This paper describes the first part of the global work done by the authors aimed at finding the best settings for a numerical model for the calculations of axial uncooled turbines using RANS approach. The authors studied more than 80 papers published over the past 5 years in the examined field. Their analysis did not allow to identify unified recommendations for the creation of numerical models. The selection of model parameters is usually motivated by general considerations of numerical simulation, which follow from the method. In none of the papers the selection of parameters is correlated with the structure of the flow in the turbine. Many specific simulation issues were not covered at all. For the research, more than 1000 models of full-size axial turbines (including multistage turbines) and their elements were created. They differed in the number, size, parameters of the elements of finite volume meshes, in turbulence models, in the degree of simplification. The results were compared with the experimental data. As a result, the following was obtained: 1. A method for developing and optimizing the working process of turbines using numerical simulation based on the RANS approach is proposed. The search for the optimal turbine configuration is carried out using light computational models, which are based on the simplified channel geometry and the finite volume mesh. Their application makes it possible to reliably find the optimal turbine configuration 2.8 times faster. The characteristics of the selected variants are verified with the help of verification models that consider the real geometry of the channels and have a minimum error. 2. Recommendations are given on the selection of parameters for finite volume meshes and the selection of turbulence models for numerical models of the working process of axial turbines designed to perform optimization and verification calculations.

The quantification of geometric and physical variables uncertainty impact on turbomachinery row workflow was conducted using several untwisted airfoil cascades of axial turbine nozzle blades with uniform section throughout the channel height. Profile loss coefficient, mass flow parameter, outlet flow angle were accepted as controlled performance criteria. The series of computational calculations were carried out for these cascades. The first group of calculations was aimed at the identification of the impact of geometric parameters uncertainty on nozzle blades parameters. The second group - at identifying the studied parameters depending on the flow parameters changes that are used as boundary conditions in the simulation. The obtained results showed that initial data uncertainty in CFD calculations has a significant impact on the obtained quantitative estimates. The difference between calculated data modified in accordance with the geometry technological tolerances and workflow parameters measurement error may exceed 5% by value of the considered criteria.

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An investigation of five models used to assess the profile losses in axial turbine cascades appears in this article: Soderberg model, Ainley&Mathieson model, Dunhem&Came model, Kaker&Ocapu model and Central Institute of Aviation Motors (CIAM, Russia) model. Using them, the calculation results were compared with experimental data for 170 airfoil cascades of axial turbines. These cascades include a diversity of blade profiles of axial turbines used in aircraft gas turbine engines. Direct comparison of the calculated and experimental results did not make it possible to uniquely choose the best model. For this reason, the analysis method of loss models based on the statistical analysis of calculation and experimental data deviation was developed. It is shown that the deviations are subject to the normal distribution law. Based on the analysis of mathematical expectations μΔζ and standard deviation σΔζ, it was found that CIAM model gives the results closest to the experimental data. It shows the deviation from the real values of the loss 2±82% with a probability of 95%.

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