On the Influence of Blade Aspect Ratio on Aerodynamic Damping

[+] Author and Article Information
Patrick Buchwald

ITSM Institute of Thermal Turbomachinery Pfaffenwaldring 6 Stuttgart, 70569 Germany buchwald@itsm.uni-stuttgart.de

Aydin Farahmand

Pfaffenwaldring 6 Stuttgart, 70569 Germany aydin.farahmand@gmail.com

Damian M. Vogt

Pfaffenwaldring 6 Stuttgart, 70569 Germany damian.vogt@itsm.uni-stuttgart.de

1Corresponding author.

Manuscript received November 5, 2018; final manuscript received May 13, 2019; published online xx xx, xxxx. Assoc. Editor: Li He.

ASME doi:10.1115/1.4043905 History: Received November 05, 2018; Accepted May 13, 2019


In order to change the blade count of axial rotor designs, a scaling technique can be applied where the blades are scaled in axial and circumferential direction while maintaining the solidity. This technique allows to adjust the blade count without changing the steady state aerodynamics, but the influences on the aerodynamic damping are unknown. The present study is focused on the investigation of the change in aerodynamic damping of a subsonic axial compressor rotor, if the blade count is changed between 13 and 25 blades. The investigation is focused on the first bending mode family and the influences of the hub geometry on the modes are neglected. First, a comparison between the influence coefficient (IC) method and the traveling wave mode (TWM) method is conducted, which shows that the application of the IC method in combination with Harmonic Balance simulations offers a fast way to compute the aerodynamic damping without introducing significant errors compared to the TWM method simulations. Regarding the aerodynamic damping of the different rotor geometries, it can be noted that the amplitude of the work per cycle influence coefficient of the center blade scales linearly with the blade scaling factor and an increase in aerodynamic damping for an increase in blade count is observed. Furthermore, a simplified analytic theory is established, which explains the phase angle change of the blade influence coefficients. In the last part of the paper, an extrapolation method is proposed, which allows for the estimation of damping S-curves for scaled rotor geometries.

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