Seite - 79 - in Intelligent Environments 2019 - Workshop Proceedings of the 15th International Conference on Intelligent Environments

This method is simple and effective for this type of grids and it especially helps to obtain higher-order schemes. High-resolution grids are used and the absolute truncation error is relatively small. Only advection scheme is using a first-order upwind approach. This guaranties that full advected quantities remain monotonic and a second- order upwind differencing scheme is applied to the rest with regards to the spatial discretisation. Also, a fully implicit method (Backward Euler method) is used for time discretisation. The Algebraic Multigrid method (AMG-CG) [12] is used to solve Poisson’s equation for pressure and the backward difference formulas along with the matrix solver Bi-CGSTAB. All the equations are formulated using The Fractional Area- Volume Obstacle Representation (FAVOR) method [5] so as to involve the aerodynamic impact of different urban objects smaller than the grid. Therefore, the sub grid effect is taken into account. In this method, the geometric information of the buildings and the ground surface is converted into volume fraction and open area ratio. The volume fraction is established as the ratio of the volume occupied by the fluid to the total volume of the mesh. The open area ratio is established for the six facets of the mesh as the ratio of the area occupied by the fluid to the total area of the facet. The drag generated from trees and urban vegetation is taken into account in this model by using the parameters given in [8]. 3. Model testing 3.1. The Comprehensive outdoor scale model (COSMO) The comprehensive outdoor scale model experiment for urban climate (COSMO) is an experimental facility that was constructed at the Nippon Institute of Technology in Saitama, Japan. The mission of this experiment was to reveal the physical background of the constitution of the urban climate focusing on the effect of building arrays. Other characteristics, i.e. human activity, heterogeneity of land use and urban configuration, were simplified. Turbulent flow over rough surface, thermal environment and water budget were monitored. The Northwest side is open to a harvested rice field about 500 metres away. The model is composed of a flat rectangular foundation concrete plate with 512 square concrete cubes on it. The plate is 50 metres by 100 metres. The square cubes are 1.5 metres (= H) on a side, a fifth of the scale of a typical residential building in Japan. The cubes are arranged regularly to give a plan area index of 0.25. Three 8- metres high meteorological towers were located at the Northwest and Southeast corners of the site, and one at the centre. Hereafter, these will be referred to as NW, SE, and CE towers, respectively. The dominant wind direction is from the Northwest in winter time, and from the Southeast in summer time, due to the seasonal variation of the pressure system in the Asian region. For the COSMO site, the Cartesian coordinate system is set to align the x-axis parallel to the long side, y-axis parallel to the short side, and z-axis is the vertical of the domain. The x-axis runs from the Northwest to the Southeast of the COSMO domain, while the y-axis runs from the centre of the shorter side (towards the northeast). The origin of the z-axis is at the floor level. The location of the meteorological towers are at 8 metres, 50 metres and 92 metres. The present study used sonic anemometers and thermocouples to detect the turbulent fluctuations in atmospheric condition. These instruments can measure the turbulent signals at single points. To cover the spatial extent of the turbulent motions, multi-point measurements were conducted. M.Bakkali andY.Ashie /RANSModelling forLocalClimates,EnergyUseandComfortPredictions 79