Pressure fluctuations in high gas volume fraction turbulent bubbly channel flows at italic Re Subscript bold italic tau Baseline bold almost equals bold 550 Re τ ≈ 550 Reτ ≈ 550

The pressure fluctuations in turbulent bubbly channel flows are investigated using incompressible large-eddy simulations under zero-gravity conditions. The volume-of-fluid method is adopted to capture the bubble–liquid interfaces. The gas volume fraction varies from 1.68 % to 11.31 % by adjusting the number and size of bubbles. A constant bulk mean velocity is imposed, yielding friction Reynolds numbers around 550, the highest achieved so far. To accurately reflect the contributions of the pressure fluctuations, the densities and viscosities are set to those of water and air under standard conditions. After careful validation of the numerical approach, the different source terms in the Poisson equation for pressure fluctuations are thoroughly examined based on the simulation results. It is found that (i) pressure fluctuations are primarily governed by spatio-temporal density variations induced by bubble motion, particularly in the channel core region; (ii) the surface-tension contribution is prominent throughout the bubble region, owing to the resulting Laplace pressure jump across the bubble interface; (iii) for the incompressible source terms, the linear component exceeds the nonlinear one beyond the buffer layer, in contrast to the behaviour in the single-phase channel flows. The inversion arises from the important contribution of spatial gradients of mean density and mean velocity due to bubble motions. Next, the wall-pressure fluctuations are analysed in terms of the wavenumber–frequency spectra. For a high gas volume fraction alpha Subscript g Baseline greater than or equivalent to 5.65 percent sign α g ≳ 5.65 % α g 5.65\,% , a unique bubble-induced convection ridge, distinct from the turbulence-induced ridge, emerges and may even dominate. Owing to bubble-induced disturbances in the near-wall boundary layer, the convection velocity of energy-containing wall-pressure fluctuations exceeds that of single-phase case and increases with gas volume fraction. The bubbly flows, even with a bubble-deficient layer near the channel wall, modify the vortex structures in the boundary layer and modulate the wall-pressure fluctuations.