Gas Turbine Exhaust Section

EXHAUST SECTION Operating Theory  Theory (internal/external gas mixing) ratio engine, the two flows are combined by a mixer ~ In a low a  low by-pass ratio engine, unit  which  which allows the by-pass air to flow into the turbine exhaust streams.  gas flow in a manner manner that ensures thorough mixing of the two streams. ratio engines, the two streams are usually exhausted ~ In high In high by-pass ratio engines,  separately.  separately. ~ The hot and cold nozzles are co-axial and the area of each nozzle is designed to obtain maximum efficiency. ~ However, an improvement can be made by combining the two  gas flows within within a common, or integrated, nozzle assembly assembly (ie.  A320/V2500 CNA). ~ This partially mixes the gas flows prior to ejection to atmosphere. ~ An example of both types of high by-pass exhaust system is shown below.

EXHAUST SECTION Operating Theory  Theory (nozzle types)

~ The exhaust gases pass to atmosphere through the propelling the  propelling nozzle, which is a convergent duct , thus increasing the gas velocity.

~ From the illustration to the left it will be seen that the convergent section exit now becomes the throat , with the exit proper now being at the end of the flared divergent section. ~ When the gas enters the convergent section of the  nozzle, the gas velocity increases with a corresponding fall fall in  static pressure. ~ The gas velocity at the throat corresponds to the local sonic velocity. ~ As the gas leaves the restriction of the throat and flows into the divergent section, it progressively it  progressively increases in velocity towards the exit . ~ The reaction to this further increase in momentum is nozzle. a  pressure force acting on the inner wall of the nozzle. axis  of the nozzle  produces the further ~A component of this force acting parallel acting  parallel to the longitudinal axis  increase in thrust.