Multiresolution analysis of tube-wall pressure fluctuations signal in the static mixers with twisted leaves

A study of multi-scales characteristics of tube pressure time series signals in a Kenics static mixer was undertaken using turbulent higher order items and the power spectrum function based on wavelet transform. By applying the method of direct determination of the flatness, the amplitudes of flatness at different scales for turbulent flow have stronger fluctuation and mainly fluctuate between 2.3 to 14.9. It was found that the flatness factors firstly increase then decrease as the frequency bands decreased. Most flatness for the approximations signal, a7, were below 3 which indicated large scale vorticities and steady flow, but the flatness factor of detail signals were above 3 which indicated small scale vorticities and unsteady flow with stronger intermittence especial in the frequency band from 500 Hz to 1000 Hz. Of course, considerably strong coherent structure exists at the tube-wall pressure. The frequency for main energy of pressure fluctuation is below 2.5 Hz, but more than eighty percent of radial fluctuation energy is below 15.625 Hz.