Badanie wielkoskalowych struktur w turbulentnym wirowym przepływie von Kármána z przegrodami

dr inż. Paweł Baj

Politechnika Warszawska


26 kwietnia 2024 12:15, Zakład Aerodynamiki, Wydział Mechaniczny Energetyki i Lotnictwa, ul. Nowowiejska 24

Investigating large-scale behavior in fluid flows is crucial for understanding complex phenomena like turbulence. We focus on the von Kármán swirling flow, generated by counter-rotating impellers, known for its significance in studying turbulence. Our analysis, conducted in two similar rigs at comparable Reynolds numbers, identifies a clear peak in power spectral density (PSD) function near the tank center, associated with a radially-oriented velocity field. Proper Orthogonal Decomposition (POD) reveals two dominant modes linked to this spectral peak, collectively capturing a significant portion of velocity fluctuations energy. The characteristic length of the structure, approximately 0.4 times the tank radius, signifies its LSM nature. Further insights into the structure's evolution are gained through consideration of associated evolution equations, contributing to a comprehensive understanding of baffled VK flow phenomena. The second part of our research considers the decay of stationary, homogeneous, high Reynolds number turbulence produced in the von Kármán flow rig. Using stereoscopic particle image velocimetry (PIV), we observe distinct phases in turbulent kinetic energy (TKE) decay, with an initial inertia-driven phase followed by classical power-law decay. Our analysis reveals different decay exponents across velocity components, highlighting the complex nature of turbulence decay. Furthermore, we investigate the reversal of mean flow patterns during the transition phase, providing insights into turbulence dynamics in confined geometries.

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