Centrifugal compressor impeller loading factor analysis

The loading factor performance modelling is an important part of centrifugal compressor performance calculation. The presented information on model stages’ test data confirms the fact that the loading factor versus flow coefficient at an impeller exit is a linear function independent of Mach number (subsonic flow). The test data and the design characteristics of the series of 10 model stages are compared with the calculation of an inviscid flow and with calculations done using the NUMECA software. Math models offered by the authors, and inviscid calculations solve the problem of a primary design. The CFD-calculation for final solution is non-satisfactory. If the loading factor is calculated by total temperature difference and flow coefficient is calculated by a continuity equation, the performance is not quite linear and lies much higher. For the considered stages CFD-calculation inaccuracy is + (0,06 … 0,12). CFD-calculated flow coefficient is inside 0,96 … 0,98 of the measured and of the calculated by the Math model

Verification of a simplified mathematical model of centrifugal compressor stages

To calculate the efficiency of a centrifugal compressor, it is sufficient to know the design parameters and similarity criteria: flow rate coefficient, loading factor, relative hub ratio, Mach number. The effect of the inlet nozzle and the diffuser type is also taken into account. The original simplified model was successfully used for calculation of compressors’ candidates in computer programs of the Universal Modelling Method. Recently, the model has undergone significant revision and been remade. The modernized model is used in the program for primary design of centrifugal compressors. The authors verified the new model, comparing the calculated efficiency with the measured efficiency of several dozens of model stages 21CV family and low flow rate model stages. In total, calculations were carried out for more than thirty model stages. The range of design parameters of analysed model stages is quite wide: flow rate coefficient 0.00564 – 0.0676; loading factor 0.384 – 0.742; hub ratio 0.258 – 0.466

The simulation of gas-dynamic characteristics of centrifugal compressors in turbo-expander units

Prof. Y. Galerkin and his team have developed and completed designs of 19 single-stage centrifugal compressors for turbo-expander packaged units applying Universal Modeling Method for the company “Turbokholod JSC” since 2005. The most powerful compressor is 6500 kW. The highest delivery pressure is 12 MPa. One hundred fifteen turbo-expander packaged units with total capacity 400 000 kW were manufactured, installed and were in operation in December 2018. The gas-dynamic characteristics of compressors comply with technical specification when operated within given range of initial temperatures and initial and final pressures up to 16 combinations for some compressors. The dimensionless characteristics of the compressor stages vary within the range of design parameters: flow rate coefficient 0.0278-0.0697, loading factor 0.43-0.71. The simulation of gas-dynamic characteristics of one of the designed compressors by the newest version of mathematical model is presented as an example, demonstrating the simulation features and effectiveness