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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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Preliminary design is an important stape in the development of centrifugal compressors and compressor stages. Basically for this purpose, various recommendations on the choice of the flow path dimensions are applied. Researchers of the Research and Development Laboratory “Gas dynamics of turbomachines” prof. Yu.B. Galerkin and A.F. Rekstin analyzed and summarized the dimensions of flow paths of 124 impellers. On the basis of this analysis, formulas were proposed for choosing the flow path dimensions of the centrifugal compressor stages, which were included in the preliminary design program. The formulas used are designed for relative Mach number of 0.7 and isentropic coefficient of 1.4. The correct application of these formulas for other Mach numbers and isentropic coefficient required development of an appropriate approach and algorithm for adjusting the height of the impeller blades at the outlet. Calculations of gas-dynamic characteristics using the Universal Modeling Method showed the need for selecting a coefficient that takes into account the influence of viscosity to obtain the required pressure characteristics of the compressor stage. This problem was also solved in the program of preliminary design. To check the quality of preliminary design, the results were verified using a non-viscous quasi-three-dimensional calculation program. Three stages were designed for parameters different to those used for development of preliminary design formulas. Analysis of the velocity diagrams of the impeller blades and distribution of meridional velocities showed good results of the preliminary design.