Vol 14, No 3-2 (2015): Special Issue

The turbine workflow is described by a large number of variables that often have contradictory impact on the turbine operating parameters. Hand-operated variation of these variables is a difficult time-consuming task. Application of mathematic optimization techniques could provide a solution of the problem. The paper outlines the basic principles of the method of mathematical optimization of an axial turbine based on the joint use of the NUMECA computational fluid dynamics software and the IOSO program optimizer. The procedure developed was implemented for a four-stage turbine developed and tested by NASA. Design models including one, two, three and four stages have been developed for the turbine under consideration. The results of calculations performed with their help showed good agreement with the experimental results. The settings of the numerical model that provide good agreement of design and experimental data but do not require large computational resource have been chosen according to the results of the research conducted. Low computational cost is very important because it allows significant reduction of the time spent to obtain the optimal solution with repeated reference to the design model. Automatic search of the turbine blade configuration allowing a 0.7 % increase of the turbine efficiency with constant mass flow and rate of expansion of gas (accuracy 0.5 %) was carried out with the help of the model created. 

Planning any pilot study brings up the question of producing test specimens. These are quite often rather complex, consisting of several individual parts put together. Test specimens are very expensive and take long time to produce using traditional technologies of production because of high accuracy required of them and absence of quantity production. Dynamically developing additive technologies (rapid prototyping) make it possible to produce plastic and metal parts of any form using a uniform technology. Therein the complexity of the part shape practically does not increase the manufacturing complexity and the need for equipment is absent or minimal. Laser stereolithography (SLA – Stereolithography Laser Additive) is one of the earliest and most precise technologies of 3D-printing. The paper presents the experience of using a prototyping machine on the basis of laser stereolithography for the production of experimental specimens for gas-dynamic investigations. On the basis of synthesis of this experience, basic requirements for similar experimental specimens are formulated: durability, rigidity and hardness, impermeability for gas or liquid, resistance to working fluid diffusion, resistance to chemically aggressive fluids (including fuels, oils). Comparison of different technologies of prototyping shows that stereolithographic models meet all listed requirements better than others. 

The article presents a CFD-modeling technique of the kerosene pump work flow. Various methods of improving CFD models have been investigated in the course of work to improve the reliability of simulation results: the selection of the type of boundary conditions, the extension of inlet and outlet pump connections, the estimation of the influence of the grid size and turbulence models. The advantage of boundary conditions of the «Opening» type with the «Opening Pressure» subtype is revealed. Rational lengths of additional pipes for correct modeling are determined:  ½ of the inlet diameter size at the inlet, 4 diameters of the outlet diameter at the outlet for rated operating conditions and 7 diameters for all other conditions. The best combination of turbulence model and mesh sizing have been identified: it is better to use the k-omega turbulence model for a fine grid with the size of the first element equal to 1 micron and the k-epsilon turbulence model for coarser grids. The convergence of solutions is evaluated by the changes of integral parameters of the pump from iteration to iteration. The amplitude of efficiency fluctuations in the process of calculation amounted to 1 % even in the case of the most accurate model. The model reliability is assessed by comparing the design characteristics obtained and the experimental data. The radial load on the impeller bearing is estimated by using the verified CFD model, which also showed qualitative agreement of the calculated and experimental data. Thus, the proposed modeling technique makes it possible to create adequate CFD pump models with the lowest computational costs. CFD-models developed according to the technique can be used for optimization studies of multistage screw centrifugal pumps. 

The article deals with the existing approaches to assessing the strength of railway wheels and the problems associated with forecasting actual spots of fatigue crack origination in operation. Solid-rolled railway wheels with a flat cone disk of standard design that have become a frequent practice in the Russian railway system are taken as an example. Calculations of the safety factor of fatigue resistance according to domestic and foreign standards have been carried out. The authors propose a procedure for assessing the wheel fatigue resistance to solve the above problems, taking into account the impact of residual technological stresses caused by heat treatment in the manufacturing process, followed by the repair of the rim, and service heat loads associated with the heating of the rim during braking, when the wheel interacts with blocks. Quantitative assessment of the impact of residual technological stresses and service heat loads on the strength of the wheels is presented. In conclusion the results of testing the computational methods described are presented, wheels of low-stress design with improved performance characteristics developed by the JSC «Vyksa Steel Works» taken as an example.

The purpose of the work is to analyze the repeatability of elastic damping properties of multilayered corrugated supports of aircraft and rocket engines in the conditions of out-of-toleranceproduction of component parts in mass production. The research is carried out by the calculation Monte-Carlo method with the use of experimentally confirmed laws of distribution of tolerances on the production of parts constituting the structure of a support. A mathematical model of virtual mass production of supports with multilayered corrugated dampers, a mathematical model of uniaxial static loading of a support, and, on their basis, a model of elastic hysteresis characteristics spread have been developed. Fields of dispersion of characteristics of supports have been investigated for different parameters of accuracy of production of the parts influencing the above characteristics. It has been found that statistical laws of distribution of elastic friction characteristics of multilayered dampers in supports are not subject to the normal law. The most probable values of these characteristics are 20-30% less than the arithmetic mean values calculated for the whole amount of sampling. The calculations showed that in common production practice of combination of tolerances on the production of damper component parts in mass production the variation of their characteristics is not unconsiderable, which results in the need of selection of parts with the required characteristics.

Operation of bearings and seals of gas turbine engines (GTE) is associated with adverse wear effects of friction parts. Boundary friction occuring in startup - shutdown and extreme engine operating modes is characterized by high values of the friction ratio and damage of friction surfaces in the contact zone. This results in damage accumulation, wear and changes in the geometry of the friction surfaces, which leads to degraded performance properties of the product and functional failure. In this case the requirements for fixed geometry in turbomachinery bearings and seals are very strong, since any undesirable change in the shape or size of the working gap leads to a decrease in unit efficiency and engine efficiency as a whole. In addition to the boundary friction regime, the efficiency of bearing and sealing units is decreased due to power friction losses. These losses are always present in friction units, but they can have a significant effect on the unit performance in off-optimum operation (including the turbulent flow regime in the working gap and the wrong choice of lubricant). Some of these problems are solved constructively by changes in the shape of working surfaces, use of special materials and advanced coatings, as well as timely control of the lubricant purity.

The article focuses on the analysis of the results of computer simulation of the process of casting the turbine blade 24.400.538-1, including prediction of occurrence of casting defects. Engineering calculations have been carried out to model the stress-strain state of the casting during solidification and after the knockout of the casting from the mold. The internal structure of the casting was analyzed for the presence of microporosity. The analysis of the results of modeling the process of grain formation in the casting made it possible to predict the size and direction of grain growth in the casting during its crystallization. Thus, on the basis of in-depth research of the group technology of a complex representative of the most loaded turbine blade and the one most difficult to produce local places of occurrence of casting defects were identified and predicted taking into account the obtained results of simulating the casting process. This made it possible to reduce the amount of defects at the stage of actual production by 8% on the average.

The influence of end mill teeth flank wear on the density of heat fluxes taking place in the cutting area is discussed in the paper. The following densities of heat fluxes are dealt with: the density of heat flux which occurs as a result of plastic deformation, the density of heat flux which occurs due to the friction of chips against the cutting face of the mill teeth and that which occurs as a result of flank surface friction against the workpiece being machined.The dependence of the cutting temperature on the value of the tool wear has been obtained. The thermal field in the tool has been calculated. The presented results of the numerical experiment have been obtained by a customized procedure that represents a revised procedure developed by Professor A.N. Resnikov for the conditions of endmilling.  The article describes the main stages of adaptation. There are four of them, and they are based on the geometrical specificity of the chip. Immediate calculation of temperature fields in the cutting area in the endmilling process was performed using a computer finite - element model. The model takes into account the hydrodynamics of the cooling lubricant which, in most cases, takes place in endmilling and other machining processes.

Production of casts of parts of gas turbine engines (GTE) is a complex and expensive process that requires a considerable amount of material resources. Various defects often occur in the manufacture of complex parts of gas turbine engines, defects that can be corrected in various ways. This paper describes a method of correcting defects in a cast alloy stator by pulsed laser cladding of stainless steel elements. After deseaming the unsound spots were reconstructed using a wire selected by matching its chemical composition with the basic material, annealing being used at different stages of surface coating. Annealing of the basic metal prior to deposition results in a two-fold increase of the transition area, the difference in the properties of the basic material and the cladding is maintained. If annealing takes place after cladding there is no clearly defined borderline between the basic materials and the steel deposited. Annealing and final hardening heat treatment is required after stainless steel is deposited on the nickel alloy.

The paper presents three algorithms for the measurement of gasturbine engine (GTE) compressor blades airfoil (suction side, pressure side, leading and trailing edges) geometry using coordinate measuring machines. The first algorithm is a single scan of the heightwise blade section using a test point. The second algorithm is based on the pre-alignment of the nominal profile with the measured actual profile. An iterative closest-point algorithm is used to carry out the procedure of the best possible alignment of the measured ptofile and the nominal one. In the third algorithm, the coordinates of the measured points of the edges are calculated using the spline defined by the coordinates of the test point (TP) center. The research of errors of measuring the geometry of the elements using the algorithms mentioned above was carried out. To perform the research a model was developed simulating the contact of the TP and the surface of the part being measured. The model makes it possible to calculate the coordinates of the contact point, the center coordinates and the coordinates of the MT of the measured points. The search for the coordinates of the contact was performed using the method of sequential quadratic programming. A procedure was also used that makes it possible to simulate the deviation of the profile and surface position from the nominal. In the course of the simulation dependences for determining the average, lower and upper boundaries of the measurement error distribution for any airfoil point being measured were obtained.

The paper emphasizes the increasingly important role of gas turbines on the power generation and gas pumping market. One of the variants of manufacturing such power plants consists in the conversion of aircraft engines into industrial gas turbine drives. The authors review the advantages of this type of production. The paper describes the operating conditions of such gas turbines and major challenges encountered in designing oil systems for aeroderivatives of this type.  Conservatism of aircraft engine developers does not make it possible to realize the changes in requirements to industrial power plants to the full extent, which results in  imperfection  of the oil system structure as it is re-designed for ground application. The paper presents the main trends in industrial gas turbine oil system development. Three levels of oil system conversion are defined: maximum (maximum possible application of the existing hardware, in which case achieving high gas turbine service life is impossible), medium (aircraft engine oil system components that do not significantly affect the engine life are partially preserved, while other components are re-designed for ground application), minimum (complete replacement of the oil system elements aimed at achieving the highest performance characteristics). 

A method of control of shot impact methods of surface plastic deformation is presented in the paper. The possibility of controlling the hardening process of parts made of titanic alloys in terms of deflection of plates made of carbon steels is shown. Because of differences in the resilient and plastic properties of materials and as they show different tendencies to hardening their deformation will occur with different speed and intensity over time. In the case of the greatest deflection of the testplate it may not be up to the required degree of hardening of the part made of another material. Cases of insufficient hardening or rehardening of the part’s surface layer may occur in controlling the hardening on plates made of U8A steel. One of the indices of the surface layer is its energy level, therefore the intensity of exoelectronic emission of the surface of the part treated can be used as a criterion of estimation of the stress-strain state of the surface layer. Non-destructive testing of hardening and finishing of the surface layer can be accomplished comparing the part tested with the reference standard.

There is a need to change the air bypass control unit performance to estimate its influence on the compressor gas-dynamic steadiness and the combustion process in the combustion chamber during the testing and operation of gas turbine engines with low-emission combustion chamber. Setting up the required air bypass valve closed (open) time by means of standard hydraulic actuator in the process of testing requires stopping the engine, removing the air bypass control unit, changing the orifice and testing the unit’s performance on the test stand that are associated with significant time and material costs. To adjust the time of restating the air bypass control unit it is proposed a screw throttle, the parameters of which are calculated on the basis of research performance of the unit. The custom screw throttle is designed and its hydraulic characteristics are researched, its effectiveness is experimentally verified within the unit at the test stand conditions. The possibility of changing the air bypass control unit performance in a wide range at different air bypass valve reaction forces is shown.