Abstract
The flow structures around the blade tip, mainly large-scale leakage vortex, exert a great influence on compressor performance. By applying unsteady jet control technology at the blade tip in this study, the performance of the compressor can be greatly improved. A numerical simulation is conducted to study the flow characteristics of a centrifugal compressor with and without a flow control. The complex flow structures cause great difficulties in the analysis of the dynamic behavior and flow control mechanism. Thus, we introduced a dynamic flow field analysis technology called dynamic mode decomposition (DMD). The global spectrums with different global energy norms and the coherent structures with different scales can be obtained through the DMD analysis of the three-dimensional controlled and uncontrolled compressors. The results show that the coherent structures are homogeneous in the controlled compressor. The leakage vortex is weakened, and its influence range of unsteady fluctuation is reduced in the controlled compressor. The effective flow control created uniform vortex structures and improved the overall order of the flow field in the compressor. This research provides a feasible direction for future flow control applications, such as transferring the energy of the dominant vortices to small-scale vortices.
Highlights
Introduction of dynamic mode decomposition (DMD) Method toStudy the DynamicStructures of a Three-Dimensional CentrifugalCompressor with and without Flow ControlShuli Hong *, Guoping Huang, Yuxuan Yang and Zepeng LiuCollege of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, Received: 8 October 2018; Accepted: 5 November 2018; Published: 9 November 2018 AbstractThe flow structures around the blade tip, mainly large-scale leakage vortex, exert a great influence on compressor performance
A semi-open centrifugal compressor allows for a high linear velocity, so that a single-stage centrifugal compressor can achieve a high-pressure ratio, which makes it widely used for different applications
Some of the characteristics of the compressor tip flow field can be obtained from the some of the characteristics of the compressor tip flow field can be obtained from the dynamic pressure change diagram, this information is imperfect if the internal flow mechanism is dynamic pressure change diagram, this information is imperfect if the internal flow mechanism is to to be understood thoroughly
Summary
A semi-open centrifugal compressor allows for a high linear velocity, so that a single-stage centrifugal compressor can achieve a high-pressure ratio, which makes it widely used for different applications. In 2003, Ibaraki [4] from the Mitsubishi Company studied the flow structure around the blade tip of a transonic centrifugal compressor through numerical simulation and vortex identification. The tip of the main blade showed a clear leakage vortex structure, and the roll up of the leakage vortex causes a strong total pressure loss. The velocity of the leakage vortex that moves toward the pressure surface of the adjacent blades by suction is approximately half of the speed of the rotor tip, which causes pressure fluctuation near the casing This wave will stall the compressor when it enters the adjacent blades. Based on the numerical simulations, the DMD method is used to analyze the flow field in a compressor with and without unsteady jet flow control technique. The control mechanism of the effective unsteady excitation on the coherent separation flow is discussed using the results of the DMD analysis
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