Glossary term
Wake
The disturbed flow region downstream of a body moving through or immersed in a fluid.
Definition
phenomenonA wake is the region of disturbed, slower, and often vortical flow downstream of a body immersed in or moving through a fluid.
Wakes form because bodies transfer momentum to the surrounding fluid through boundary layers, separation, pressure drag, and vortex formation. They affect drag, lift, noise, mixing, downstream inflow quality, thermal plumes, vehicle spacing, propeller performance, turbine arrays, structural loading, and flow-induced vibration.
A wake is created when a body disturbs the velocity, pressure, and vorticity field of a fluid. Behind bluff bodies, the wake may contain separated shear layers and alternating vortices. Behind streamlined bodies, the wake may be narrower but still contains momentum deficit and turbulence generated by boundary-layer losses.
The wake is not just a visual trail. It represents lost momentum and energy in the flow, which is why wake structure is tied to aerodynamic drag. Its size and behavior depend on body shape, angle of attack, Reynolds number, Mach number, surface roughness, turbulence level, boundary conditions, and nearby surfaces.
Engineering use
Wake analysis matters for aircraft formation spacing, vehicle drag reduction, wind-turbine arrays, propeller and fan inflow, heat-exchanger tube banks, bridges, masts, ships, submarines, and sports equipment. A wake from an upstream body can reduce performance or increase fatigue loading on downstream bodies.
Wakes are measured with pressure probes, hot-wire anemometry, particle image velocimetry, force balances, flow visualization, and wind-tunnel or water-channel testing. Computational models must resolve or model separation and turbulence consistently with the intended decision.
Common mistakes
A common mistake is treating wake effects as purely downstream and harmless to the source body. The wake is a consequence of forces on the body and can indicate drag, unsteady loading, and separation. Another is comparing wake data without matching Reynolds number, blockage, turbulence intensity, model support effects, and measurement plane. A strong wake review states body geometry, flow speed, Reynolds number, Mach number where relevant, upstream turbulence, measurement method, downstream location, and whether the wake is steady, unsteady, laminar, transitional, or turbulent.