Vol 13, No 5-1 (2014): Special Issue

Taking into account the universal character and high energy intensity of the mechanism of low cycle fatigue (LCF) crack stable growth which ensures a long safety period for the growth of such cracks a conception of cycle life additivity is proposed. According to the conception the cycle life of an aero engine disk is determined up to the limiting state connected with the transition of a LCF crack to unstable growth in the critical area of a disk. The cycle life prior to the first overhaul is calculated by adding the life cycle before the crack origination and that of stable crack growth (survivability resource); the overhaul period is determined by the survivability resource. The latter is also the lower bound of the disk life at the design stage. To estimate the overhaul period we suggest using survivability diagrams representing the dependence of LCF crack stable growth in the critical area of the disk on the size of the crack. Methods of constructing survivability diagrams have been developed for simple and complex loading cycles. Examples of applying the conception for the estimation of cycle life of aero engine disks made of wrought and powder alloys are presented.

This article considers single-mass elastic-damper model of oscillating system; simplified classic versions with pendants in the form of rheological models of Poynting-Thomson, Kelvin, Maxwell, Hooke can be derived from this model. The difference between this model and other classic versions is that the components of researched model suspension system are based on different foundations; one of foundations can be vibro-active. Model has two modifications, the difference between these modifications is that in one case elastic part of suspension system is based on vibro potentially active foundation and in other case elastic – damper part of suspension system is based on vibro potentially active foundation. The article also contains mathematical models of these modifications with allowance for damping of nonlinear type. Dynamical functions of variation are researched. In this variation vibrations can be transmitted from foundation to protected mass through elastic component. Article shows the cases of force and kinematic vibro-loading of mass with appliance of frequency functions on absolute and relative parameters. Dynamics of researched model is identical to dynamics of classic model in case of force vibro-loading of researched model. New properties (two invariant points) appear on amplitudefrequency characteristic of relative parameter in case of kinematic vibro-loading. This fact is used for optimization of damping level in order to minimize the resonance amplitude. The range of low-frequency vibration isolation is not less than the range of conservative oscillating system. Its size depends on damping and stiffness of elastic elements, so the choice of these values is associated with the achievement of compromise between
limitation of the range of resonance oscillations and providing of the low-frequency vibration isolation of the required quality.

The purpose of the work is to develop methods of managing the cycle of bifuel and single-fuel vehicles with engines running both on petrol and gas fuel as well as physically and mathematically reasonable algorithms for an electronic control system. On the basis of full-scale tests of an internal combustion spark-ignition piston engine and a technique developed for designing an ejeсtor with non-stationary physical parameters of working bodies a method of compensating power losses by ejecting a portion of air with the help of pressure difference on the valve of a gas electromagnetic injector is proposed. On the basis of the theoretical analysis and experimental data an algorithm of determining the fuel injection rate taking into account the subcritical or critical fuel discharge from the injector nozzle, the change in the speed of sound, the gas fuel pressure undershoot in the process of fuel feeding and the power supply voltage on the electromagnetic coil of the gas injector is developed. A method of determining the ignition advance angle when switching from petrol to gas fuel is developed for an electronic control system of an internal combustion spark-ignition engine which serves as the basis for calculating
the adjusting factors for liquefied petroleum gas and compressed natural gas.

The paper presents the results of analyzing the process of diamond burnishing of a sample made of heat-resistant wrought steel 15Cr12Ni2MoVWANb-S using an indenter made of natural diamond OST2 I77-5-75. Burnishing of the sample was carried out after previous turning. The process of turning was carried out by a carbide cutting tool with a mark T15K6 plate with the test sample fixed in a holder with the snap-action tailstock center. Burnishing was performed using two different methods of fixing the sample (in the centers and in a three- jaw chuck with a snap-action tailstock center). The roughness parameters were measured using the automated profilograph-profilometer of the BV-7669 model. The studies have shown the possibility of macrorelief formation on the burnished surface if the sample was machined in the centers and its absence if the sample was machined in the holder with a snap-action tailstock center. In order to obtain the empirical relationships linking the surface roughness with the diamond burnishing process parameters (pressing force, speed, feed, the initial peak-to-trough height and the radius of the diamond burnishing tool) a series of single-factor experiments treated with the use of the method of least squares was carried out. The results obtained correlate well with the experimental results previously obtained in studying the process of diamond burnishing with the use of a diamond burnishing tool made of synthetic diamond ASB-1.

Methods of improving the safety and efficiency of gas turbines are analyzed. The existing diagnostic methodologies and software for compression stations are reviewed. Lists of significant diagnostics parameters, typical faults and their causes are compiled. A model of a hybrid intellectual system of gas turbine fault diagnosis based on artificial neural network and fuzzy inference is introduced. The fuzzy inference method which allows processing an arbitrary number of intermediate variables and transitive relations is described. Moreover, the method makes it possible to take into account the inaccuracies in expert knowledge not only in describing the facts of an application domain but also in cause-and-effect relations between them. The implementation of the proposed model and the method in the system of taking decisions that makes it possible to reveal both the presence and character of the faults and their possible causes is described. The proposed system makes it possible to improve the accuracy and completeness of gas turbine diagnostics, which, in its turn, will increase the labor safety for the compression station staff as well as the promptness of repair and maintenance. Thus, the application of the system may have a positive effect on the service life and economic feasibility of gas turbines.

An important engineering challenge of providing the reliability of products made of composite materials (CM) is the identification of dangerous types of defects, their permissible values and developing techniques for their detection. A set of techniques of non-destructive testing (NDT) is presented as applied to the problem of monitoring and identification of the acceptable limits of technological defects of aircraft engine parts made of composite materials. The paper also includes experimental tests aimed at determining the effect of a fiber defect on the mechanical characteristics of a polymer composite material. Joint use of different NDT techniques is necessary for the detection of multiple types of technological defects typical for CMs. Defect detection is an integral part of the processing of composite materials into products. Test samples with artificially damaged fibers show their significant influence on tensile strength characteristics and shear modulus in the plane of the layer. The effect of possible defects on the mechanical characteristics of fiber should be considered when designing CM products.

Research to develop a 50 N thrust correction low-thrust liquid rocket engine with a deflector-centrifugal scheme of mixing nitrogen tetroxide and unsymmetrical dimethylhydrazine propellants on the inner wall of the combustion chamber has been conducted at the Chemical Machinery Design Bureau named after A.M. Isaev. In the deflector-centrifugal mixing scheme developed at the Chemical Machinery Design Bureau the oxidizer gets to the conical deflector via the jet nozzle and is transformed into a primary film running off the edge of the deflector onto the inner wall of the combustion chamber where it is transformed into a secondary film that flows along the wall of the chamber to the point of meeting the film from the centrifugal fuel spray nozzle coaxial with the combustion chamber. Upon meeting the films of oxidizer and fuel continue flowing along the wall of the combustion chamber at the same time penetrating each other and carrying out the liquid-phase mixing with the formation of transformation products of hypergolic fuel. Thus, practically all the fuel gets to the inner wall of the combustion chamber, participating in its cooling and removal of a considerable part of the heat flow directed along the wall of the combustion chamber from its critical section in the direction of the nozzle head. The engine has the highest (in its class) geometric nozzle expansion ratio ( Fа =200) among analogues of domestic production, meanwhile preserving acceptable dimensions and weight characteristics. The combustion chamber in the engine designed is made of a niobium alloy with a protective heat resistant coating - molybdenum disilicide MoSi2 deposited on the inner surface while niobium disilicide NbSi2 formed by silicon impregnation of a niobium alloy is used on the outer surface. During the firing tests the jet centrifugal scheme of organizing the work process in the combustion chamber designed at the Chemical Machinery Design Bureau confirmed its efficiency in a 50 N-thrust engine. The adopted design and technological solutions in creating a 50N thrust engine ensured high power and energy-mass characteristics, as well as stable engine performance in a wide range of pressures of fuel entering the engine: up to 70.3 N in power augmentation and up to 45.9 N in throttling

Computational and experimental work to select optimal design parameters of a fuel injector in order to obtain high-energy characteristics of low-thrust liquid rocket engines (LTLRE) with a deflector-centrifugal mixing scheme with 400 N thrust was carried out. A centrifugal atomizer is installed coaxially with the combustion chamber in the deflector-centrifugal mixing scheme. The engine thrust increases with the diameter of the combustion chamber and, consequently, the length of the free span of the fuel film in the cone of the fuel spray of the centrifugal injector also increases before hitting the inner wall of the combustion chamber. Thus, it is necessary to determine the parameters of the injector which provide the stability of the fuel film (absence of the film decay) along the span before it gets to the wall of the combustion chamber. For efficient organization of liquid-phase mixing of fuel components on the inner wall of the combustion chamber the design parameters of the centrifugal nozzle (the diameter of tangential holes, the length and diameter of the vortex chamber, the length and diameter of the injector nozzle) that would ensure the stability of the fuel film all along the free span up to the inner wall of the combustion chamber, as well as the speed, the film thickness and the angle of the atomization cone were calculated. In case of the optimal choice of parameters the films of oxidizer and fuel interpenetrate each other through their thickness. Thus, complete conversion of the fuel components takes place, which ultimately provides higher power characteristics of the engine. The article presents the results of firing tests of a 400 N LTLRE with different design parameters of an injector with the deflector-centrifugal mixing scheme. It follows from the test results that as the nominal pressure drop across the centrifugal nozzle decreases to a certain limit the value of the specific impulse increases. If the inlet pressure is considerably reduced and, as a consequence, there is a significant reduction in the pressure drop across the centrifugal nozzle, the amplitude of the pressure oscillations in the engine’s combustion chamber is increased. The analysis of the test results made it possible to optimize the design parameters of the fuel swirler for a regular 400N LTLRE.

The paper is focused on the evaluation of integral and local parameters of advanced aero engine highpressure and low-pressure turbines using the method of 3D numeric simulation in ANSYS CFX. The models used were very detailed high-pressure and low-pressure turbine models with adjoined cavities and a transition duct consisting of 577 million finite elements. Numerical analysis was conducted both in stationary and nonstationary setup using BSL and SST models of turbulence. The resulted design data were verified against the turbine test results. Deviations between design and test data, both local and integral, are insignificant (local deviation is not more than 5%). The results of numerical analysis show high level of turbines’ efficiency. The current configuration was optimized based on the results of verification, which allowed increasing HPT design efficiency by 0.4%. The model was taken as a basis for a series of works aimed at improving the key parameters of both individual turbine components and the module on the whole.

The paper presents a methodology of calculating negative heat flows in the cylinder-piston group of the Stirling engine. Some of the most important of them are the shuttle effect and the pumping losses. The introductory part of the article describes the physical side of the phenomena under investigation. The main relationships recommended by the researchers for the calculation of the shuttle effect and pumping losses are presented in the paper. A mathematical model is developed for the purpose of calculating the heat losses mentioned. The model is based on representing the phenomenon as quasistationary radial heat transfer by means of convection and radiation. A system of algebraic differential equations of heat exchange between single elements of arrays is presented. The system of the main equations is solved by a numerical method of integration (a variety of Euler method - the method of limiting overrelaxation). Algorithms of controlling the accuracy of the calculations performed are incorporated in the program of calculation. The algorithm is used for defining the level of shuttle conduction and pumping loss in the1R30/6 Stirling engine designed at Saint-Petersburg State Marine Technical University. In addition a methodology of finding the heat dissipation factor in the gap between the displacer and the cylinder wall was developed. The extent of influence of the engine design data on the phenomena under consideration is analyzed. Rank diagrams are constructed that visualize the results obtained.

The problem of weight decrease is crucial for modern gas turbine engines. Application of supersonic and transonic compressors is one of the ways of solving this problem. This allows reaching a higher pressure ratio at each stage than while using subsonic compressors and thus reducing the number of stages required to produce the desired value of pressure ratio. In compressors of this kind the flow is slowed down due to a system of shockwaves in the supersonic part and due to the flow deflection in the diffuser channels formed by the rotor blades and guide vanes in the subsonic part. The design of new compressors and modernization of old ones is inextricably connected with the usage of computational fluid dynamics methods at the present stage of engine construction development. The necessity of simulating a shockwave system imposes high demands on the construction of a computational mesh. In particular, the choice of the method of parameter passing between the domains of rotating blades and those of fixed guide vanes is an urgent task. It is shown in the paper that the use of different methods of averaging and parameter passing between domains can make a significant difference in compressor design characteristics (for example, a three-stage low-pressure compressor). Three methods of passing parameters between the domains that are used in the software package NUMECA/Fine Turbo are analyzed. The calculated compressor characteristics are compared with the experimental data at different rotation frequencies
of the rotor. The data obtained show the adequacy of the numerical model of the work process in the compressor under investigation. Typically, air bleeding for various needs takes place in compressors. Compressor performance changes when the air enters it, which should be considered in the calculations. It is shown in the example of the compressor tested that the inclusion of air bleeding results in quantitative and qualitative changes in the compressor performance. Among other things, parameters like pressure ratio and dynamic stability margin are changed, which may lead to inconsistent operation of the compressor as part of the engine. Thus, a conclusion about the necessity of taking into account the simulation of air bleeding in the calculation of supersonic compressors is made. The results obtained make it possible to expand the understanding of the working process of supersonic and transonic compressors and can be used later in the creation of numerical computational models of compressors of this type.

Nowadays, screw booster pumps (BP) are used in engines of large and small thrust both of Russian and foreign designs to reduce the pressure in the tanks. Cavitation may occur in BPs like in any hydraulic systems. To determine the cavitation characteristics of screw and centrifugal pumps a number of empirical formulas were obtained which do not fully take into account all the geometrical features of variable-step screws. Various models of cavitation are used in CFD programs; cavitation properties of any geometry can be obtained on the basis of these models. The paper presents the results of numerical analysis of the cavitating flow in a booster pump and their comparison with the experimental ones. Modeling was performed by ANSYS CFX. The cavitation phenomena were simulated in a stationary approach using the Rayleigh-Plesset model. The geometrical model included an axial-radial wheel and straightening vanes. The analysis was performed with and without a shroud ring, a clearance gap and roughness. On this basis, a method of calculating the stall cavitation characteristics is developed using ANSYS CFX.

The possibility of using elastic porous elements made of "metallic rubber" (MR) as rotor seals is discussed in the paper. The technology of manufacturing of such elements is developed for the mechanical damping of vibration in mechanical systems where they are widely used. Comparative analysis of rating curves of labyrinth, honeycomb, brush seals and seals made of MR material has shown that seals made of MR material have better rating curves than labyrinth and honeycomb seals, but slightly worse ones than those of the brush design. Therefore, the use of porous MR material shows promise for making parts of the seals for gas or oil cavities of rotors. Seals made of MR material are designed for optimum performance in the most demanding aerospace sealing applications where high speed and vibration are the norm, and where axial shaft movement takes place. An installation imitating conditions of using rotor seals is designed for the purpose of analyzing seals made with the use of MR material.

Considerable efforts are made to generate drop-in aviation fuels from microalgae to avoid competition with food production. Synthetic biofuel from oil-rich biomass is produced along four process lines: cultivation, harvest, extraction of raw material and conversion to fuel. This study deals with the life cycle assessment of fuel obtained from cultivation of the fresh water alga Auxenochlorella protothecoides and concentrates on the cultivation in open ponds as well as the harvesting steps preconcentration, electroporation and dewatering. Energy balance and environmental impact is analysed using GaBi software and data base. The main goal is to identify those factors or processes exerting the strongest impact, either environmentally or from the point of view of the energy balance. Production of one kilogram of dry oil-rich algal biomass (kg DM) consumes 118.56 MJ of primary energy. The primary energy demand is apportioned as follows: 71.7 % during proliferation in Erlenmeyer flags and bubble columns, 15.5 % by cultivation in raceway ponds and 12.8 % in preconcentration, electroporation and dewatering. This converts into a net energy ratio (NER) of 0.266 and a CO2-equivalent of 6.45 kg CO2 per kg DM. These values are disadvantageous when compared to kerosene (NER=0.867, 0.384 kg CO2 per kg kerosene). Production can be optimized using process energy from regenerative sources such as hydroelectric power (NER = 0.545, 1.27 CO2 per kg DM). In this case total primary energy input must be corrected for the portion of renewable sources resulting in a NERcorr of 3.04. CO2-equivalents per kg DM remain unfavourably high as compared to kerosene; the main driver responsible for this discrepancy is the usage of freshwater and fertilizer.