Tuning and mistuning of turbocharger impeller wheels for automotive applications

  • Christian Ellis

Student thesis: Doctoral Thesis

Abstract

High cycle fatigue with regard to impeller wheels has been researched for many years, notably within the aerospace industry. It is understood and well documented for large blades from low-volume high-cost manufacturing techniques that produce blades with defined frequencies and hence assemblies that are both tuned and mistuned by design. In more recent years the automotive industry has developed small low- cost turbochargers that have become increasingly more popular (and in some instances necessary) to meet demands for performance and emissions. Due to the low-cost manufacturing techniques used for high- volume production both the turbine and compressor wheels have a vibrational behaviour in terms of frequency which can only be described as random. This randomness is unacceptable within the aerospace industry and the methodologies used eliminate it, completely. Within the automotive industry it is accepted but its cause and effects are not understood.

This research looks at the contributing factors that add to the randomness of frequencies and how each one affects the frequency vibrational behaviour of the wheel. It also looks at how during operation the frequencies shift due to inputs from speed and temperature. The aim is not to understand the amplitude of vibration but the frequency of vibration to allow a better understanding of failure risk and prevention within the design and testing stages of an engine application program.

The notable findings are as follows;-
• The nominal design geometry does not present mistuning.
• Moving from design to manufactured part mistuning is introduced through several variables associated to the manufacturing process, notably tolerancing and grain structure.
• These variables introduce an amount of mistuning that is not intentional and random.

Whilst understanding the variables from manufacturing allows a more robust impellor through design it does not take into account the effects of operation, notably speed and temperature. These have also been addressed by a methodology for defining correction factors.

Also highlighted are concerns regarding the methodology used widely within the aerospace industry, notably the interference diagram and why this should be used with caution for randomly mistuned wheels.
Date of Award12 Dec 2024
Original languageEnglish
SponsorsBorgWarner Turbo Systems
SupervisorJohn Allport (Main Supervisor) & Simon Barrans (Co-Supervisor)

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