Outflowing

Outflowing is an adjective describing motion of material, energy, or other quantities moving outward from a source, center, or region. It denotes flow away from a system rather than toward it and is commonly contrasted with inflowing or inflow.

In astrophysics, outflows are a widespread phenomenon around forming stars and active galaxies. Protostellar winds and jets eject gas from the central object or accretion disk, sometimes forming narrow, highly collimated streams and, in other cases, broader winds. Outflows are thought to be driven by radiation pressure, magnetic forces, and thermal gradients, and they play a key role in regulating accretion and redistributing material and angular momentum. Observationally, outflows are characterized by Doppler-shifted spectral features and emission-line profiles, which yield estimates of flow velocity and mass outflow rate and their relation to accretion rates.

In fluid dynamics and engineering, outflow can describe both a physical discharge and a boundary condition in simulations. An outflow boundary condition allows fluid to exit a domain with minimal artificial reflection, often employing zero-gradient or fixed-pressure assumptions. Incorrect specification can produce numerical artifacts, especially for unsteady or compressible flows. In meteorology, the term also describes outward-moving air from storms, which forms gust fronts, and in hydrology, it denotes water leaving a reservoir or lake as part of the basin's water balance.

Across disciplines, the concept emphasizes outward transport from a source.