The water entry of a sphere in a jet. (25th March 2019)

• Record Type: Journal Article
• Authors: Speirs, Nathan B.; Belden, Jesse; Pan, Zhao; Holekamp, Sean; Badlissi, George; Jones, Matthew; Truscott, Tadd T.
• Is Part Of: Journal of fluid mechanics. Volume 863(2019)
• Page Start: 956
• Page End: 968
• Publication Date: 2019-03-25
• Subjects: drag reduction, -- flow–structure interactions, -- interfacial flows (free surface); Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2018.931
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : The forces on an object impacting the water are extreme in the early moments of water entry and can cause structural damage to biological and man-made bodies alike. These early-time forces arise largely from added mass, peaking when the submergence is much less than one body length. We experimentally investigate a means of reducing impact forces on a rigid sphere by placing the sphere inside a jet of water so that the jet strikes the quiescent water surface prior to entry of the sphere into the pool. The water jet accelerates the pool liquid and forms a cavity into which a sphere falls. Through on-board accelerometer measurements and high-speed imaging, we quantify the force reduction compared to the case of a sphere entering a quiescent pool. Finally, we find the emergence of a critical jet volume required to maximize force reduction; the critical volume is rationalized using scaling arguments informed by near-surface particle image velocimetry (PIV) data.