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Dynamic Stall On Helicopter Rotors
The dynamic stall is one of the hazardous phenomena on helicopter rotors, which can cause the onset of large torsional airloads and vibrations on the rotor blades. Unlike fixed-wing aircraft, of which the Stall (fluid dynamics), stall occurs at relatively low flight speed, the dynamic stall on a helicopter rotor emerges at high airspeeds or/and during manoeuvres with high load factors of helicopters, when the angle of attack(AOA) of blade elements varies intensively due to time-dependent blade flapping, cyclic pitch and wake inflow. For example, during forward flight at the velocity close to VNE, VNE, ''velocity, never exceed'', the advancing and retreating blades almost reach their operation limits whereas flows are still attached to the blade surfaces. That is, the advancing blades operate at high Mach numbers so low values of AOA is needed but shock-induced flow separation may happen, while the retreating blade operates at much lower Mach numbers but the high values of AoA result ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Stall Region
Dynamics (from Greek language, Greek δυναμικός ''dynamikos'' "powerful", from δύναμις ''dynamis'' "power (other), power") or dynamic may refer to: Physics and engineering * Dynamics (mechanics), the study of forces and their effect on motion Brands and enterprises * Dynamic (record label), an Italian record label in Genoa Mathematics * Dynamical system, a concept describing a point's time dependency ** Topological dynamics, the study of dynamical systems from the viewpoint of general topology * Symbolic dynamics, a method to model dynamical systems Social science * Group dynamics, the study of social group processes especially * Population dynamics, in life sciences, the changes in the composition of a population * Psychodynamics, the study of psychological forces driving human behavior * Social dynamics, the ability of a society to react to changes * Spiral Dynamics, a social development theory Other uses * Dynamics (music), the softness or loudn ... [...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 bounda ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Angle Of Attack
In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a Airfoil#Airfoil terminology, reference line on a body (often the chord (aircraft), chord line of an airfoil) and the vector (geometry), vector representing the relative motion between the body and the fluid through which it is moving. Angle of attack is the angle between the body's reference line and the oncoming flow. This article focuses on the most common application, the angle of attack of a wing or airfoil moving through air. In aerodynamics, angle of attack specifies the angle between the chord line of the wing of a fixed-wing aircraft and the vector representing the relative motion between the aircraft and the atmosphere. Since a wing can have twist, a chord line of the whole wing may not be definable, so an alternate reference line is simply defined. Often, the chord line of the Wing root, root of the wing is chosen as the reference line. Another choice is to use a horizontal line on the fuse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lift Coefficient
In fluid dynamics, the lift coefficient () is a dimensionless quantity that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity and an associated reference area. A lifting body is a foil or a complete foil-bearing body such as a fixed-wing aircraft. is a function of the angle of the body to the flow, its Reynolds number and its Mach number. The section lift coefficient refers to the dynamic lift characteristics of a two-dimensional foil section, with the reference area replaced by the foil chord. Abbott, Ira H., and Doenhoff, Albert E. von: ''Theory of Wing Sections''. Section 1.2 Definitions The lift coefficient ''C''L is defined by :C_\mathrm L \equiv \frac = = , where L\, is the lift force, S\, is the relevant surface area and q\, is the fluid dynamic pressure, in turn linked to the fluid density \rho\,, and to the flow speed u\,. The choice of the reference surface should be specified since it is arbitrary. For e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reduced Frequency
Reduced frequency is the dimensionless number used in general for the case of unsteady aerodynamics and aeroelasticity Aeroelasticity is the branch of physics and engineering studying the interactions between the inertial, elastic, and aerodynamic forces occurring while an elastic body is exposed to a fluid flow. The study of aeroelasticity may be broadly classi .... It is one of the parameters that defines the degree of unsteadiness of the problem. For the case of flutter analysis, lift history for the motion obtained from the Wagner analysis ( Herbert A. Wagner) with varying frequency of oscillation shows that magnitude of lift decreases and a phase lag develops between the aircraft motion and the unsteady aerodynamic forces. Reduced frequency can be used to explain the amplitude attenuation and the phase lag of the unsteady aerodynamic forces compared to the quasi steady analysis (which in theory assumes no phase lag). Reduced frequency is denoted by the letter "k" and given ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helicopter Rotor
On a helicopter, the main rotor or rotor system is the combination of several rotary wings (rotor blades) with a control system, that generates the aerodynamic lift (force), lift force that supports the weight of the helicopter, and the thrust that counteracts aerodynamic drag in forward flight. Each main rotor is mounted on a vertical mast over the top of the helicopter, as opposed to a helicopter tail rotor, which connects through a combination of drive shaft(s) and gearboxes along the tail boom. The blade pitch is typically controlled by the pilot using the helicopter flight controls. Helicopters are one example of rotary-wing aircraft (rotorcraft). The name is derived from the Greek words ''helix'', helik-, meaning spiral; and ''pteron'' meaning wing. Design principles Overview The helicopter rotor is powered by the engine, through the transmission, to the rotating mast. The mast is a cylindrical metal shaft that extends upward from—and is driven by—the transmission. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rotorcraft
A rotary-wing aircraft, rotorwing aircraft or rotorcraft is a heavier-than-air aircraft with rotor wing, rotary wings that spin around a vertical mast to generate lift (force), lift. Part 1 (Definitions and Abbreviations) of Subchapter A of Chapter I of Title 14 of the U. S. Code of Federal Regulations states that rotorcraft "means a heavier-than-air aircraft that depends principally for its support in flight on the lift generated by one or more rotors." The assembly of several rotor blades mounted on a single mast is referred to as a helicopter rotor, rotor. The International Civil Aviation Organization (ICAO) defines a rotorcraft as "supported in flight by the reactions of the air on one or more rotors". Rotorcraft generally include aircraft where one or more rotors provide lift throughout the entire flight, such as helicopters, gyroplanes, autogyros, and gyrodynes Compound rotorcraft augment the rotor with additional thrust engines, propellers, or static lifting surfaces. Some ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flowchart Of Leishman-Beddoes Dynamic Stall Model
A flowchart is a type of diagram that represents a workflow or process. A flowchart can also be defined as a diagrammatic representation of an algorithm, a step-by-step approach to solving a task. The flowchart shows the steps as boxes of various kinds, and their order by connecting the boxes with arrows. This diagrammatic representation illustrates a solution model to a given problem. Flowcharts are used in analyzing, designing, documenting or managing a process or program in various fields. * ''Document flowcharts'', showing controls over a document-flow through a system * ''Data flowcharts'', showing controls over a data-flow in a system * ''System flowcharts'', showing controls at a physical or resource level * ''Program flowchart'', showing the controls in a program within a system Notice that every type of flowchart focuses on some kind of control, rather than on the particular flow itself. However, there are some different classifications. For example, Andrew Veronis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computational Fluid Dynamics
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid dynamics, fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid (liquids and gases) with surfaces defined by Boundary value problem#Boundary value conditions, boundary conditions. With high-speed supercomputers, better solutions can be achieved, and are often required to solve the largest and most complex problems. Ongoing research yields software that improves the accuracy and speed of complex simulation scenarios such as transonic or turbulence, turbulent flows. Initial validation of such software is typically performed using experimental apparatus such as wind tunnels. In addition, previously performed Closed-form solution, analytical or Empirical research, empirical analysis of a particular problem can be used for compa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Effect Of Reynolds Number On Dynamic Stall
Effect may refer to: * A result or change of something ** List of effects ** Cause and effect, an idiom describing causality Pharmacy and pharmacology * Drug effect, a change resulting from the administration of a drug ** Therapeutic effect, a beneficial change in medical condition, often caused by a drug ** Adverse effect or side effect, an unwanted change in medical condition caused by a drug In media * Special effect, an artificial illusion ** Sound effect, an artificially created or enhanced sound ** Visual effects, artificially created or enhanced images *Audio signal processing ** Effects unit, a device used to manipulate electronic sound *** Effects pedal, a small device attached to an instrument to modify its sound Other uses * Effects, one's personal property or belongings * Effects (G.I. Joe), a fictional character in the G.I. Joe universe * ''Effects'' (film), a 1979 film (give a wide release in 2005) * Effect size, a measure of the strength of a relationship bet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reduced Frequency
Reduced frequency is the dimensionless number used in general for the case of unsteady aerodynamics and aeroelasticity Aeroelasticity is the branch of physics and engineering studying the interactions between the inertial, elastic, and aerodynamic forces occurring while an elastic body is exposed to a fluid flow. The study of aeroelasticity may be broadly classi .... It is one of the parameters that defines the degree of unsteadiness of the problem. For the case of flutter analysis, lift history for the motion obtained from the Wagner analysis ( Herbert A. Wagner) with varying frequency of oscillation shows that magnitude of lift decreases and a phase lag develops between the aircraft motion and the unsteady aerodynamic forces. Reduced frequency can be used to explain the amplitude attenuation and the phase lag of the unsteady aerodynamic forces compared to the quasi steady analysis (which in theory assumes no phase lag). Reduced frequency is denoted by the letter "k" and given ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hysteresis
Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of the moment often form a loop or hysteresis curve, where there are different values of one variable depending on the direction of change of another variable. This history dependence is the basis of memory in a hard disk drive and the remanence that retains a record of the Earth's magnetic field magnitude in the past. Hysteresis occurs in ferromagnetic and ferroelectricity, ferroelectric materials, as well as in the deformation (mechanics), deformation of rubber bands and shape-memory alloys and many other natural phenomena. In natural systems, it is often associated with irreversible process, irreversible thermodynamic change such as phase transitions and with internal friction; and dissipation is a common side effect. Hysteresis can be fou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
