Effects of hydrophobic surface on skin-friction drag are investigated through direct numerical simulations of a turbulent channel flow. Hydrophobic surface is represented by a slip-boundary condition on the surface. When a slip-boundary condition is used in the streamwise direction, the skin-friction drag decreases and turbulence intensities and turbulence structures, near-wall streamwise vorti...

We investigate the phenomenon of drag reduction in a viscoelastic fluid model of dilute polymer solutions. By means of direct numerical simulations of the three-dimensional turbulent Kolmogorov flow we show that drag reduction takes place above a critical Reynolds number Re(c). An explicit expression for the dependence of Re(c) on polymer elasticity and diffusivity is derived. The values of the...

Raptors - falcons, hawks and eagles in this study - such as peregrine falcons (Falco peregrinus) that attack distant prey from high-speed dives face a paradox. Anatomical and behavioral measurements show that raptors of many species must turn their heads approximately 40 degrees to one side to see the prey straight ahead with maximum visual acuity, yet turning the head would presumably slow the...

In the off-equatorial region of Jupiter’s and Saturn’s atmospheres, baroclinic eddies transport angular momentum out of retrograde and into prograde jets. In a statistically steady state, this angular momentum transfer by eddies must be balanced by dissipation, likely produced bymagnetohydrodynamic (MHD) drag in the planetary interior. This paper examines systematically how an idealized represe...

The aim of this study was to assess the effects of 8-weeks of training on active drag in young swimmers of both genders. Eight girls and twelve boys' belonging to the same swimming team and with regular competitive participation in national and regional events for the previous two seasons participated in this study. Active drag measurements were conducted in two different evaluation moments: at...

Polymer induced drag reduction in turbulent pipe flow was investigated using a non-intrusive laser based diagnostic technique, namely Particle Image Velocimetry (PIV). The drag reduction was measured in a pressure-driven flow facility, in a horizontal pipe of inner diameter 25.3 mm at Reynolds numbers ranging from 35 000 to 210 000. Three highmolecular-weight polymers (polyethylene oxide 2×10 6...

In many applications the flow that past bluff bodies has frequency nature (oscillated) and it is not uniform. This kind of flow has effects on the formation of vortex shedding behind bluff bodies. In this paper the flow around a circular cylinder was numerically simulated. The effects of frequency variation at inlet flow on the vortex shedding frequency were investigated. The transient Two-Dime...

Aerodynamic drag is an important factor in vehicles fuel consumption. Pressure drag which is the main component of total drag is a result of boundary layer separation from vehicle surface. Flow control methods are applied to avoid or at least delay separation. Depending upon whether these methods consume energy to control the flow or not, they are called active or passive control methods. In th...

Simulation of an underwater glider to investigate the effect of angle of attack on the hydrodynamic coefficients such as lift, drag, and torque. Due to the vital role of these coefficients in designing the controllers of a glider and to obtain an accurate result, this simulation has been studied at a range of operating velocities. The total length of the underwater glider with two wings is 900 ...