Session: 22-03 Advanced Aeroelastic Prediction and Validation

Paper Number: 122612

122612 - Numerical Investigation of the Influence of Tyler-Sofrin Modes on the Increase in Blade Unsteady Pressure in a Subsonic Axial Compressor 

Excessive blade vibration caused by rotor-stator interaction leads to high-cycle fatigue and can result in blade failure. Therefore it is an important problem in the design of axial compressors. The primary source of the pressure fluctuation due to rotor-stator interaction is considered to be the potential from downstream blade row or the wake from upstream balde row. However, previous study has shown that pressure amplitude on blade surface is changed by blade count ratio between rotor and stator, even when steady blade loading is maintained. Furthermore, it has also shown that the pressure amplitude increases at specific blade count ratio. It is supposed that the Tyler-Sofrin modes (TSM) due to rotor-stator interaction are related to this increase of pressure amplitude.
The present paper describes an investigation on the increase of pressure fluctuation due to TSMs. The investigation was conducted numerically by using CFD simulation. CFD simulations are unsteady RANS calculation on a quasi-3D model of single stage extracted from a 3.5-stage subsonic axial compressor. Several parameters such as blade count, rotor speed and speed of sound, was varied to change characteristics of TSMs. This paper focus on the pressure amplitude of the 1st harmonic of vane passing frequency as a representation of excitation force for blade vibration. The 1st harmonic component is obtained by applying Fourier transformation of the time-series pressure data obtained by unsteady RANS calculations.
As a result of the investigation, it is found that the pressure amplitude increases at some specific conditions of blade count, rotor speed and speed of sound. Furthermore, the modal phase velocity of TSM is highly related to the pressure amplitude. A parameter called Phase Speed Ratio (PSR) is introduced to express the relation between the modal phase velocity of TSM and the velocity of acoustic propagation in circumferential direction. In the region where the PSR is lower than 1.0, the pressure amplitude increases starting from around 0.5 and peaks around 1.0. When the PSR exceeds 1.0, the amplitude rapidly decreases. In the region where the PSR is smaller than 1.0, the modal phase velocity of the TSM is slower than the circumferential propagation of acoustic disturbance. As the modal phase velocity of the TSM increases and approaches the propagation velocity of acoustic disturbance, the TSM and the disturbances in the circumferential direction interfere with each other within the blade row. And it leads to an increase in the pressure amplitude on the blade surface. Since a condition of the PSR = 1.0 is almost the same as the condition for the TSM to become cut-on, the phenomenon changes at PSR = 1.0 boundary. When PSR exceeds 1.0, the TSM and acoustic disturbance propagation form wave fronts outside the blade row, causing the waves to be emitted to the outside. Therefore, the pressure fluctuation occurring between the blades is less influenced by the TSM, resulting in a decrease in the pressure amplitude on the blade surface. The detailed mechanism of this increase of pressure fluctuation will be discussed in the paper.

Presenting Author: Tetsuya Oshio IHI Corporation

Presenting Author Biography: Affiliation: IHI Corporation
Academic credentials: Master of engineering, Osaka University, Japan (2014)
Work experience:
Research on unsteady aerodynamics and blade vibration of axial turbomachinery
Aerodynamic design of axial and centrifugal turbomachinery

Authors:

Tetsuya Oshio IHI Corporation
Mizuho Aotsuka IHI Corpotation
Shinya Kusuda IHI Corporation
Atsushi Tateishi IHI Corporation