Wavelet and POD Analysis of Turbulent Flow Within Street Canyon

Wavelet analysis of flow inside the street canyon is applied on high repetition PIV and high-frequency hot wire data. Experiment is performed in wind channel with floor covered by series of street canyons. Different roof geometry is tested since the different shape of building causes different intermittent dynamics inside canyon. The intermittency further influences ventilation in the street. Morlet and Mexican hat function is used as a mother wavelet. The passage of sweep and ejection events is detected as being long-term signature in lower frequencies. The passage of vortex is recognizable as circular patterns in higher frequencies on Wavelet spectrum. The Wavelet power spectrum and Fourier power spectrum for particular frequencies is compared. Comparison between analysis based on hot wire data and PIV measurement is done as well. Quadrant analysis is executed with temporally based mean velocity value either with several estimated convective velocity of vortex cores. When using velocity vectors as input data, proper orthogonal decomposition (POD) reveals the most dominant modes in terms of turbulent kinetic energy. Rate of convergence of cumulative relative contribution from individual modes deviates for various regions in street canyon. The convergence is fastest in region with the supposedly highest coherence, what is upper part of street canyon. POD taken vorticity as input data is tested as well.