Alexander Khotsianovsky

Dr. Alexander Khotsianovsky， National Academy of Sciences of Ukraine， Pisarenko Institute of Strength of Materials， Ukraine； In-water motion speed of modern surface vessels is limited by viscous resistance/drag of water， which increases with the motion speed. The lecture describes the latest developments worldwide in drastic drag reduction by separating the vessel hull from water using a disk- or cone-shaped cavitator， which “opens an umbrella” over the major part of the hull to produce an ellipsoidal air bubble （supercavity） inflated by an artificial or natural air inflow， thus providing a very high motion speed. This supercavitating principle was implemented in high-speed underwater vehicles （HSUV） and small water plane area twin hull （SWATH） vessels， as well as in famous military applications， such as Shkval （USSR， 1977） and Barracuda （Germany， 2005） high-speed torpedoes. In this respect， very promising are the latest developments of Chinese scientists， which imply organization of the developed cavitation flow by supply of aqueous solutions of high-molecular linear-chain polymers， which form a “liquid membrane” around an underwater vehicle and ensure its stable in-water ultrasonic motion. In this lecture， these achievements are compared to those of post-Soviet school of Shkval developers （Ukraine） and HSUV （US）， which envisage alternative application of inflated high-elastic "skirts" in the stern part and vector thrust propulsion principle. New experimental and numerical results on drag reduction by polymer aqueous solutions are presented by a team of Ukrainian scientists including the author， as well as a brief discussion of the state-of-the-art experimental research techniques for investigation of cavitating flows， in particular， underwater photography and pressure measurements， simulation of ventilated cavity bubbles near a free surface， experimental gas consumption and numerical predictions of cavity gas entrainment on the basis of assessment of characteristics of laminar-turbulent shear layer of gas at cavity surface， simulation of liquid weightiness and free border effects， organization of the developed cavitation flow by supply of aqueous solutions of high-molecular linear-chain polymers. The revealed advantages and deficiencies of the above approaches and possible ways of their improvement are discussed.