Search results
Results From The WOW.Com Content Network
The propulsive efficiency is always less than one, because conservation of momentum requires that the exhaust have some of the kinetic energy, and the propulsive mechanism (whether propeller, jet exhaust, or ducted fan) is never perfectly efficient. It is greatly dependent on exhaust expulsion velocity and airspeed.
The ratio between a propeller's efficiency attached to a ship and in open water (′) is termed relative rotative efficiency. The overall propulsive efficiency (an extension of effective power ()) is developed from the propulsive coefficient (), which is derived from the installed shaft power modified by the effective power for the hull with ...
Specific impulse should not be confused with energy efficiency, which can decrease as specific impulse increases, since propulsion systems that give high specific impulse require high energy to do so. [3] Specific impulse should not be confused with total thrust. Thrust is the force supplied by the engine and depends on the propellant mass flow ...
Propulsive efficiency comparison for various gas turbine engine configurations. In a zero-bypass (turbojet) engine the high temperature and high pressure exhaust gas is accelerated by expansion through a propelling nozzle and produces all the thrust. The compressor absorbs all the mechanical power produced by the turbine.
A propulsion system consists of a source of mechanical power, and a propulsor (means of converting this power into propulsive force). Plucking a guitar string to induce a vibratory translation is technically a form of propulsion of the guitar string; this is not commonly depicted in this vocabulary, even though human muscles are considered to ...
In addition to propulsive efficiency, another factor is cycle efficiency; a jet engine is a form of heat engine. Heat engine efficiency is determined by the ratio of temperatures reached in the engine to that exhausted at the nozzle. This has improved constantly over time as new materials have been introduced to allow higher maximum cycle ...
Therefore, turbines are more efficient for aircraft propulsion than might be indicated by a simplistic look at the table below. SFC varies with throttle setting, altitude, climate. For jet engines, air flight speed is an important factor too. Air flight speed counteracts the jet's exhaust speed.
The Kort nozzle is a shrouded propeller assembly for marine propulsion. The cross-section of the shroud has the form of a foil, and the shroud can offer hydrodynamic advantages over bare propellers, under certain conditions. Advantages are increased efficiency at lower speeds (<10 knots), better course stability and less vulnerability to debris.