# What is Stagnation Pressure – Pitot Pressure – Definition

Stagnation Pressure – Pitot Pressure. Stagnation pressure (or pitot pressure or total pressure) is the static pressure at a stagnation point in a fluid flow. Thermal Engineering

## Stagnation Pressure – Pitot Pressure

In general, pressure is a measure of the force exerted per unit area on the boundaries of a substance. In fluid dynamics and aerodynamics, stagnation pressure (or pitot pressure or total pressure) is the static pressure at a stagnation point in a fluid flow. At a stagnation point the fluid velocity is zero and all kinetic energy has been converted into pressure energy (isentropically). This effect is widely used in aerodynamics (velocity measurement or ram-air intake).

Stagnation pressure is equal to the sum of the free-stream dynamic pressure and free-stream static pressure.

Static pressure and dynamic pressure are terms of Bernoulli’s equation:

The Bernoulli’s effect causes the lowering of fluid pressure (static pressure – p) in regions where the flow velocity is increased. This lowering of pressure in a constriction of a flow path may seem counterintuitive, but seems less so when you consider pressure to be energy density. In the high velocity flow through the constriction, kinetic energy (dynamic pressure – ½.ρ.v2) must increase at the expense of pressure energy (static pressure – p).

The simplified form of Bernoulli’s equation can be summarized in the following memorable word equation:

static pressure + dynamic pressure = total pressure (stagnation pressure)

Total and dynamic pressure are not pressures in the usual sense – they cannot be measured using an aneroid, Bourdon tube or mercury column.

Stagnation pressure is sometimes referred to as pitot pressure because it is measured using a pitot tube. A Pitot tube is a pressure measurement instrument used to measure fluid flow velocity. Velocity can be determined using the following formula:

where:

• u is flow velocity to be measured in m/s,
• pis stagnation or total pressure in Pa,
• pt is static pressure in Pa,
• ρ is fluid density in kg/m3.

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