Bypass Ratio

Bypass Ratio

The bypass air is shown in pink, whilst the core gases are shown in red.

The term bypass ratio (BPR) relates to the design of turbofan engines, commonly used in aviation. It is defined as the ratio between the mass flow rate of air drawn through a fan disk which bypasses the engine core (un-combusted air), to the mass flow rate passing through the engine core which is involved in combustion to produce mechanical energy. For example, with a 10:1 bypass ratio, for every 1 kg of air passing through the combustion chamber, 10 kg of air passes around the combustion chamber through the ducted fan alone.

In a high-bypass design, the vast majority of the thrust is derived from the ducted fan, rather than from combustion gases expanding in a nozzle. A high bypass ratio provides a lower thrust specific fuel consumption (grams/sec fuel per unit of thrust in kN using SI units) for reasons explained below, especially at zero velocity (at takeoff) and at the cruise speed of most commercial jet aircraft. They are by far the dominant type for all commercial passenger aircraft and both civilian and military jet transports. Lower exhaust velocities also figure strongly in lower noise output which is a decided advantage over earlier low or zero bypass designs.

Low bypass ratios tend to be favored for military combat aircraft as a compromise between improved fuel economy and the requirements of combat, which values higher power-to-weight ratios, supersonic performance, and the ability to use afterburners which are more compatible with low bypass engines. A good example of the differences between a pure jet engine and a low-bypass turbofan may be seen in the Spey turbofan used in the F-4 Phantom.

Read more about Bypass RatioPrinciples, Description

Other articles related to "bypass ratio, ratio, bypass, ratios":

IHI Corporation F7 - Development
... IHI started development work on the high bypass ratio turbofan engine in 1998, based on the low bypass ratio engine XF5-1 ... Take off thrust is 60kN(6,100kg/13,500lbs), bypass ratio is 8.2, and SFC is 0.34 kg/hr/daN ...
Turbofan - Introduction
... make it easier to throttle back compression systems with a high design overall pressure ratio (i.e ... Civil-aviation high-bypass turbofans usually have a single large fan disk, whereas most military-aviation low-bypass turbofans (e.g ... aircraft applications) have multi-disk compressors as a compromise between greater power-to-weight ratios, supersonic performance, and the capability of using afterburners, versus the higher ...
Description - Engine Bypass Ratios
... Engine Aircraft Bypass ratio Rolls-Royce/Snecma Olympus 593 Concorde (turbojet) 01 Rolls-Royce Tay Gulfstream IV, Fokker 70, Fokker 100 3.11 SNECMA M88 Dassault Rafale 0.301 Pratt Whitney JT8D DC-9 ...
Pratt & Whitney Canada PW600 - Design and Development
... Little is known about the engine cycle, although the bypass ratio is believed to be about 1.83 ... Bypass ratio of PW615F amounts to 2.8. 7,180 N) thrust PW617F, with a 17.6 inch (44.7 cm) diameter fan and bypass ratio of 2.7, is the largest in the family and is designed to power the Embraer ...
Turbofan - Technical Discussion
... It is fairly obvious, the higher the Fan Pressure Ratio (fan discharge pressure/fan inlet pressure), the higher the jet velocity and the corresponding specific thrust ... this set-up with an equivalent turbofan - same airflow and same fan pressure ratio ... The corresponding bypass ratio is therefore relatively low ...

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