Economic globalization has made today’s world more closely linked, where transportation (e.g. shipping, pipeline) has played an important role. Approximately over 60% (in air), 80% (underwater), and 100% (in pipeline) propulsive power is used to overcome surface drag, so reducing surface drag will have a substantial impact economically and environmentally.
To develop a surface that has lower drag, the intuitive idea is to convert no-slip boundary conditions to slip or partial slip ones. To achieve that, the most promising approach is to replace the solid-liquid boundaries completely or partially with gas-liquid or liquid-liquid boundaries, because the shear stress is much smaller at the gas-liquid and liquid-liquid interfaces compared to that at solid-liquid interfaces.
In this work, a perforated surface that can effectively trap gas (air) or liquid (water) near the surface was designed, fabricated, and characterized with a customized test configuration. An analytical model was developed to extract the representative quantities that reflect the overall slip effects, which was used to analyze the experimental data. Within the mass flow rate range of 1.382 g/s ~ 2.764 g/s, the drag reduction observed in water-filled cases was up to 66%, and such a large drag reduction was due to bypass flow, which was confirmed by experiments and simulations. As for the air-filled cases, the air was effectively trapped in the holes, and the air-water interface was able to resist the water pressure and viscous shear forces even at the highest mass flow rate, 2.764 g/s. The drag reduction range was from 22% to 34% for air-filled cases, which corresponds to the effective slip length from 90 µm ~ 180 µm. Such a large drag reduction and effective slip length were achieved with the large feature size (up to 1 mm) and without chemically modifying the surface, which is favored by many application scenarios. In addition, numerical simulations were utilized to have more insight into the flow behaviors, such as the effect of the bypass flow on flow resistance, the effect of the air-water interface shape on the effective slip length, and the effect of the shape and layout of the pattern on the effective slip length.
David A. Willis
Paul S. Krueger
Gary A. Evans
Number of Pages
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License
Tan, Haosen, "The Effect of Surface Gas/Liquid Entrapment on Drag Reduction" (2022). Mechanical Engineering Research Theses and Dissertations. 43.
Available for download on Tuesday, May 14, 2024