On the Influence of Blade Aspect Ratio on Aerodynamic Damping

Abstract

In order to change the blade count (BC) of axial rotor designs, a scaling technique can be applied where the blades are scaled in axial and circumferential directions 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 with 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 due to the blade scaling. In the last part of the paper, an extrapolation method is proposed for the investigated geometry and mode family, which allows for the estimation of damping S-curves for scaled rotor geometries based on only one IC method simulation.

Influence mechanism of tip clearance on flutter stability with different aerodynamic coupling effects for transonic compressor

“…Compared to the traditional TWM which needs multiple full-annulus simulations to obtain the aerodynamic dampings at all NDs for NASA Rotor 67, the PSB only requires a double-passage domain in each simulation. On the other hand, the ICM simply needs a one-time calculation in an odd multi-passage domain to obtain the aerodynamic damping at each ND, whose reliability has been confirmed by some researches [10,[19][20][21][22]. During the entire computing process of ICM, only the middle blade marked as the reference blade vibrates with a specific mode shape, amplitude and frequency, while the other blades remain stationary.…”

Flutter Measurement of a Linear Turbine Blade Cascade with an Angular Position Deviation of One Blade

“…In the ICM testing, only one blade oscillates, and the response is measured on all the cascade blades. Both techniques theoretically lead to the same results by assuming a linear superposition of the unsteady pressures in the cascade for low amplitude vibration; however, the level of an agreement depends on the specific situation [24,25].…”

Effect of Intake Acoustic Reflection on Blade Vibration Characteristics

“…Aerospace 2024, 11, x FOR PEER REVIEW 5 of 17 length was established between the bump and the inlet boundary to prevent numerical reflections. Buffer zones are extensively applied in aeroacoustic [35] and aeroelastic [36] studies due to their simplicity and ease of implementation. To mitigate the detrimental impact of boundary layer growth on the flow in front of the blades, an inviscid slip wall boundary condition was employed for the hub and shroud of the intake.…”