Ramtryck

Ramtryck, or ram pressure, is the pressure exerted on an object by a fluid in relative motion. It occurs when a body moves through a fluid or when fluid flows around a stationary object, causing momentum transfer as fluid is displaced or accelerated. The magnitude depends on the fluid density, the relative speed, and the area exposed to the flow. In many practical contexts the ram pressure is expressed as P_ram ≈ ρ v^2, and the resulting force is roughly F ≈ P_ram A. Some aerodynamics references instead use the dynamic pressure q = 1/2 ρ v^2, with F ≈ q C_d A to account for shape via a drag coefficient.

In aerodynamics, ram pressure is related to stagnation pressure: the stagnation pressure P0 equals the static pressure P plus the dynamic contribution 1/2 ρ v^2 for incompressible flow. For compressible flows at high speeds, the relationship becomes more complex but the concept remains that motion through a fluid adds pressure on the leading surface.

Ram pressure is also a key concept in astrophysics. A galaxy moving through the hot intracluster medium experiences ram pressure proportional to ρ v^2, which can strip gas from its disk if the external pressure exceeds gravitational restoring forces. This ram-pressure stripping shapes galaxy evolution in dense environments and is described by criteria that compare P_ram to the galaxy’s mass distribution.

Applications of ram pressure span engineering and natural phenomena: designing aircraft, vehicles, wind-exposed structures, and spacecraft re-entry; analyzing meteorological wind loads; and studying astrophysical gas dynamics. It is measured in pascals (or newtons per square meter) and is influenced by fluid density, speed, and geometry.