Coanda Air Throw
& Velocity Profiler
Audit terminal diffuser velocities against core boundary geometries to model absolute throw distances and drop scales.
Fluid Dynamics & The Physics of the Coanda Effect in Room Air Distribution Overview
How supply air travels within an occupied space is governed by fluid dynamics and boundary layer properties known as the Coanda Effect. When a jet of conditioned air streams out of a supply register mounted flush to a flat ceiling line, a localized zone of low pressure develops between the moving air stream and the solid ceiling surface. This drop in pressure creates a continuous suction force that lifts the fluid mass upward, forcing it to slide horizontally across the ceiling surface instead of falling straight down. This horizontal path provides vital space conditioning advantages. By keeping the cold, dense air hugging the ceiling ceiling line over an elongated throw distance, it maximizes room air induction—the process where high-speed supply air gently blends with stagnant room air currents—establishing perfect thermal equilibrium across the floor template without subjecting occupants to cold drafts.
Frequently Asked Questions
A: If register discharge velocity falls too low, the fluid air jet lacks the necessary kinetic energy to create the low-pressure suction zone required for Coanda adhesion. Lacking this boundary support, gravity takes over immediately at the face of the grille. The cold, heavy supply air drops straight down into the room below like water from a bucket, creating a localized zone of high-velocity cold air (“dumping”) that makes occupants uncomfortable while causing temperature stratification elsewhere in the room.
A: Any physical protrusion that extends below the ceiling plane breaks the continuous boundary layer. When the air stream hits an obstacle like a structural beam drop, the horizontal low-pressure zone collapses instantly. This forces the air jet to detach from the ceiling boundary premature, causing it to drop straight down into the occupied living zone below and creating cold drafts well ahead of its designed throw limits.