Abstract
Acoustic impedance model of slits plays a crucial role in addressing noise reduction challenges in aircraft engines. To gain further insights into the sound absorption mechanisms of slits and to develop acoustic impedance model, this study investigates the bias flow effect on the acoustic impedance of compressor blade tip slit. The evolution of the blade tip leakage flow is calculated by the combination of two-dimensional discrete vortex model and one-dimensional acoustic propagation model. In this manner, the bias flow effects on the acoustic characteristics of the blade tip slits, such as slit impedance and sound absorption coefficient, are investigated. The model is validated through the experiment of bias flow effect on a circular orifice. It is further extended to calculate the flow field response of slits with different blade height and different aspect ratios. The results show that the acoustic impedance of equal area slits aligns closer with circular orifice experimental results than the acoustic impedance of equal width slits. Larger hub to shroud distances causes less influence on the blade slits of the same width. Increasing hub to shroud distance reduces the Ma of the maximum absorption coefficient. As aspect ratio increases, the acoustic reactance component corresponding to the acoustic mass of the slit decreases. Increasing the hub to shroud distance and increasing the aspect ratio of blade chord length to slit width can both improve the sound absorption under feasible conditions.
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Abbreviations
- AR:
-
Aspect ratio of the blade chord length to the slit width
- h :
-
Distance of shroud to hub
- H :
-
Height of compressor blade
- u(z):
-
Complex velocity of vortices
- u*(z):
-
Conjugate complex velocity of vortices
- s :
-
Width of the compressor blade tip slit
- ρ :
-
Density of the air
- v :
-
Kinematic viscosity of the air
- Pcos(ωt):
-
Incident sound pressure of the blade tip slit
- ω :
-
Circular frequency of incident pressure
- P :
-
Amplitude of induced pressure
- t :
-
Physical time
- t v :
-
Existence time of vortices
- Δt :
-
Time step of the model
- z :
-
Complex coordinate of vortices in physical domain
- ζ :
-
Complex coordinate of vortices in calculation domain
- W :
-
Complex potential function of the flow field
- Γ:
-
Circulation of vortices
- u g :
-
Bias flow velocity through the slit
- Q :
-
Volume flux through the slit
- V av :
-
Average flow velocity through the slit
- r v :
-
Radius of vortex core
- b :
-
Length of blade chord
- A 0 :
-
Opening section area of the slit
- c :
-
Local sound speed
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Acknowledgements
This investigation is supported by the National Natural Science Foundation of China (No. 51976116), the Open Research Subject of Key Laboratory of Aerodynamic Noise Control (No. ANCL20230201), and the National Science and Technology Major Project (No. J2019-II-0006-0026). The authors are grateful to Prof. Xiwen Dai for the discussion and comments.
Funding
National Natural Science Foundation of China, No. 51976116, Xiaohua Liu, Open Research Subject of Key Laboratory of Aerodynamic Noise Control, No. ANCL20230201, Xiaohua Liu, National Science and Technology Major Project, No. J2019-II-0006-0026, Xiaohua Liu.
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Lu, J., Liu, X. A theoretical model of the impedance at blade tip clearance in aeroengine compressor. AS (2024). https://doi.org/10.1007/s42401-024-00299-w
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DOI: https://doi.org/10.1007/s42401-024-00299-w