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.

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 Past Ships in Shallow Water

2002 ◽  
Author(s):  
A. Ganguly ◽  
V. Shigunov ◽  
O. Turan
Keyword(s):  
Free Surface ◽  
Stokes Equations ◽  
Near Field ◽  
Free Surface Flow ◽  
Steady State Solution ◽  
Surface Flow ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Medium Speed ◽  
Measured Resistance

A finite volume method with a multiphase type free surface description is employed to calculate the flow around ships in shallow and restricted channels. The flows at critical and supercritical depth Froude numbers (Fnd = 1.0 and Fnd = 1.18) are calculated for Series–60 monohull and a medium speed catamaran. A steady state solution for Reynolds-averaged Navier-Stokes equations with a k-ε turbulence model is obtained by time marching. Computed wave profiles are in good agreement with model tests in the near field of the ship. The computed and measured resistance agree fairly well.

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.

scholarly journals Determinants of modelling choices for 1-D free-surface flow and morphodynamics in hydrology and hydraulics: a review

2016 ◽  
Vol 20 (9) ◽  
pp. 3799-3830 ◽  
Author(s):  
Bruno Cheviron ◽  
Roger Moussa
Keyword(s):  
Free Surface ◽  
Flow Characteristics ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Navier Stokes ◽  
Dimensionless Time ◽  
Dimensionless Numbers ◽  
Model Refinement ◽  
Modelling Strategies ◽  
Spatiotemporal Scales

Abstract. This review paper investigates the determinants of modelling choices, for numerous applications of 1-D free-surface flow and morphodynamic equations in hydrology and hydraulics, across multiple spatiotemporal scales. We aim to characterize each case study by its signature composed of model refinement (Navier–Stokes: NS; Reynolds-averaged Navier–Stokes: RANS; Saint-Venant: SV; or approximations to Saint-Venant: ASV), spatiotemporal scales and subscales (domain length: L from 1 cm to 1000 km; temporal scale: T from 1 s to 1 year; flow depth: H from 1 mm to 10 m; spatial step for modelling: δL; temporal step: δT), flow typology (Overland: O; High gradient: Hg; Bedforms: B; Fluvial: F), and dimensionless numbers (dimensionless time period T*, Reynolds number Re, Froude number Fr, slope S, inundation ratio Λz, Shields number θ). The determinants of modelling choices are therefore sought in the interplay between flow characteristics and cross-scale and scale-independent views. The influence of spatiotemporal scales on modelling choices is first quantified through the expected correlation between increasing scales and decreasing model refinements (though modelling objectives also show through the chosen spatial and temporal subscales). Then flow typology appears a secondary but important determinant in the choice of model refinement. This finding is confirmed by the discriminating values of several dimensionless numbers, which prove preferential associations between model refinements and flow typologies. This review is intended to help modellers in positioning their choices with respect to the most frequent practices, within a generic, normative procedure possibly enriched by the community for a larger, comprehensive and updated image of modelling strategies.

scholarly journals Determinants of modelling choices for 1-D free-surface flow and erosion issues in hydrology: a review

2015 ◽  
Vol 12 (9) ◽  
pp. 9091-9155
Author(s):  
B. Cheviron ◽  
R. Moussa
Keyword(s):  
Free Surface ◽  
Flow Characteristics ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Navier Stokes ◽  
Dimensionless Time ◽  
Dimensionless Numbers ◽  
Model Refinement ◽  
Modelling Strategies ◽  
Spatiotemporal Scales

Abstract. This review paper investigates the determinants of modelling choices, for numerous applications of 1-D free-surface flow and erosion equations, across multiple spatiotemporal scales. We aim to characterize each case study by its signature composed of model refinement (Navier-Stokes: NS, Reynolds-Averaged Navier-Stokes: RANS, Saint-Venant: SV or Approximations of Saint-Venant: ASV), spatiotemporal scales (domain length: L from 1 cm to 1000 km; temporal scale: T from 1 second to 1 year; flow depth: H from 1 mm to 10 m), flow typology (Overland: O, High gradient: Hg, Bedforms: B, Fluvial: F) and dimensionless numbers (Dimensionless time period T*, Reynolds number Re, Froude number Fr, Slope S, Inundation ratio Λz, Shields number θ). The determinants of modelling choices are therefore sought in the interplay between flow characteristics, cross-scale and scale-independent views. The influence of spatiotemporal scales on modelling choices is first quantified through the expected correlation between increasing scales and decreasing model refinements, identifying then flow typology a secondary but mattering determinant in the choice of model refinement. This finding is confirmed by the discriminating values of several dimensionless numbers, that prove preferential associations between model refinements and flow typologies. This review is intended to help each modeller positioning his (her) choices with respect to the most frequent practices, within a generic, normative procedure possibly enriched by the community for a larger, comprehensive and updated image of modelling strategies.

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