dhawald3
Topic Author
Posts: 16
Joined: Tue Jun 28, 2011 3:10 pm

Why Do Turbine Blades Have Firtree Roots?

Thu Feb 07, 2013 5:14 am

Generally in almost all engines the compressor blades have dovetail roots and the turbine blades have the fir-tree roots.

What is the science behind this?
 
SAAFNAV
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RE: Why Do Turbine Blades Have Firtree Roots?

Thu Feb 07, 2013 1:27 pm

Most probably increase the area that makes contact with the turbine wheel.

The larger the area, the more surface available to 'wick' the heat away to the big heatsink that is the turbine wheel.
L-382 Loadmaster; ex C-130B Navigator
 
SAAFNAV
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RE: Why Do Turbine Blades Have Firtree Roots?

Fri Feb 08, 2013 8:21 am

Spoke to a metallurgist today.

He concurs with what I said above, but he also said that a fir-tree is probably the most effective design to ensure proper 'grip' of the blade wrt. thermal expansion coefficients.

Erich
L-382 Loadmaster; ex C-130B Navigator
 
BMI727
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RE: Why Do Turbine Blades Have Firtree Roots?

Fri Feb 08, 2013 8:47 am

Quoting SAAFNAV (Reply 2):
He concurs with what I said above, but he also said that a fir-tree is probably the most effective design to ensure proper 'grip' of the blade wrt. thermal expansion coefficients.

That's what I would have figured. The turbines will experience more heat and therefore more expansion which probably affects the design.
Why do Aerospace Engineering students have to turn things in on time?
 
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HAWK21M
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RE: Why Do Turbine Blades Have Firtree Roots?

Sat Feb 09, 2013 11:13 am

With the Heat having to be withstanded....The fir tree design seems the best bet.
I may not win often, but I damn well never lose!!! ;)
 
dhawald3
Topic Author
Posts: 16
Joined: Tue Jun 28, 2011 3:10 pm

RE: Why Do Turbine Blades Have Firtree Roots?

Sun Feb 10, 2013 3:31 am

After much searching on Google in addition to the above explanation I found this.

Fir tree root gives it a large bearing area to take up the heavy stresses, and this bearing area is nearer to the axis of the blade.
Resulting in resistance to cracking at the root as compared to the root in which the bearing area is at a more distance from the axis of the blade.

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