## 6 Results and Discussion
Figure 10: Velocity streamlines of the mean flow field on the symmetry plane of the computational domain for Scenario A. The surface temperatures of the cube are the result of an energy balance between the incoming thermal radiation that is absorbed and reflected or emitted, and heat convection by the airflow. The amount of radiation that reaches the surfaces of the cube and the visibility of the solar path are determined by Athens's longitude and latitude. Albedo and emissivity of the surfaces control the shortwave and longwave radiation components reflected and emitted, respectively. The albedo and emissivity coefficients are 0.2 and 0.95, respectively, typical values for concrete material. The thermal heat capacity and thermal conductivity of the cube control its ability to store and conduct heat, respectively. Figure 11: Normalized temperature profiles at the wake region of the flow for Scenario C, at X = 7 H and Y = 5.5 H, where \(T\) is the mean temperature, \(T_{a}\) is the ambient temperature, and \(T_{f}\) is the temperature at the floor of the computational domain [41]. The temperature on the cube surfaces depends primarily on the convective thermal energy loss. In regions, where turbulence exists high heat exchange takes place. At the lower part of the frontal surface of the cube, where the horseshoe-shaped vortex appears, low surface temperatures appear. On the contrary, on the upper part of the frontal surface of the cube higher surface temperatures are shown. Similarly, on the wake zone of the cube where the arc vortex is present, low surface temperatures are shown because of the high heat exchange rate. On the first part of the roof surface where the flow separates the heat exchange is small, so the surface temperature is high, and on the second part it is reduced where the flow reattaches. Figure 13 present the vertical mean pollutant concentration profiles computed for the time period from 800-1400 (s), at which all variables are statistically stationary on the symmetry plane for both Scenarios A and C at the Cartesian coordinate positions of X: 7 H, for a, X: 7.2 H for b, and 7.4 H, for c. The height Z extends from 0 to 2 H.  
In Figure 13, the highest mean concentration of the pollutant is observed for Scenario A, where a large amount of the pollutant is trapped inside the wake region. In contrast, in Scenario C where because of the high buoyancy forces the maximum pollutant concentration is small in the above region as the pollutant is shifted almost one cube height higher away from the floor, thus creating a recirculation region of larger length and height than that corresponding for Scenario A. As the pollutant in Scenario A is trapped inside the wake region of the cubical building, it becomes very harmful to the pedestrian's health. In Scenario C, this problem is exempted to a large extent, as the high levels of pollutant concentrations are at much higher heights than those of the pedestrians. This behavior is the result primarily of the buoyant forces acting on the roof and on the leeward surfaces of the building. Figure 14 present the distribution of the flux concentration on the symmetry plane because of the x-velocity component for Scenarios A and C at the x-positions: (a) (X: 7 H, Y: 5.5 H), (b) (X: 7.2 H, Y: 5.5 H), and (c) (X: 7.4 H, Y: 5.5 H) for heights Z that extend from 0 to 2 H.  
Figure 12: Temperature distribution on the vertical and horizontal surfaces of the building for the Scenario C along three different streamwise paths. Figure 13: _Cont._  
In the wake region, up to the height of the cube, the flux concentration is similar for both cases A and C. At heights higher than the building, the concentration flux for Scenario A is larger of that of C because of the important influence of higher free stream air velocity. Additionally, the wake zone height in Scenario C exceeds the height of the building and the low values of air velocity produce low concentration fluxes.