Adverse pressure gradient

Adverse pressure gradient

An adverse pressure gradient occurs when the static pressure increases in the direction of the flow. This is important for boundary layers, since increasing the fluid pressure is akin to increasing the potential energy of the fluid, leading to a reduced kinetic energy and a deceleration of the fluid. Since the fluid in the inner part of the boundary layer is relatively slower, it is more greatly affected by the increasing pressure gradient. For a large enough pressure increase, this fluid may slow to zero velocity or even become reversed. When flow reversal occurs, the flow is said to be separated from the surface. This has very significant consequences in aerodynamics since flow separation significantly modifies the pressure distribution along the surface and hence the lift and drag characteristics.

Turbulent boundary layers tend to be able to sustain an adverse pressure gradient better than an equivalent laminar boundary layer. The more efficient mixing which occurs in a turbulent boundary layer transports kinetic energy from the edge of the boundary layer to the low momentum flow at the solid surface, often preventing the separation which would occur for a laminar boundary layer under the same conditions. This physical fact has led to a variety of schemes to actually produce turbulent boundary layers when boundary layer separation is dominant at high Reynolds numbers. The dimples on a golf ball, the fuzz on a tennis ball, or the seams on a baseball are good examples. Aeroplane wings are often engineered with vortex generators on the upper surface to produce a turbulent boundary layer.

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Blood pressure — For information about high blood pressure, see Hypertension. Blood pressure Diagnostics A sphygmomanometer, a device used for measuring arterial pressure. MeSH …   Wikipedia

  • Boundary layer separation — is when the thin layer of viscous fluid leaves the surface of the body that it is flowing over. The viscosity of the fluid causes the boundary layer separation. [Wilcox, David C. Basic Fluid Mechanics. 3rd ed. Mill Valley: DCW Industries, Inc.,… …   Wikipedia

  • Couette flow — In fluid dynamics, Couette flow refers to the laminar flow of a viscous fluid in the space between two parallel plates, one of which is moving relative to the other. The flow is driven by virtue of viscous drag force acting on the fluid and the… …   Wikipedia

  • Boundary layer — For the anatomical structure, see Boundary layer of uterus. Boundary layer visualization, showing transition from laminar to turbulent condition In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of… …   Wikipedia

  • Boundary-layer thickness — This page describes some parameters used to measure the properties of boundary layers. Consider a stationary body with a turbulent flow moving around it, like the semi infinite flat plate with air flowing over the top of the plate. At the solid… …   Wikipedia

  • Flow separation — All solid objects travelling through a fluid (or alternatively a stationary object exposed to a moving fluid) acquire a boundary layer of fluid around them where viscous forces occur in the layer of fluid close to the solid surface. Boundary… …   Wikipedia

  • Shape factor (boundary layer flow) — A shape factor is used in boundary layer flow to determine the nature of the flow.:H= frac {delta^*}{ heta}where H is the shape factor, delta^* is the displacement thickness and θ is the momentum thickness. Displacement thickness is defined as… …   Wikipedia

  • повышение давления в направлении потока — — [А.С.Гольдберг. Англо русский энергетический словарь. 2006 г.] Тематики энергетика в целом EN adverse pressure gradient …   Справочник технического переводчика

  • poison — poisoner, n. poisonless, adj. poisonlessness, n. /poy zeuhn/, n. 1. a substance with an inherent property that tends to destroy life or impair health. 2. something harmful or pernicious, as to happiness or well being: the poison of slander. 3.… …   Universalium

  • Hypoxia (medical) — Hypoxia ICD 9 799.02 MeSH D000860 Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole (generalized hypoxia) or a region of the body (tissue hypoxia) is deprived of adequate ox …   Wikipedia

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.