**4. Urban physics and microclimatic comfort analysis with CFD**

When both the applications and the literature are examined, it is seen that the number of research studies and applications that take into account the wind, which is the most important parameter of the microclimatic comfort parameter in urban design, is inadequate. Although most of the literature studies generally focus on the details and technical aspects of wind simulation used in the analysis, there are not many studies for urban planning practitioners on how they can apply wind simulation to improve their designs. This naturally means that wind simulation is not used enough in city planning at the moment, which reduces the quality of the outdoor urban area, and unqualified designs are produced.

The application of wind simulation in urban planning in conceptual design, schematic design, and detail design processes in the urban planning process can be preferred especially in schematic and detail design processes since the conceptual design phase is not very detailed by nature. During the schematic design phase, wind behavior between buildings can be considered on a rather macro scale. In the detail stage, wind analyzes may not be very effective in the wind-design relationship, since it is a scale that can be handled at the scale of the building envelope, and at this stage the settlement, shape-form decisions are determined.

There are four methods for analyzing wind speeds and directions. The first is on-site measurements. These provide detailed information, but extensive field measurements are time-consuming and expensive. They only work when analyzing current situations, so their use in predicting the impact of changes on the built environment is limited.

The second is the testing of scale models in wind tunnels. The modeling process itself is fairly simple and sensors can be used to get precise data on wind speeds, but it has two drawbacks. First, measurements are only made where the sensors are located, so their placement becomes critical to the results. Second, a wind tunnel is a specialized piece of equipment and not everyone has physical and financial access to it, which may be seen by urban planners as a barrier to its adoption.

The third method consists of simplified calculation methods. Rather than simulating the actual physical processes that together determine wind behavior, they use simplified, empirical mathematical models to predict wind speed based on surrounding urban geometry. These techniques have a relatively low computational cost but are also less accurate. There is also a lack of user-friendly software for the implementation of these techniques, making them less suitable for practitioners [10].

The fourth method of analyzing wind is computational fluid dynamics (CFD). This is using a computer-based model to simulate real physical processes that together determine the behavior of the wind. CFD provides a complete picture of wind behavior across the entire model and is well established in a variety of fields, making it more accessible than field measurements, wind tunnel experiments, or simplified mathematical models in general. CFD is also becoming more applicable due to advances in computer technology [11].

Considering all the advantages and disadvantages, wind analyzes, whether alone or comprehensively as a part of microclimate analysis, cannot be used sufficiently in urban planning processes at present [3]. The barriers for CFD are lower than for other techniques, so CFD is the focus of this chapter. When we look at the historical background of urban microclimate studies, they have mostly been done with observational methods such as field measurements. In recent years, with advances in computational resources, numerical simulation approaches have become increasingly popular. Nowadays, especially CFD is frequently used to evaluate the urban microclimate. Computational simulations in urban physics and urban design studies can be used to study urban microclimate at different scales, from meteorological macro–micro scale to building scale [12–14]. Most of the CFD urban physics for microclimate studies have focused on parameters related to temperature, wind flow, thermal comfort, and heat transfer. CFD has repeatedly demonstrated its predictive ability in validation studies focusing on different parameters. CFD provides the possibilities of detailed indoor and outdoor comfort modeling of each building by evaluating inter-building microclimatic parameters at an urban scale. In the past, articles have been published that provide extensive reviews of meteorological micro-scale CFD studies [15, 16].

Advances in the application of computational simulations in recent years have allowed them to develop best practice guidelines in urban microscale studies, so the popularity of the use of CFDs has continued to grow steadily [13, 17, 18]. Microscale CFD studies in urban design, pedestrian level comfort between buildings, wind flow around buildings [19–23] pedestrian wind comfort [24, 25] pedestrian thermal comfort [26] the effect of wind-induced rain on buildings [27, 28]. It includes the distribution of urban air quality [29–32] etc. In the literature, there are studies on natural ventilation studies and convective heat transfer coefficients CFD studies for the analysis of the microclimate at the pedestrian level around the buildings at the building scale [12, 13, 15, 16, 21, 26, 33–36]. The smallest-scale studies using CFD on microclimatic analyzes at urban scale are the ones dealing with the indoor microclimatic comfort conditions of the building, where the horizontal distances between buildings are approximately 10 m and the focus is on the indoor climate. CFD has been used primarily for indoor ventilation studies and HVAC design issues in studies on this scale [22, 37–42]. In the last decade, the popularity of topics such as urban settlement/location, urban street canyons, building blocks, courtyards, and urban microclimate has been increasing year by year in studies with CFD on the microclimatic scale of urban physics [43–53]. Most of the studies on real urban areas appear to have been conducted in mid-latitude climates [54].

In the literature, CFD studies on urban physics and microclimatic comfort studies appear as validated and unvalidated studies. CFD studies on the unvalidated real urban area are mostly comparative studies comparing current real comfort conditions of different urban configurations, design parameters, neighborhoods, and districts within the same urban area. Most of these studies target to achieve best-case scenarios based on optimization of a target parameter (e.g. outdoor thermal comfort) [55–58] Most of the CFD urban microclimate studies are conducted without verification. The percentage share of unvalidated studies seems to have remained fairly stable in recent years. However, it is imperative that CFD urban microclimate studies include much more frequent validation to provide the desired reliability and predictive capability. The most common reason for the lack of validation in CFD microclimate studies may be the lack of relevant and well-documented measurement data [54].

When the field measurements method is used in microclimate studies in real urban areas, meteorological measurements such as field measurements of wind and

#### *The Impacts of Air Pressure Differences on Microclimatic Wind Comfort among Low-Rise… DOI: http://dx.doi.org/10.5772/intechopen.101743*

air temperature around the street and building are made, this method is relatively simple. However, this methodology may not be possible to use in all urban studies. However, there may be certain limitations in the use of these data for scientific purposes and, in particular, their suitability for validation purposes. This is because the meteorological conditions in the measured urban area are complex and constantly changing, and not only requires careful measurement of a large number of parameters (to be used as boundary conditions in simulations), but also a fairly complete reporting of the urban area, measurement systematics, at the same time, a detailed and comprehensive validation study of the urban area, measurement scheme, measurement accuracy, etc., would not be possible without them [55–58].

When the related articles studies in the literature are examined, in addition to experimental wind tunnel tests and field measurements studies, numerical analysis studies with CFD have been increasing in recent years to examine pedestrian level comfort wind conditions in urban areas. Compared to both wind tunnel tests and field measurements, CFD has some advantages. One of the major advantages of CFD over wind tunnel testing is that it gives detailed flow area data of associated parameters across the entire calculation area.

Another advantage of CFD over wind tunnel measurements is that, in general, wind tunnel measurements are performed at only a few selected points in the model, while CFD provides a more detailed analysis of wind flow around the building(s) by providing data on relevant parameters at all points of the calculation areas [59–61].

This study aims to investigate the effect of building orientation and forms, and street orientations in terms of pedestrian level microclimatic comfort and natural ventilation of pedestrian level comfort conditions in the urban area within the dense structure of the city of the case study area, which is located in the historical texture of Montenegro region. The aim is to answer the questions on the relation of the prevailing wind and the wind behavior in the built-up area. For this purpose, in the case study area of Montenegro, which is a historical settlement area, wind analyzes were carried out in 10 different directions (North, South, East, West, North-East, North-West, South-East, South-West, North- North-East, East- North-East) using the highest wind speed of 30.5 m/s, considering the worst scenarios in the light of meteorological data, as well as cardinal and intercardinal directions as boundary conditions.

This study focuses on the role of wind, which is the most important parameter affecting urban microclimatic comfort, which should be considered in the urban design process. Wind affects primarily urban air pollution and air pressure, as well as the energy exchange of buildings and users with the effect of convective heat transfer. Thus, it becomes one of the main driving forces of urban physics and urban microclimate. To evaluate the natural ventilation potential in the hot-humid climate of the Bay of Kotor region of Montenegro, the air exchange coefficients of the buildings in the case study region were examined. In the study of Moreau and Gandermer [62], on the evaluation of natural ventilation and pedestrian level comfort conditions in the urban area, a table is given about the air exchange rates


**Table 1.** *Guidelines for natural ventilation potential [62].* of the buildings in the urban texture and the relationship between natural ventilation (**Table 1**). Guidelines are based on the pressure coefficient differential ∆Cp between upwind and downwind sidewalls of a building.
