ANSYS-CFX

CFX [146] is a FVM-based, general purpose CFD tool that possesses similar capabilities as the ANSYS-Fluent software reported above, at least for airflows within urban canopies. The main differences are focused on mesh-generation algorithms and solution algorithm as well as differences in functionality and operability of available GUIs related to user's actions during pre- and post-processing. By means of spatial discretization, Fluent uses a cell-centered approach, while CFX uses a vertex-centered approach; hence, Fluent can handle polyhedral mesh and cut-cell meshes, while CFX is limited to the traditional tetraand hexa-mesh topologies. Concerning the comparison between the results obtained by CFX and Fluent, they present similar accuracy; however, Fluent has presented a slightly better accuracy for incompressible flows, although it requires more computational time to converge. This happens due to the fewer computational nodes in CFX grids in comparison to Fluent grids. Fluent has a more functional pre-processor and, thus, it requires less time

to prepare the grid and work on available GUIs. Fluent has post-processing capabilities of its own while CFX needs a dedicated post-processor.

Priyadarsini et al. (2008) [147] used CFX to investigate the UHI effect on temperature rising in the urban canopy in Singapore. They determined the key factors causing the phenomenon and investigated the possibilities of improving heat release rate by optimizing airflow in selected hot spots. The main parameters put to the test were building geometry, materials of façades, and the location of air-conditioning units and their impact on the outdoor air temperature. Although a simple model was used (evapotranspiration from vegetation was ignored), good agreement between the computed and the measured results was obtained. It has been demonstrated that the software is particularly useful for urban morphology optimization in terms of acceptable wind speeds within the urban canopy [148], as well as to verify the performance of several bioclimatic interventions (e.g., cool materials) with respect to the reduction of urban surface temperature on hot summer days [149,150].
