scholarly journals Laminar-turbulent transitions during thermal gravitational-capillary convection in horizontal liquid layers heated from below

2021 ◽  
Vol 2119 (1) ◽  
pp. 012166
Author(s):  
V S Berdnikov ◽  
V A Grishkov ◽  
A V Mikhailov ◽  
V O Ryabov
Keyword(s):  
Free Surface ◽  
Rayleigh Number ◽  
Ethyl Alcohol ◽  
Temperature Fields ◽  
Thermal Imager ◽  
Spatial Form ◽  
Free Surfaces

Abstract The evolution of the spatial form of the flow versus the Rayleigh number in layers with two rigid horizontal boundaries and layers with a free surface is experimentally investigated depending on the Rayleigh and Marangoni numbers. The experiments were carried out with layers of ethyl alcohol and water. A thermal imager was used to measure temperature fields on free surfaces of liquids.

scholarly journals Influence of thermal gravitational-capillary convection on temperature fields in a thin wall

2021 ◽  
Vol 2119 (1) ◽  
pp. 012162
Author(s):  
N I Bodneva ◽  
V S Berdnikov ◽  
V A Grishkov ◽  
A V Mikhailov
Keyword(s):  
Free Surface ◽  
Ethyl Alcohol ◽  
Liquid Layer ◽  
Convective Flow ◽  
Vertical Wall ◽  
Temperature Gradients ◽  
Temperature Fields ◽  
Thin Wall ◽  
Vertical Walls ◽  
Thermal Films

Abstract The development of convective flow in a layer of ethyl alcohol when heating one of the vertical walls of a rectangular cavity was investigated experimentally. Thermal films were obtained, whose processing allowed plotting in time the distribution of temperature and temperature gradients on the free surface of the liquid layer and the opposite thin vertical wall of the cavity after the flow of heated liquid on it.

Thermocapillary Convection With Undeformable Curved Surfaces in Open Cylinders

2001 ◽  
Author(s):  
Bok-Cheol Sim ◽  
Abdelfattah Zebib
Keyword(s):  
Free Surface ◽  
Critical Frequency ◽  
Thermocapillary Convection ◽  
Three Dimensional ◽  
Quantitative Agreement ◽  
Fluid Volume ◽  
Uniform Heat Flux ◽  
Free Surfaces ◽  
Space Experiments ◽  
Steady Convection

Abstract Thermocapillary convection driven by a uniform heat flux in an open cylindrical container of unit aspect ratio is investigated by two- and three-dimensional numerical simulations. The undeformable free surface is either flat or curved as determined by the fluid volume (V ≤ 1) and the Young-Laplace equation. Convection is steady and axisymmetric at sufficiently low values of the Reynolds number (Re) with either flat or curved interfaces. Only steady convection is possible in strictly axisymmetric computations. Transition to oscillatory three-dimensional motions occurs as Re increases beyond a critical value dependent on Pr and V. With a flat free surface (V = 1), two-lobed pulsating waves are found on the free surface and prevail with increasing Re. While the critical Re increases with increasing Pr, the critical frequency decreases. In the case of a concave surface, four azimuthal waves are found rotating clockwise on the surface. The critical Re decreases with increasing fluid volume, and the critical frequency is found to increase. The numerical results with either flat or curved free surfaces are in good quantitative agreement with space experiments.

scholarly journals Two-Dimensional Convection Induced by Gravity and Centrifugal Forces in a Rotating Porous Layer Far Away from the Axis of Rotation

1998 ◽  
Vol 4 (2) ◽  
pp. 73-90 ◽  
Author(s):  
Peter Vadasz ◽  
Saneshan Govender
Keyword(s):  
Rayleigh Number ◽  
Porous Layer ◽  
Temperature Fields ◽  
Wave Number ◽  
Marginal Stability ◽  
Two Dimensional ◽  
Wide Range ◽  
Gravity Driven ◽  
Gravity Driven Flow ◽  
The Stability

The stability and onset of two-dimensional convection in a rotating fluid saturated porous layer subject to gravity and centrifugal body forces is investigated analytically. The problem corresponding to a layer placed far away from the centre of rotation was identified as a distinct case and therefore justifying special attention. The stability of a basic gravity driven convection is analysed. The marginal stability criterion is established in terms of a critical centrifugal Rayleigh number and a critical wave number for different values of the gravity related Rayleigh number. For any given value of the gravity related Rayleigh number there is a transitional value of the wave number, beyond which the basic gravity driven flow is stable. The results provide the stability map for a wide range of values of the gravity related Rayleigh number, as well as the corresponding flow and temperature fields.

scholarly journals Effects of Anisotropy on Natural Convection in a Vertical Porous Cavity Filled with a Heat Generation

2020 ◽  
pp. 12-27
Author(s):  
Degan Gerard ◽  
Sokpoli Amavi Ernest ◽  
Akowanou Djidjoho Christian ◽  
Vodounnou Edmond Claude
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Temperature Fields ◽  
Poisson Equations ◽  
Gravitational Vector ◽  
Side Walls ◽  
Rayleigh Numbers ◽  
Vertical Cavity

This research was devoted to the analytical study of heat transfer by natural convection in a vertical cavity, confining a porous medium, and containing a heat source. The porous medium is hydrodynamically anisotropic in permeability whose axes of permeability tensor are obliquely oriented relative to the gravitational vector and saturated with a Newtonian fluid. The side walls are cooled to the temperature  and the horizontal walls are kept adiabatic. An analytical solution to this problem is found for low Rayleigh numbers by writing the solutions of mathematical model in polynomial form of degree n of the Rayleigh number. Poisson equations obtained are solved by the modified Galerkin method. The results are presented in term of streamlines and isotherms. The distribution of the streamlines and the temperature fields are greatly influenced by the permeability anisotropy parameters and the thermal conductivity. The heat transfer decreases considerably when the Rayleigh number increases.

scholarly journals Effect of Heat Source Position in Fluid Flow, Heat Transfer and Entropy Generation in a Naturally Ventilated Room

Mathematics ◽  
2022 ◽  
Vol 10 (2) ◽  
pp. 178
Author(s):  
Mohammed Alghaseb ◽  
Walid Hassen ◽  
Abdelhakim Mesloub ◽  
Lioua Kolsi
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Heat Source ◽  
Numerical Study ◽  
Temperature Fields ◽  
Left Wall ◽  
Heating Efficiency ◽  
Discrete Heat Source ◽  
Volume Method ◽  
The Impact

In this study, a 3D numerical study of free ventilated room equipped with a discrete heat source was performed using the Finite Volume Method (FVM). To ensure good ventilation, two parallel openings were created in the room. A suction opening was located at the bottom of the left wall and another opening was located at the top of the opposite wall; the heat source was placed at various positions in order to compare the heating efficiency. The effects of Rayleigh number (103 ≤ Ra ≤ 106) for six heater positions was studied. The results focus on the impact of these parameters on the particle trajectories, temperature fields and on the heat transfer inside the room. It was found that the position of the heater has a dramatic effect on the behavior and topography of the flow in the room. When the heat source was placed on the wall with the suction opening, two antagonistic behaviors were recorded: an improvement in heat transfer of about 31.6%, compared to the other positions, and a low Rayleigh number against 22% attenuation for high Ra values was noted.

scholarly journals Asymptotic behaviour of dam break flow for small times

2019 ◽  
pp. 7-27
Author(s):  
Дамла Исидичи Демирель ◽  
Алессандро Яфрати ◽  
Александр Коробкин ◽  
Огуз Йилмаз
Keyword(s):  
Free Surface ◽  
Corner Point ◽  
Domain Decomposition Method ◽  
Second Order ◽  
Lagrangian Description ◽  
Bottom Part ◽  
Free Surfaces ◽  
Lagrangian Variables ◽  
Gravity Driven Flow ◽  
Horizontal Portion

Двумерное импульсное течение жидкости изучается в рамках теории потенциального потока. Первоначально жидкость находится в состоянии покоя и удерживается на одной стороне вертикальной пластины. Она внезапно убирается и поток жидкости начинает течь под действием силы тяжести. Внимание уделяется особому поведению поля скоростей в нижней точке, где вертикальная свободная поверхность встречается с жестким дном. Линейная задача решается методом рядов Фурье. Решение внутренней области находится с помощью преобразования Меллина в нижней точке. Формирование струи наблюдается в нижней точке. Разрыв в верхней угловой точке исследуется с помощью Лагранжевых переменных. Для внешней задачи второго порядка используется метод декомпозиции области. Сравнение форм свободных поверхностей вблизи верхней угловой точки с решениями переднего и второго порядка показывает, что внешнее решение второго порядка имеет большее различие в вертикальной свободной поверхности, чем в горизонтальной части, по сравнению с решением ведущего порядка. Получена картина форм свободных поверхностей с использованием Лагранжевого описания для верхней части и Эйлерого описания для нижней части во втором порядке. Two dimensional impulsive flow of a fluid is studied within the potential flow theory. Initially the fluid is at rest and is held on one side of a vertical plate. The plate is withdrawn suddenly and gravity driven flow of the fluid starts. Attention is paid to the singular behaviour of the velocity field at the bottom point, where the vertical free surface meets the rigid bottom. The linear problem is solved by the Fourier series method. An inner region solution is found using Mellin transform at the bottom point. The jet formation is observed at the bottom point. Also the discontinuity at the upper corner point is dealt with Lagrangian variables. For the second order outer problem, domain decomposition method is used. Comparison of the shapes of the free surfaces near the upper corner point with leading and second order solutions shows that the second order outer solution outer makes a larger difference in the vertical free surface than in the horizontal portion, compared with leading order solution.The complete picture of the shapes of the free surfaces using Lagrangian description for the upper part and Eulerian description for the bottom part at the second order is obtained.

Natural Convection Heat Transfer in a Partially Open Square Cavity With a Thin Fin Attached to the Hot Wall

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
Abdullatif Ben-Nakhi ◽  
M. M. Eftekhari ◽  
D. I. Loveday
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Inclination Angle ◽  
Computational Study ◽  
Vertical Wall ◽  
Temperature Fields ◽  
Arbitrary Length ◽  
Flow Modification ◽  
The Impact

A computational study of steady, laminar, natural convective fluid flow in a partially open square enclosure with a highly conductive thin fin of arbitrary length attached to the hot wall at various levels is considered. The horizontal walls and the partially open vertical wall are adiabatic while the vertical wall facing the partial opening is isothermally hot. The current work investigates the flow modification due to the (a) attachment of a highly conductive thin fin of length equal to 20%, 35%, or 50% of the enclosure width, attached to the hot wall at different heights, and (b) variation of the size and height of the aperture located on the vertical wall facing the hot wall. Furthermore, the study examines the impact of Rayleigh number (104⩽Ra⩽107) and inclination of the enclosure. The problem is put into dimensionless formulation and solved numerically by means of the finite-volume method. The results show that the presence of the fin has counteracting effects on flow and temperature fields. These effects are dependent, in a complex way, on the fin level and length, aperture altitude and size, cavity inclination angle, and Rayleigh number. In general, Nusselt number is directly related to aperture altitude and size. However, after reaching a peak Nusselt number, Nusselt number may decrease slightly if the aperture’s size increases further. The impact of aperture altitude diminishes for large aperture sizes because the geometrical differences decrease. Furthermore, a longer fin causes higher rate of heat transfer to the fluid, although the equivalent finless cavity may have higher heat transfer rate. In general, the volumetric flow rate and the rate of heat loss from the hot surfaces are interrelated and are increasing functions of Rayleigh number. The relationship between Nusselt number and the inclination angle is nonlinear.

A Lattice Boltzmann Bluff Body Model for VIV Suppression

2006 ◽  
Author(s):  
Jannette B. Frandsen
Keyword(s):  
Reynolds Number ◽  
Free Surface ◽  
Lattice Boltzmann ◽  
Water Waves ◽  
Bluff Body ◽  
Numerical Models ◽  
Bluff Bodies ◽  
Free Surfaces ◽  
Viv Suppression ◽  
Reynolds Number Flows

In this paper, the suitability of a mesoscopic approach involving a single phase Lattice Boltzmann (LB) model is examined. In contrast, to continuum based numerical models, where only space and time are discrete, the discrete variables of the LB model are space, time and particle velocity. With reference to the Boltzmann equation of classical kinetic theory, the distribution of fluid molecules is represented by particle distribution functions. The LB method simulates fluid flow by tracking particle distributions. It is notable that the formulation avoids the need to include the Poisson equation. An elastic-collision scheme with no-slip walls is prescribed. The central idea behind proposing the present formulation is many fold. One goal is to capture smaller scales naturally, postponing the need of applying empirical turbulence models. Another goal is to get further insight into nonlinearities in steep and breaking free surfaces to improve current continuum mechanics solutions. Although the long term goal is to predict bluff-body high Reynolds number flows and breaking water waves, the present study is limited to laminar flow simulations and continuous free surfaces. The case studies presented include bluff bodies embedded in Reynolds number flows in the order of 100–200. The free surface test cases represent bore propagation past a single and multiple structures. The 2-D uniform grid solutions are compared with findings reported in the literature. Vortex patterns are studied when single or several objects are located in the bluff-body wakes. From a mitigation point of view, the model presents an easy means of re-arranging bluff bodies to study optimum solutions for VIV suppression with/without a free surface.

scholarly journals Masonry using “Termo Blok” blocks

2019 ◽  
Vol 91 ◽  
pp. 02022
Author(s):  
Paul Stratiy ◽  
Anastasia Melnikova ◽  
Ilya Klykov ◽  
Aleksandr Russkiy
Keyword(s):  
Energy Efficient ◽  
Temperature Sensors ◽  
Temperature Fields ◽  
Thermal Engineering ◽  
Thermal Imager ◽  
Compression Tests ◽  
Engineering Model ◽  
Insulating Layer ◽  
Operational Characteristics ◽  
Additional Control

The following article reviews a new masonry energy-efficient erection technology using hollow blocks termosblocks, which provides construction of vertically continuous and horizontally intermittent insulating layer. Thermal insolent insets are placed inside the inner cavities of the block. The study is aimed to establish the boundaries of using this technology. Therefore, central compression tests were conducted in order to determine the tensile strength of the block. Also, a reduced thermal resistance and energy-efficiency of a masonry fragment was calculated. In order to verify thermal engineering model, an experiment was conducted in which the temperature inside the structure was measured using contact temperature sensors. Additional control of temperature fields spreading was proceeded using thermal imager. On the basis of the obtained data, termosblocks masonry operational characteristics were estimated, and the study result was defined.

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