Unsteady Effects of Wake on Downstream Rotor at Low Reynolds Numbers
In a compressor, the periodic wake is an inherently unsteady phenomenon that affects the downstream flow conditions and loading distribution. Thus, understanding the physical mechanisms of these unsteady effects is important for eliminating flow losses and improving compressor performance, particula...
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MDPI AG
2022-09-01
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| Series: | Energies |
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| Online Access: | https://www.mdpi.com/1996-1073/15/18/6692 |
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| author | Lin Li Wei Tan Jianshe Zhang Ge Han Yanfeng Zhang |
| author_facet | Lin Li Wei Tan Jianshe Zhang Ge Han Yanfeng Zhang |
| author_sort | Lin Li |
| collection | DOAJ |
| description | In a compressor, the periodic wake is an inherently unsteady phenomenon that affects the downstream flow conditions and loading distribution. Thus, understanding the physical mechanisms of these unsteady effects is important for eliminating flow losses and improving compressor performance, particularly at low Reynolds numbers. To understand the influence of the upstream wake on the downstream flow field structure, this paper describes numerical simulations of a one-stage high-pressure compressor at altitudes of 10–20 km. The influence of the wake on rotor flow blockage at different Reynolds numbers is analyzed, and the unsteady interaction between the upstream wake and boundary layer or tip leakage flow is discussed. The results indicate that the wake has a beneficial effect on the efficiency of the rotor at high Reynolds numbers, but this weakens and becomes negative as the Reynolds number decreases. The wake can reduce the flow blockage in the mainflow region. Due to the wake, the length of the laminar separation bubble at high Reynolds numbers decreases and that at low Reynolds numbers increases. In addition, the unsteadiness of the wake causes separation bubbles to appear periodically at high Reynolds numbers and induces an open separation bubble at low Reynolds numbers. The Kelvin–Helmholtz instability can dominate the transition process of the boundary layer, which is also affected by the disturbance vortex induced by the wake. Regarding the tip leakage flow, the wake can reduce the flow blockage at high Reynolds numbers but increase the flow blockage at low Reynolds numbers. The interaction at low Reynolds numbers causes a double-leakage flow, which finally leads to the large-scale separation of the suction surface boundary layer. The large-scale separation causes flow blockage in the tip region and prevents the rotor wake from propagating downstream. On the contrary, the unsteady wake can pass through the tip clearance vortex and inhibit the separation of the suction boundary layer at high Reynolds numbers, which is reflected in a larger amplitude of one blade passage frequency. Therefore, the flow loss in the downstream flow field at high Reynolds numbers is significantly reduced at high Reynolds numbers. |
| first_indexed | 2024-03-10T00:07:49Z |
| format | Article |
| id | doaj.art-11a6b9ae89e24f2aa1d2630f37b87d58 |
| institution | Directory Open Access Journal |
| issn | 1996-1073 |
| language | English |
| last_indexed | 2024-03-10T00:07:49Z |
| publishDate | 2022-09-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Energies |
| spelling | doaj.art-11a6b9ae89e24f2aa1d2630f37b87d582023-11-23T16:04:09ZengMDPI AGEnergies1996-10732022-09-011518669210.3390/en15186692Unsteady Effects of Wake on Downstream Rotor at Low Reynolds NumbersLin Li0Wei Tan1Jianshe Zhang2Ge Han3Yanfeng Zhang4Key Laboratory of Light-Duty Gas-Turbine, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, ChinaKey Laboratory of Light-Duty Gas-Turbine, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, ChinaKey Laboratory of Light-Duty Gas-Turbine, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, ChinaKey Laboratory of Light-Duty Gas-Turbine, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, ChinaKey Laboratory of Light-Duty Gas-Turbine, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, ChinaIn a compressor, the periodic wake is an inherently unsteady phenomenon that affects the downstream flow conditions and loading distribution. Thus, understanding the physical mechanisms of these unsteady effects is important for eliminating flow losses and improving compressor performance, particularly at low Reynolds numbers. To understand the influence of the upstream wake on the downstream flow field structure, this paper describes numerical simulations of a one-stage high-pressure compressor at altitudes of 10–20 km. The influence of the wake on rotor flow blockage at different Reynolds numbers is analyzed, and the unsteady interaction between the upstream wake and boundary layer or tip leakage flow is discussed. The results indicate that the wake has a beneficial effect on the efficiency of the rotor at high Reynolds numbers, but this weakens and becomes negative as the Reynolds number decreases. The wake can reduce the flow blockage in the mainflow region. Due to the wake, the length of the laminar separation bubble at high Reynolds numbers decreases and that at low Reynolds numbers increases. In addition, the unsteadiness of the wake causes separation bubbles to appear periodically at high Reynolds numbers and induces an open separation bubble at low Reynolds numbers. The Kelvin–Helmholtz instability can dominate the transition process of the boundary layer, which is also affected by the disturbance vortex induced by the wake. Regarding the tip leakage flow, the wake can reduce the flow blockage at high Reynolds numbers but increase the flow blockage at low Reynolds numbers. The interaction at low Reynolds numbers causes a double-leakage flow, which finally leads to the large-scale separation of the suction surface boundary layer. The large-scale separation causes flow blockage in the tip region and prevents the rotor wake from propagating downstream. On the contrary, the unsteady wake can pass through the tip clearance vortex and inhibit the separation of the suction boundary layer at high Reynolds numbers, which is reflected in a larger amplitude of one blade passage frequency. Therefore, the flow loss in the downstream flow field at high Reynolds numbers is significantly reduced at high Reynolds numbers.https://www.mdpi.com/1996-1073/15/18/6692numerical simulationunsteady effectslow Reynolds numberwaketip clearance vortex |
| spellingShingle | Lin Li Wei Tan Jianshe Zhang Ge Han Yanfeng Zhang Unsteady Effects of Wake on Downstream Rotor at Low Reynolds Numbers Energies numerical simulation unsteady effects low Reynolds number wake tip clearance vortex |
| title | Unsteady Effects of Wake on Downstream Rotor at Low Reynolds Numbers |
| title_full | Unsteady Effects of Wake on Downstream Rotor at Low Reynolds Numbers |
| title_fullStr | Unsteady Effects of Wake on Downstream Rotor at Low Reynolds Numbers |
| title_full_unstemmed | Unsteady Effects of Wake on Downstream Rotor at Low Reynolds Numbers |
| title_short | Unsteady Effects of Wake on Downstream Rotor at Low Reynolds Numbers |
| title_sort | unsteady effects of wake on downstream rotor at low reynolds numbers |
| topic | numerical simulation unsteady effects low Reynolds number wake tip clearance vortex |
| url | https://www.mdpi.com/1996-1073/15/18/6692 |
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