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# Topic: Boundary layer

###### In the News (Sun 26 May 19)

 Boundary Layer The details of the flow within the boundary layer are very important for many problems in aerodynamics, including wing stall, the skin friction drag on an object, and the heat transfer that occurs in high speed flight. For lower Reynolds numbers, the boundary layer is laminar and the streamwise velocity changes uniformly as one moves away from the wall, as shown on the left side of the figure. The effects of the boundary layer on lift are contained in the lift coefficient and the effects on drag are contained in the drag coefficient. www.grc.nasa.gov /WWW/K-12/airplane/boundlay.html   (785 words)

 Boundary Layer   (Site not responding. Last check: 2007-11-02) A boundary layer is defined as the region close to a body at which the speed of fluid changes rapidly from that of the body to that of the primary stream condition. If effect, the boundary layer is necessary to uphold what is called "the no slip condition," which states that the fluid contacting a surface is not moving in relation to surface. Boundary layer intersection is much of the reason that a Zipp disk is flat. www.zipp.com /Default.aspx?tabid=80   (725 words)

 Boundary Layer   (Site not responding. Last check: 2007-11-02) The boundary layer is a thin layer of a flowing gas or liquid in contact with a surface such as that of an airplane wing or of the inside of a pipe. Boundary layers are thinner at the leading edge of an aircraft wing and thicker toward the trailing edge. The flow in such boundary layers is generally laminar at the leading or upstream portion and turbulent in the trailing or downstream portion. abyss.uoregon.edu /~js/glossary/boundary_layer.html   (130 words)

 PowerPedia:Boundary layer effect - PESWiki The thin shear layer which develops on an oscillating body is an example of a Stokes layer, whilst the Blasius boundary layer refers to the well-known similarity solution for the steady boundary layer attached to a flat plate held in an oncoming unidirectional flow. The thickness of the velocity boundary layer is normally defined as the distance from the solid body at which the flow velocity is 99% of the freestream velocity, that is, the velocity that is calculated at the surface of the body in an inviscid flow solution. It is referred to as a bladeless turbine because it uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine. peswiki.com /index.php/PowerPedia:Boundary_layer_effect   (1637 words)

 BOUNDARY LAYER DECOUPLING   (Site not responding. Last check: 2007-11-02) Boundary layer decoupling is the term used for the change in weather conditions that occurs in the vertical due to significant radiational cooling of the earth's surface. A layer of air that is much cooler than it was during the day will develop nearest the surface with warmer air aloft in a layer known as the residual layer. If the winds in the boundary layer are brisk, a front is moving through or storms are influencing the area then the boundary layer will tend to not decouple at night or it will not decouple as significantly. www.theweatherprediction.com /habyhints2/420   (375 words)

 Definition of Boundary layer In the atmosphere the boundary layer is the air layer near the ground affected by diurnal heat, moisture or momentum transfer to or from the surface. On an aircraft wing the boundary layer is the part of the flow close to the wing. The boundary layer is particularly important in aerodynamics because it is responsible for a considerable amount of drag. www.wordiq.com /definition/Boundary_layer   (728 words)

 Boundary Layer Control Boundary layer control (BLC) is a generic definition to classify all those methods that can be used to reduce the skin friction drag, by controlling the turbulent transition, the development of the turbulent flows, and the separation (laminar as well as turbulent), all phenomena occurring within the boundary layer. Understanding the stability of the boundary layer is in fact of great importance for the development of technology for skin friction drag reduction. Boundary layer suction is is used on aircraft wings to prevent laminar and turbulent separation, by removing flow of low momentum. www.aerodyn.org /Drag/blc.html   (544 words)

 Boundary layer [Oulu]   (Site not responding. Last check: 2007-11-02) Magnetospheric boundary layer is a region close to the magnetopause in which magnetosheath plasma has strong influence. A new boundary called the free-flow boundary has been suggested to exists between the exterior cusp and the magnetosheath (this is the boundary that is often plotted as a dashed line in schematic figures of the magnetosphere). Boundary layer is a very special region, not only because of the presence of magnetosheath plasma, but also because of the still uncertain topology. www.oulu.fi /~spaceweb/textbook/blayer.html   (451 words)

 Design Tips – boundary layers :: School of Engineering Sciences Laminar boundary layers consist of layers of air molecules that smoothly flow on top of one another, so that the air at any given point in the boundary layer is moving in the main flow direction. Turbulent boundary layers are more chaotic, however, and small eddies swirl the molecules up from the surface away to the edge of the boundary layer, and vice-versa. Laminar boundary layer on a smooth ball means flow separates at around halfway point (12 o'clock and 6 o'clock positions), causing a wide wake. www.soton.ac.uk /ses/outreach/greenpower/boundarylayers.html   (654 words)

 Met Office: Boundary layer research The boundary layer, also called the atmospheric or planetary boundary layer, is the part of the atmosphere which is directly influenced by the surface. Accurate modelling of processes in the boundary layer is important for the forecasting of conditions at or near the surface, such as the formation and dissipation of fog or extremes of temperature. A key distinction is made between unstable boundary layers, where the surface transfers heat to the atmosphere, and stable boundary layers, where the transfer of heat is reversed. www.metoffice.gov.uk /research/apr/boundary_layer.html   (325 words)

 boundary layer At its transition point, the boundary layer changes from laminar, where the velocity changes uniformly as one moves away from the object's surface, to turbulent, where the velocity is characterized by unsteady (changing with time) swirling flows inside the boundary layer. The boundary layer may also lift off or separate from the body, creating an effective shape much different from the physical shape of the object and causing a dramatic decrease in lift and increase in drag. As well as the development of airfoil stall, the details of the flow within the boundary layer are very important for many problems in aerodynamics, including the skin friction drag of an object and the heat transfer that occurs in high-speed flight. www.daviddarling.info /encyclopedia/B/boundary_layer.html   (437 words)

 Boundary layer The boundary layer is a very thin layer of air flowing over the surface of an aircraft wing, or airfoil, (as well as other surfaces of the aircraft). Each layer of molecules within the boundary layer moves faster than the layer that is closer to the surface of the wing. As the boundary layer moves toward the center of the wing, it begins to lose speed due to skin friction drag. www.centennialofflight.gov /essay/Dictionary/boundary_layer/DI134.htm   (452 words)

 Boundary-Layer Separation Since the velocity in the boundary layer drops towards the wall, the kinetic energy of fluid particles inside the boundary layer appears to be less than that at the outer edge of the boundary layer, in fact the closer a fluid particle is to the wall the smaller appears to be its kinetic energy. The secondary shock is provoked by the thickening of the boundary layer which, in its turn, is caused by propagation of disturbances through the boundary layer from the region of higher pressure downstream of the main shock. It does not produce any noticeable contribution to the displacement effect of the boundary layer, which means that all the stream lines in the middle tier are parallel to each other and carry the deformation produced by the displacement effect of the viscous sublayer. www.maths.manchester.ac.uk /~ruban/blsep.html   (1923 words)

 2.4. The Boundary Layer Processes at the air-sea interface are directly affected by the boundary layers of the upper ocean and the lower atmosphere, which in turn are modulated by the exchanges of heat, moisture, momentum and trace constituents across the air-sea interface. The boundary layers are also affected directly by processes within the interior of the fluid that affect the transfer of energy across the inversion and the pycnocline. In the atmosphere, clouds connect the boundary layer with the free troposphere modulating the ventilation of the boundary layer. www.agu.org /revgeophys/rogers01/node6.html   (627 words)

 AMS Glossary It is often turbulent and is capped by a statically stable layer of air or temperature inversion. During daytime, a mixed layer of vigorous turbulence grows in depth, capped by a statically stable entrainment zone of intermittent turbulence. During nighttime, the bottom of the residual layer is transformed into a statically stable boundary layer by contact with the radiatively cooled surface. amsglossary.allenpress.com /glossary/search?id=atmospheric-boundary-layer1   (216 words)

 Boundary Layer Equations   All of the viscous effects of the flowfield are confined to the boundary layer, adjacent to the wall. The boundary conditions of the boundary layer region are the no-slip condition at the wall, and the free-stream condition at infinity: According to Assumption 1, the region near the wall is a viscous boundary layer. www.aerojockey.com /papers/bl/node3.html   (747 words)

# Turbulent Boundary Layers

The boundary layer on a long slender cylinder in axial flow is of interest because of its application to linear towed sonar arrays, a long hose filled with hydrophones that is towed behind a ship or submarine.
The turbulent boundary layer that develops on the array generates wall pressure fluctuations that are of the same magnitude as the far-field sound resulting in a noise problem.
At Northwestern I expanded my investigation of the turbulent boundary layer on a cylinder in axial flow to the complex problem of relating the stress field at the wall of the cylinder to the turbulent velocity field.
www.mech.northwestern.edu /fac/lueptow/turbulentboundarylayerflow.html   (1088 words)

 Instructions The flow inside a turbulent boundary layer is unsteady and irregular and it is the time-averaged boundary layer equations that must be solved in this case. The WALZ surface properties dialog box therefore asks you to specify whether the leading edge is sharp (initial boundary layer thickness zero) or rounded (initial non-zero boundary layer thickness computed from the inviscid velocity distribution you specify using the stagnation point solution of the Navier Stokes). Even though the boundary layer method becomes invalid when the flow separates like this, you may be able to very crudely model this situation using the applets by treating the laminar separation location as though it were a transition location, and continuing calculations from this point using one of the turbulent boundary layer applets. www.engapplets.vt.edu /fluids/bls2/instructions.html   (2930 words)

 micro boundary layer This layer can build to substantial thickness, trapping and carrying particles with a diameter less than the boundary layer thickness. This method, however, has severe limitations, since in the process of overpowering the web’s boundary layer, the air knife creates a new thinner boundary layer, perhaps 50 to 100 microns thick. These pulses knock the trapped particles out of the boundary layer so they can be removed by the vacuum without any damage to the substrate. www.wsinfo.com /html/micro_boundary_layer.html   (221 words)

 Boundary Layers We define the thickness of this boundary layer as the distance from the wall to the point where the velocity is 99% of the "free stream" velocity, the velocity in the middle of the pipe or river. As the boundary layer thickness becomes greater, so the velocity gradient become smaller and the shear stress decreases until it is no longer enough to drag the slow fluid near the surface along. This boundary layer separation and increase in the turbulence because of the vortices results in very large energy losses in the flow. www.cartage.org.lb /en/themes/Sciences/Physics/Mechanics/FluidMechanics/RealFluids/BoundaryLayers/BoundaryLayers.htm   (2263 words)

 Wing Design - Level 3 - WING BOUNDARY LAYER Boundary layer effects play a very important part in determining the drag for the aircraft. The boundary layer is a very thin layer of air lying over the surface of the wing (and, for that matter, all other surfaces of the airplane). As the boundary layer approaches the center of the wing, it begins to lose speed due to skin friction and it becomes thicker and turbulent. www.allstar.fiu.edu /aerojava/Wing34.htm   (588 words)

 informationsphere.com: Boundary Layer Specifically, the term most often refers to the planetary boundary layer, which is the layer within which the effects of friction are significant. For the earth, this layer is considered to be roughly the lowest one or two kilometers of the atmosphere. This layer is only a part of the planetary boundary layer, and represents the layer within which friction effects are more or less constant throughout (as opposed to decreasing with height, as they do above it). www.informationsphere.com /html/1908.htm   (208 words)

 Turbulent Boundary Layers   (Site not responding. Last check: 2007-11-02) Shown in the figure is a three-dimensional perspective of velocity isosurfaces in a spatially developing turbulent boundary layer. A canonical turbulent boundary layer at momentum thickness Reynolds number 1500 is introduced approximately five bump heights upstream of the leading edge of the bump. A canonical turbulent boundary layer at momentum thickness Reynolds number 1500 is introduced approximately six bump heights upstream of the leading edge of the bump, the bump is swept at 45 degrees with respect to the upstream flow.. www.eas.asu.edu /~squires/turbulentboundarylayers.html   (272 words)

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