**4. Computational fluid dynamics in aerodynamics of buildings**

In recent years, computational fluid dynamics (CFD) simulations have witnessed a spread use and applications as a potential tool in aerodynamic investigations of buildings. However, by considering the constraints of experimental testing in wind tunnels that limit producing the low-frequency large-scale turbulence and the inherent issues with limited integral length scale, implementing appropriate turbulence closure in CFD and developing a proper inlet transient

velocity may alleviate the issues with experimental measurements in wind engineering. In CFD, the scale is not an immediate issue, as a full-scale model of the structure can be modeled and tested under various extreme wind scenarios. The simulation can be repeated to yield the same results any time. Even large-scale problems, such as simulating an urban area with condensed high-rise buildings for pollutant dispersion studies can be performed in CFD [33]; this can be challenging in laboratory testing due to scale issues.

monitoring the vertical profiles. Achieving horizontal homogeneity ensures that the inlet, approach and incident flow are the same and eventually provide results with higher accuracy [50]. In several previously conducted studies, maintaining a consistent profile of mean wind speed and turbulent kinetic energy was an issue with different turbulence closure models. Significant near wall flow acceleration was found to cause unwanted change in mean wind speed and turbulent kinetic energy in simulation conducted in [51]. Additionally, issues in maintaining a consistent profile for turbulent kinetic energy were observed in [52, 53]. For accurate CFD results, maintaining consistent vertical profiles throughout the domain is important. Minor change in the profiles can create significant changes in the flow field. For flow around buildings, the importance of retaining the vertical flow profiles was

*Aerodynamics of Low-Rise Buildings: Challenges and Recent Advances in Experimental…*

In Section 2, the main characteristics of ABL wind were presented. One of the main parts of any wind engineering study is to appropriately reproduce the wind characteristics in a controlled manner, to examine the response of a structure in the scope of a certain wind event. This means that first the wind flow characteristics should be simulated following an acceptable protocol and following that windinduced pressures and loads on the surfaces of a building can be obtained by aerodynamic testing, according to the laws of similitude [55]. In order to satisfy these requirements, there are some tools used for ABL processes, including wind

For several decades, wind tunnel modeling has been widely used as a technique to estimate wind-induced pressures and loads on buildings. **Figure 7** shows a view of a wind tunnel at the University of Western Ontario and a 1:100 scale low-rise building model. The arrangement and height of passive roughness elements are designed to reproduce wind flow over an open-terrain exposure with *z0* = 0.01 *m* [57]. This test case was selected benchmark for validation and comparison with other computational and experimental measurements. For accurate estimation of aerodynamic forces on buildings, proper replication of wind speed, turbulence intensity profiles, and spectral characteristics is essential [58]. Matching the spectral

*A view of a wind tunnel at the University of Western Ontario: (a) 1:100 low-rise building model and the roughness element arrangement for an open-terrain exposure simulating* z0 *= 0.01* m *and (b) a closer view of*

stressed in Refs. [50, 54].

*DOI: http://dx.doi.org/10.5772/intechopen.92794*

**5. Aerodynamic testing**

tunnels and open-jet facilities [56].

**5.1 Wind tunnel testing**

**Figure 7.**

**39**

*the test model instrumented with pressure taps [57].*

CFD is gaining popularity within the wind engineering community along with the rise of computational power. Nowadays, CFD is commonly used to address wind engineering problems such as pollutant dispersion, wind comfort for pedestrians, aerodynamic loads on structures, or effects of bridge scour [34–37]. CFDbased numerical simulations will eventually complement the existing experimental practices for a number of wind engineering applications [38–40]. In most cases, numerical approaches are less time-consuming than experiments, and detailed information at higher resolution can be retrieved for scaled models from numerical simulations. In few earlier studies, the accuracy of analyzing bluff bodies with CFD has been questioned [41–43]. The reason behind inaccuracies was detachment of shear layer at sharp edges of bluff bodies. Detachment of shear layer makes the overall flow in the domain more responsive to local behaviors. The local effects are influenced by turbulence intensity and turbulence length scales of the incoming flow [36, 44]. Inaccurate replication of incoming turbulence properties in earlier studies was considered a reason for discrepancies in results. In Ref. [45], careful replication of horizontal turbulence properties at roof height of low-rise buildings was declared important. Few earlier studies focused on comparing surface pressures from numerical simulations with experiments and full-scale measurements. Good agreement was found among different data sources for mean pressure coefficient, while differences were found for fluctuating pressure coefficient [46].

Large eddy simulation (LES) can yield better results than turbulence closures that are based on Reynolds-Averaged Navier-Stokes (RANS), however, for higher cost of computations. The accuracy of solution of any wind engineering problem with CFD depends on the precise simulation of wind flow. A number of studies have indicated better performance of LES turbulence model for predicting mean and instantaneous flow field around bluff bodies [42, 47]. The concept of LES involves resolving the large scales in fluid flow and modeling the small scales. This approach is theoretically suitable for wind engineering applications as normally large scales are responsible for forces of interest [42]. Earlier applications of LES involving treatment of flows at low-Reynolds number yielded satisfactory results. Simply, the use of LES does not guarantee meaningful and accurate results. For flows with higher turbulence, results become more sensitive to the quality of the model [42]. Modeling of small-scale turbulence has gone through stages of improvement over the years. Sub-grid scale modeling remains the commonly used modeling technique. To yield accurate results, maintaining proper inflow boundary condition (IBC) is fundamental. Three methods are identified for generating IBC, and they are [48] (a) precursor database, (b) recycling method, and (c) turbulence synthesizing. The first two methods are computationally demanding; the third method is promising [49].

Maintaining horizontal homogeneity in the computational domain is another challenge in CFD simulations. Horizontally homogeneous boundary layer refers to the absence of artificial acceleration near the ground or stream-wise gradients in vertical profiles of mean velocity and turbulence intensity [50]. One may run steady-state simulation until it reaches convergence and monitors the vertical profiles of velocity and turbulence intensity at different locations in the domain. In case of LES, the mean value should be taken from the velocity time history for

*Aerodynamics of Low-Rise Buildings: Challenges and Recent Advances in Experimental… DOI: http://dx.doi.org/10.5772/intechopen.92794*

monitoring the vertical profiles. Achieving horizontal homogeneity ensures that the inlet, approach and incident flow are the same and eventually provide results with higher accuracy [50]. In several previously conducted studies, maintaining a consistent profile of mean wind speed and turbulent kinetic energy was an issue with different turbulence closure models. Significant near wall flow acceleration was found to cause unwanted change in mean wind speed and turbulent kinetic energy in simulation conducted in [51]. Additionally, issues in maintaining a consistent profile for turbulent kinetic energy were observed in [52, 53]. For accurate CFD results, maintaining consistent vertical profiles throughout the domain is important. Minor change in the profiles can create significant changes in the flow field. For flow around buildings, the importance of retaining the vertical flow profiles was stressed in Refs. [50, 54].
