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Adverse Pressure Gradient
In fluid dynamics, an adverse pressure gradient is a pressure gradient in which the static pressure increases in the direction of the flow. Mathematically this is expressed as for a flow in the positive -direction. This is important for boundary layers. 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 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 causing a flow separation. 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. Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fluid Dynamics
In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation. Fluid dynamics offers a systematic structure—which underlies these practical disciplines—that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves the calculation of various properties of the fluid, such as flow velocity, pressure, density, and temperature, as functions of space and ti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Momentum
In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass and is its velocity (also a vector quantity), then the object's momentum is : \mathbf = m \mathbf. In the International System of Units (SI), the unit of measurement of momentum is the kilogram metre per second (kg⋅m/s), which is equivalent to the newton-second. Newton's second law of motion states that the rate of change of a body's momentum is equal to the net force acting on it. Momentum depends on the frame of reference, but in any inertial frame it is a ''conserved'' quantity, meaning that if a closed system is not affected by external forces, its total linear momentum does not change. Momentum is also conserved in special relativity (with a modified formula) and, in a modified form, in electrodynamics, quantum mechanics, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
McGraw-Hill
McGraw Hill is an American educational publishing company and one of the "big three" educational publishers that publishes educational content, software, and services for pre-K through postgraduate education. The company also publishes reference and trade publications for the medical, business, and engineering professions. McGraw Hill operates in 28 countries, has about 4,000 employees globally, and offers products and services to about 140 countries in about 60 languages. Formerly a division of The McGraw Hill Companies (later renamed McGraw Hill Financial, now S&P Global), McGraw Hill Education was divested and acquired by Apollo Global Management in March 2013 for $2.4 billion in cash. McGraw Hill was sold in 2021 to Platinum Equity for $4.5 billion. Corporate History McGraw Hill was founded in 1888 when James H. McGraw, co-founder of the company, purchased the ''American Journal of Railway Appliances''. He continued to add further publications, eventually establishin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ernst R
Ernst is both a surname and a given name, the German, Dutch, and Scandinavian form of Ernest. Notable people with the name include: Surname * Adolf Ernst (1832–1899) German botanist known by the author abbreviation "Ernst" * Anton Ernst (1975-) South African Film Producer * Alice Henson Ernst (1880-1980), American writer and historian * Britta Ernst (born 1961), German politician * Cornelia Ernst, German politician * Edzard Ernst, German-British Professor of Complementary Medicine * Emil Ernst, astronomer * Ernie Ernst (1924/25–2013), former District Judge in Walker County, Texas * Eugen Ernst (1864–1954), German politician * Fabian Ernst, German soccer player * Gustav Ernst, Austrian writer * Heinrich Wilhelm Ernst, Moravian violinist and composer * Jim Ernst, Canadian politician * Jimmy Ernst, American painter, son of Max Ernst * Joni Ernst, U.S. Senator from Iowa * K.S. Ernst, American visual poet * Karl Friedrich Paul Ernst, German writer (1866–1933) * Ken Ernst, U ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flow Separation
In fluid dynamics, flow separation or boundary layer separation is the detachment of a boundary layer from a surface into a wake. A boundary layer exists whenever there is relative movement between a fluid and a solid surface with viscous forces present in the layer of fluid close to the surface. The flow can be externally, around a body, or internally, in an enclosed passage. Boundary layers can be either laminar or turbulent. A reasonable assessment of whether the boundary layer will be laminar or turbulent can be made by calculating the Reynolds number of the local flow conditions. Separation occurs in flow that is slowing down, with pressure increasing, after passing the thickest part of a streamline body or passing through a widening passage, for example. Flowing against an increasing pressure is known as flowing in an adverse pressure gradient. The boundary layer separates when it has travelled far enough in an adverse pressure gradient that the speed of the bound ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vortex Generator
A vortex generator (VG) is an aerodynamic device, consisting of a small vane usually attached to a lifting surface (or airfoil, such as an aircraft wing) or a rotor blade of a wind turbine.Wind Turbine Vortex Generators UpWind Solutions. VGs may also be attached to some part of an aerodynamic vehicle such as an aircraft fuselage or a car. When the airfoil or the body is in motion relative to the air, the VG creates a ,Peppler, I.L.: ''From The Ground Up'', page 23. Aviation Publishers Co. Limited, Ottawa Ontario, Twenty Seventh Revised Edition, 1996. which, by removing some part of the slow-moving bo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Aeroplane Wing
The wing configuration of a fixed-wing aircraft (including both gliders and powered aeroplanes) is its arrangement of lifting and related surfaces. Aircraft designs are often classified by their wing configuration. For example, the Supermarine Spitfire is a conventional low wing cantilever monoplane of straight elliptical planform with moderate aspect ratio and slight dihedral. Many variations have been tried. Sometimes the distinction between them is blurred, for example the wings of many modern combat aircraft may be described either as cropped compound deltas with (forwards or backwards) swept trailing edge, or as sharply tapered swept wings with large leading edge root extensions (or LERX). Some are therefore duplicated here under more than one heading. This is particularly so for variable geometry and combined (closed) wing types. Most of the configurations described here have flown (if only very briefly) on full-size aircraft. A few theoretical designs are also notab ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Baseball (ball)
A baseball is a ball used in the sport of the same name. The ball consists of a rubber or cork center wrapped in yarn and covered with white natural horsehide or cowhide, or a synthetic composite leather. A regulation baseball is 9 to 9¼ inches (229 to 235mm) in circumference ie 2.86 to 2.94 inches (72.9 to 74.8 mm) in diameter, with a weight of 5to 5¼oz. (142 to 149g). A baseball is bound together by 108 hand-woven stitches through the cowhide leather. The leather cover is commonly formed from two saddle-shaped pieces stitched together, typically with red-dyed thread. That stitching plays a significant role in the trajectory of a thrown baseball due to the drag caused by the interaction between the stitching and the air. Controlling the orientation of the stitches and the speed of the ball's rotation allows a pitcher to affect the behavior of the pitched ball in specific ways. Commonly employed pitches include the curveball, the slider, the two-seam fastball, the four ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tennis Ball
A tennis ball is a ball designed for the sport of tennis. Tennis balls are fluorescent yellow in organised competitions, but in recreational play can be virtually any color. Tennis balls are covered in a fibrous felt which modifies their aerodynamic properties, and each has a white curvilinear oval covering it. Specifications Modern tennis balls must conform to certain criteria for size, weight, deformation, and bounce criteria to be approved for regulation play. The International Tennis Federation (ITF) defines the official diameter as . Balls must have masses in the range . Yellow and white are the only colors approved by the ITF, and most balls produced are a fluorescent yellow known as "optic yellow", first introduced in 1972 following research demonstrating they were more visible on television. Tennis balls are filled with air and are surfaced by a uniform felt-covered rubber compound. The felt delays flow separation in the boundary layer which reduces aerodynamic drag an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Golf Ball
A golf ball is a special ball designed to be used in the game of golf. Under the rules of golf, a golf ball has a mass no more than , has a diameter not less than , and performs within specified velocity, distance, and symmetry limits. Like golf clubs, golf balls are subject to testing and approval by The R&A (formerly part of the Royal and Ancient Golf Club of St Andrews) and the United States Golf Association, and those that do not conform with regulations may not be used in competitions ''(Rule 5–1)''. History Early Balls It is commonly believed that hard wooden, round balls, made from hardwoods such as beech and box, were the first balls used for golf between the 14th through the 17th centuries. Though wooden balls were no doubt used for other similar contemporary stick and ball games, there is no definite evidence that they were actually used in golf in Scotland. It is equally, if not more likely, that leather balls filled with cows' hair were used, imported from th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reynolds Number
In fluid mechanics, the Reynolds number () is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between inertial and viscous forces. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers flows tend to be turbulent. The turbulence results from differences in the fluid's speed and direction, which may sometimes intersect or even move counter to the overall direction of the flow (eddy currents). These eddy currents begin to churn the flow, using up energy in the process, which for liquids increases the chances of cavitation. The Reynolds number has wide applications, ranging from liquid flow in a pipe to the passage of air over an aircraft wing. It is used to predict the transition from laminar to turbulent flow and is used in the scaling of similar but different-sized flow situations, such as between an aircraft model in a wind tunnel and the full-size v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laminar Flow
In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing. At low velocities, the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross-currents perpendicular to the direction of flow, nor eddies or swirls of fluids. In laminar flow, the motion of the particles of the fluid is very orderly with particles close to a solid surface moving in straight lines parallel to that surface. Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection. When a fluid is flowing through a closed channel such as a pipe or between two flat plates, either of two types of flow may occur depending on the velocity and viscosity of the fluid: laminar flow or turbulent flow. Laminar flow occurs at lower velocities, below a threshold at which the flow becomes turbulent. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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