| 1. |
- Li, Xiaojian, 1991, et al.
(författare)
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A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19
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Tidskriftsartikel (refereegranskat)abstract
- Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.
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| 2. |
- Li, Xiaojian, 1991, et al.
(författare)
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A new method for performance map prediction of automotive turbocharger compressors with both vaneless and vaned diffusers
- 2021
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. - : SAGE Publications. - 2041-2991 .- 0954-4070. ; 235:6, s. 1734-1747
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Tidskriftsartikel (refereegranskat)abstract
- A new approach to predict the performance maps of automotive turbocharger compressors is presented. Firstly, a polynomial equation is applied to fit the experimental data of flow coefficient ratios for the centrifugal compressors with both vaneless and vaned diffusers. Based on this equation, the choke and surge flow coefficients under different machine Mach numbers can be quickly predicted. Secondly, a physically based piecewise elliptic equation is used to define compressors’ characteristic curves in terms of efficiency ratio. By introducing the flow coefficient ratio into the efficiency correlation, the empirical coefficients in the piecewise elliptic equation are uniquely calibrated by the experimental data, forming a unified algebraic equation to match the efficiency maps of the compressors with both vaneless and vaned diffusers. Then, a new universal equation, which connects the work coefficient, the impeller outlet flow coefficient and the non-dimensional equivalent impeller outlet width, is derived by using classical aerothermodynamic method. The off-design pressure ratio is predicted based on the equivalent impeller outlet width with less knowledge of the compressor geometry and no empirical coefficients. Finally, three state-of-the-art turbocharger compressors (one with vaneless diffuser, two with vaned diffusers) are chosen to validate the proposed method, and the results show a satisfactory accuracy for the performance map prediction. This method can be used for the preliminary design of turbocharger compressors with both vaneless and vaned diffusers, or to assess the design feasibility and challenges of the given design specifications.
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| 3. |
- Li, Xiaojian, 1991, et al.
(författare)
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Installation effects on engine design
- 2020
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Increasing the engine bypass ratio is one way to improve propulsive efficiency. However, an increase in the bypass ratio (BPR) has usually been associated with an increase in the fan diameter. Consequently, there can be a notable increase in the impact of the engine installation on the overall aircraft performance. In order to achieve a better balance between those factors, it requires novel nacelle and engine design concepts. This report mainly reviews installation effects on engine design. Firstly, the installation effects assessment methods are introduced. Then, the installation effects on engine cycle design, intake design and exhaust design are sequentially reviewed.
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| 4. |
- Zhao, Ming, et al.
(författare)
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A hierarchical reconstruction for DG/FV method with low dispersion: Basic formulation and applications
- 2021
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Ingår i: Computers and Fluids. - : Elsevier BV. - 0045-7930. ; 231
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the numerical dispersion of a hierarchical reconstruction strategy for DG/FV method has been optimized. For the hierarchical strategy, the cell averages and the first derivatives are reconstructed based on the Hermite WENO method; the second derivatives are reconstructed via Green-Gauss integration and WENO reconstruction. Then, the numerical dispersion has been optimized by minimizing error with bandwidth optimization technique. Furthermore, to adjust the loss of compactness due to the reconstructed second derivatives, two modifications were also proposed with optimal weights. Eventually, from the implementations in scalar and compressible Euler equations, the superiority of numerical dispersion and accuracy of present methods could be validated. The shock capturing capacity has also been validated in 1D and 2D cases.
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