Turbulent Natural Convection in Partitioned Square Cavities with Different Lengths and Positions

2018 ◽  
Vol 877 ◽  
pp. 313-319
Author(s):  
A. Nouri-Borujerdi ◽  
F. Sepahi
Keyword(s):  
Natural Convection ◽  
Turbulent Flow ◽  
Stokes Equations ◽  
Control Volume ◽  
Bottom Wall ◽  
Staggered Grid ◽  
Viscous Effects ◽  
Left Wall ◽  
Turbulent Natural Convection ◽  
Upwind Schemes

The effect of partition on turbulent natural convection has been investigated numerically with different lengths and positions in an air filled square cavity. The top wall of the cavity is assumed to be cold and the other three walls are hot. Two-dimensional governing equations based on Reynolds-averaged Navier-Stokes equations are solved numerically by control volume method in a staggered grid manner. The iterative SIMPLE algorithm is also used to solve the discretized momentum equations to compute the intermediate velocity and pressure fields linked through the momentum equations. The hybrid differencing scheme which is based on a combination of central and upwind schemes is employed to discretize the convective and diffusion terms of the equations respectively. To describe the structure of turbulent flow which is changed due to the increasing importance of viscous effects, wall function was applied to simulate the turbulent flow. The results show that when the partition is placed on the top or bottom wall, the heat transfer rate through the bottom wall increases by increasing the partition length. The number of vortices established in the cavity depends on the partition length. Furthermore, when the partition is mounted on the left or right wall, only a small part of the top wall has a direct interaction with the left wall and the rest of that has an indirect interaction with the bottom wall.

Oscillatory Flow Induced Developing Convection in a Shallow Enclosure: Effect of Sinusoidal Bottom Wall Temperature

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Saeid R. Angeneh ◽  
Murat K. Aktas
Keyword(s):  
Heat Transfer ◽  
Oscillatory Flow ◽  
Stokes Equations ◽  
Control Volume ◽  
Acoustic Streaming ◽  
Fluid Motion ◽  
Side Wall ◽  
Convective Transport ◽  
Bottom Wall ◽  
Mean Flow

Abstract The influence of hydrodynamically developing nonzero mean acoustic streaming motion on transient convective heat transfer in an air-filled rectangular enclosure is studied numerically. The enclosure is two-dimensional with sinusoidal bottom wall spatial temperature distribution. The oscillatory flow under relatively large Womersley number regime conditions is actuated by the periodic vibrations of the enclosure side wall. The side walls of the enclosure are adiabatic, while the top wall is isothermal. The compressible form of the Navier–Stokes equations is considered to predict the oscillatory- and time-averaged mean flow fields. A control-volume method based explicit computational scheme is used to simulate the convective transport in the enclosure. The longitudinal and the transverse temperature gradients strongly affect the flow structure in the enclosure. The mean fluid motion alters the heat transfer behavior compared to the pure conduction.

Thermal Convection in an Enclosure With Sinusoidal Bottom Wall Temperature: Effect of Vibrating Side Wall

2012 ◽  
Author(s):  
Murat K. Aktas
Keyword(s):  
Wall Temperature ◽  
Stokes Equations ◽  
Control Volume ◽  
Fluid Motion ◽  
Side Wall ◽  
Convective Transport ◽  
Bottom Wall ◽  
Navier Stokes ◽  
Test Case ◽  
Mean Flow

The effects of a vibrating side wall on flow structure and heat transport in an air-filled two dimensional rectangular shallow enclosure with sinusoidal spatial bottom wall temperature distribution is studied numerically. The vibrating side wall induces an oscillating flow having nonzero mean component in the enclosure. The side walls of the enclosure are adiabatic. The top wall is isothermal and kept at initial temperature. The fully compressible form of the Navier–Stokes equations are considered to predict the oscillatory and time averaged mean flow fields. A control-volume method based, explicit computational scheme is used to simulate the convective transport in the enclosure. The simulation results of a test case for an unheated enclosure are compared with the existing literature for code validation. The sinusoidal temperature gradient of the bottom wall strongly affects the flow structures and velocities. The mean fluid motion significantly alters the overall heat transfer from the bottom wall.

Natural Convection Ventilation in Fully Open Enclosures

2010 ◽  
Author(s):  
Morteza Nateghi ◽  
Steven W. Armfield
Keyword(s):  
Natural Convection ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Full Range ◽  
Vertical Wall ◽  
Staggered Grid ◽  
Finite Volume Scheme ◽  
Full Development ◽  
Prandtl Numbers ◽  
Rayleigh Numbers

The present study is concerned with natural convection ventilation in a two dimensional fully open enclosure (cavity) with thermally stratified ambient for both transient and steady-state flow. The left hand vertical wall of the enclosure is heated and the right hand facing boundary is open, with the top and bottom boundaries insulated. The numerical solutions will be obtained by solving the Navier-Stokes equations and the temperature transport equation on a non-staggered grid using an unsteady second-order finite-volume scheme with a pressure correction equation used to simultaneously provide an update for the pressure field and enforce the divergence free condition. Results will be presented for Rayleigh numbers in the range 1 × 105 to 1 × 1010 with Prandtl numbers in the range 0.2 to 1.0. It will be shown that the flow transits from steady to unsteady, at full development, with increasing Rayleigh number for Pr <= 1.0, as observed for the similar closed enclosure flow. For higher Prandtl numbers the flow is steady at full development for the full range of Rayleigh numbers considered, again as for the similar fully closed enclosure. Streamline and temperature contour plots will be presented to illustrate the basic flow behaviours and to demonstrate the effect of the Prandtl number.

Combined Natural Convection and Volumetric Radiation in a Horizontal Annulus: Spectral and Finite Volume Predictions

1999 ◽  
Vol 121 (3) ◽  
pp. 610-615 ◽  
Author(s):  
D.-C. Kuo ◽  
J. C. Morales ◽  
K. S. Ball
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Stokes Equations ◽  
Control Volume ◽  
Navier Stokes ◽  
Differential Approximation ◽  
Navier Stokes Equations ◽  
Influence Matrix ◽  
Potential Benefits ◽  
The Mathematical Model

Combined natural convection and radiation in a two-dimensional horizontal annulus filled with a radiatively participating gray medium is studied numerically by using a control-volume-based finite difference method and a spectral collocation method coupled with an influence matrix technique. The mathematical model includes the continuity equation, the incompressible Navier-Stokes equations, the energy equation, and the radiative transfer equation (RTE), which is modeled using the P1 differential approximation. Computed results for two Rayleigh numbers, Ra = 104 and Ra = 105, for several combinations of the radiation-conduction parameter, NR, and the optical thickness, τ, are presented. The differences observed in the predicted flow structures and heat transfer characteristics are described. Furthermore, an unusual flow structure is studied in detail, and multiple solutions are found. Finally, the potential benefits of applying spectral methods to problems involving radiative heat transfer are demonstrated.

scholarly journals Viscous Flow and Dynamic Stall Effects on Vertical-Axis Wind Turbines

1995 ◽  
Vol 2 (1) ◽  
pp. 1-14 ◽  
Author(s):  
A. Allet ◽  
I. Paraschivoiu
Keyword(s):  
Wind Turbines ◽  
Stokes Equations ◽  
Control Volume ◽  
Numerical Procedure ◽  
Vertical Axis ◽  
Dynamic Stall ◽  
Staggered Grid ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbines ◽  
Control Volume Approach

The present paper describes a numerical method, aimed to simulate the flow field of vertical-axis wind turbines, based on the solution of the steady, incompressible, laminar Navier-Stokes equations in cylindrical coordinates. The flow equations, written in conservation law form, are discretized using a control volume approach on a staggered grid. The effect of the spinning blades is simulated by distributing a time-averaged source terms in the ring of control volumes that lie in the path of turbine blades. The numerical procedure used here, based on the control volume approach, is the widely known “SIMPLER” algorithm. The resulting algebraic equations are solved by the TriDiagonal Matrix Algorithm (TDMA) in the r- and z-directions and the Cyclic TDMA in the 0-direction. The indicial model is used to simulate the effect of dynamic stall at low tip-speed ratio values. The viscous model, developed here, is used to predict aerodynamic loads and performance for the Sandia 17-m wind turbine. Predictions of the viscous model are compared with both experimental data and results from the CARDAAV aerodynamic code based on the Double-Multiple Streamtube Model. According to the experimental results, the analysis of local and global performance predictions by the 3D viscous model including dynamic stall effects shows a good improvement with respect to previous 2D models.

Numerical Modeling of the Frosting Process on a Cold Finned Surface With Variable Fin Spacing

2014 ◽  
Author(s):  
Assem El Zaabalawy ◽  
Aya Diab ◽  
Zakaria Ghoneim
Keyword(s):  
Stokes Equations ◽  
Positive Impact ◽  
Control Volume ◽  
Simple Algorithm ◽  
Staggered Grid ◽  
Electrical Transmission ◽  
Frost Formation ◽  
The Impact ◽  
Fin Spacing ◽  
Frost Layer

Frost formation can incur damage to agricultural crops, roads, railways, electrical transmission lines, transport of oil and natural gas in cold climates, as well as refrigeration and air-conditioning equipment. Modeling of the frost formation process involves coupled heat and mass transport phenomena which are not only function of time but also of space. To model such complex interactions, a transient two dimensional mathematical model has been developed using a control volume approach, discretizing Navier-Stokes equations over a fixed Cartesian staggered grid coupling the pressure and velocity via the SIMPLE algorithm. To identify the interface between the air and the frost sub-domains, a cut cell approach has been used. The validated numerical model is used to investigate the impact of the heat exchanger configuration on the frost layer distribution. Specifically, a variable fin spacing (converging channel) is compared to the regular configuration (with straight fins) and is shown to have a positive impact on the frost layer distribution.

Numerical Analysis of Turbulent Natural Convection Heat Transfer Inside a Trangular Shaped Enclosure Utilizing Computational Fluid Dynamic Code

2006 ◽  
Author(s):  
M. Ghassemi ◽  
M. Fathabadi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Computational Fluid Dynamic ◽  
Numerical Study ◽  
Control Volume ◽  
Fluid Dynamic ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Turbulent Natural Convection

Numerical study of turbulent natural convection heat transfer inside a triangular shaped enclosure is considered. A k-ε model along with mass, momentum and energy equations is utilized to solve the flow and temperature field. A computational fluid dynamic based code (CFD), Fluent, that is commercially available is used is to solve the non-linear partial differential equations. The steady state, two-dimensional, incompressible heat transfer results are presented in terms of non dimensional temperature, heat flux, and the Nusselt number as a function of aspect ratio (Ar), angle between sloped and horizontal wall (θ), and the Grashof number (Gr). The obtained results are compared with results that are calculated by a control volume based method. Results obtained by the Fluent code shows closed agreement with the control volume ones. It is again shown that heat transfer is higher in turbulent settings and results are function of the angle between two walls of the enclosure (θ).

Turbulent Natural Convection Inside a Square Enclosure With Baffles

2010 ◽  
Author(s):  
Khudheyer S. Mushatet
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Staggered Grid ◽  
Algebraic Equations ◽  
Turbulent Natural Convection ◽  
Square Enclosure ◽  
Thermal Fields ◽  
Energy Equations ◽  
Volume Method

In this paper, the turbulent natural convection heat transfer and fluid flow inside a square enclosure having two conducting solid baffles has been numerically investigated. Fully elliptic Navier-Stockes and energy equations are disrectized using finite volume method along with a staggered grid techniques. The resulting algebraic equations were solved by using semi-implicit line by line Guase elimination scheme. The effect of turbulence was incorporated to treat the regions near the walls. The flow and thermal fields are investigated for different parameters such as the relative baffles height, Rayleigh number and the distance between baffles. The conducted results indicated that the resulting vortices are decreased in number and elongated with the decrease of the dimensionless relative baffle heights. Also the results show that the rate of heat transfer is increased with the increase of Ra especially for the region near the baffles.

scholarly journals Turbulent Flow Characteristics in a Model of a Solid Rocket Motor Chamber with Sidewall Mass Injection and End-Wall Disturbance

2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
F. A. Albatati ◽  
A. M. Hegab ◽  
M. A. Rady ◽  
A. A. Abuhabaya ◽  
S. M. El-Behery
Keyword(s):  
Flow Field ◽  
Turbulent Flow ◽  
Stokes Equations ◽  
Numerical Study ◽  
Rocket Motor ◽  
Staggered Grid ◽  
Computational Time ◽  
Solid Rocket Motor ◽  
Solid Rocket ◽  
End Wall

The present analytical, numerical, and experimental investigations are performed to study the flow field in acoustically simulated solid rocket motor (SRM) chamber geometry. The computational solution is carried out for a high Reynolds number and low Mach number internal flows driven by sidewall mass addition in a long chamber with end-wall disturbances. This kind of flow (transient, weakly viscous, and contains vorticity) have several features in common with a turbulent flow field. The numerical study is performed by solving the unsteady Reynolds-averaged Navier–Stokes equations along with the energy equation using the control volume approach based on a staggered grid system. The v2-f turbulence model has been implemented in the current study. A comparison of the SIMPLE and PISO algorithms showed that both algorithms provide identical results, and the computational time using the PISO algorithm is higher by about 6% than the corresponding value of the SIMPLE algorithm. A fair agreement has been obtained between the numerical, analytical, and experimental results. Moreover, the results showed that the complex turbulent internal flow patterns are induced inside the chamber due to the strong interaction of the sidewall injection with the traveling acoustic waves. Such a complex internal structure is shown to be dependent on the piston frequency and sidewall mass flux. The current study, for the first time, emphasizes the acoustic-fluid dynamics interaction mechanism and the accompanying unsteady rotational fields along with the effect of the generated turbulence on the unsteady vorticity and its impact on the real burning rate.

Computational Simulation of Turbulent Natural Convection in a Volumetrically Heated Square Cavity

2013 ◽  
Author(s):  
Camila Braga Vieira ◽  
Bojan Niceno ◽  
Jian Su
Keyword(s):  
Natural Convection ◽  
Turbulence Modeling ◽  
Stokes Equations ◽  
Computational Simulation ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Oxide Material ◽  
Square Cavity ◽  
Navier Stokes Equations ◽  
Turbulent Natural Convection

This work aimed to analyze the turbulent natural convection in a volumetrically heated fluid with Prandtl number equal to 0.6, representing the oxide material layer of a corium. Four turbulence models were scrutinized in order to select the most appropriate one for turbulence modeling based on Reynolds Averaged Navier-Stokes equations (RANS) of natural convection in a molten core. The turbulence models scrutinized are the standard k-ε, Shear Stress Transport (SST), low-Reynolds-k-ε (Launder-Sharma) and also an elliptic blending model ν2-f. The simulations were carried out in a square cavity with isothermal walls, for Rayleigh numbers (Ra) ranging from 109 to 1011. The numerical simulations, performed in an open-source of Computational Fluid Dynamics (CFD) - OpenFOAM (Open Field Operation and Manipulation), provided outcomes of average Nusselt number as function of Ra number, which were in a reasonable agreement with an experimental correlation and other authors’ simulations. It was also possible to observe the limitations and robustness of each model analyzed, enabling to conclude that the most adequate turbulence models for the present physical problem were SST and ν2-f.

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