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How to identify that a given fan is a compressor fan or a turbine fan, just by visual inspection? Also, can visual inspection of a fan help in identifying the compressor/turbine stage i.e. if the fan is from a High Pressure Turbine/Compressor blade or Low Pressure Turbine/Compressor blade?

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Assuming we are speaking of axial compressors/turbines

Compressor blades are generally thin and straight, and resemble a tiny rectangular wing with low camber thickness.

enter image description here

Image source

Turbine blades are more curved, often in almost "U" shapes (like the ones seen here). In particularly large and recent engines, where efficiency is critical, turbine blades will often be full of tiny holes:

enter image description here

Image source

To distinguish between high pressure and low pressure stages (compressor or turbine does not matter), the length of the blade and its torsion (i.e. how much the aerodynamic profile turns around the axis of the blade going from the root to the tip) are key: shorter and more twisted blades will be high pressure ones, longer and straighter blades will be low pressure.

Note that two blades of the same length could come one from a high pressure stage and the other from a low pressure one of a different engine: "short" and "long" are relative to the engine size.

On the other hand, radial compressors and radial turbines are more difficult to distinguish.

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  • $\begingroup$ Thanx. Voted up for the description. I'd like to know if there is a way to identify the stage from visual inspection too? $\endgroup$
    – Victor Juliet
    Jun 12, 2015 at 6:22
  • $\begingroup$ @VictorJuliet if you can look at the blades what's preventing you from identifying it? $\endgroup$
    – Federico
    Jun 12, 2015 at 6:23
  • $\begingroup$ Editted the quesion for better understanding.! I am talking about differentiating between the HPT and LPT stages $\endgroup$
    – Victor Juliet
    Jun 12, 2015 at 6:30
  • $\begingroup$ @VictorJuliet answer updated. $\endgroup$
    – Federico
    Jun 12, 2015 at 6:37
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    $\begingroup$ I'm confused; there is no such thing as a "turbine fan". A "fan" is an apparatus with rotating blades that creates a current of air. That's not what turbines do. A turbine converts fluid (water, air, steam, etc.) into rotational movement or power. They are opposites. Someone had to say it. Pedantic $\endgroup$
    – Tim Nevins
    Jun 20, 2019 at 16:20

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