Variable inlet prewhirl is an effective way to suppress compressor instability. Compressors usually employ a high degree of positive inlet prewhirl to shift the surge line in the performance map to a lower mass flow region. However, the efficiency of a compressor at high inlet prewhirl is far lower than that at zero or low prewhirl. This paper investigates the performances of a centrifugal compressor with different prewhirl, discusses the mechanisms thought to be responsible for the production of extra loss induced by high inlet prewhirl and develops flow control methods to improve efficiency at high inlet prewhirl. The approach combines steady three-dimensional Reynolds average Navier-Stockes (RANS) simulations with theoretical analysis and modeling. In order to make the study universal to various applications with inlet prewhirl, the inlet prewhirl was modeled by modifying the velocity condition at the inlet boundary. Simulation results show that the peak efficiency at high inlet prewhirl is reduced compared to that at zero prewhirl by over 7.6 percentage points. The extra loss is produced upstream and downstream of the impeller. Severe flow separation was found near the inlet hub which reduces efficiency by 2.3 percentage points. High inlet prewhirl works like a centrifuge gathering low-kinetic-energy fluid to hub, inducing the separation. A dimensionless parameter C is defined to measure the centrifugal component of flow. As for the extra loss produced downstream of the impeller, the flow mismatch of impeller and diffuser at high prewhirl causes a violent backflow near the diffuser vanes’ leading edges. An analytical model is built to predict diffuser choking mass flow which proves that the diffuser flow operates outside of stable conditions. Based on the two loss mechanisms, hub curve and diffuser stager angle were modified and adjusted for seeking higher efficiency at high prewhirl. The efficiency improvement of a modification of the hub is 1.1 percentage points and that of the combined optimization is 2.4 percentage points. During optimizing, constant distribution of inlet prewhirl was found to induce reverse flow at the leading edge of the blade root, which turned out being uncorrelated with blade angle. By revealing loss mechanisms and proposing flow control ideas, this paper lays a theoretical basis for overcoming the efficiency drop induced by high inlet prewhirl and for developing compressors with high inlet prewhirl.
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ASME Turbo Expo 2015: Turbine Technical Conference and Exposition
June 15–19, 2015
Montreal, Quebec, Canada
Conference Sponsors:
- International Gas Turbine Institute
ISBN:
978-0-7918-5665-9
PROCEEDINGS PAPER
Loss Mechanisms and Flow Control for Improved Efficiency of a Centrifugal Compressor at High Inlet Prewhirl Available to Purchase
Zheng Xinqian,
Zheng Xinqian
Tsinghua University, Beijing, China
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Huang Qiangqiang,
Huang Qiangqiang
Tsinghua University, Beijing, China
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Liu Anxiong
Liu Anxiong
Tsinghua University, Beijing, China
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Zheng Xinqian
Tsinghua University, Beijing, China
Huang Qiangqiang
Tsinghua University, Beijing, China
Liu Anxiong
Tsinghua University, Beijing, China
Paper No:
GT2015-42107, V02CT42A005; 12 pages
Published Online:
August 12, 2015
Citation
Xinqian, Z, Qiangqiang, H, & Anxiong, L. "Loss Mechanisms and Flow Control for Improved Efficiency of a Centrifugal Compressor at High Inlet Prewhirl." Proceedings of the ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. Volume 2C: Turbomachinery. Montreal, Quebec, Canada. June 15–19, 2015. V02CT42A005. ASME. https://doi.org/10.1115/GT2015-42107
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