Dynamic pressure

In fluid dynamics, dynamic pressure (denoted by q or Q and sometimes called velocity pressure) is the quantity defined by:[1] where (in SI units): It can be thought of as the fluid's kinetic energy per unit volume.

Dynamic pressure is the kinetic energy per unit volume of a fluid.

Dynamic pressure is one of the terms of Bernoulli's equation, which can be derived from the conservation of energy for a fluid in motion.

[1] Another important aspect of dynamic pressure is that, as dimensional analysis shows, the aerodynamic stress (i.e. stress within a structure subject to aerodynamic forces) experienced by an aircraft travelling at speed

during flight, it is possible to determine how the stress will vary and in particular when it will reach its maximum value.

The point of maximum aerodynamic load is often referred to as max q and it is a critical parameter in many applications, such as launch vehicles.

Dynamic pressure can also appear as a term in the incompressible Navier-Stokes equation which may be written: By a vector calculus identity (

), the second term on the left in the Navier-Stokes equation is just the gradient of the dynamic pressure.

is known as the hydraulic velocity head (hv) so that the dynamic pressure is equal to

The three terms are used to define the state of a closed system of an incompressible, constant-density fluid.

In a venturi flow meter, the differential pressure head can be used to calculate the differential velocity head, which are equivalent in the adjacent picture.

Many authors define dynamic pressure only for incompressible flows.

(For compressible flows, these authors use the concept of impact pressure.)

However, the definition of dynamic pressure can be extended to include compressible flows.