Efficiency of Steady Motion and Its Improvement with the Use of Unseparated and Supercavitating Flow Patterns

Abstract

Background. The efficiency of the steady subsonic motion of vehicles and animals in air and water is estimated with the use of different drag coefficients, the drag-to-weight and power-to-weight ratios.

Objective. The improvement of these characteristics with the use of special shaped hulls and wing profiles which remove boundary layer separation and with the use of the supercavitating flow pattern for the high-speed motion in water.

Methods. Analytical and numerical estimations with the use of known results for flow on slender unseparated body of revolution and airfoil and for the steady supercavitating flow pattern.

Results. Simple analytic formulae were obtained for the movement efficiency, the critical Reynolds numbers of the laminar-to-turbulent transition etc. and applied for different terrestrial, aquatic and airborne vehicles, animals and human sport activity. In a rather large range of the Reynolds number \[10^{6}\leqslant \textrm{Re}_{V}\leqslant 10^{8},\] the use of unseparated shapes yields very substantial reduction of the drag in comparison with the conventional bodies of revolution. In water at \[\textrm{Re}_{V}> 10^{7}\] the supercavitating flow pattern can be preferable.

Conclusions. This drag reduction opens up prospects for designing different kinds of very effective airborne and high-speed underwater vehicles.