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Recently, increased attention has been given to the coupling of computational fluid dynamics (CFD) with the fuzzy logic control system for obtaining the optimum prediction of many complex engineering problems. The data provided to the fuzzy system can be obtained from the accurate computational fluid dynamics of such engineering problems. Windcatcher performance to achieve thermal comfort conditions in buildings, especially in hot climate regions, is considered as one such complex problem. Windcatchers can be used as natural ventilation and passive cooling systems in arid and windy regions in Saudi Arabia. Such systems can be considered as the optimum solution for energy-saving and obtaining thermal comfort in residential buildings in such regions. In the present paper, three-dimensional numerical simulations for a newly-developed windcatcher model have been performed using ANSYS FLUENT-14 software. The adopted numerical algorithm is first validated against previous experimental measurements for pressure coefficient distribution. Different turbulence models have been firstly applied in the numerical simulations, namely, standard k-epsilon model (1st and 2nd order), standard Wilcox k-omega model (1st and 2nd order), and SST k-omega model. In order to assess the accuracy of each turbulence model in obtaining the performance of the proposed model of the windcatcher system, it is found that the second order k-epsilon turbulence model gave the best results when compared with the previous experimental measurements. A new windcatcher internal design is proposed to enhance the ventilation performance. The fluid dynamics characteristics of the proposed model are presented, and the ventilation performance of the present model is estimated. The numerical velocity profiles showed good agreement with the experimental measurements for the turbulence model. The obtained results have shown that the second order k-epsilon turbulence can predict the different important parameters of the windcatcher model. Moreover, the coupling algorithm of CFD and the fuzzy system for obtaining the optimum operating parameters of the windcatcher design are described.

In windy and arid regions of different countries worldwide and especially in Saudi Arabia, windcatchers can be considered as the optimum solution for energy-saving and obtaining indoor thermal comfort in a natural way. Previously, different shape designs of windcatchers have been proposed and tested either numerically or experimentally, and their ventilation performance has been evaluated. Extended reviews of different theoretical and experimental methods employed to evaluate the performance characteristics of windcatchers can be found in [

Computational fluid dynamics has recently received great attention in the numerical simulation of the windcatcher model design and performance. Different parameters have been found to have important effects on the obtained results, such as the resolution of the computational grid, the order of discretization scheme, and the turbulence model adopted. Most of the previous studies have been performed for 3D steady RANS for traditional two-sided windcatcher models [

Generally, it can be concluded from the previous literature that no investigations have been performed to study the effect of the internal design of the windcatcher model on the ventilation performance. Moreover, most of the previous CFD simulation has considered the known standard turbulence models. In our previous paper [

In the present paper, computational fluid dynamics (CFD) for the proposed design of the windcatcher using ANSYS FLUENT-14 software is performed. Different turbulence models have been used firstly for validation of the numerical scheme. The verified model is then used for the following prediction of the windcatcher performance.

The new design of the internal section of the windcatcher is illustrated in Figure

The proposed windcatcher and its geometrical parameters (

The Reynolds number of the incoming air is calculated according to the relation: Re = _{h}/_{h} is the hydraulic diameter of the cross-section (_{h} = 4

In the described design shown above, it is assumed that interior of the windcatcher is divided into four separated sections. Each section has a square opening with width _{in} in the normal direction of the incident wind. An inclined wall with an angle _{1}/_{2} (see Figure

This innovative design of the internal section of the windcatcher that receives the incident wind can lead to an increase of the wind velocity due to the convergent nozzle shape applied. After the streaming of the incoming air flow through the opening with width _{2}, air pressure will increase due to the cross-section area expansion. Consequently, the air flow is directed to the building interior with high pressure, enabling uniform air distribution in a natural way. The model parameters, such as (_{1}/_{2},

The problem will be addressed in this study using CFD techniques. The four-sided windcatcher, previously proposed by the authors in an earlier study [

The three-dimensional computational model is set up to simulate the considered windcatcher geometry. Also, the boundary conditions and the model operating conditions are also defined. The solution is carried out using the commercial software ANSYS FLUENT-14. The computational domain along with the boundary conditions has been described as shown in Figure ^{+} < 5 in the viscous sublayer). The upstream velocity was imposed to the inlet section of the model.

Computational domain and boundary conditions.

The flow characteristics inside the proposed design of the windcatcher can be predicted by solving a set of the governing equations in the form of Reynolds-averaged Navier–Stokes equations, as follows:

The continuity and momentum equations for incompressible and steady turbulent flow, known as RANS equations, at each grid point of the flow field can be described by the following equations after omitting the body force:

In the above system of equations,

The turbulent kinetic energy

For the problem under consideration, as it can be shown in Figure

In order to validate the proposed numerical algorithm, a three-dimensional model was setup to replicate the experimental model of the one-sided windcatcher of Montazeri and Azizian [

Comparison of different turbulent models with experimental data for pressure recovery coefficient (Cp) on (a) back wall and (b) side wall of windcatcher.

The new model with the proposed modifications was tested numerically and pressure recovery coefficient was compared along the length of the windcatcher. The effect of changing the slab length, opening of the windcatcher, and Reynolds number was explored. For all cases, velocity contours, velocity streamlines, and velocity vectors were also compared.

The slab length for the proposed windcatcher model was varied as 1/3, ½, and 2/3 of the side of the square cross-section of the windcatcher. The baseline case of without slab was also included in the study. Figure

Effect of slab length (_{1}) on pressure recovery coefficient (Cp) on (a) back wall and (b) side wall of windcatcher.

Velocity contours at different lengths of slab. (a) _{1}/_{2} = 0.33, (b) _{1}/_{2} = 0.5, and (c) _{1}/_{2} = 0.66.

The opening of the proposed windcatcher model to atmosphere was varied in terms of the slant angle as _{1}/_{2} = 0.5 was selected for this analysis. Figure

Effect of slant angle (

Velocity contours at different slant angles (

The effect of Reynolds number was investigated by imposing three different inlet velocities viz. 5 m/s, 10 m/s, and 15 m/s in the windcatcher model. The slab length was _{1}/_{2} = 0.5 and inlet opening was taken as

Effect of Reynolds number (Re) on pressure recovery coefficient (Cp) on (a) back wall and (b) side wall of windcatcher.

Velocity contours at different Reynolds number (Re).

As seen in the previous section, the numerical results obtained from the computational fluid dynamics of the proposed internal design of a windcatcher model are dependent on a number of operating parameters, namely, _{1}/_{2} ratio, the angle (

The complete system CFD fuzzy system diagram.

Figure

The fuzzy control surface.

In this study, a novel model of windcatcher was proposed to employ in passive cooling of living spaces. The suggested four-way model has openings on four sides that lead the incoming air to the duct downstream. In the present study, only one side of the system is modelled. A slab near the inlet opening was placed to create a nozzle effect to enhance the pressure recovery downstream. The model was studied numerically for the variation of slab length, Reynolds number of incoming wind velocity, and inlet opening to the atmosphere. The data analysis revealed that the introduction of a slab near the inlet improved pressure recovery, which increased with the length of the slab. Higher value of pressure recovery was also observed with increasing opening of inlet section. The effect of Reynolds number on pressure recovery was seen up to a moderate value of Re, after which it did not change significantly. The new model can help in optimizing the design parameters of windcatcher for given local atmospheric conditions. In the future work, the fuzzy logic system will be applied for obtaining the optimum values of the operating parameters.

No data were used to support this study.

The authors declare no conflicts of interest.