Wheel reliability

Fahlin Racing

Fahlin Racing

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May 9, 2012
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Ok, all of you turbo gurus I am here to ask a few questions, mainly to understand breakage on over speeding, wheel breakage due to fatigue and whatever else. Stock wheels verse aftermarkets who handles fatigue better? I have been told in some apps stock will outlast aftermarket. Big or small designs.

How the breaks look at the separation point, stress risers and anything to really see why the overspeeding or other damage causes occur.

Anyone is welcome to join the conversation :pop: (this just may help designing as a whole for racers)
 
If I take some examples from Mr MacInnes book Turbochargers, we have 90 degree radial wheels, curved inducer bladed wheels - some 'backward curved' compressor wheel. He goes to explain that with a curved blade wheel it 'prepares' the air to be at the same angle as the blades themselves to reduce inlet losses.

He mentions shock losses also. Would someone be able to explain a shock-loss?
 
It is fairly well known that machined-from-solid wheels have a greater fatigue life than cast. All things being geometrically equal, forged aluminum will be stronger than cast in yield strength as long as it has been annealed or heat treated to mitigate work hardening. This should equate to a higher burst speed, but to my understanding it's usually vibrations through the rotor assembly that make the wheel contact the housing and go kablooey.

Many aftermarket companies trim the hub line as well as make the blades thinner so I wouldn't be surprised if they are less reliable than OEM. You also have to remember that the clientele who pay for aftermarket wheels usually run the piss out of them at absurd shaft speed so I don't think it's an apples to apples comparison.

As far as aero, good god we're all guessing. It'd take a $50,000 fluid dynamics package and probably a grad student to tell us. Most, if not all, of the aftermarket just does trial and error.
 
So one cause is/could be the exhaust-pulse impact on the turbine you are saying? How much do you believe could be due to air-charge-mass loading on the blades too.

You can run the piss outta of a stock wheel too so its not likes it is a total wash. The constant is the wheel itself as a whole. As far as the shaft speed verse shaft clearances to allow a contact occurrence with the housing I wonder if the shaft material has a hand in this too by flexing not just the wheel's weight distribution.

The Aerodynamic of the blades from the tip to the heel, on both the concave or convex sides since there has been many many designs out there it is more of a observation on current designs and assessment.

What usually breaks first the tips or has there been the area more towards I call the 'heel' break?
 
Bringing up in a search since my turbo books aren't indepth more than just sizing and basic design.

Shock losses seem to be three-dimensional also mentioning profile losses on a brief overview of a page I have looked at involving mach numbers on another page you will find transonic and supersonic rates, haven't look into which design they tested on that one. More great things to read!

Key losses in turbine blades from wikipedia - Effects of Mach number and shock losses in turbomachines
Profile loss associated with boundary layer growth.
Shock loss arising from normal or oblique shocks at trailing edge.
Mixing loss due to rapid dissipation of the wake and shock-boundary layer interaction.
Click to expand...
 
I am sure some experience would be more common if we compared a curved wheel verse a reversed curved wheel?
 
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