Definition
A type of turbine in which the kinetic energy (velocity) of a high-speed gas stream is used to spin the turbine wheel, with little or no further pressure drop occurring across the rotating blades themselves. The pressure drop and acceleration of the gas happen in the stationary nozzles upstream of the wheel; the moving blades simply change the direction of the fast-moving gas, and that change in direction produces the force that turns the wheel. Also called an impulse turbine.
Plain English
A turbine that is driven by the speed of the gas hitting its blades, rather than by the gas expanding as it passes through them. The gas is sped up first by fixed nozzles, then slammed into the blades to spin the wheel.
Context Anchor
Seen in turbine engine and turbocharger discussions, especially when describing how exhaust or hot gas energy turns a turbine wheel.
Derivation
Velocity comes from the Latin velocitas, meaning swiftness or speed. The name describes how the turbine works: it extracts energy from the speed of the gas stream, not from gas expansion across the blades.
Why Pilots Care
Maintenance technicians and pilots studying powerplant theory need to recognize that different turbine designs handle gas flow differently. A velocity (impulse) turbine relies on nozzle-generated speed, which affects how the engine builds power and how the turbine section is inspected and maintained.
Analogy
Think of a water wheel being spun by a jet of water from a hose nozzle. The hose nozzle speeds the water up, and the water's speed alone pushes the paddles around. The paddles don't squeeze or expand the water — they just redirect it.
Intuition Check
Velocity does not mean the turbine itself is simply moving fast. Here, it means the turbine gets its driving force mainly from the speed of the gas striking the blades.
Example Sentence 1
In a velocity turbine, the stationary nozzles accelerate the gas before it reaches the rotating blades.
Example Sentence 2
High exhaust velocity allows the velocity turbine to extract enough energy to drive the compressor section.