Investigation on drag reduction mechanism of trans-media vehicle with spike in high-speed underwater motion

· The interPhaseChangeFoam solver was developed for multiphase flowfield simulation. · A novel approach combining trans-media vehicles with spikes was proposed for drag reduction. · Impact of design parameters on the drag of the vehicle was evaluated with analysis of variance. · Vehicles equipped with spikes of three configurations was considered. · Three types of cavities were formed for different configurations. Trans-media vehicles experience pronounced drag during high-speed water entry and subsequent underwater operation. Consequently, the implementation of innovative drag-reduction strategies is critical to mitigate the attendant physical challenges. A novel approach combining trans-media vehicles with spikes is adopted, with three-dimensional Reynolds-averaged Navier–Stokes computations based on the interPhaseChangeFoam solver in the open-source platform OpenFOAM®. Numerical simulations are performed on the multiphase flowfield about vehicles equipped with spikes of varying configurations, namely flat-faced spike, hemispherical aerodisk and flat-faced aerodisk, aiming to investigate the flow and drag reduction mechanisms. Furthermore, in conjunction with analysis of variance, the impact of design parameters on the drag of the vehicle is examined. The results reveal that the spike reduces drag by reshaping the flowfield and regulating cavity morphology. The flat-faced spike achieves a 56.9% drag reduction rate by using its frontal stagnation effect to buffer the incoming flow. For the hemispherical aerodisk, due to its curved-surface characteristics and flow reattachment phenomenon, the body drag accounts for up to 64.4% of the total resistance. The flat-faced aerodisk generates a stable cavity that envelops the vehicle body, reducing the total drag to 272.38 N, significantly lower than the 798.20 N observed without a spike. Results from the analysis of variance demonstrate that velocity (50-200 m/s), angle of attack (0-6°), and diameter of aerodisk (5-8 mm) exert significant influences on the drag force, and within a certain range, the drag force exhibits an increasing trend with the increase in these three factors, while the influence of the length-to-diameter ratio (0.7-2.2) is not significant.