Design of Fan for Turbofan engine

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Discussion Overview

The discussion revolves around the design of a fan for a turbofan engine, specifically focusing on the determination of the pitch to chord ratio and the challenges faced in applying design methods from established literature. Participants explore various design methodologies, blade configurations, and computational fluid dynamics (CFD) analysis techniques.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant is following the axial compressor preliminary design method from a specific textbook but is struggling with determining the pitch to chord ratio based on a graph in the book.
  • Another participant expresses confusion about finding a suitable design method for the fan.
  • A turbine mechanic suggests that having an even number of blades simplifies repairs and balancing.
  • A turbomachinery engineer counters that an odd and prime number of blades is preferred to avoid resonance.
  • A participant mentions using the McKenzie method but encountered issues with blade shape, leading to an assumption of a pitch to chord ratio of 1 from hub to tip.
  • There is a discussion about the preference for odd and prime numbers of blades in rotors and even numbers in stators, along with a new challenge regarding CFD analysis using ANSYS software.
  • Another participant reflects on the reasoning behind the choice of blade numbers, noting the practical implications for maintenance in specific engine models.

Areas of Agreement / Disagreement

Participants express differing views on the optimal number of blades for turbofan engines, with some advocating for even numbers for ease of repair and others for odd numbers to prevent resonance. The discussion remains unresolved regarding the best design approach and the challenges faced in CFD analysis.

Contextual Notes

Participants mention limitations in available guidance for drawing blades and performing CFD analysis, indicating a dependence on specific software tools and design methods that may not be fully understood.

Johnny99
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I currently doing by final project about designing fan for turbofan engine.After discussing with my lecturer,I decided to do it based on axial compressor preliminary design method in Gas Turbine Theory : G. F. C. Rogers, H. I. H. Saravanamuttoo, Henry Cohen book.Now after following the design method,I'm stucked at determining the pitch to chord ratio for five points from hub to tip.According to the book,it is determined from the graph Air deflection versus air outlet angle in Fig 5.14 pp139 but i got the air deflection beyond the the value of the air deflection in the graph.I tried searching for the bigger graph but no luck.

Your helps is very appreciated.
 
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anyone? at least give some reference to design the fan ..I 'm really confused right now finding suitable design method for this..please help me...:cry:
 
As a turbine mechanic I can say that having a even number of blades would be greatly appreciated. This make repairs and balancing much easier. This probably doesn't help at all.
 
That's kind of funny, because as a turbomachinery engineer, we prefer to have the number of blades odd and prime if possible.
 
Thanks for reply guys although it seems not related to my question.At first I followed McKenzie method to determine the pitch chord ratio but I got weird blade shape.It has very small chord at hub and very large at mean radius and become smaller at tip.I end up assuming pitch to chord ratio is equal to 1 from hub to tip.so now I got blade chord increase from hub to tip.As for what you guys discussed,from my reading,for rotor ,it is preferred to have odd and prime number of blade to avoid resonance while in stator it is preferred for it to be even.Now I got new problem on how to draw my blade and do cfd analysis for it using ansys cfx.I tried googling but there are not enough guide for it.I tried using ansys bladegen software but not quite understand how can I draw naca profile blade and vary the inlet and outlet angle for it from hub to tip.Any guide for this subject is really appreciated.
 
Johnny99 said:
Thanks for reply guys although it seems not related to my question.At first I followed McKenzie method to determine the pitch chord ratio but I got weird blade shape.It has very small chord at hub and very large at mean radius and become smaller at tip.I end up assuming pitch to chord ratio is equal to 1 from hub to tip.so now I got blade chord increase from hub to tip.As for what you guys discussed,from my reading,for rotor ,it is preferred to have odd and prime number of blade to avoid resonance while in stator it is preferred for it to be even.Now I got new problem on how to draw my blade and do cfd analysis for it using ansys cfx.I tried googling but there are not enough guide for it.I tried using ansys bladegen software but not quite understand how can I draw naca profile blade and vary the inlet and outlet angle for it from hub to tip.Any guide for this subject is really appreciated.

Really, I didn't know that there is was a reason for the odd number of blades. I know that the GE engines that the Army uses have an even number of blades to ease repairs when a blade is chipped or worn. (You only have to file the blade on the opposite side to balance as opposed to balancing all the blades.) I imagine I'll learn more about this in my future studies. Good luck with your work. I hope it goes well.
 

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