# aerodynamic force

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## Aerodynamic force

The force exerted on a body whenever there is a relative velocity between the body and the air. There are only two basic sources of aerodynamic force: the pressure distribution and the frictional shear stress distribution exerted by the airflow on the body surface. The pressure exerted by the air at a point on the surface acts perpendicular to the surface at that point; and the shear stress, which is due to the frictional action of the air rubbing against the surface, acts tangentially to the surface at that point. The distribution of pressure and shear stress represent a distributed load over the surface. The net aerodynamic force on the body is due to the net imbalance between these distributed loads as they are summed (integrated) over the entire surface. See Boundary-layer flow, Fluid flow

For purposes of discussion, it is convenient to consider the aerodynamic force on an airfoil (see illustration). The net resultant aerodynamic force R acting through the center of pressure on the airfoil represents mechanically the same effect as that due to the actual pressure and shear stress loads distributed over the body surface. The velocity of the airflow V is called the free-stream velocity or the free-stream relative wind. By definition, the component of R perpendicular to the relative wind is the lift, L, and the component of R parallel to the relative wind is the drag D. The orientation of the body with respect to the direction of the free stream is given by the angle of attack, α. The magnitude of the aerodynamic force R is governed by the density &rgr; and velocity of the free stream, the size of the body, and the angle of attack. See Airfoil

An important measure of aerodynamic efficiency is the ratio of lift to drag, L/D. The higher the value of L/D, the more efficient is the lifting action of the body. The value of L/D reaches a maximum, denoted by (L/D)max, at a relatively low angle of attack. Beyond a certain angle the lift decreases with increasing α. In this region, the wing is said to be stalled. In the stall region the flow has separated from the top surface of the wing, creating a type of slowly recirculating dead-air region, which decreases the lift and substantially increases the drag.

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

## aerodynamic force

[‚e·ro·dī′nam·ik ′fȯrs]
(fluid mechanics)
The force between a body and a gaseous fluid caused by their relative motion. Also known as aerodynamic load.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## Aerodynamic force

The force exerted on a body whenever there is a relative velocity between the body and the air. There are only two basic sources of aerodynamic force: the pressure distribution and the frictional shear stress distribution exerted by the airflow on the body surface. The pressure exerted by the air at a point on the surface acts perpendicular to the surface at that point; and the shear stress, which is due to the frictional action of the air rubbing against the surface, acts tangentially to the surface at that point. The distribution of pressure and shear stress represent a distributed load over the surface. The net aerodynamic force on the body is due to the net imbalance between these distributed loads as they are summed (integrated) over the entire surface.

For purposes of discussion, it is convenient to consider the aerodynamic force on an airfoil (see illustration). The net resultant aerodynamic force R acting through the center of pressure on the airfoil represents mechanically the same effect as that due to the actual pressure and shear stress loads distributed over the body surface. The velocity of the airflow V is called the free-stream velocity or the free-stream relative wind. By definition, the component of R perpendicular to the relative wind is the lift, L, and the component of R parallel to the relative wind is the drag D. The orientation of the body with respect to the direction of the free stream is given by the angle of attack, α. The magnitude of the aerodynamic force R is governed by the density &rgr; and velocity of the free stream, the size of the body, and the angle of attack.

An important measure of aerodynamic efficiency is the ratio of lift to drag, L/D. The higher the value of L/D, the more efficient is the lifting action of the body. The value of L/D reaches a maximum, denoted by (L/D)max, at a relatively low angle of attack. Beyond a certain angle the lift decreases with increasing α. In this region, the wing is said to be stalled. In the stall region the flow has separated from the top surface of the wing, creating a type of slowly recirculating dead-air region, which decreases the lift and substantially increases the drag.

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The aerodynamic forces are computed using the static lift, drag, and moment coefficient correlations for the studied debris shape, neglecting the shape effects on the flow field.
Moreover, complex vortex patterns are observed under the wake of the flexible wing with [[rho].sup.*] = 750, and the weakest vortex is generated around the flexible wing with [[rho].sup.*] = 2000, which indicates that the flexible wing with [[rho].sup.*] = 750 needs more energy to perform the wing hovering, and the flexible wing with [[rho].sup.*] = 2000 generates the smallest aerodynamic force, as shown in Figure 13.
Flutter is a potentially damaging dynamic aeroelastic phenomenon where aerodynamic forces with the natural modes of vibration cause a periodic motion of a structure going unstable.
The experimental setup is shown in Figure 1(c), where two balances are applied to measure the aerodynamic forces. Both ends of the conductor are fixed on a balance by the connector, respectively.
To this end, the quasi-steady aerodynamic force coefficients of iced contact wire are simulated by FLUENT.
The aerodynamic force and moment due to canard 1, as shown in Figure 2, are given by
Hence, the unsteady aerodynamic force is also assumed to be oscillating with flutter frequency.
20 suitably modified to take into account inertia, gravity, surface tension, and, most importantly, the aerodynamic force due to the tangentially air jet.
The change of wing structure deformation not only influences aerodynamic force but also changes flight pose for flapping wing.
The aerodynamic force necessary to stay aloft is created solely because of the so-called bound vortex (or circulation), which is complementary to the starting vortex and constitutes a measure of difference in flow speeds over and under the wing.

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