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Why Do Turbine Blades Have Firtree Roots?  
User currently offlinedhawald3 From India, joined Jun 2011, 17 posts, RR: 0
Posted (1 year 7 months 1 week 5 days 23 hours ago) and read 5524 times:

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?

5 replies: All unread, jump to last
 
User currently onlineSAAFNAV From South Africa, joined Mar 2010, 275 posts, RR: 1
Reply 1, posted (1 year 7 months 1 week 5 days 15 hours ago) and read 5377 times:

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.



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User currently onlineSAAFNAV From South Africa, joined Mar 2010, 275 posts, RR: 1
Reply 2, posted (1 year 7 months 1 week 4 days 20 hours ago) and read 5048 times:

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



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User currently offlineBMI727 From United States of America, joined Feb 2009, 15742 posts, RR: 27
Reply 3, posted (1 year 7 months 1 week 4 days 19 hours ago) and read 5032 times:

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?
User currently offlineHAWK21M From India, joined Jan 2001, 31684 posts, RR: 56
Reply 4, posted (1 year 7 months 1 week 3 days 17 hours ago) and read 4719 times:

With the Heat having to be withstanded....The fir tree design seems the best bet.


Think of the brighter side!
User currently offlinedhawald3 From India, joined Jun 2011, 17 posts, RR: 0
Reply 5, posted (1 year 7 months 1 week 3 days ago) and read 4596 times:

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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