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The paper considers the analysis and comparison of three methods of thermodynamic calculation for real gas in relation to the design of the flow part and modeling of the working process of centrifugal compressors for refrigeration, gas, chemical and other industries. A comparative analysis of these equations and comparison with experimental data were carried out. The equations were studied and their applicability was checked. Practical recommendations were given on the application of the considered equations. [ABSTRACT FROM AUTHOR]

The aim of the research is to optimize the 3D impeller and compare various methods of its design, evaluate the influence of each of the considered parameters, and develop recommendations for the optimal design. The meridional form of the 3D impeller was optimized, as well as the shape of the blade row. The meridional form of 3D impeller was researched using the Universal Modeling Method, the profiling of the impeller blades was carried out in the program of inviscid quasi-three-dimensional calculation 3DM.023. Since experimental verification of all designed impellers is not possible, the model tests were replaced by virtual ones, i.e. by CFD calculations. We have designed ten variants of 3D impeller using the program calculating inviscid quasi-three-dimensional flows, and researched blades height at the impeller exit, "gas-dynamic" and "geometric" approaches of blade profiling, the variation of the exit blade angle along blades height, the exit bulk angle, and the impeller axial length. Using a mathematical model, we have researched the influence of several impeller geometric parameters, such as impeller axial length, impeller inlet diameter, blade leading edge position, exit blade height, and number of blades. The research made it possible to increase the efficiency of the stage in all operating modes, the efficiency of the stage at the design point was increased by 1.02%, and the characteristic efficiency was increased by an average of 0.88%. [ABSTRACT FROM AUTHOR]

At the Department of Compressor, Vacuum and Refrigeration Engineering (KVHT), St. Petersburg Polytechnic University is studying processes in a centrifugal compressor [4-12], including non-stationary processes. One of the main goals of these studies is to develop ways to protect centrifugal compressors from surging. The work performed showed the advantages of the so-called feature method of protecting centrifugal compressors from surging in comparison with the parametric method [5-7]. With the parametric method, the approach of the turbocharger to the zone of global stability loss (surge) is determined by the current flow rate determined by measuring the statistical pressure at the inlet to the machine. The essence of the characteristic method is to detect characteristic signs of the behavior of the flow of the working medium (gas, air) in the flow part of the turbocharger before the surge. [ABSTRACT FROM AUTHOR]

The Universal Modeling Method is a complex of computer programs for calculating characteristics and optimizing design of centrifugal compressors based on mathematical models of efficiency and head. Practical experience allows improving mathematical models that underlie the Method. Determining the non-incidence inlet in a blade cascade is an important part of calculating the compressor gas-dynamic characteristics. In the 8th version of the Universal Modeling Method, a formula was used to calculate the direction of the critical stream line, containing an empirical coefficient X. The practice of application has shown that the value of the empirical coefficient changes the amount of losses in the impeller in off-design flow rates. A new scheme for modeling velocity diagrams was proposed. It was made for the stage operation mode corresponding to the zero incidence angle. The successful application of the model for the impeller design made it possible to extend it to the vane diffuser and return channel. Several other improvements were made, too. A new mathematical model was developed for calculating the flow parameters in the exit nozzles of centrifugal compressor stage. The mathematical model for calculating the flow parameters in the vaneless diffusers was modernized. The limit of applicability of the new model was expanded to a range of diffusers of low consumption stages with a relative width of up to 0.006. The resulting mathematical model was identified by the test results of two families of model stages and factory tests of industrial compressors. [ABSTRACT FROM AUTHOR]

An important element of the multistage centrifugal compressor flow path is a return channel, which has a complex configuration, its flow path is determined by a large number of parameters and sizes. Designing and optimizing stator elements is a long and laborious process. The use of modern computing systems can significantly reduce the time spent, make calculations of different variants for the return channel execution and choose the best. The aim of this work was to construct a parameterized model of stator elements. The process of constructing sketches in the DesingnModeler program of the ANSYS CFX software package with the output of variable values to the Workbench parameter table is considered in detail. It also describes the process of transferring data to a TurboGrid grid generator, the peculiarities of setting boundary conditions for a parameterized model in CFX-Pre, and the possibility of outputting data to a parameter table according to the calculation results from the CFD-Post program. The stator elements of the model stage 0028-058- 0373 were selected as the object under study. When constructing the flow path in the DesignModeler program, geometric parameters are determined that are subject to optimization. For simple optimization, it is enough to indicate the range of one parameter variation, in this case, the blade height at the outlet of the vane cascade, referred to the blade height at the inlet b6/b5. To assess the effectiveness of the vane cascade, the loss of total pressure was set Δ p 3 − o u t * = p 3 * − p o u t * . The optimization results in the program are presented in tabular form, for clarity, a graph is built. Each calculated point can be opened in the CFD-Post, see the flow structure and calculate the necessary gas-dynamic characteristics. The use of modern computing systems makes it possible to carry out more complex optimization with several variable parameters and different performance criteria, which allows you to calculate a large number of variants and significantly saves time for setting a new task. [ABSTRACT FROM AUTHOR]

The work considers the issue of choosing a turbulence model and taking into account surface roughness when creating a design model of low-flow centrifugal compressor stages for calculations using computational gas dynamics methods. The research object is a low-flow stage with a conditional flow coefficient Φ=0.008 and with a relative width at the output of the impeller b2/D2=0.0133. The issue of modeling friction losses in low-flow stages is of principal importance and is directly related to the turbulence model choice and taking into account surface roughness. It is shown that the choice of low-Reynolds turbulence models in the case of unloaded and continuous low-flow stages can be made from among the main common models (Spalart-Allmaras, SST, k-ω) based on the cost-effective calculations, the rate of convergence, the stability of the solution and the relevance of the obtained results. On the other hand, the use of low- Reynolds turbulence models is not relevant due to the inability to correctly introduce roughness corrections. For wall- mounted models, the quality of the grid model and compliance with the dimensionless distance to the wall y+ in the entire design area are particularly important. If y+=25...50 is provided on all calculated area friction surfaces, the grid independence of the solution for the entire gas dynamic characteristic is ensured at the optimal operating mode. y+ cannot enter the transition region 4...15 between the viscous sublayer and the logarithmic velocity profile region. The two main issues of roughness accounting are the conversion of natural roughness to equivalent roughness used in calculations, and the quality requirements of the grid model. The influence of roughness on the low-flow stage characteristics and the disk friction and leaks coefficients is estimated, and the independence of the full head of the stage from the surface roughness is revealed. A separate analysis of the impeller roughness and fixed elements influence was performed. [ABSTRACT FROM AUTHOR]

In this work, a test calculation of the model of a transonic centrifugal compressor stage with an input guide vane (IGV) and an unshrouded impeller was performed. The flow study was carried out using the Navier-Stokes equations closed by the Shear Stress Transport (SST) turbulence model. Modeling was performed for the entire frequency control range and three VNA rotation angles: initial position θv0=+ 25.2 °, positive δθv=+ 20 ° (θv=+ 45.2°) and negative rotation angle δθv=-10 ° (θv0=+ 15.2 °) before entering the impeller. As a result, good agreement between the integral parameters of the stage was obtained in the rotation frequency range from 28,076 to 35,085 rpm. The greatest discrepancies with experimental data were obtained at maximum rotational frequencies corresponding to supersonic flow at the exit of the impeller; this issue requires further study. [ABSTRACT FROM AUTHOR]

The paper presents the results of a numerical study of the viscous gas flow in a model stage centrifugal compressor with a low-flow coefficient using the Ansys CFX software package. The object of study is a model stage centrifugal compressor with low-flow coefficient, designed and tested at the Department of Compressor, Vacuum and Refrigeration Engineering of St. Petersburg Polytechnic University (hereinafter referred to as the Department of CVRE). To conduct a numerical experiment, a study on grid independence is carried out. The characteristics obtained from the results of a numerical study are compared with experimental characteristics. In the mathematical model of the stage, the magnitude of the axial clearance between the covering disk of the impeller and the compressor housing varies from 1 mm to 5.5 mm and the effect of changes in this value on the characteristic of the loss complex 1 + βfr + βpr is estimated. [ABSTRACT FROM AUTHOR]

When designing centrifugal compressors and turbomachines for various purposes one must carry out the calculation of flow through their fixed and movable elements. One approach to solving this problem is to use the well-proven classical quasi-three-dimensional model. Previously, the authors developed a method for accounting for the compressibility of a gas stream in the flow part of a turbomachine. This article demonstrates the work of a software package compiled on this basis that performs calculations taking into account the mutual influence of the solutions of two two-dimensional problems in the case of a subsonic gas flow. [ABSTRACT FROM AUTHOR]

Compressor machines are an integral part of power plants, used in the oil and gas industry, refrigeration and many other industries. Increasing the efficiency of the stage is necessary, especially for centrifugal compressors. The relatively low efficiency of such machines is due to the complexity of the processes taking place in the flow section. For complex tasks solution to increase operation efficiency of the whole stage it is necessary to consider both rotating parts of compressor (impeller) and stationary parts (diffuser, inlet chamber, reverse guide vanes). In operation, the inlet radial chambers of the centrifugal compressor are investigated, which have a significant influence on the operation of the compressor stage. When designing inlet chambers to reduce loss and flow non-uniformity at the compressor impeller inlet, it is important to thoroughly investigate the flow in the flow part in order to improve the efficiency of the stage. [ABSTRACT FROM AUTHOR]

The paper presents results of CFD simulations of a series of centrifugal compressor stage vane diffusers in the Ansys CFX. Objects of research are vane diffusers with external relative diameter (relative to the diameter of the impeller) equal to 1.5, vane inlet angles of 15, 20, 25 and 30 degrees, relative vane heights of 0.025, 0.045, 0.06, 0.08, vane profile curvature angles of 10, 15, 20 degrees. The characteristics of the polytropic efficiency, the loss coefficient, the recovery coefficient, the inlet-outlet velocity ratio, the flow deviation angle depending on the incidence angle are calculated. The analysis of the flow pattern in the intervane channel is presented. Increasing the vane curvature angle leads to a diffuser characteristics shift to the area of negative incidence angles. The flow deviation angle is almost independent of the diffuser width and increases with the curvature angle. In most calculations, a narrow diffuser (0.025) shows higher values of characteristics in the area of positive incidence angles. Characteristics of diffusers with a large inlet angle (25-30°) do not have a strong maximum. [ABSTRACT FROM AUTHOR]

The paper analyzes the methods of increasing efficiency and environmental safety of refrigeration systems for oil and gas refineries. A comparative assessment of the effectiveness in refrigeration cycles using various refrigerants was implemented. Particular attention is paid to increase effectiveness of centrifugal compressors by reducing irreversible losses in refrigeration cycles and the use of new scheme solutions. The main approaches for the terms of reference formation how to manufacture compressor equipment taking into account the optimal control methods were revealed. [ABSTRACT FROM AUTHOR]

The paper presents research on a rotating stall that can occur in centrifugal compressors. It can lead to vibration and imbalance in the construction. The number of zones and the speed of their movement must be determined to analyze and control these rotating stalls. Therefore, the study shows a method for automatically determining the number of stall zones and the speed of their movement in a centrifugal compressor. The results of the compressor stage experiments and data processing according to the proposed stall parameter determination method are given. The proposed methodology allows automatically determining the parameters of symmetric and asymmetric rotating stall. The parameters of the rotational stall and the influence of non-stationary process on the operating characteristics can be taken into account for optimizing the geometry and improving the anti-surge protection systems. [ABSTRACT FROM AUTHOR]

The article covers the issues of digital engineering of low flow rate centrifugal compressors. The additive technologies of parts and assembly units manufacture with the use of 3D-printing by metallic and non-metallic materials mastered by the Russian and foreign enterprises in different fields of industry (including aerospace construction and power engineering) have been revealed, the most prospective materials, achievements and trends of development have been analyzed. The experience in application of air and gas centrifugal compressors has been analyzed, the metallic and non-metallic materials used for their manufacture have been studied. The main factors determining the cost indexes and efficiency of centrifugal compressors have been revealed. Optimum structure and parameters of centrifugal compressors have been determined. The engineering and manufacturing methods providing decrease in the material consumption and increase in the strength of compressor parts and assemblies have been proposed. [ABSTRACT FROM AUTHOR]

The paper presents the problem of defining the flow part computational domain with computational fluid dynamics (CFD) RANS-method of a viscous gas on a low-flow centrifugal compressor stage. The conditional flow coefficient Φ of investigated stage is 0.008. Several variations of computational domain are considered: the main flow path; including the inlet pipe and fairing; accounting of cavities and labyrinth seals regions with full connection with flow path and one-sided connection at the impeller exit; computational domain with friction surfaces of large work disk base. It is shown that in the case of axial stage suction the inlet pipe and fairing do not have significant effect on flow parameters upstream the impeller and gas dynamic characteristics of the stage. The simulation without account of disk friction and leakage through labyrinths seals have unacceptable qualitative and quantitative result. The most relevant option to account disk friction and leakages is the full two-sided connection of work and shroud disk cavities with flow part, since the one-sided connection simulate only the disk friction and leakages well, but do not account the influence on the impeller flow. In some cases, it is important to take into account additional regions involved in friction losses. In addition, the influence of total pressure measuring tools placed in three section along the diameter is evaluated. It is concluded that the measuring tools have a minor effect compared to the other types and sources of low-flow stage losses. The task of flow path and cavities grid independence is considered. The cavities grid independence is important not less than the main flow path and blade rows. The influence of the dimensionless wall distance y+ of the first near-wall layer for low-Reynolds turbulence model Spalart-Allmaras is estimated. [ABSTRACT FROM AUTHOR]

The article describes the design of the experimental stand and the measurement system necessary for taking and recording readings of instrumentation and automation equipment. The basis of the stand is a centrifugal compressor unit of the multiplier type. The analysis of the results of experimental studies of a thrust sliding bearing with fixed pads at nominal and transient modes of operation of a centrifugal compressor with a closed impeller is given. The pulsations of the oil pressure in the bearing layer and the temperature of the working surface were measured at different rotor speeds depending on the lubricant supply temperature. [ABSTRACT FROM AUTHOR]