Multi-scale analysis of pressure fluctuation in vertical upward bubbly flow

The mechanism of pressure fluctuation in bubbly flow was investigated on basis of the physical model of ideal single moving bubble. And the multi-scale time-frequency characteristics of the fluctuation were analyzed with both the discrete wavelet and the statistics theory. The results were induced as followed. The pressure fluctuation in bubbly flow is resulted from the moving bubble, the derivational turbulence by bubble, and the liquid turbulence. The fluctuation amplitude resulted from moving bubble can be greater than that resulted from other two reasons under the condition of low liquid velocity. The distribution of RMS pressure has a distinguished difference across a critical frequency, where the RMS pressure increases with frequency in the frequency region lower than the critical frequency while decreases in the region greater than the critical one. The time-frequency characteristic of pressure signal has a distinct change at the flow pattern transition, which the maximum RMS pressure will transfer to a lower frequency.