Hassane Naji

Comparative Investigation on Heated Swirling Jets Using Experimental and Numerical Computations

The purpose of this paper is to investigate both experimentally and numerically the influence of various parameters on the different blowing configurations of multiple swirling jets. Flow rate was adjusted at Reynolds numbers ranging from 104 to 3 × 104. The current study is carried out under uniform heat flux condition for each diffuser, at Reynolds number of 3 × 104, with air being the working fluid. Experiments concerning the fusion of several jets show that the resulting jet is clearly more homogenized under swirling influence. Afterward, numerical simulation is also carried out using the finite-volume computational fluid dynamics solver FLUENT 6.3, in which the standard k − ϵ and the Reynolds stress turbulence model (RSM) were used for turbulence computations. The findings of this study show that the diffuser vane angle and a balance and an imbalance in temperature between the central and peripheral jets affect the quality of the thermal homogenization of the ambiance. Overall predictions obtained with the RSM model are in better agreement with the experimental data compared to those of the standard k − ϵ model.

Towards numerical computation of double-diffusive natural convection within an eccentric horizontal cylindrical annulus

Purpose – The purpose of this paper is to numerically study the double-diffusive natural convection within an eccentric horizontal cylindrical annulus filled with a Newtonian fluid. The annulus walls are maintained at uniform temperatures and concentrations so as to induce aiding thermal and mass buoyancy forces within the fluid. For that, this simulation span a moderate range of thermal Rayleigh number (100RaT100,000), Lewis (0.1Le10), buoyancy ratio (0N5) and Prandtl number (Pr=0.71) to examine their effects on flow motion and heat and mass transfers. Design/methodology/approach – A finite volume method in conjunction with the successive under-relaxation algorithm has been developed to solve the bipolar equations. These are written in dimensionless form in terms of vorticity, stream function, temperature and concentration. Beforehand, the implemented computer code has been validated through already published findings in the literature. The isotherms, streamlines and iso-concentrations are exhibited for various values of Rayleigh and Lewis numbers, and buoyancy ratio. In addition, heat and mass transfer rates in the annulus are translated in terms of Nusslet and Sherwood numbers along the enclosure’s sides. Findings – It is observed that, for the range of parameters considered here, the results show that the average Sherwood number increases with, while the average Nusselt number slightly dips as the Lewis number increases. It is also found that, under the convective mode, the local Nusselt number (or Sherwood) increases with the buoyancy ratio. Likewise, according to Lewis number’s value, the flow pattern is either symmetric and stable or asymmetric and random. Besides that, the heat transfer is transiting from a conductive mode to a convective mode with increasing the thermal Rayleigh number, and the flow structure and the rates of heat and mass transfer are significantly influenced by this parameter. Research limitations/implications – The range of the Rayleigh number considered here covers only the laminar case, with some constant parameters, namely the Prandtl number (Pr = 0.71), and the tilt angle (α=90°). The analysis here is only valid for steady, two-dimensional, laminar and aiding flow within an eccentric horizontal cylindrical annulus. This motivates further investigations involving other relevant parameters as N (opposite flows), Ra, Pr, Le, the eccentricity, the tilt angle, etc. Practical implications – An original framework for handling the double-diffusive natural convection within annuli is available, based on the bipolar equations. In addition, the achievement of this work could help researchers design thermal systems supported by annulus passages. Applications of the results can be of value in various arrangements such as storage of liquefied gases, electronic cable cooling systems, nuclear reactors, underground disposal of nuclear wastes, manifolds of solar energy collectors, etc. Originality/value – Given the geometry concerned, the bipolar coordinates have been used to set the inner and outer walls boundary conditions properly without interpolation. In addition, since studies on double-diffusive natural convection in annuli are lacking, the obtained results may be of interest to handle other configurations (e.g., elliptical-shaped speakers) with other boundary conditions.

Computational of the wind velocity effect on infiltration rates in an individual building using multi-zone airflow model

ABSTRACT This paper presents and discusses numerical simulation of the wind velocitys effect on infiltration rates in an individual building using multi-zone modelling. The governing equations are expressed in terms of unknown pressures at points where flow paths connect. Their implementation was achieved using an advanced numerical model, which was developed via the MATLAB environment. Such a numerical approach has been validated through available results. A good agreement has been observed between available data and our studys results. Moreover, the model implemented allows to determine the reference pressure in each zone to compute the air infiltration rate by each connection. To perform this, a large range of input data is needed. These include leakage characteristics of airflow elements, wind pressure coefficients, and ventilation system characteristics. To sum up, it is found that the wind velocity increase produces a strongly variation on computed infiltration rates.

On the evaluation of linear and non-linear models using DNS data of turbulent channel flows

In this paper, a priori and a posteriori analyses of algebraic linear and non-linear models are carried out in order to compare their ability to predict near wall turbulent flows. Tests were done using data from a direct numerical simulation (DNS) of a plane channel flow for three Reynolds numbers, based on the friction velocity, Reτ = 180, Reτ = 395 and Reτ = 590 . These models include the linear standard k - e model, the linear v2- f (Manceau et al., 2002) and the non-linear model of Shih (Shih et al., 1995). The results obtained are then compared with the DNS data of Moser et al. (1999). The comparisons are shown for the mean velocity profile, components of the Reynolds stress tensor, the turbulent kinetic energy (k), and the dissipation rate (e). The results suggest that the v2 - f is an efficient model to capture the turbulent shear stress component of the Reynolds stress near wall flows. However, it is unable to predict correctly the level of anisotropy between normal components of the Reynolds stress tensor. Furthermore, it is shown that the presence of non-linear terms in a turbulent model improves the ability to predict the anisotropy