Pressure coefficient

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Physical key figure
Surname Pressure coefficient,
pressure coefficient
Formula symbol
dimension dimensionless
Pressure of the inflow
Flow velocity
scope of application viscous currents

The pressure coefficient , often also referred to as the pressure coefficient , is a dimensionless quantity from aerodynamics that is often used in the design and analysis of wings , but also in other areas of aerodynamics, e.g. B. with internal currents.

He will u. a. used to describe or graph the pressure distribution on the wing of aircraft ; The pressure distribution means the pressure on all points on the entire surface of the wing.

In relation to a certain point, the pressure coefficient represents the ratio of static pressure to dynamic pressure .

The pressure coefficient at the end of a body that flows through (e.g. a valve ) is called the pressure loss coefficient .


The pressure coefficient is defined as follows:

Assuming an incompressible flow ( Ma  <0.3) also applies:

Here are:

  • = the static pressure measured at a given point
  • = the static pressure in the inflow
  • = the density of the surrounding medium (e.g. air )
  • = Amount of the local speed of the surrounding medium (e.g. air); instead of is often also used or for the velocity component in the x direction.
  • = the flow velocity of the surrounding medium (analogous are also and common)


The denominator of the fraction represents the back pressure is (or dynamic pressure) of the free inflow, therefore, 1 is the highest value that the pressure coefficient can be reached in an incompressible flow around rigid body and without energy supply (in stagnation point ).

The sign of the derivation of the pressure according to the length of the run indicates whether the flow is accelerated or decelerated compared to the inflow:

  • negative signs mean pressure decrease (i.e. acceleration)
  • positive signs indicate pressure increase (i.e. areas where the flow is decelerated or at friction-prone flow detaches ).

By relating the coefficient to the dynamic pressure, the distribution of the pressure coefficient around a body does not change if the speed, density or static pressure of the inflow change, because then all the individual values ​​of the coefficient distributed around the body change in the same or similar way . The distribution also applies to all geometrically similar bodies. The actual pressures can therefore be calculated for a large range of flight speeds and altitudes from the pressure distribution around a wing profile .

Strictly speaking, these relationships only apply in a smooth, incompressible flow, but can often be used as a sufficient approximation in the general case. They do not apply to: Positions behind collisions, in the boundary layer , in flows with detachments and in flows with a variable position of the transition point between laminar and turbulent boundary layer.

See also