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Similarity theory principles are widely applied in gas dynamic design. But completely new solutions must be realized on a base of engineering approaches to predict performances. The heart of the Universal modeling engineering method is the physical model that is based on flow visualization and measurements inside rotating impellers. The math model is a sum of algebraic equations for calculation of head losses. Normalized velocity gradients along and normal to blade surfaces are arguments. Empirical coefficients values are established in a course of the identification — calculated performances are compared with the measured ones for several dozens of model stages tests with wide range of design parameters. The 4th version of the TU SPb modeling method (the set of the several computer programs) was applied in design practice in 1993–2010. Some Russian and foreign manufacturers realized several dozens of designed compressors with power up to 25 MW. The level of design point parameters prediction was so satisfactory that the manufacturers do not prove designs by model tests anymore. The whole performance prediction was not so good. The other difficulty — to predict design point efficiency with accuracy about 0.5% the very careful choice of empirical coefficients is necessary. The difficulties have been overcome in the new 5th and 6th versions. Most effective multistage compressors plant test performances were modeled successfully by 5th version program with the single set of empirical coefficients. Calculated performances and geometry of several dozens of stages of these compressors can be are applied in designs as usual model stages. The current designs are executed by the 5th and 6th version computer programs. The single stage 32 MW pipe line compressor was recently designed for the Ukrainian partner who offered high-RPM drive and favorable single-stage scheme. The test of the model at the 1:2 scale validated project parameters. Design pressure ratio and efficiency curves have matched completely. The predicted maximum efficiency 90% was proven.

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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.

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