Abstract
Flutter instability because of the blade vibrations is a major problem in axial compressor cascades. This paper investigates the effects of blade oscillations on aerodynamic performance and turbulent flow characteristics of modern gas-turbine compressors. Highly accurate direct numerical simulations (DNS) are performed based on the spectral-hp element method to predict the flow instabilities, pressure fluctuations and vortex generation on the surface of the compressor blades by considering all complex physical parameters at different vibration frequencies (0 < f < 8.28 Hz). The main novelty of this study is to consider the aeroelastic vibrations of the compressor blades in DNS analysis. The novel proposed method enables the detailed analysis of complex structure fluid interactions, which cannot be obtained using other methods such as RANS models. The simulations revealed that the blade oscillations have a huge impact on the vortex generation and laminar separation bubble on the suction side of the blade. Moreover, the amplitude of unsteady pressure distribution is greater at 90% span, with the phage angle deviating between 100° and 350°. Strong fluctuations are observed at the centre of the wake region of the vibrating blade cascade. These fluctuations are activated by the flow disturbances resulting from the blade oscillation. Moreover, intense pressure fluctuations happen in the wake region of the oscillating compressor blade compared with the stationary one. The separating point occurred 8.28% sooner on the suction surface of the vibrating blade with k = 0.4 (Xsep/C = 0.288) compared to the stationary blade with Xsep/C = 0.314.
Highlights
In the past decade, with increasing energy demands, there has been increased competition in improving performance while decreasing the weight of the power energy production systems such as wind or gas turbines [1, 2]
The results show that the computed wall+ values are in the acceptable range of the direct numerical simulations (DNS) analysis
High-fidelity DNS simulations are performed on a compressor cascade blade
Summary
With increasing energy demands, there has been increased competition in improving performance while decreasing the weight of the power energy production systems such as wind or gas turbines [1, 2]. The blades aeroelastic oscillations have a noticeable impact on vortex generation and flow separation point on the surface of the compressor blades. These vibrations usually cause damage to turbine blades due to unpredicted flutter instabilities and pressure fluctuations on the surface of the compressor blades. Developing a high-fidelity transient numerical method is vital to accurately capture the flow behaviour on the blade surface under transitional flow regimes. This is especially crucial for advanced aircraft gas turbine compressors, which are made of light-weight aerofoils, and the flutter prediction is essential in the design of these compressor blade cascades
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