Application of wavelet multi-resolution analysis to pressure fluctuations of gas–solid two-phase flow in a horizontal pipe

In order to reveal the unsteady features of gas–solid two-phase flow in both Fourier and physical spaces, the wavelet multi-resolution analysis was first employed to analyze the experimental data of the wall pressure–time signal. Then the definitions of the wavelet multi-resolution root mean square (RMS), skewness factor and probability density function (PDF) were developed and were applied to the statistical analysis of gas–solid two-phase flow in the frequency space. From the random-like pressure fluctuations, the fluctuating pressure components due to the dispersed suspension flow and the dune flow can be extracted based on the wavelet multi-resolution analysis over a time–frequency plane. It was found that the larger gas velocity results in the larger RMS pressure component at the higher frequency, while the lower gas velocity results in the larger RMS pressure component at the lower frequency. At a low velocity, the wavelet multi-resolution probability density function shifted to a unimodel from a bimodel distribution when increasing the frequency. In the acceleration region the pressure fluctuation components of the higher frequency deviated from the Gaussian-type fluctuation and resulted in the larger negative convectional skewness factor.