Wake

In fluid dynamics, a wake may either be:For slow swimmers, low Froude number, the Lighthill−Whitham geometric argument that the opening of the Kelvin chevron (wedge, V pattern) is universal goes as follows. Consider a boat moving from right to left with constant speed v, emitting waves of varying wavelength, and thus wavenumber k and phase velocity c(k), of interest when < v for a shock wave (cf., e.g., Sonic boom or Cherenkov radiation). Equivalently, and more intuitively, fix the position of the boat and have the water flow in the opposite direction, like a piling in a river.Wake of a boat crossing an alpine lake (Koenigsee)39° ship wakeThe wakes of two slow-moving boats. The nearer boat has made a striking series of ruler-straight wavesJohn Harvard Biles: 'The Design and Construction of Ships, Vol. II: Stability, Resistance, Propulsion and Oscillation of Ships' (1908)Wake from a fast, small motorboat with an outboard motorWake simulationKelvin wake simulationVideo of barge wakeWake behind a large motorboatGermany's only consistent surf spot is a giant wake from a shipWake from a fast motor yacht on the Indian River looking at the 17th Street BridgeWake behind a ferry in the Baltic SeaWake of a boat in the Hawaiian IslandsWake of a ferryboat just off British Columbia, Canada. In fluid dynamics, a wake may either be: The wake is the region of disturbed flow (often turbulent) downstream of a solid body moving through a fluid, caused by the flow of the fluid around the body. For a blunt body in subsonic external flow, for example the Apollo or Orion capsules during descent and landing, the wake is massively separated and behind the body is a reverse flow region where the flow is moving toward the body. This phenomenon is often observed in wind tunnel testing of aircraft, and is especially important when parachute systems are involved, because unless the parachute lines extend the canopy beyond the reverse flow region, the chute can fail to inflate and thus collapse. Parachutes deployed into wakes suffer dynamic pressure deficits which reduce their expected drag forces. High-fidelity computational fluid dynamics simulations are often undertaken to model wake flows, although such modeling has uncertainties associated with turbulence modeling (for example RANS versus LES implementations), in addition to unsteady flow effects. Example applications include rocket stage separation and aircraft store separation. In incompressible fluids (liquids) such as water, a bow wake is created when a watercraft moves through the medium; as the medium cannot be compressed, it must be displaced instead, resulting in a wave. As with all wave forms, it spreads outward from the source until its energy is overcome or lost, usually by friction or dispersion. The non-dimensional parameter of interest is the Froude number. Waterfowl and boats moving across the surface of water produce a wake pattern, first explained mathematically by Lord Kelvin and known today as the Kelvin wake pattern.