Proper Orthogonal Decomposition of Turbulent Flow above Urban Area

This contribution describes the character of turbulent flow generated above series of street canyons in wind-channel. Main concern is to clarify how intermittent dynamics of the flow determines the ventilation process inside the canyon. Since geometry of building around street canyon significantly affects the flow regime, two shapes of building are studied and comparison of these two regimes is done. During experiment, velocity data are measured using PIV with high-repetition rate. Over than three thousand snapshots of instantaneous velocity are then analysed by Proper Orthogonal Decomposition (POD). This method reveals the measure of coherence of the flow and decomposes the individual snapshots into dynamics modes. For example, the first mode in shear layer (localised at the roof level) contains almost 55% of global turbulent kinetic energy, what is an i