Tandem Interference Effects for Noncavitating and Supercavitating Hydrofoils

Abstract

Experimental studies had previously been made at this Laboratory to determine the tandem interference effects for noncavitating hydrofoils. The results are compared with theory in this report, and good agreement is shown to exist. The experimental studies have now been extended to include fully submerged, ventilated foils of finite span. Both forced and naturally ventilated foils were employed in various configurations. The surface wave generated by the ventilated foil and the total interference effect of the forward foil on the force and cavity characteristics of the aft foil were of particular interest. The surface wave generated by the forward foil had relatively little influence on the force and cavity characteristics of the aft foil. For forced-ventilated foils, considerable change due to interference effects was observed in the cavity pressure of the aft foil. For long initial cavities on the forward and aft foil, the interference effect on the forces was relatively small, whereas for small initial cavities, the interference effect was much larger. Similar trends were observed for the naturally ventilated foils. Lateral separation of the forward foils reduced the interference effects to essentially negligible values.