How to Calculate Stagnation Pressure

Written by doug leenhouts
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How to Calculate Stagnation Pressure
Stagnation pressure is pertinent to air speed calculators. (aircraft image by yaros from Fotolia.com)

Stagnation pressure is the pressure produced by a fluid in a pipe at a location that has a velocity of zero. Total pressure, also known as stagnation pressure, is calculated as the sum of the static pressure and the dynamic pressure. This has applications in aircraft speedometers, as it is determined by a pitot tube which is open to the atmosphere. This equation stems from Bernoulli's Principle, which determines the pressure of a liquid in ideal conditions, assuming there is a steady flow and no friction.

Skill level:
Easy

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Things you need

  • Calculator
  • Pitot tube
  • Beaker
  • Scale

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Instructions

  1. 1

    Calculate the dynamic pressure of the fluid. This is found using the formula for dynamic from Bernoulli's equation, P(dynamic) = (1/2)(p)(v²), where "p" is the density of the fluid and "v" is the fluid's velocity. The density can be found by measuring the mass of a sample of fluid and dividing it by the volume of the sample, and the velocity can be measured using a pitot tube and referencing the associated velocity reading on a velocity head chart.

  2. 2

    Calculate the static pressure of the fluid. This is found using the equation P(static) = (p)(g)(h), where "p" is the fluid density, as calculated before, "g" is the acceleration due to gravity and "h" is the depth of the fluid.

  3. 3

    Add the static and dynamic pressure together to get the stagnation pressure. For example, water (density = 1 gram per cubic centimetre) flowing in a river 1 meter deep at a velocity of 2 meters per second has a dynamic pressure equal to (1/2)(1)(2²), or 2 kilogram meters per second. Its static pressure is therefore (1)(9.8)(1) = 9.8 kilogram meters per second, and the stagnation pressure is therefore 2 + 9.8 = 11.8 kilogram meters per second.

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