Prandtl Number Effect on Be´nard Convection in Porous Media

1986 ◽  
Vol 108 (2) ◽  
pp. 284-290 ◽  
Author(s):  
J. G. Georgiadis ◽  
I. Catton
Keyword(s):  
Energy Equation ◽  
Nonequilibrium Thermodynamics ◽  
Numerical Study ◽  
Laboratory Data ◽  
Two Dimensional ◽  
Average Temperature ◽  
The Mean ◽  
Convection In Porous Media ◽  
Good Agreement

A numerical study of buoyancy-driven two-dimensional convection in a fluid-saturated horizontal porous layer is reported emphasizing the nonlinear inertial effect on heat transport. The Forchheimer–Brinkman–Darcy–Boussinesq formulation and a single energy equation for the volume-average temperature are used. Closure to the wavenumber selection problem is sought through a criterion based on the Glansdorff and Prigogine theory of nonequilibrium thermodynamics. Good agreement with laboratory data and the analogy with the Rayleigh–Be´nard problem are corroborative facts which justify similar non-Darcian formulations and demonstrate the role of the quadratic inertial terms in decreasing the mean convective heat transfer across the layer.

Analysis of Oil Film Thickness on a Piston Ring of Diesel Engine: Effect of Oil Film Temperature

2001 ◽  
Author(s):  
Yasuo Harigaya ◽  
Michiyoshi Suzuki ◽  
Masaaki Takiguchi
Keyword(s):  
Diesel Engine ◽  
Temperature Distribution ◽  
Heat Flow ◽  
Film Thickness ◽  
Piston Ring ◽  
Reynolds Equation ◽  
Energy Equation ◽  
Two Dimensional ◽  
Oil Film ◽  
The Mean

Abstract This paper describes that an analysis of oil film thickness on a piston ring of diesel engine. The oil film thickness has been performed by using Reynolds equation and unsteady, two-dimensional (2-D) energy equation with a heat generated from viscous dissipation. The temperature distribution in the oil film is calculated by using the energy equation and the mean oil film temperature is computed. Then the viscosity of oil film is estimated by using the mean oil film temperature. The effect of oil film temperature on the oil film thickness of a piston ring was examined. This model has been verified with published experimental results. Moreover, the heat flow at ring and liner surfaces was examined. As a result, the oil film thickness could be calculated by using the viscosity estimated from the mean oil film temperature and the calculated value is agreement with the measured values.

Free Fall Water Entry of a Two-Dimensional Asymmetric Wedge in Oblique Slamming: A Numerical Study

2020 ◽  
Author(s):  
Saeed Hosseinzadeh ◽  
Mohammad Izadi ◽  
Kristjan Tabri
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Free Fall ◽  
Water Entry ◽  
Vertical Acceleration ◽  
Two Dimensional ◽  
Pile Up ◽  
Real Phenomenon ◽  
Precise Simulation ◽  
Good Agreement

Abstract This paper examines the hydrodynamic problem of a two-dimensional symmetric and asymmetric wedge water entry through freefall motion. The gravity effect on the flow is considered and because of precise simulation close to the real phenomenon, the oblique slamming is analyzed. The defined problem is numerically studied using SIMPLE and HRIC schemes and by implementing an overset mesh approach. In order to evaluate the accuracy of the numerical model, the present results are compared and validated with previous experimental studies and showed good agreement. The results are presented and compared for each symmetry and asymmetry in different deadrise angles, drop heights and heel angles. Based on a comparison of the measured vertical acceleration of the experimental wedge data, it is determined that the proposed numerical method has relatively good accuracy in predicting the slamming phenomenon and wedge response. The influence of viscous regime on water entry simulations is investigated, in according to results, effect of viscosity is negligible. Results show that the heel angle dramatically affects the wedge dynamics, pile-up evolution, and pressure distribution. These results suggest evidence for a complex interaction between geometric parameters on the water entry of rigid wedges, which could finally develop our understanding of planing vessels operating in real sea conditions.

Rayleigh-Be´nard Convection in a Small Aspect Ratio Enclosure: Part II—Bifurcation to Chaos

1993 ◽  
Vol 115 (2) ◽  
pp. 367-376 ◽  
Author(s):  
D. Mukutmoni ◽  
K. T. Yang
Keyword(s):  
Numerical Study ◽  
Period Doubling ◽  
Small Aspect Ratio ◽  
Mean Flow ◽  
Average Temperature ◽  
Aspect Ratios ◽  
Transition To Chaos ◽  
The Mean ◽  
Route To Chaos ◽  
Boussinesq Fluid

The present numerical study documents bifurcation sequences for Rayleigh-Be´nard convection in a rectangular enclosure with insulated sidewalls. The aspect ratios are 3.5 and 2.1 and the Boussinesq fluid is water (average temperature of 70°C) with a Prandtl number of 2.5. The transition to chaos observed in the simulations and experiments is similar to the period-doubling (Feigenbaum) route to chaos. However, special symmetry conditions must be imposed numerically, otherwise the route to chaos is different (Ruelle-Takens-Newhouse). In particular, the Feigenbaum route to chaos can be realized only if the oscillating velocity and temperature field preserves the fourfold symmetry that is observed in the mean flow in the horizontal plane.

The Role of Residual Nonturbulent Disturbances on Transition Onset in Two-Dimensional Boundary Layers

1991 ◽  
Vol 113 (1) ◽  
pp. 147-149 ◽  
Author(s):  
Rama Govindarajan ◽  
R. Narasimha
Keyword(s):  
Boundary Layer Thickness ◽  
Free Stream ◽  
Two Dimensional ◽  
Poor Agreement ◽  
Free Stream Turbulence ◽  
New Correlation ◽  
Dimensional Boundary ◽  
Onset Location ◽  
Good Agreement

An analysis of procedures in current use for prediction of transition onset location shows that they are generally in poor agreement with data obtained in test facilities at low freestream turbulence levels. It has been shown elsewhere that under such conditions transition is driven by residual nonturbulent disturbances in the facility. A method is developed for taking such disturbances into account by defining an equivalent free-stream turbulence intensity; values for this parameter are derived for each facility from which onset data are available. A new correlation incorporating this effect is shown to be in good agreement with all available data on two-dimensional flows with pressure gradient. The correlation suggests that the onset Reynolds number (based on boundary-layer thickness) depends inversely on the total disturbance level when the latter is low.

The Interaction of Thermal Radiation in Optically Thick Boundary Layers

1967 ◽  
Vol 89 (4) ◽  
pp. 309-312 ◽  
Author(s):  
J. L. Novotny ◽  
Kwang-Tzu Yang
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Boundary Layers ◽  
Optical Thickness ◽  
Asymptotic Expansions ◽  
Energy Equation ◽  
Two Dimensional ◽  
Small Temperature ◽  
Dimensional Boundary

An analysis is presented to examine the role of the Rosseland or optically thick approximation in convection-radiation interaction situations. The analysis is formulated for the flow of a gray gas in a laminar two-dimensional boundary layer under the restriction of small temperature differences within the flow field. The boundary-layer energy equation is treated using the method of matched asymptotic expansions based on a parameter which characterizes the optical thickness of the gas. Two illustrative examples of the resulting equations are presented.

scholarly journals Magnetohydrodynamic convection in molten gallium

1999 ◽  
Vol 378 ◽  
pp. 97-118 ◽  
Author(s):  
A. JUEL ◽  
T. MULLIN ◽  
H. BEN HADID ◽  
D. HENRY
Keyword(s):  
Magnetic Field ◽  
Free Convection ◽  
Numerical Study ◽  
Two Dimensions ◽  
Main Flow ◽  
Temperature Gradients ◽  
Two Dimensional ◽  
Steady Magnetic Field ◽  
The Magnetic Field ◽  
Good Agreement

We present the results of an experimental and numerical study of the effects of a steady magnetic field on sidewall convection in molten gallium. The magnetic field is applied in a direction which is orthogonal to the main flow which reduces the convection and good agreement is found for the scaling of this effect with the relevant parameters. Moreover, qualitatively similar changes in the structure of the bulk of the flow are observed in the experiment and the numerical simulations. In particular, the flow is restricted to two dimensions by the magnetic field, but it remains different to that found in two-dimensional free convection calculations. We also show that oscillations found at even greater temperature gradients can be suppressed by the magnetic field.

Incompressible Navier-Stokes Computation of the NREL Airfoils Using a Symmetric Total Variational Diminishing Scheme

1994 ◽  
Vol 116 (4) ◽  
pp. 174-182 ◽  
Author(s):  
S. L. Yang ◽  
Y. L. Chang ◽  
O. Arici
Keyword(s):  
Turbulence Model ◽  
Numerical Solutions ◽  
Numerical Study ◽  
Wind Tunnel Test ◽  
Factorization Method ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Approximate Factorization ◽  
Two Dimensional Flow ◽  
Good Agreement

The purpose of this paper is to present a numerical study of flow fields for the NREL S805 and S809 airfoils using a spatially second-order symmetric total variational diminishing scheme. The steady two-dimensional flow is modeled as turbulent, viscous, and incompressible and is formulated in the pseudo-compressible form. The turbulent flow is closed by the Baldwin-Lomax algebraic turbulence model. Numerical solutions are obtained by the implicit approximate-factorization method. The accuracy of the numerical results is compared with the Delft two-dimensional wind tunnel test data. For comparison, the Eppler code results are also included. Numerical solutions of pressure and lift coefficients show good agreement with the experimental data, but not the drag coefficients. To properly simulate the post-stall flow field, a better turbulence model should be used.

Numerical Study of the Turbulent Wake of a Towed or Auto-Propelled Axisymmetrical Body in a Stratified Medium Using LES-VMS

2013 ◽  
Author(s):  
B. Sainte-Rose ◽  
X. Lenhardt ◽  
O. Allain ◽  
A. Dervieux
Keyword(s):  
Numerical Study ◽  
Three Dimensional ◽  
Turbulent Wake ◽  
Flow Dynamics ◽  
Stratified Medium ◽  
Two Dimensional ◽  
Multi Scale ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Good Agreement

Numerical simulations of close and far wakes behind an axisymmetrical body in a stratified medium are carried out. Towed and auto-propelled regimes are considered. The parameters of the flow are Pr = 7, Re = 10000 based on the diameter of the cylinder and F = 25. Turbulence is modelled with a Large Eddy Simulation - Variational Multi-Scale approach. Realistic results are obtained for the towed case where the so-called three-dimensional (3D), non-equilibrium (NEQ) and quasi two-dimensional (Q2D) regimes are exhibited with very good agreement with the experiments. In addition, the effect of auto-propulsion on the flow dynamics is satisfactorily addressed.

Analysis of Numerical Simulation on Near Surface Beneath Clean and Contaminated Small-Scale Wind-Driven Water Waves

2007 ◽  
Author(s):  
Xiaoxia Hu ◽  
Ali Dolatabadi ◽  
Kamran Siddiqul
Keyword(s):  
Numerical Model ◽  
Water Waves ◽  
Numerical Study ◽  
Surface Region ◽  
Surface Flow ◽  
Small Scale ◽  
Mean Velocity ◽  
Near Surface ◽  
The Mean ◽  
Good Agreement

We report on a numerical study conducted to investigate the near-surface flow beneath clean and contaminated small-scale wind-driven water surfaces. The numerical model is validated in terms of the velocity and surface wave characteristics. A good agreement is observed between the experimental and numerical values. The results from the numerical model show that the mean velocity in the near-surface region is 25–50% higher beneath the contaminated surface as compared to the clear surface. The present trend is also in agreement with the previous experimental observations.

Advanced Experimental and Numerical Analysis of the Pressurized Air Wave Bearings

2007 ◽  
Author(s):  
Adrian Sescu ◽  
Florin Dimofte ◽  
Carmen Sescu ◽  
Abdollah A. Afjeh ◽  
Robert Handschuh
Keyword(s):  
Finite Difference ◽  
Reynolds Equation ◽  
Numerical Study ◽  
Three Dimensional ◽  
Experimental Tests ◽  
Two Dimensional ◽  
Commercial Code ◽  
Type Boundary ◽  
Experimental Rig ◽  
Good Agreement

Experimental, analytical, and numerical investigations have been done in the field of gas lubrication, but few people focused on details of fluid flow between the sliding surfaces. In this work the entire pressurized wave bearing is analyzed in detail. The numerical study using a three-dimensional commercial code and a two-dimensional finite difference code gives information about the flow at many levels. The numerically computed flow rates using the commercial code are compared with experimental results determined at NASA Glenn Research Center on an experimental rig. The calculated discharge coefficient is used in the finite difference code which solves the Reynolds equation. The holes effect is considered as a source term, instead of applying hybrid type boundary conditions on the holes contours. Data from experimental tests, commercial three-dimensional code, and two-dimensional code are reported and compared to each other. Good agreement was found between numerical study and experiment.

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