The propulsive efficiency (ηp) of a high-bypass ratio (HBR) turbofan engine is a measure of how effectively the engine converts the energy from the combustion of fuel into useful thrust for propulsion. High-bypass ratio turbofan engines are known for their efficiency due to the significant contribution of bypass air to thrust. In SI units, the formula for calculating the propulsive efficiency of an HBR turbofan engine is as follows:
ηp = (2 * V * (Vj – Vb)) / (g * (Vj^2))
Where:
- ηp is the propulsive efficiency (unitless, a dimensionless ratio).
- V is the airspeed of the aircraft in meters per second (m/s).
- Vj is the jet exhaust velocity of the engine in meters per second (m/s).
- Vb is the velocity of the bypass air in meters per second (m/s).
- g is the acceleration due to gravity, approximately 9.81 m/s².
The propulsive efficiency equation quantifies how effectively the HBR turbofan engine converts the energy in the fuel into useful thrust for propulsion. It considers the difference between the airspeed of the aircraft (V) and the effective exhaust velocity of the jet exhaust (Vj) minus the velocity of the bypass air (Vb).
HBR turbofan engines are used in modern aircraft and are designed for fuel efficiency, reduced noise, and increased performance. The formula above provides a way to quantify and compare the effectiveness of these engines in converting fuel energy into thrust for propulsion, taking into account both the jet exhaust and bypass air contributions to thrust.