Mean flow pattern through a simple mock urban array – water channel experiments and modeling

Systematic and hierarchical water channel experiments were conducted in the newly established laboratory for Environmental Flow Modeling at the University of California, Riverside, to measure the flow through three dimensional building arrays. A Particle Image Velocimetry (PIV) system was used for comprehensive flow measurements within a modeled urban setup. Buildings were reproduced using acrylic blocks whose refraction index is the same as the refraction index of salty water. Such setup allowed for laser sheet illumination through the obstacles enabling detailed measurements between the mock buildings. Two building array layouts were tested: 1) an array of 3 x 3 cubical buildings and 2) an array of 5 x 5 cubical buildings. Experiments were also performed with the middle building of double height. Measurement planes and flow conditions were systematically varied for shear inflow perpendicular to the building faces. This is the first time that such detailed flow measurements are available for such arrays. It was found that the lateral array size has significant influence on the mean flow structure in a way that it may affect dispersion pattern. Smaller array size led to flow channeling at right angles to the prevailing flow direction which may cause a significant initial plume spread. This novel flow feature, lateral channeling, observed and quantitatively measured within the modeled mock urban array will be presented and discussed. CFD (k-e) modeling of the water channel experimental configurations was performed at full scale and with air as the fluid by the team at the Seoul National University. The k-e model successfully reproduced the measured mean flow pattern.