THE APPLICATION OF SNAPSHOT POD METHOD IN CHARACTERIZATION AND ANALYSIS OF NUMERICALLY SIMULATED FIRE-INDUCED FLOWS

Snapshot proper orthogonal decomposition (POD) was performed on the analysis of dominant structures of fire-induced flows. The data for POD analysis was obtained from large eddy simulation (LES). Identification and analysis of dominant flow patterns have been carried out for two important types of fire-induced flows, including vertical plumes induced by pool fire and fire-induced horizontal channel flows. The essential features or energetic motions of these fire-induced flows were identified by combination of desired orders of POD modes. For the fire plumes, the counter-rotating vortex tubes were identified as the most dominant flow patterns. It is revealed that the oscillation dynamics of fire plume were related to the vortices near these vortex tubes. A larger number of small-scale structures and more structure scales were found in the fire plumes with higher Reynolds number (or higher heat release rate). For fire-induced horizontal channel flows, both the energy fractions and the structure patterns associated with POD modes depend more strongly on Reynolds number than those for fire plumes. The energy fractions contained within the most energetic modes significantly decrease with the increase of Reynolds number (or extraction flow rate) for fire-induced channel flows. It is found that the locations of strong vortices areas identified by POD mode are higher than the interface heights estimated by Janssens' method, especially at the positions where counter flow mixing is strong.