Session: 27-01: Controls and Probability in Rotordynamics

Paper Number: 153893

Correlation and Repeatability Improvement Between Tie Bolt Stretch, Vibration Levels and Process Control Using Automated Stretch Tool and Regression Analysis – Part II 

Auxiliary Power Units (APU) are gas turbine engines with rotor systems that often use radial flow rotor systems that are made up of a compressor and turbine section which are joined mechanically for ease of assembly and maintenance using a single curvic coupling or possibly two curvic couplings.  For the single curvic style of radial gas turbine, a compressor and turbine stage are often joined using a tie-bolt fixing together the stages mechanically through radial contact via the curvic coupling with an associated torque retaining adapter.

Our previous paper showed the promising correlation between each plane unbalance and vibration level for this single curvic coupling style assembly.  This portion of the study further extended into process control using the measured modulus of elasticity as an enabler for predictable process control through assembly related measured and reported parameters.

For some aircraft applications, the APU also provides significant mass flow of pressurized air for main engine start. This model of APU is generally inclusive of an additional impeller joined into the rotor assembly. That load compressor results in turbomachinery consisting of three rotors, whereas that assembly features those three rotors existing as joined using two curvic couplings, an adapter and tie bolt as required.  

The preliminary potential for design and measured correlation for the two curvic model was demonstrated in an initial review. This continued investigation first presents the initial basis for the design changes to the load impeller static and dynamic unbalance state as initial unbalance limits design changes as the enabling precursor to the full follow-on two curvic design evaluation and testing. That up-change pilot group and later full production sample series demonstrate that the rotor stretch tooling and process improvements as resulting in the two curvic APU up-change design as being capable for reduced vibration levels through improved rotor stiffness/straightness control and approaching the correlated predictive tolerance design intent vibration values in a similar manner using regression analysis to values exhibited for the single curvic from the previous study.

This two curvic coupling assembly is also explored to show the influence of mode in the vibration levels in addition to unbalance as part of this study. This correlation study part II as applied to the two curvic coupling also goes further to include additional parameter exploration such as runout, stretch load, and clocking among others that exist in the system specifically as process control parameters.

 

 

REFERENCES

[1] Lajos H. Horvath et al. “Correlation and Repeatability Improvement Between Tie Bolt Stretch and Vibration Levels Using Automated Stretch Tool and Regression Analysis”, Proceedings of ASME Turbo Expo 2024 Turbomachinery Technical Conference and Exposition, GT2024-125266, June 24-28, 2024, London, England.

[2] Konrad Juethner et al. “Finite Element Analysis of Bent Rotors”, Proceedings of ASME Turbo Expo 2022 Turbomachinery Technical Conference and Exposition, GT2022-79752, June 13-17, 2022, Rotterdam, The Netherlands.

[3] P. Mathuria, J. R. Seyler, J Bellavia, L.H. Horvath, K.Pripusich, “Method and System For Applying Pre-Stretch to Shaft and Component Connection” US Patent Pending 177378US01; 67097-4602US1

Presenting Author: Lajos Horvath Pratt and Whitney

Presenting Author Biography: Lajos Horvath currently serves as Lead Technical Production Project Engineer for the APU Engineering Group as part of Pratt & Whiney Military Engines. He has over 39 years of gas turbine engines engineering experience in various disciples with specific concentration currently focused in small radial engines design, manufacturing, and test.

Authors:

Lajos Horvath Pratt and Whitney
Parag Mathuria Pratt & Whitney
Gregory Savela Pratt & Whitney
Tsing-Yi Liu Pratt & Whitney