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The Coandă effect (/ ˈ k w ɑː n d ə / or / ˈ k w æ-/) is the tendency of a fluid jet to stay attached to a surface of any form. [1] Merriam-Webster describes it as "the tendency of a jet of fluid emerging from an orifice to follow an adjacent flat or curved surface and to entrain fluid from the surroundings so that a region of lower ...
In real life, though, there is often a situation where the surfaces are not completely dry, but also not so lubricated that they do not touch. This "boundary friction" produces various effects, like an increase in lubrication through the generation of shearing forces , or an oscillation effect during motion, as the friction increases and decreases.
The friction drag force, which is a tangential force on the aircraft surface, depends substantially on boundary layer configuration and viscosity. The net friction drag, , is calculated as the downstream projection of the viscous forces evaluated over the body's surface. The sum of friction drag and pressure (form) drag is called viscous drag.
First steps towards solving the paradox were made by Saint-Venant, who modelled viscous fluid friction. Saint-Venant states in 1847: [11] But one finds another result if, instead of an ideal fluid – object of the calculations of the geometers of the last century – one uses a real fluid, composed of a finite number of molecules and exerting in its state of motion unequal pressure forces or ...
Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. [7] [8] Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces. [9] [10] [11] Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body.
The sudden application of force—by stabbing the surface with a finger, for example, or rapidly inverting the container holding it—causes the fluid to behave like a solid rather than a liquid. This is the "shear thickening" property of this non-Newtonian fluid. More gentle treatment, such as slowly inserting a spoon, will leave it in its ...
As an example, wine may exhibit a visible effect called "tears of wine". The effect is a consequence of the fact that alcohol has a lower surface tension and higher volatility than water. The water/alcohol solution rises up the surface of the glass lowering the surface energy of the glass. Alcohol evaporates from the film leaving behind liquid ...
where the vortex strength (assuming that the surrounding fluid obeys the no-slip condition) is given by Γ = 2 π ω r 2 {\displaystyle \Gamma =2\pi \omega r^{2}} [ 2 ] where ω is the angular velocity of the cylinder (in rad/s) and r is the radius of the cylinder (in m).