Vortex is sometimes called vortex.It refers to a kind ofradiusThe rotation of a very small cylinder in a stationary fluid causes the surrounding fluid toCircular motionThe flow phenomenon of.Generally, there is a dense area of vorticity inside the vortex, called vortex core, whose movement is similarrigid bodyRotate.The above cylinder is the vortex core similar to the vortex.Outside it, the circumferential velocity of the fluid is inversely proportional to the radius;Inside it, it is proportional to the radius, and the circumferential velocity at the vortex center is zero.Vortex is an important flow phenomenon in the flow around aircraftAerodynamicsCharacteristics have an important influence (see Aerodynamic characteristics of wings andAirframe aerodynamic characteristics）。 Generally speaking, the vortex formed by flowing water is called vortex, and the vortex formed by atmosphere may be formedTropical cycloneperhapstornado。
Vortex, sometimes called vortex, is the rotating movement of fluid mass.Generally, there is a dense area of vorticity inside the vortex, called the vortex core, whose movement is similar torigid bodyRotation, the speed is proportional to the radius.Outside it, the circumferential velocity of the fluid is inversely proportional to the radius.
Small scale air vortex
Vortex is a form of vortex, specifically referring to the uneven and irregular vortices of various sizes in turbulent motion.Its size is of the same order of magnitude as that of the whole turbulence, such asturbulent boundary layer Medium, maximum vortex andBoundary layer thicknessEquivalent level;Small ones are as small as the momentum exchange of molecular viscosity.In turbulent motion, due to the mutual stretching mechanism of vortices, the vortices change from large to slightly smaller, smaller and smaller vortices of various sizes.Vortex rotationenergyThen it is transferred from the large vortex to the smaller vortex, and then to the smaller vortex, until the viscosity on the smallest vortexstressDirectly act to transform rotational kinetic energy intoheat energyanddissipationDrop.
useInviscid ideal fluid theoryMany concepts of ideal vortex are needed to study the flow around wings.If the radius of the vortex core is zero, the velocity on the vortex core isInfinity；The vortex surface formed by the arrangement of numerous concentrated vortices is a discontinuous surface of tangential velocity;In steady flow, the vortex line with the same vortex axis and airflow velocity direction is free vortex, otherwise it is attached vortex;The vortex surface that does not bear the pressure difference in the flow field is called the free vortex surface, otherwise it is the attached vortex surface.These ideal vortices are the basis of lift line theory and lift surface theory of finite span wings.There are also detached vortex and wake vortex in the actual flow field.
The vortex motion is described by the following important physical quantities[1]：
Vorticity：set upvIs the velocity vector, so Ω=▽ⅹ v is defined as the vortex vector, which is called vorticity for short.
Vortex line: the curve tangent to the vortex vector everywhere is called vortex line, which is composed of different fluid particles at the same time.Each fluid micro cluster on the vortex line rotates around the tangent direction of the vortex line.
Vortex tube: take a closed curve without vortex line and self intersection in the vortex fieldLAll vortex lines passing through it form a tubular surface, which is called vortex tube.If the curveLInfinitely small, it is called vortex tube element.If the vorticity of the fluid around the vortex tube is zero, the vortex tube is called an isolated vortex tube
Encyclopedia x confusion: graphical vortex
Detached vortex
Detached vortexThe vortex separated from the leeward side of the missile body or the sharp leading edge of the wing.They are all free vortices, and the strength of the vortices increases continuously in the downstream direction until they become wake vortices.After they break away from the separation line, the end of the vortex layer rolls into a vortex with a vortex core.In the figure is a picture of the detached vortex center on the upper surface of the delta wing displayed by the smoke trace method.Before vortex breakdown, additional vortex lift is generated on the wing due to the low pressure at the vortex.After the vortex breaks, it suddenly diffuses to form a turbulent cluster.The figure also shows two types of fracture.The upper part is spiral fracture, and the lower part is vortex bubble fracture.After the vortex above the wing surface breaks, the lift drops suddenly and the pressure center moves forward.
Wake vortex
Wake vortexFor example, the detached vortex on the leeward side of a two-dimensional cylinder, including the famousCarmen Vortex Street, as well as the vortex starting to roll up at the trailing edge of the wing.After a certain distance, the wing wake vortex gradually rolls into a pair of vortices with vortex cores (also called wingtip vortex).Since then, due to the convection and viscous dissipation of vorticity, the vortex radius gradually expands, and the internal pressure and velocity gradually approach the incoming flow value.largeaircraftThe wake vortex of may cause disastrous consequences for small aircraft in the wake area.The wake vortex of a supersonic aircraft can travel far away.
Living vortex
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Tropical cyclone
Vortex can be seen sometimes, as in the atmospheretornado、pierPostVortex regionWhen rowingOarVortex generated, etc;There are also many small vortices that are difficult to observe, such as small vortices in the boundary layer of objects moving in the fluid, and random vortices in turbulence.Vortex intensity can be expressed by vortex flux or velocity circulation.Vortex flux is the flux of vorticity passing through a certain section S, and the vorticity at a certain point in the vortex is twice the average angular velocity of the fluid micro cluster rotating around the point, and the direction coincides with the instantaneous rotation axis of the micro cluster.The vortex is accompanied bymechanical energyTo produce fluid resistance to the object and reduce its mechanical efficiency.But inaerodynamicsMiddle, it is the vortex that makes the wing get lift;In water conservancy projects, the vortex formed at the outfall is used to consume the kinetic energy of water flow, so as to protect the dam foundation from being damaged by the torrential flow.
Tidal vortex
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tideAndebbThe large-scale vortex generated by interaction is called vortex, which is a kind of rotationocean current。The downward movement of the center is called vortex, which will appear when the coastal and submarine terrain has a relatively deep narrow channel.riversThe vortex motion in is slightly different.At a certain stage of turbulence, there will be a rotating flow with the center moving upward, called a surge, which is easy to see on the water surface.worldThere are some famous large eddies on theGarofalo vortex、Messina vortex、Merstom vortex、Whooping door vortexwait.JapanAwaji Island andFour countriesThere is a narrow channel about 1.3 kilometers long between them, calledMingmen Strait。Vortex is a phenomenon caused by the difference of tide levels between the Seto Inland Sea and the Outer Sea. When the sea water passes through the narrow Seto, the tide becomes faster, and the reefs in the way form large and small eddies.When the tide is full, when the beach is sown and when the tide is ebbingJiyi StraitWhirlpool caused by side,springandautumnThe best time to watch the tide is on spring tide day.There is a 450 meter long promenade in the truss of Mingmen Bridge, and a new scenic spot of Mingmen Vortex Sightseeing with a roundabout lookout facility in the front.Looking down through the glass window about 45 meters above the sea, the vortex is breathtaking and breathtaking.The diameter of the vortex here can reach 20 meters.The picture above is a big vortex shot in Mingmen.
Tropical cyclone
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Tropical cyclone
tropicCyclone is a kind ofLow atmospheric pressureWeather system, away from tropical areasequatorAverage 3-5latitudeOuter sea surface (such as north and souththe pacific ocean, NorthAtlantic，the indian ocean）Formed on the top, other movements are mainly affected byCoriolis forceAnd other large-scale weather systems, and finally dissipate and transform intoExtratropical cycloneOr dissipate after landing on land.Tropical cyclones landing on land can cause serious property or human casualties, which is a kind of natural disasters caused by weather.However, tropical cyclones are also part of the atmospheric cycle, which canheat energyandearthThe angular momentum of rotation is determined byequatorThe area is higherlatitude。
Tropical cycloneThe biggest feature ofenergycome fromsteamReleased during cooling and solidificationlatent heat。Other weather systems such asExtratropical cycloneIt is mainly caused by the air temperature difference on the cold north horizontal plane.After the tropical cyclone lands, or when it moves to the ocean surface with lower temperature, it will lose the warm and humid air supplyenergyTo weaken, dissipate or transform intoExtratropical cyclone。
The airflow of tropical cyclone is affected byCoriolis forceAnd revolves around the center.In the northern hemisphere, the tropical cyclone rotates counterclockwise, while in the southern hemisphereClockwise rotation。
Different regions have different names for tropical cyclones.China, TaiwanJapan, Vietnam, the Philippines and other places are used to calling local tropical cyclones typhoon.The Atlantic is used to calling local tropical cyclones hurricanes.Other places also have different names for tropical cyclones. In Australia, they are called "power".Meteorologically, only tropical cyclones whose wind speed reaches a certain level will be crowned“typhoon”、“hurricane”Etc.
The water will rotate when it moves rapidly, so the so-called "vortex" is formed.
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Rotating motion of fluid mass.staynatureThe vortex can sometimes be seen clearly, such as in the atmosphere
Ocean vortex
Oftornado，pierThe vortex area formed by the back flow, the vortex generated during rowing, etc.But in more cases, it is difficult to detect the existence of vortex.For example, when an object moves in a real fluid, a thin layer ofboundary layer, every point in the thin shear layer is vortex;Another example is that a large number of turbulent movements in nature are filled with vortices of different scales, which are difficult to identify with the naked eye.
Aircraft wake vortex
The generation of vortex is accompanied by the loss of mechanical energy, thus the relative object（aircraft, shipsWater turbine、Steam turbine）GenerationFluid resistanceOr lower itMechanical efficiency。However, on the other hand, it is the vortex that enables the wing to obtain lifting force.In hydraulic projects such as water outlets, in order to protect the dam foundation from being damaged by the torrential water, energy dissipation equipment is used to artificially create vortices to consume the kinetic energy of the water flow.These are the actual background of vortex research.
