Experimental analysis of surface piercing cylinders

It is well known that for operational purposes, submarines are required to approach and pierce the free surface with a vertically mounted appendage such as a periscope or a snorkel, which is typically a bluff body such as a cylinder. At high Froude numbers, the flow around these surface piercing cylinders can generate significant wake and plume profiles. However, there has been very limited experimental or numerical data analysing the flow regimes around a surface piercing cylinder, especially at the higher end of the speed range of such applications. This paper presents and discusses the results from an experimental investigation of flow around a cylinder with different submerged depths up to a Froude number of 4.0. The first set of experiments utilised a cylinder having a submerged depth equal to twice its diameter in order to validate the work against existing published data. The second experimental setup involved extending the submerged depth of the cylinder to 10 times the diameter to analysis the end effect.

The former was found to give a good correlation to previously published experimental data when comparing the plume structure, whilst the longer cylinder showed an increase in plume size due to the reduction in the end effect. It was also found that the plume structure, which in the past has been considered as one element, is generated from two different flow phenomenon from the cylinder creating two regions of separated flow. The experimental data presented in this paper enables numerical models to be validated and thus conduct numerical investigations into the flow profile generated by surface piercing bluff bodies such as a cylinder.