Investigation Of Turbulent Natural Convection Research Articles

Investigation of Turbulent Natural Convection Combined with Radiation in a Square Enclosure with a Partition

Investigation of Turbulent Natural Convection Combined with Radiation in a Square Enclosure with a Partition

Experimental and numerical investigation of turbulent natural convection between two horizontal concentric cylinders at different axis ratios and orientation angles

Turbulent natural convection between two horizontal concentric cylinders with different orientation and axis ratios for the outer cylinder with both open-ended has been investigated experimentally and numerically. A Constant heat flux was imposed at the outer cylinder at five different heat fluxes 503, 751, 1002, 1251 and 1508 W/m2, while the inner cylinder was insulated. The hydraulic diameter was kept constant at 60 mm.The Rayleigh number Ra was varied from 1.017×107 to 3.25×107. The outer cylinder orientation angle, ϕ was varied from 0° to 90° with 15° increment. The influence of the axis ratio (major to minor axis) for the outer cylinder was studied at range from 1.0 to 2.0. A finite difference method for the governing equations related with the standard k-ε model has been utilized. The surface temperature distribution at outer cylinder, the axial velocity and average Nusselt number were estimated at different orientation angles and axis ratios of the outer cylinder. Turbulent intensity and axial velocity distribution were estimated numerically. Both experimental and numerical results for the average Nusselt number show good agreement. The results show that the heat transfer enhancement starts as the outer cylinder orientation angle increase more than the critical angle. The maximum increase in the average Nusselt number reaches 25% at vertical position and axis ratio at 2 for the outer cylinder.

Numerical Investigation of Turbulent Natural Convection for a Cavity Having Sinusoidal Protuberances on a Vertical Wall

Numerical Investigation of Turbulent Natural Convection for a Cavity Having Sinusoidal Protuberances on a Vertical Wall

Experimental investigation of turbulent natural convection in a vertical water channel with symmetric heating: Flow and heat transfer

The operating temperature of building integrated photovoltaic cells is a key factor in terms of energy efficiency. In order to cool them by natural convection, they are mounted in a double-skin façade configuration, meaning that they are separated from the building wall by a ventilated air channel. Identifying and analysing the physical phenomena governing the air flow and heat transfer in this vertical channel are therefore essential to improve cell-cooling. This analysis can only be performed by detailed numerical simulations coupled with experimental studies to validate the results. In the present work, an experimental model is developed in order to study the coupling between the flow and heat transfer of a natural convection flow in a vertical channel. An original approach is taken, using water as the working fluid to avoid radiative heat transfer and obtain a pure convective flow. First the experimental set-up, the boundary conditions and instruments used to obtain reference data are described. Then simultaneous temperature and velocity measurements are provided. Finally, an analysis of the mean velocity and fluctuations profiles shows a change of the flow behaviour occurring at a sufficiently high Rayleigh number.

Natural convection in a sidewall heated cube using an immersed boundary method

Numerical simulation of a square cavity was conducted to validate an implementation of an Immersed Boundary Method (IBM). The cavity consists of two differentially heated side walls and adiabatic top and bottom walls. A Cartesian grid is used with a finite volume, fractional step pressure correction method. Simulations use Dirichlet boundaries for vertical walls and Neumann boundaries for horizontal walls. The Immersed Boundary Method involves modifying the Navier--Stokes equations to include a forcing function in the momentum and energy equations that creates a virtual boundary. This method is useful because the boundary does not necessarily have to coincide with grid points; however, it is much less computationally expensive than other similar methods such as the cut cell method. The IBM is commonly used in simulations involving complex objects and can also accommodate moving boundaries. A standard numerical simulation with grid aligned with the boundary is first compared with previous results. The same geometry is then simulated by tilting the grid at various angles and using the IBM for each of the walls, and comparing these results with those initially obtained. We detail the implementation method and common problems associated with this. Velocity and temperature profiles are presented and the IBM is shown to maintain second order spatial accuracy. References E. A. Fadlun, R. Verzicco, P. Orlandi, and J. Mohd-Yusof. Combined immersed-boundary finite-difference methods for three-dimensional complex flow simulations. Journal of Computational Physics, 161(1):35--60, 2000. doi:10.1006/jcph.2000.6484 T. Gao, Y. H. Tseng, and X. Y. Lu. An improved hybrid cartesian/immersed boundary method for fluid-solid flows. International Journal for Numerical Methods in Fluids, 55(12):1189--1211, 2007. doi:10.1002/fld.1522 M. P. Kirkpatrick and S. W. Armfield. Experimental and large eddy simulation results for the purging of salt water from a cavity by an overflow of fresh water. International Journal of Heat and Mass Transfer, 48(2):341--359, 2005. doi:10.1016/j.ijheatmasstransfer.2004.08.016 M. P. Kirkpatrick, S. W. Armfield, and J. H. Kent. A representation of curved boundaries for the solution of the navier-stokes equations on a staggered three-dimensional cartesian grid. Journal of Computational Physics, 184(1):1--36, 2003. doi:10.1016/S0021-9991(02)00013-X B. P. Leonard and Simin Mokhtari. Beyond first-order upwinding: The ultra-sharp alternative for non-oscillatory steady-state simulation of convection. International Journal for Numerical Methods in Engineering, 30(4):729--766, 1990. doi:10.1002/nme.1620300412 S. H. Peng and L. Davidson. Large eddy simulation for turbulent buoyant flow in a confined cavity. volume 22, pages 323--331, 2001. doi:10.1016/S0142-727X(01)00095-9 C. S. Peskin. Numerical-analysis of blood-flow in heart. Journal of Computational Physics, 25(3):220--252, 1977. doi:10.1016/0021-9991(77)90100-0 J. Salat, S. Xin, P. Joubert, A. Sergent, F. Penot, and P. Le Quere. Experimental and numerical investigation of turbulent natural convection in a large air-filled cavity. International Journal of Heat and Fluid Flow, 25:824--832, 2004. doi:10.1016/j.ijheatfluidflow.2004.04.003 Y. H. Tseng and J. H. Ferziger. A ghost-cell immersed boundary method for flow in complex geometry. Journal of Computational Physics, 192(2):593--623, 2003. doi:10.1016/j/jcp.2003.07.024 N. Zhang and Z. C. Zheng. An improved direct-forcing immersed-boundary method for finite difference applications. Journal of Computational Physics, 221(1):250--268, 2007. doi:10.1016/j.jcp.2006.06.012 N. Zhang, Z. C. Zheng, and S. Eckels. Study of heat-transfer on the surface of a circular cylinder in flow using an immersed-boundary method. International Journal of Heat and Fluid Flow, 29(6):1558--1566, 2008. doi:10.1016/j.ijheatfluidflow.2008.08.009

Turbulent natural convection in an enclosure with localized heating from below

This study reports the results of a numerical investigation of turbulent natural convection in a square enclosure with localized heating from below and symmetrical cooling from the vertical side walls. The present study simulates the case of an accidental heat generation due to fire in a typical isolated building of a nuclear reactor or electronic components cabin. The source of fire is considered to be centrally located at the bottom wall with different heated widths, which is assumed to be either isothermal or with isoflux. For the purpose of the analysis, the source length is varied from 20 to 80% of the total width of the bottom wall. The top wall and the unheated portion of the bottom wall are considered to be adiabatic, whereas sidewalls are isothermal. Steady as well as transient forms of two-dimensional Reynolds–Averaged-Navier–Stokes equations and conservation equations of mass and energy, coupled with the Boussinesq approximation, are solved by the control volume based discretisation method employing the SIMPLE algorithm for pressure–velocity coupling. Turbulence is modeled using the standard k – ε model. Rayleigh number, Ra, based on the enclosure height is varied from 10 8 to 10 12. Stream lines and isotherms are presented for various combinations of Ra and the heated width. A double cell flow pattern is observed with marginal loss in symmetry as Ra increases. The results are reported in the form of local and average Nusselt number on the heated floor. Correlations are developed to predict the heat transfer rates from the enclosure as a function of dimensionless heated width of the bottom wall and Ra, by least square linear regression analysis.

Numerical investigation of turbulent natural convection in an inclined square cavity with a hot wavy wall

The turbulent natural convection of air flow in a confined cavity with two differentially heated side walls is investigated numerically up to Rayleigh number of 10 12. The objective of the present work is to study the effect of the inclination angle and the amplitude of the undulation on turbulent heat transfer. The low-Reynolds-number k– ε, k– ω, k– ω–SST RANS models and a coarse DNS are used and compared to the experimental benchmark data of Ampofo and Karayiannis [F. Ampofo, T.G. Karayiannis, Experimental benchmark data for turbulent natural convection in an air filled square cavity, Int. J. Heat Mass Transfer 46 (2003) 3551–3572]. The k– ω–SST model is then used for the following test-cases as it gives the closest results to experimental data and coarse DNS for this case. The mean flow quantities and temperature field show good agreement with coarse DNS and measurements, but there are some slight discrepancies in the prediction of the turbulent statistics. Also, the numerical results of the heat flux at the hot wall are over predicted. The strong influence of the undulation of the cavity and its orientation is well shown. The trend of the local heat transfer is wavy with different frequencies for each undulation. The turbulence causes an increase in the convective heat transfer on the wavy wall surface compared to the square cavity for high Rayleigh numbers. A correlation of the mean Nusselt number function of the Rayleigh number is also proposed for the range of Rayleigh numbers of 10 9–10 12.

Experimental and numerical investigation of turbulent natural convection in a large air-filled cavity

We investigate experimentally and numerically the turbulent natural convection flow that develops in a differentially heated cavity of height H=1 m, width W= H and depth D=0.32 H, submitted to a temperature difference between the active vertical walls equal to 15 K resulting in a characteristic Rayleigh number equal to 1.5 × 10 9. In the experiment temperature is measured by 25 μm micro-thermocouples and velocity by a Laser Doppler Anemometer. Both 2D and 3D LES and 3D DNS are performed. DNS uses a Chebyshev spectral method and LES a finite volume method with a local subgrid diffusivity model. Numerical simulations are performed for both adiabatic conditions and experimentally measured temperature on the horizontal walls. Time-averaged quantities and turbulent statistics in the median vertical plane are presented and compared.

An experimental investigation of turbulent natural convection in air at low pressure along a vertical heated flat plate

An experimental investigation of turbulent natural convection in air is described. The results of this study show good agreement with early investigations and remarkable agreement with the analytical correlation of Bayley [4]: Nu = 0·10 Ra 1 3 for Rayleigh numbers up to 10 12. Extensive measurements of the temperature field indicate a good similarity in the temperature profiles when compared on the basis of the natural coordinate ty. The use of power law temperature profiles is shown to be undesirable for the case of turbulent natural convection.