The presence of near wall bubbles may reduce the skin friction drag. This phenomenon has been studied by well designed experiments and combined computational fluid dynamics (CFD) and population balance model (PBM) simulations in this paper. Drag reductions and bubble distributions over a flat plate have been implemented in cavitation tunnel experiments at various flow speeds and air injection rates. CFD-PBM modeling for bubble drag reduction (BDR) has been modified and validated by the flat plate experiments. Drag and lift forces are fully modeled, and bubble breakup and coalescence are calculated. A wide range of bubble sizes are well captured base on the aforementioned numerical consideration. And this modeling work can be further used to design full-scale BDR ships and to discover detailed BDR mechanisms. The predicted drag reductions and bubble distributions are in reasonable accordance with the experimental results. Approximately 30% of BDR is achieved both in the numerical and experimental results. The influence of flow speeds and air injection rates on drag reductions and bubble distributions is discussed. In particular, the mechanism of BDR is analyzed based on the detailed flow filed profiles from numerical simulations. Higher air injection rates generally lead to thicker bubble layer thickness from the rear-part of buffer region (20 < y+ < 30) to turbulent region (y+ > 30). And noticeable increases of air volume fraction in the laminar region (y+ < 5) and forepart of buffer region (5 < y+ < 20). The change of the velocity gradient in the near wall region is considered to be directly related to drag reduction.
- Fluids Engineering Division
Experimental and Numerical Study of Bubble Drag Reduction on a Flat Plate
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Qin, S, & Wu, D. "Experimental and Numerical Study of Bubble Drag Reduction on a Flat Plate." Proceedings of the ASME 2017 Fluids Engineering Division Summer Meeting. Volume 1C, Symposia: Gas-Liquid Two-Phase Flows; Gas and Liquid-Solid Two-Phase Flows; Numerical Methods for Multiphase Flow; Turbulent Flows: Issues and Perspectives; Flow Applications in Aerospace; Fluid Power; Bio-Inspired Fluid Mechanics; Flow Manipulation and Active Control; Fundamental Issues and Perspectives in Fluid Mechanics; Transport Phenomena in Energy Conversion From Clean and Sustainable Resources; Transport Phenomena in Materials Processing and Manufacturing Processes. Waikoloa, Hawaii, USA. July 30–August 3, 2017. V01CT16A004. ASME. https://doi.org/10.1115/FEDSM2017-69113
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