Blade root attachment design

[Nutria360]

Hi guys! I am studying mechanical engineering and have set myself a personal project to design a blade, either for a compressor or an axial fan (to learn a bit). I have found quite a few books on the aerodynamic and thermodynamic design of such equipment, but I still haven't found information about root attachments for blades (Dovetail and Tree are a couple that I have come across). I wanted to know if you have any information about their initial geometric relationships (to get an idea of the dimensions and initial shape they would have). Thank you very much!

 

[Baluncore]

Welcome to PF.

Google: turbine blade root design
The design will depend on the fluid. Is that an air, steam, or combustion gas turbine?

 

[Flyboy]

It’s also going to depend on what machining capabilities you have access to.

That said, I can’t recall the last time I saw an actual dovetail blade root. Maybe on a fan stage? The fir tree design is popular because it fits better into a hub of densely packed blades, provides excellent surface area for load distribution, and uses less material overall to achieve the same load bearing capacity. The tradeoff is the higher level of precision machining required, but if you’re doing axial flow turbines, you need that level to precision machining anyways.

 

[Nutria360]

Welcome to PF.

Google: turbine blade root design
The design will depend on the fluid. Is that an air, steam, or combustion gas turbine?

Well, my idea is to design an axial fan whose working fluid is air. As I mentioned, I have found many documents and books that cover the design of the blades, but very few show the blade with its root (whether dovetail or tree).

 

[Nutria360]

It’s also going to depend on what machining capabilities you have access to.

That said, I can’t recall the last time I saw an actual dovetail blade root. Maybe on a fan stage? The fir tree design is popular because it fits better into a hub of densely packed blades, provides excellent surface area for load distribution, and uses less material overall to achieve the same load bearing capacity. The tradeoff is the higher level of precision machining required, but if you’re doing axial flow turbines, you need that level to precision machining anyways.

Yes, what I want to design is an axial fan. According to my research, it is also necessary to consider rotordynamics and aeroelasticity. While I have found both types of roots and their profiles, I haven’t found some basic relationships to have a starting point. I imagine that I would have to create a preliminary design following the profile and then refine the dimensions until I achieve a more precise design. Machining is not an issue because I don’t have access to CNC in my country, so the idea is to make it more conceptual.

 

[Flyboy]

Yes, what I want to design is an axial fan. According to my research, it is also necessary to consider rotordynamics and aeroelasticity. While I have found both types of roots and their profiles, I haven’t found some basic relationships to have a starting point. I imagine that I would have to create a preliminary design following the profile and then refine the dimensions until I achieve a more precise design. Machining is not an issue because I don’t have access to CNC in my country, so the idea is to make it more conceptual.

Then a dovetail design would be my recommendation, just for the simpler geometry and calculations

 

[Nutria360]

Thank you very much for your recommendation; I will take it into account for the design I will be working on. If I am not mistaken, the most optimal way to achieve an acceptable design would also be to consider the rotor design and develop both aspects in parallel.

 

[Flyboy]

Yes, since it’s a complete system.

That said, axial flow compressors and fans have very different requirements and behaviors. I would suggest narrowing that choice down early.