Objective This study aims to advance the development of composite drag reduction technology involving super-hydrophobic surfaces and bubbles by investigating the coalescence characteristics of bubbles on wetting surfaces and revealing the effects of surface wettability, bubble spacing, and bubble size on bubble coalescence.

Methods A numerical model of bubble coalescence on an underwater wetting surface is established based on the volume of fluid (VOF) method. The coalescence and spreading characteristics of bubbles on different wetting surfaces are analyzed by varying the surface contact angle, bubble spacing, and bubble size. The accuracy of the simulation results is validated by comparing them with experimental data.

Results The results show that increasing the contact angle of the wetting surface and decreasing bubble spacing facilitate bubble coalescence, while increasing bubble size slows down the spreading speed of bubbles on the surface and is not conducive to accelerating bubble coalescence. Specifically, when the contact angle increases from 130° to 170°, the initial coalescence time of bubbles decreases from 5.6 ms to 3.2 ms (a reduction of 42.9%), and the maximum spreading distance of bubbles increases from 6.53 mm to 9.4 mm (an increase of 138%).

Conclusions The findings provide a theoretical basis for the coupling design of super-hydrophobic surfaces and bubble drag reduction technology. Optimizing surface wettability and bubble spacing can significantly enhance bubble coalescence, thereby improving the stability and efficiency of bubble drag reduction.