The known information of satisfactory correlation of calculated and measured stator part performances is a foundation for the numerical investigation. Stator parts «Vane (vaneless) diffuser + crossover + return channel» of stages with different specific speed were designed in accordance with standard recommendations and investigated by CFD calculations. Flow structure demonstrated advantages and disadvantages of design. Flow separation in crossovers was eliminated by its shape modification for stages with diffusers relative width of diffusers. The stage with medium flow rate and low loading factor was designed with traditional and modified crossovers. Calculated efficiency performance becomes better. The information obtained is useful for design method better calibration. Index Terms-gas dynamic design, pipeline compressor, test results performance, centrifugal compressor, efficiency, mathematical model NOMENCLATURE b-width of channel; 2 c-absolute velocity at an impeller exit; 1 D-blade inlet diameter; 2 D-impeller diameter; p-pressure; R-radius of curvature; T-temperature; absolute velocity angle related to tangential direction; -loss coefficient; -efficiency; -pressure ratio; T -loading factor; i-incidence angle; k-isentropic exponent; -flow rate coefficient.
Stator part of a centrifugal compressor stage is a proper object of study by CFD calculations meaning better understanding of flow behavior, checking of field type design methods and possible improvements. Several stators with vane and vaneless diffusers for stages with different specific speed were designed by standard methodology and numerically analyzed. Results were verified. Calculation in a whole has demonstrated validity of existing recommendation. The specific velocity for stators is introduced which can be applied to match an impeller and a stator. Calculations demonstrated quick efficiency drop for stators with specific speed less than 0,215. Return channel vane cascades were studied in wide range of solidity with constant vane height and with constant radial component of velocity. Empirical formulae with non-dimensional circulation as an argument are proposed for loss coefficient, profile loss coefficient, optimal incidence angle and exit lag angle. Candidates of the low specific speed stator have demonstrated that an arbitrary channels’ wideness to diminish friction losses is not effective. Better flow organization is preferable. Modification of a crossover demonstrated positive results for high and low specific speed stators.
Calculations performed with modern CFD programs aid in optimizing flow paths of centrifugal compressors. Characteristics of stator elements of flow paths, calculated via CFD methods, are considered quite accurate. We present optimized return channels (RCh) of three model industrial compressor stages with vaneless diffusers. A parameterized model was created for optimization. The MOGA (Multi-Objective Genetic Algorithm) optimization method was applied in the Direct Optimization program of the ANSYS (Analysis System) software package. Optimization objects were return channels of the stages with high flow rate 0.15. The stages have three different loading factors 0.45, 0.60, 0.70. The optimization goal was to achieve the minimum loss coefficient at the design point. During the optimization process, we varied the following: the number of vanes, the inlet angle of the vanes, the height of the vanes at the inlet, the outer and inner radii of curvature of the U-bend. The outlet angle of the vanes was selected to minimize outlet circumferential velocity. In comparison with preliminary design, the optimized RCh are more efficient across the entire range of flow rates. The optimization reduced the loss coefficient by 20% at the design flow rate.
Published data on flat grid purges allow to evaluate the efficiency of blade devices with different kinematic scheme of stages and design parameters. The authors present the main provisions of the calculation program algorithm and some results of numerical analysis of the efficiency of flat grids of axial stages with different combinations of design parameters. The content of the article and the computer program are addressed to people who are improving their knowledge of gas dynamics of axial compressors. Some of the results may be of interest to specialists working professionally in this field.
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