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The drag curve or drag polar is the relationship between the drag on an aircraft and other variables, such as lift, the coefficient of lift, angle-of-attack or speed. It may be described by an equation or displayed as a graph (sometimes called a "polar plot"). [1] Drag may be expressed as actual drag or the coefficient of drag.
drag force F d. Using the algorithm of the Buckingham π theorem, these five variables can be reduced to two dimensionless groups: drag coefficient c d and; Reynolds number Re. That this is so becomes apparent when the drag force F d is expressed as part of a function of the other variables in the problem:
The Morison equation is the sum of two force components: an inertia force in phase with the local flow acceleration and a drag force proportional to the (signed) square of the instantaneous flow velocity. The inertia force is of the functional form as found in potential flow theory, while the drag force has the form as found for a body placed ...
Creeping flow past a falling sphere in a fluid (e.g., a droplet of fog falling through the air): streamlines, drag force F d and force by gravity F g. At terminal (or settling) velocity, the excess force F e due to the difference between the weight and buoyancy of the sphere (both caused by gravity [7]) is given by:
Viscous drag of fluid in a pipe: Drag force on the immobile pipe decreases fluid velocity relative to the pipe. [ 4 ] [ 5 ] In the physics of sports, drag force is necessary to explain the motion of balls, javelins, arrows, and frisbees and the performance of runners and swimmers. [ 6 ]
Drag coefficients in fluids with Reynolds number approximately 10 4 [1] [2] Shapes are depicted with the same projected frontal area. In fluid dynamics, the drag coefficient (commonly denoted as: , or ) is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water.
Terminal velocity depends on atmospheric drag, the coefficient of drag for the object, the (instantaneous) velocity of the object, and the area presented to the airflow. Apart from the last formula, these formulas also assume that g negligibly varies with height during the fall (that is, they assume constant acceleration).
The most typical case of air resistance, in case of Reynolds numbers above about 1000, is Newton drag with a drag force proportional to the speed squared, =. In air, which has a kinematic viscosity around 0.15 cm 2 /s, this means that the product of object speed and diameter must be more than about 0.015 m 2 /s.