I’m a freshman in Aircraft maintenance and my prof in Powerplant 2 (Gas Turbine Engine) explained to us about the venturi duct within the compressor of the Turbine engine. I get that the compressor increases the pressure of the air but what I don’t get is his statement that according to Bernoulli’s principle once the air passes through the inlet duct and towards the compressor the air’s pressure decreases and the velocity increases as it passes through the venturi duct the pressure only increases after it reaches the divergent part of the venturi duct before it gets to the combustion chamber.
So what I want to know is why does the pressure decrease first before it enters the compressor?
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Hiya fellow jet mech! This may help: [https://youtu.be/efB3chu8J3o](https://youtu.be/efB3chu8J3o)
Depending on if you work on Pratt or GE, Pratt calls them Civv’s (compressor inlet variable vanes for the fan) RCVV’s (rear compressor variable vanes for the core) and GE calls them VSV’s throughout (variable stator vanes). They slow and direct the airflow in the fan and core. Depending on the engine you’re working on (220/229/119/404/110/101/108/118 etc) there are various stages of fan and compressor, and not all have variable vanes before each stage of compression.
An easy way to look at it from a convergent/divergent way is to look at an augmentor/afterburner on the engine you’re working on and picture the airflow coming out of the nozzle 🙂
One other thing, the aircraft inlets and ducting also play a part during ground idle and at speed. I’m speaking about fighter aircraft, not heavies 🙂
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