Spectral Analysis of the Velocity Fluctuations in a Mechanically Stirred Tank

Jianhua Fan, Qi Rao, Yundong Wang, Weiyang Fei

Research output: Contribution to journalJournal articleResearchpeer-review


To characterize the flow instabilities in mechanically agitated vessels, digital particle image velocimetry (DPIV) was used to measure the flow fields within baffled, stirred tank, equipped with a Ruston turbine impeller of large impeller and tank diameter ratio. The near-instantaneous flow fields obtained was rather complex and stochastic, so spatially averaged vorticity was introduced to identify the change of flow patterns and Fast Fourier Transform method (FFT) was used to analyze the obtained time series of the spatially averaged vorticity. Results show that the flow fields are not steady; rather, they are subject to macro instability (MI) with period ranging from 100 to 200 blade passage period; The dominant frequency of MI increases linearly with that of the impeller revolution; At lower impeller rotational speed (30~60 rmin-1), apparent MI phenomenon can be observed; With the increase of rotational speed (120~180 rmin-1), MI tends to weaken while random velocity fluctuations tend to strengthen.
Original languageChinese
JournalJournal of Chemical Engineering of Chinese Universities
Issue number3
Pages (from-to)287-292
Publication statusPublished - 2004
Externally publishedYes

Cite this