- Zero-stage
Jet engine s are often uprated by adding a zero-stage to the front of a compressor. At a given core size, adding a stage to the front of the compressor not only increases the cycle overall pressure ratio, but increases the core mass flow.This is demonstrated by the following relationship:
w_2 = (w_2 sqrt{T_3}/P_3) * (P_3/P_2) * (sqrt{T_2/T_3}) * (P_2/sqrt{T_2}) ,
where:
core mass flow = w_2 ,
core size =w_2 sqrt{T_3}/P_3) ,
core total head pressure ratio = P_3/P_2) , inverse of core total head temperature ratio = T_2/T_3 , i.e. f(P_3/P_2 ,)
core entry total pressure = P_2 ,
core entry total temperature = T_2 ,
On the other hand, adding a stage to the rear of the compressor increases overall pressure ratio, decreases core size, but has no effect on core flow. This option also needs a turbine with a significantly smaller flow capacity to drive the compressor.
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