s):  
Shaymaa Mukhlif Shraida ◽  
Graeme Hocking
Keyword(s):  
Free Surface ◽  
Flow Rate ◽  
Water Waves ◽  
Line Source ◽  
Free Surface Flow ◽  
Finite Depth ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Theoretical Research ◽  
Line Sink

We consider the outflow of water from the peak of a triangular ridge into a channel of finite depth. Solutions are computed for different flow rates and bottom angles. A numerical method is used to compute the flow from the source for small values of flow rate and it is found that there is a maximum flow rate beyond which steady solutions do not seem to exist. Limiting flows are computed for each geometrical configuration. One application of this work is as a model of saline water being returned to the ocean after desalination. References Craya, A. ''Theoretical research on the flow of nonhomogeneous fluids''. La Houille Blanche, (1):22–55, 1949. doi:10.1051/lhb/1949017 Dun, C. R. and Hocking, G. C. ''Withdrawal of fluid through a line sink beneath a free surface above a sloping boundary''. J. Eng. Math. 29:1–10, 1995. doi:10.1007/bf00046379 Hocking, G. ''Cusp-like free-surface flows due to a submerged source or sink in the presence of a flat or sloping bottom''. ANZIAM J. 26:470–486, 1985. doi:10.1017/s0334270000004665 Hocking, G. C. and Forbes, L. K. ''Subcritical free-surface flow caused by a line source in a fluid of finite depth''. J. Eng. Math. 26:455-466, 1992. doi:10.1007/bf00042763 Hocking, G. C. ''Supercritical withdrawal from a two-layer fluid through a line sink", J. Fluid Mech. 297:37–47, 1995. doi:10.1017/s0022112095002990 Hocking, G. C., Nguyen, H. H. N., Forbes, L. K. and Stokes,T. E. ''The effect of surface tension on free surface flow induced by a point sink''. ANZIAM J., 57:417–428, 2016. doi:10.1017/S1446181116000018 Landrini, M. and Tyvand, P. A. ''Generation of water waves and bores by impulsive bottom flux'', J. Eng. Math. 39(1–4):131-170, 2001. doi:10.1023/A:1004857624937 Lustri, C. J., McCue, S. W. and Chapman, S. J. ''Exponential asymptotics of free surface flow due to a line source''. IMA J. Appl. Math., 78(4):697–713, 2013. doi:10.1093/imamat/hxt016 Stokes, T. E., Hocking, G. C. and Forbes, L.K. ''Unsteady free surface flow induced by a line sink in a fluid of finite depth'', Comp. Fluids, 37(3):236–249, 2008. doi:10.1016/j.compfluid.2007.06.002 Tuck, E. O. and Vanden-Broeck, J.-M. ''A cusp-like free-surface flow due to a submerged source or sink''. ANZIAM J. 25:443–450, 1984. doi:10.1017/s0334270000004197 Vanden-Broeck, J.-M., Schwartz, L. W. and Tuck, E. O. ''Divergent low-Froude-number series expansion of nonlinear free-surface flow problems". Proc. Roy. Soc. A., 361(1705):207–224, 1978. doi:10.1098/rspa.1978.0099 Vanden-Broeck, J.-M. and Keller, J. B. ''Free surface flow due to a sink'', J. Fluid Mech, 175:109–117, 1987. doi:10.1017/s0022112087000314 Yih, C.-S. Stratified flows. Academic Press, New York, 1980. doi:10.1016/B978-0-12-771050-1.X5001-3

scholarly journals A physically consistent particle method for high-viscous free-surface flow calculation

2021 ◽  
Author(s):  
Masahiro Kondo ◽  
Takahiro Fujiwara ◽  
Issei Masaie ◽  
Junichi Matsumoto
Keyword(s):  
Angular Momentum ◽  
Free Surface ◽  
Particle Method ◽  
Free Surface Flow ◽  
Momentum Conservation ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Particle Methods ◽  
Surface Flows ◽  
Angular Momentum Conservation

AbstractParticle methods for high-viscous free-surface flows are of great use to capture flow behaviors which are intermediate between solid and liquid. In general, it is important for numerical methods to satisfy the fundamental laws of physics such as the conservation laws of mass and momentum and the thermodynamic laws. Especially, the angular momentum conservation is necessary to calculate rotational motion of high-viscous objects. However, most of the particle methods do not satisfy the physical laws in their spatially discretized system. The angular momentum conservation law is broken mostly because of the viscosity models, which may result in physically strange behavior when high-viscous free-surface flow is calculated. In this study, a physically consistent particle method for high-viscous free-surface flows is developed. The present method was verified, and its performance was shown with calculating flow in a rotating circular pipe, high-viscous Taylor–Couette flow, and offset collision of a high-viscous object.

Numerical Simulation of Free Surface Flows Using STACS-VOF Method

2007 ◽  
Author(s):  
Vedanth Srinivasan ◽  
De Ming Wang
Keyword(s):  
Free Surface ◽  
Stokes Equations ◽  
Current Method ◽  
Coupled System ◽  
Free Surface Flow ◽  
Surface Force ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Air Entrapment ◽  
Simple Strategy

This paper presents a numerical method that couples the incompressible Navier-Stokes equations with the Volume of Fluid method in a Cartesian co-ordinate system for tracking immiscible interfaces in multiple dimensions. The governing equations are discretized based on a finite volume method on a non-staggered fixed grid. The free surface flow problem is solved as a single phase flow system in which the free surface is captured using a Switching Technique for Advection and Capturing of Surfaces (STACS) scheme. The effects of surface tension at the interfaces are treated using a Continuum Surface Force (CSF) model. The pressure velocity coupling is achieved using a SIMPLE strategy. The coupled system, implemented in the commercial CFD software, AVL FIRE/SWIFT, is applied to a two dimensional dam breaking problem. The simulation results reveal a multitude of phenomena such as, free surface vortex generation, air entrapment and splashing of the liquid surge front. The computational results are in good agreement with experimental data, wherever available. The effects of time and grid resolution on the solution behavior are elaborated in detail. Different convection schemes are tested and the current method is compared to another existing interface capturing methodology.

Coupled Algebraic Multigrid for Free Surface Flow Simulations

2007 ◽  
Author(s):  
Philip J. Zwart ◽  
Alan D. Burns ◽  
Paul F. Galpin
Keyword(s):  
Free Surface ◽  
Volume Fraction ◽  
Mesh Size ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Solution Algorithm ◽  
Surface Flow ◽  
Algebraic Multigrid ◽  
Ansys Cfx ◽  
Velocity Pressure

An accurate, efficient algorithm for solving free surface flows with ANSYS CFX is described. Accuracy is achieved using a compressive advection discretization which maintains a sharp free surface interface representation without relying on a small timestep. Efficiency is obtained using a solution algorithm which implicitly couples velocity, pressure, and volume fractions in the same matrix, and solves these equations using algebraic multigrid. This coupled strategy overcomes difficulties encountered with segregated volume fraction algorithms, where heavy underrelaxation and long solution times are required. The resulting solution algorithm is scalable, leading to solution times which increase linearly with mesh size.

Numerical Simulations of Two Back-To-Back Horizontal Axis Tidal Stream Turbines in Free-Surface Flows

2020 ◽  
Vol 87 (6) ◽  
Author(s):  
Jinhui Yan ◽  
Xiaowei Deng ◽  
Fei Xu ◽  
Songzhe Xu ◽  
Qiming Zhu
Keyword(s):  
Free Surface ◽  
Surface Effect ◽  
Mathematical Formulation ◽  
Time History ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Wake Effect ◽  
Tidal Turbine ◽  
Tidal Stream

Abstract We simulate two back-to-back full-scale tidal turbines using an in-house computational free-surface flow code. We briefly present the mathematical formulation of the computational framework. We first validate the proposed method on a single turbine configuration. A mesh refinement study is conducted to ensure the result is converged. We then quantify the wake effect and free-surface effect on tidal turbine performance by a case study. To investigate the free-surface effect, we perform both pure hydrodynamics and free-surface simulations. The time history of thrust and production coefficients is quantified. In both pure hydrodynamics and free-surface flow simulations, thrust and production coefficients of the downstream turbines drop significantly due to the velocity deficit in the wake. By comparing the result between free-surface flow and pure hydrodynamics simulations for the configuration considered here, we find that the free-surface does not affect the upstream turbine but significantly affects the downstream turbine.

scholarly journals On ice-induced instability in free-surface flows

2007 ◽  
Vol 577 ◽  
pp. 25-52 ◽  
Author(s):  
EVGENIY SHAPIRO ◽  
SERGEI TIMOSHIN
Keyword(s):  
Free Surface ◽  
Three Dimensional ◽  
Water Film ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Two Dimensional ◽  
Instability Waves ◽  
Ice Surface ◽  
Neutral Curves

The problem of stability of a water-coated ice layer is investigated for a free-surface flow of a thin water film down an inclined plane. An asymptotic (double-deck) theory is developed for a flow with large Reynolds and Froude numbers which is then used to investigate linear two-dimensional, three-dimensional and nonlinear two-dimensional stability characteristics. A new mode of upstream-propagating instability arising from the interaction of the ice surface with the flow is discovered and its properties are investigated. In the linear limit, closed-form expressions for the dispersion relation and neutral curves are obtained for the case ofPr= 1. For the general case, the linear stability problem is solved numerically and the applicability of the solution withPr= 1 is analysed. Nonlinear double-deck equations are solved with a novel global-marching-type scheme and the effects of nonlinearity are investigated. An explanation of the physical mechanism leading to the upstream propagation of instability waves is provided.

A Stable Semi-Implicit Method for Free Surface Flows

2005 ◽  
Vol 73 (6) ◽  
pp. 940-947 ◽  
Author(s):  
Cassio M. Oishi ◽  
José A. Cuminato ◽  
Valdemir G. Ferreira ◽  
Murilo F. Tomé ◽  
Antonio Castelo ◽  
...  
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Stokes Equations ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Navier Stokes ◽  
Variable Order ◽  
Implicit Methods ◽  
Time Lagged

The present work is concerned with a semi-implicit modification of the GENSMAC method for solving the two-dimensional time-dependent incompressible Navier-Stokes equations in primitive variables formulation with a free surface. A projection method is employed to uncouple the velocity components and pressure, thus allowing the solution of each variable separately (a segregated approach). The viscous terms are treated by the implicit backward method in time and a centered second order method in space, and the nonlinear convection terms are explicitly approximated by the high order upwind variable-order nonoscillatory scheme method in space. The boundary conditions at the free surface couple the otherwise segregated velocity and pressure fields. The present work proposes a method that allows the segregated solution of free surface flow problems to be computed by semi-implicit schemes that preserve the stability conditions of the related coupled semi-implicit scheme. The numerical method is applied to both the simulation of free surface and to confined flows. The numerical results demonstrate that the present technique eliminates the parabolic stability restriction required by the original explicit GENSMAC method, and also found in segregated semi-implicit methods with time-lagged boundary conditions. For low Reynolds number flows, the method is robust and very efficient when compared to the original GENSMAC method.

Inviscid free-surface flow over a periodic wall

1991 ◽  
Vol 226 ◽  
pp. 189-203 ◽  
Author(s):  
V. Bontozoglou ◽  
S. Kalliadasis ◽  
A. J. Karabelas
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Surface Shape ◽  
Flow Parameters ◽  
Material Deposition ◽  
Straightforward Method ◽  
Wide Range ◽  
Free Surface Shape

A numerical method is described, based on the hodograph formulation, for analysing in viscid, free-surface flows over a periodic wall. An efficient implementation of the wall boundary condition results in a straightforward method, accurate for a wide range of bottom undulation heights and flow parameters. It is demonstrated that a series of resonances is possible between the bottom undulations and the free surface. The steady, free-surface profiles are accurately calculated for a wide range of current velocities and are shown to be significantly dimpled by higher harmonics. A study of the flow field indicates that the free-surface shape strongly affects the velocities close to the wall, leading to distributions which change dramatically with current velocity. Some implications of the new results on the phenomena of wall dissolution or material deposition, Bragg scattering of surface waves and sediment transport in rivers, are discussed.

scholarly journals Free-surface flow due to a source submerged in a fluid of infinite depth with two stagnant regions

1993 ◽  
Vol 34 (3) ◽  
pp. 368-376 ◽  
Author(s):  
Hocine Mekias ◽  
Jean-Marc Vanden-Broeck
Keyword(s):  
Free Surface ◽  
Surface Profile ◽  
Free Surface Flow ◽  
Shear Layers ◽  
Free Surface Flows ◽  
Surface Flow ◽  
Surface Flows ◽  
Infinite Depth ◽  
Free Surface Profile ◽  
Series Truncation Method

AbstractTwo-dimensional free-surface flows produced by a submerged source in a fluid of infinite depth are considered. It is assumed that the point on the free surface just above the source is a stagnation point and that the fluid outside two shear layers is at rest. The free-surface profile and the shape of the shear layers are determined numerically by using a series-truncation method. It is shown that there is a solution for each value of the Froude number F > 0. When F tends to infinity, the flow also describes a thin jet impinging in a fluid at rest.

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