In this work, the effect of scale on the macroinstability is examined using data from a 1.22 m
diameter tank. In a previous study coherent macroinstabilities (MI) in a stirred tank agitated
with a pitched blade turbine were captured in a small tank of diameter T= 0.24 m. Exactly the
same dimensionless frequency (fMI= 0.186 N) or Strouhal number (St= fMI/N= 0.186) is
observed at both scales, with greater coherence over a wider range of off-bottom clearances
and Reynolds numbers at the large scale. Large eddy simulations (LES) successfully predict …

In this thesis, the macroinstabilities (MI) produced by three axial impellers; the 45 degree
pitched blade turbine (PBT), the Lightnin fluidfoil (A310) and the Chemineer high efficiency
HE3, are studied. These phenomena are observed as an unsteady, lowperiod variation of
the velocity as measured with Laser Doppler Velocimetry (LDV). The process of particle
arrival is random and therefore the time between measured samples is non-uniform. This
precludes the use of standard spectral estimators. The frequencies from unequally spaced …