Experimental study on the drag reduction of underwater vehicles by drag-reducing agents injection

Underwater vehicles consume much energy to overcome flow resistance; therefore, reducing drag is essential to enhancing its performance. This paper proposes a drag reduction method for underwater vehicles by injecting drag-reducing agents into the turbulent boundary layer of the underwater vehicles and experimentally evaluates its performance based on the scaled suboff model. To this end, the unique injection structure and location are carefully designed to ensure the adherence of the drag-reducing solution on the wall. The polyethyleneoxide (PEO) and ceytltrimethyl ammonium chloride (CTAC) solutions are chosen as the drag-reducing agents. The effects of concentrations, flow rates, and mainstream Reynolds numbers (Re) on the drag reduction performance are investigated by measuring the total drag resistance of the scaled suboff model under different conditions. The results demonstrate that this heterogeneous drag-reducing solution injection strategy performs well in terms of drag reduction for the suboff model. The specially designed injection structure can uniformly distribute the drag-reducing solution to the near-wall region of the suboff model. Under certain conditions, both PEO and CTAC solutions can significantly reduce the total drag resistance and have an optimal concentration at different Re. At their optimal concentrations, the drag reduction of the total resistance can achieve about 59.38% and 48.31% for PEO and CTAC solutions, respectively, at Re = 2.7 × 10⁴. However, with the current design, the drag reduction decreases with the increase of Re due to the difficulty of the drag-reducing agent wrapping around the suboff model effectively. Further work is still necessary to improve the design and the location of the injection structure so that it can adapt to high-Re cases.