scholarly journals Experimental study of eddy viscosity for breaking waves on sloping bottom and comparisons with empirical and numerical predictions

2019 ◽  
Vol 68 (3) ◽  
pp. 299
Author(s):  
N Oldekop ◽  
T Liiv ◽  
J Laanearu
Keyword(s):  
Experimental Study ◽  
Eddy Viscosity ◽  
Breaking Waves ◽  
Numerical Predictions ◽  
Sloping Bottom

Experimental and Numerical Study of Methanol-Water Mixture Single-Phase Heat Transfer in a Micro-Channel Heat Sink

2012 ◽  
Author(s):  
Chun K. Kwok ◽  
Matthew M. Asada ◽  
Jonathan R. Mita ◽  
Weilin Qu
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Sink ◽  
Single Phase ◽  
Numerical Study ◽  
Pure Water ◽  
Molar Fraction ◽  
Water Mixture ◽  
Micro Channel ◽  
Numerical Predictions

This paper presents an experimental study of single-phase heat transfer characteristics of binary methanol-water mixtures in a micro-channel heat sink containing an array of 22 microchannels with 240μm × 630μm cross-section. Pure water, pure methanol, and five methanol-water mixtures with methanol molar fraction of 16%, 36%, 50%, 63% and 82% were tested. Key parametric trends were identified and discussed. The experimental study was complemented by a three-dimensional numerical simulation. Numerical predictions and experimental data are in good agreement with a mean absolute error (MAE) of 0.87%.

scholarly journals PARAMETERIZATION OF EVOLUTION OF BIPHASE DURING NONLINEAR TRANSFORMATION OF WAVES IN COASTAL ZONE

2017 ◽  
pp. 3
Author(s):  
Yana Saprykina ◽  
Sergey Kuznetsov ◽  
Margarita Shtremel
Keyword(s):  
Experimental Data ◽  
Phase Shift ◽  
Coastal Zone ◽  
Energy Exchange ◽  
Wave Motion ◽  
Empirical Relation ◽  
Breaking Waves ◽  
Wave Transformation ◽  
Nonlinear Harmonics ◽  
Sloping Bottom

Based on experimental data, the problem of parametrization of spatial variation of the phase shift (biphase) between the first and second nonlinear harmonics of wave motion during wave transformation over sloping bottom in the coastal zone is discussed. It is revealed that the biphase values vary in the range [–π/2, π/2]. Biphase variations rigorously follow fluctuations in amplitudes of the first and second harmonics and the periodicity of energy exchange between them. The empirical relation applied in modern practice to calculate the biphase, which depends on the Ursell number, is incorrect for calculating the biphase for wave evolution in the coastal zone, because it does not take into account periodic energy exchange between the nonlinear harmonics. The new approximations of the biphase values for typical scenarios of wave transformations are suggested. It was demonstrated that the biphase of breaking waves defines breaking index and breaking type.

On Application of Nonlinear k-ε Models for Internal Combustion Engine Flows

2002 ◽  
Vol 124 (3) ◽  
pp. 668-677 ◽  
Author(s):  
G. M. Bianchi ◽  
G. Cantore ◽  
P. Parmeggiani ◽  
V. Michelassi
Keyword(s):  
Internal Combustion Engine ◽  
Eddy Viscosity ◽  
Combustion Engine ◽  
Turbulence Models ◽  
Internal Combustion ◽  
Moment Closure ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Numerical Predictions ◽  
Viscosity Models

The linear k-ε model, in its different formulations, still remains the most widely used turbulence model for the solutions of internal combustion engine (ICE) flows thanks to the use of only two scale-determining transport variables and the simple constitutive relation. This paper discusses the application of nonlinear k-ε turbulence models for internal combustion engine flows. Motivations to nonlinear eddy viscosity models use arise from the consideration that such models combine the simplicity of linear eddy-viscosity models with the predictive properties of second moment closure. In this research the nonlinear k-ε models developed by Speziale in quadratic expansion, and Craft et al. in cubic expansion, have been applied to a practical tumble flow. Comparisons between calculated and measured mean velocity components and turbulence intensity were performed for simple flow structure case. The effects of quadratic and cubic formulations on numerical predictions were investigated too, with particular emphasis on anisotropy and influence of streamline curvature on Reynolds stresses.

scholarly journals Experimental study on plunging breaking waves in deep water

2015 ◽  
Vol 120 (3) ◽  
pp. 2007-2049 ◽  
Author(s):  
Ho-Joon Lim ◽  
Kuang-An Chang ◽  
Zhi-Cheng Huang ◽  
Byoungjoon Na
Keyword(s):  
Experimental Study ◽  
Deep Water ◽  
Breaking Waves

An Experimental Study of the Enhancement of Air-Cooling Limits for Telecom/Datacom Heat Sink Applications Using an Impinging Air Jet

2005 ◽  
Vol 128 (2) ◽  
pp. 166-171 ◽  
Author(s):  
Eric Sansoucy ◽  
Patrick H. Oosthuizen ◽  
Gamal Refai-Ahmed
Keyword(s):  
Experimental Study ◽  
Flat Plate ◽  
Heat Sink ◽  
Target Surface ◽  
Junction Temperature ◽  
Air Cooling ◽  
Nusselt Numbers ◽  
Air Jet ◽  
Numerical Predictions ◽  
Nozzle Plate

An experimental study was conducted to investigate the heat transfer from a parallel flat plate heat sink under a turbulent impinging air jet. A horizontal nozzle plate confined the target surface. The jet was discharged from a sharp-edged nozzle in the nozzle plate. Average Nusselt numbers are reported for Pr=0.7, 5000⩽Re⩽30,000, L∕d=2.5, and 0.833 at H∕d=3 where L, H, and d define the length of the square heat source, nozzle-to-target spacing, and nozzle diameter, respectively. Tests were also conducted for an impinging flow over a flat plate, flush with the top surface of the target plate. The average Nusselt numbers from the heat sink were compared to those for a flat plate to determine the overall performance of the heat sink in a confined impingement arrangement. The experimental results were compared with the numerical predictions obtained in an earlier study. Although the average Nusselt numbers obtained from numerical simulations differed from the experimental measurements by 18%, the disagreement is much less significant when related to the junction temperature. Under typical conditions, it was shown that such discrepancy in the Nusselt number lead to an error of 6% in the prediction of the junction temperature of the device.

An experimental study of weakly three-dimensional non-breaking and breaking waves

2015 ◽  
Vol 52 ◽  
pp. 206-216 ◽  
Author(s):  
Dianyong Liu ◽  
Yuxiang Ma ◽  
Guohai Dong ◽  
Marc Perlin
Keyword(s):  
Experimental Study ◽  
Three Dimensional ◽  
Breaking Waves

Buckling of Externally Pressurised Prolate Ellipsoidal Domes

2006 ◽  
Author(s):  
P. Smith ◽  
J. Blachut
Keyword(s):  
Experimental Study ◽  
Test Procedure ◽  
External Pressure ◽  
Design Codes ◽  
Numerical Predictions ◽  
Current Design ◽  
Section Viii ◽  
Base Radius ◽  
Division 2 ◽  
Prolate Ellipsoidal

Details are given of a numerical and experimental study into buckling of steel ellipsoidal domes loaded by static external pressure. A range of geometries and thicknesses of domes is examined, as is the influence of different boundary conditions. Shells are examined on the basis of having the same mass. The main focus of the study is on prolate domes, i.e., those taller than a hemisphere of the same base radius. Numerical predictions are confirmed by pressurising six laboratory scale prolate domes to destruction. Details are given of the manufacture and test procedure for the domes. The adverse effects of variations in shape, and wall thickness are discussed, and FE predictions are made for geometrically imperfect domes. Correlation between the two sets of results is good. Numerical and experimentally obtained results are related to the current design codes: ASME Boiler & Pressure Vessel Code, Section VIII, Division 2 (described hereon as ASME VIII), PD5500, and ECCS recommendations [1–3], which at present make no provision for prolate domes. Suggestions are made for the possible inclusion of such domes into the standards.

scholarly journals NEW METHODS FOR STABILIZING RANS TURBULENCE MODELS WITH APPLICATION TO LARGE SCALE BREAKING WAVES

2020 ◽  
pp. 19
Author(s):  
Georgios Azorakos ◽  
Bjarke Eltard Larsen ◽  
David R. Fuhrman
Keyword(s):  
Turbulence Model ◽  
Large Scale ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Breaking Waves ◽  
Wide Spread ◽  
Cfd Simulations ◽  
New Methods ◽  
Rans Turbulence Models ◽  
Scale Breaking

Recently, Larsen and Fuhrman (2018) have shown that seemingly all commonly used (both k-omega and k-epsilon variants) two-equation RANS turbulence closure models are unconditionally unstable in the potential flow beneath surface waves, helping to explain the wide-spread over-production of turbulent kinetic energy in CFD simulations, relative to measurements. They devised and tested a new formally stabilized formulation of the widely used k-omega turbulence model, making use of a modified eddy viscosity. In the present work, three new formally-stable k-omega turbulence model formulations are derived and tested in CFD simulations involving the flow and dynamics beneath large-scale plunging breaking waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/T2fFRgq3I8E

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