Dynamic Pressure

Dynamic pressure is the kinetic energy of a flowing fluid - liquid or gas - per unit volume - and can be expressed as

p_d = 1/2 ρ v²(1)

where

p_d = dynamic pressure (N/m²(Pa), lb_f /ft²(psf))

ρ = density of fluid (kg/m³, slugs /ft³ )

v = velocity (m/s, ft/s)

Dynamic Pressure Calculator - SI Units

The default values below are for water with density of 1000 kg/m³ .

ρ - density of fluid (kg/m³ )

v - velocity (m/s)

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• 1 N/m²= 1 Pa = 1.4504x10^-4 lb_f /in²(psi) = 0.02089 lb_f /ft²(psf) = 1x10 ^-5 bar = 4.03x10^-3 in water = 0.336x10^-3 ft water = 0.1024 mm water = 0.295x10^-3 in mercury = 7.55x10^-3 mm mercury = 0.1024 kp/m²= 0.993x10 ^-5 atm

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Dynamic Pressure Calculator - Imperial Units

The default values below are for water with density of 1.940 slugs .

ρ - density of fluid ( slugs /ft³ )

v - velocity (ft/s)

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• more about mass and weight - and slugs

Some common densities at atmospheric pressure:

• Water - 0 ^oC - 1000 kg/m³
• Water - 32 ^oF - 1.940 slugs/ft³
  
• Air - 20 ^oC - 1.2 kg/m³
• Air - 60 ^oF - 2.373 10^-3 slugs/ft³
  

Example - The Dynamic Pressure in a Water Flow

The dynamic pressure in water with - temperature 20 ^oC - density 1000 kg/m³ and velocity 5 m/s - can be calculated as

p_d = 1/2 (1000 kg/m³ ) (5 m/s)²

= 12500 Pa

= 12.5 kPa

Example - Hurricane and Force acting on a Wall

The dynamic pressure in a hurricane with air temperature 20 ^oC, density of air 1.2 kg/m³ and wind speed 37 m/s can be calculated as

p_d = 1/2 (1.2 kg/m³ ) (37 m/s)²

= 821 Pa (N/m²)

The force acting directly on a wall with area 10 m² can be calculated as

F = p_d A

= (821 N/m²) (10 m²)

= 8210 N

= 8.2 kN

- almost the weight of a small car.

Note! - the real force acting on the wall - or an other obstruction in the wind - is in general more complicated to calculate due to drag , turbulence and other effects.

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