Turbochargers - clearance between turbine wheel and housing. Is it important?

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Discussion Overview

The discussion centers around the significance of the clearance between the turbine wheel and the housing in turbochargers, particularly in relation to the performance of diesel engines. Participants explore the implications of this gap on efficiency and operational safety under various conditions.

Discussion Character

  • Technical explanation, Debate/contested, Experimental/applied

Main Points Raised

  • Some participants propose that the gap is crucial for performance, as it could allow pressurized air to escape, thereby reducing turbine efficiency.
  • Others argue that the clearance is important not only for performance but also to prevent mechanical interference during extreme operating conditions, such as misalignment, overspeed, and thermal expansion.
  • A participant shares an experimental experience indicating that insufficient clearance led to severe mechanical failure at high RPMs, suggesting that the gap must accommodate rotor expansion.

Areas of Agreement / Disagreement

Participants generally agree on the importance of the clearance between the turbine wheel and housing, but the specific implications and thresholds for this parameter remain contested.

Contextual Notes

Participants mention various operating conditions that could affect the performance and safety of the turbocharger, indicating that the discussion may depend on specific design parameters and operational contexts.

scutarius
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I am trying to find authority that the gap between the turbine wheel and the housing is important to the performance the turbocharger will be able to add to a diesel engine.
 
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My guess is that is a very important parameter. The turbine is pressurizing air and a gap between the turbine and the housing would provide a path for pressurized air to escape, reducing the efficiency of the turbine.
 
Yes, it's a very important parameter. Not just from a performance point of view, but to avoid interference under extreme operating conditions (when the housing axis moves away from the shaft axis, overspeed, high temperatures, low oil pressure etc).
 
brewnog said:
Yes, it's a very important parameter. Not just from a performance point of view, but to avoid interference under extreme operating conditions (when the housing axis moves away from the shaft axis, overspeed, high temperatures, low oil pressure etc).

Yep. An experimental supercharger I was working on had too little clearance. Worked fine until about 30,000 RPM, then the blade tips all but welded themselves to the casing. After running FEA, we found that the rotors were growing about 0.015" (radius) at full speed, instead of the 0.007"-0.010" of our other models.
 

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