Vol 18, No 2 (2019)
- Year: 2019
- Articles: 15
- URL: https://journals.ssau.ru/vestnik/issue/view/362
Full Issue
AIRCRAFT AND SPACE ROCKET ENGINEERING
Disturbed motion of a hypersonic vehicle in climb
Abstract
Disturbed motion of a hypersonic vehicle in climb is analyzed. Deviations of atmospheric density from standard values and deviations of aerodynamic force coefficients from nominal values are taken as disturbances. Disturbed motion of a hypersonic vehicle with the optimum angle-of-attack schedule and nominal flight characteristics is modeled. Deviations of terminal conditions of disturbed motion from the target values of velocity, altitude and path inclination are determined. Using the method of Pontryagin’s maximum principle the problem of fuel mass minimum consumed in hypersonic acceleration climb is solved for disturbed motion. Optimal angle-of-attack schedules, optimal flight paths and finite values of the hypersonic vehicle’s mass are determined. Comparative analysis of optimal control programs and flight paths obtained for disturbed and undisturbed motion is carried out.
7-20
Relative equilibria of dynamically symmetric CubeSat nanosatellite under the action of aerodynamic and gravitational torques
Abstract
Motion of a dynamically symmetric CubeSat nanosatellite around the mass center on the circular orbit under the action of aerodynamic and gravitational torques is considered. We determined the nanosatellite equilibrium positions in the flight path axis system. We took into account the fact that the CubeSat nanosatellite has a rectangular parallelepiped shape and, therefore, the aerodynamic drag force coefficient depends on the angles of attack and proper rotation. We obtained formulae which allow calculating the values of the angles of attack, precession and proper rotation that correspond to the equilibrium positions, depending on the mass-inertia and geometric parameters of the nanosatellite, the orbit altitude, and the atmospheric density. It is shown that if the gravitational moment predominates over the aerodynamic one, there are 16 equilibrium positions, if the aerodynamic moment predominates over the gravitational one, there are 8 equilibrium positions, and in the case when both moments have comparable values there are 8, 12 or 16 equilibrium positions. Using the formulae obtained, we determined the equilibrium positions of the SamSat-QB50 nanosatellite. We calculated the ranges of altitudes where SamSat-QB50 nanosatellite has 8, 12, or 16 relative equilibrium positions.
21-32
Reducing the influence of interference of spacecraft magnetic field on magnetic measurements
Abstract
The article presents constructive ways of reducing the influence of magnetic interference from spacecraft, due to its own magnetic fields, on the on-board magnetic measurements, as well as reducing the resulting magnetic moments. Well-known methods of removing magnetometer sensors from the locations of the most powerful sources of magnetic fields of a spacecraft, in particular, using extendable booms, are considered. In addition, methods for reducing the influence of spacecraft self- magnetic fields on the onboard magnetometric navigation support systems using known closed and proposed hemispherical ferromagnetic shields are considered
33-40
Determining the dynamics of spacecraft rotational motion with the use of information provided by global navigation satellite systems
Abstract
The paper shows the possibility of using navigation user equipment in the task of determining the dynamics of spacecraft rotational motion. An approach is proposed that makes it possible to estimate the parameters of the rotational motion of a spacecraft by analyzing the geometric visibility of navigational spacecraft of global navigation satellite systems. The proposed approach consists in approximation of the accumulated information on the position of the spacecraft longitudinal axis using the angular motion model and the measurement model. The approximation is made on the basis of minimizing the sum of squared deviations between the calculated coordinates of the vector of the longitudinal axis and their simulated values. The minimization procedure is based on the algorithm of differential evolution. The proposed approach allows us to estimate the angular velocity of the nanosatellite with an accuracy of at least 0.3 deg/s and orientation angles with an accuracy of at least 15 degrees.
41-51
Theory of gas turbine engine optimal gas generator
Abstract
The article substantiates the necessity of designing an optimal gas generator of a gas turbine engine. The generator is to provide coordinated joint operation of its units: compressor, combustion chamber and compressor turbine with the purpose of reducing the period of development of new products, improving their fuel efficiency, providing operability of the blades of a high-temperature cooled compressor turbine and meeting all operational requirements related to the operation of the optimal combustion chamber including a wide range of stable combustion modes, high-altitude start at subzero air and fuel temperature conditions and prevention of the atmosphere pollution by toxic emissions. Methods of optimizing the parameters of coordinated joint operation of gas generator units are developed. These parameters include superficial flow velocities in the boundary interface cross sections between the compressor and the combustion chamber, as well as between the combustion chamber and the compressor turbine. The effective efficiency of the engine thermodynamic cycle is the optimization target function. The required depth of the turbine blades cooling is a functional constraint evaluated with account for calculations of irregularity and instability of the gas temperature field and the actual flow turbulence intensity at the blades’ inlet. We carried out theoretical analysis of the influence of various factors on the gas flow that causes changes in the flow total pressure in the channels of the gas generator gas dynamic model, i.e. changes in the efficiencies of its units. It is shown that the long period (about five years) of the engine final development time, is due to the necessity to perform expensive full-scale tests of prototypes, in particular, it is connected with an incoordinate assignment in designing the values of the flow superficial velocities in the boundary sections between the gas generator units. Designing of an optimal gas generator is only possible on the basis of an integral mathematical model of an optimal combustion chamber.
52-61
Technology of computational analysis of the working process parameters of low-thrust rocket engines running on gaseous oxygen-hydrogen fuel with the use of ANSYS CFD
Abstract
The paper presents the description of a mathematical model of the working process of a low-thrust rocket engine operating on gaseous oxygen-hydrogen fuel and some fragments of the technology of computational analysis of distribution of gas-dynamic parameters in the engine duct. We present the results of calculating the stream line distribution, the distribution of total temperature profile along the flow path of the engine chamber and at its characteristic cross sections, the axial component of (total) speed of combustion products in the Laval nozzle output section. The results of calculating the temperature in the area of the rocket engine’s inner wall are presented. It is shown that the distribution of the combustion products’ stagnation temperature has a significant impact on the efficiency of fuel conversion in the engine chamber, its thermal state and makes it possible to identify the ways of improving the workflow of the low-thrust rocket engine.
62-74
Calculation of lubricant flow in the slide bearing of the aviation engine reducer
Abstract
A method has been developed for calculating the pressure distribution in a cylindrical slide bearing. We present the process of designing a heavy-duty slide bearing as a component of the reduction gearbox of a bypass turbojet engine as the object of our investigation. The process comprises the following stages: specification of the supporting structure; calculation of pressure distribution in the slide bearing for different eccentricities and angles of rotation of the shaft journal; calculation of the effect of shaft journal precession on pressure distribution; calculation of pressure distribution taking into account the channels of oil supply to the bearing. The results obtained in the experimental activities are given. The analysis carried out shows that the calculation helps to predict the location and size of pressure and rarefaction areas, to position the holes for oil supply, which will significantly improve the conditions of lubricant flow in the bearing.
75-88
Research of hafnium-containing defects in granular nickel EP741NP alloy using electron microscopy
Abstract
In the process of low-cycle fatigue testing of blanks of turbine disks of turbojet engines made of granular EP741NP nickel alloy, fracture samples were obtained. The fracture area was examined by various electron microscopy methods. Accumulation of rounded high-hafnium micro-particles was detected in the center of the fracture according to the data of energy-dispersive X-ray microanalysis. Such clusters are observed in about half the instances of fractures in similar blanks. Hafnium is an alloying element, but its content is strictly limited and should not exceed 0.4 mass %. Elucidation of the nature of the formation of this type of defects is a subject of scientific and practical interest. Using high-resolution transmission electron microscopy, energy-dispersive X-ray microanalysis and electron diffraction, it was determined that these particles are monoclinic single crystal HfO2 structures. Some particles contain nuclei that differ in their elemental composition and structure. Some of the nuclei contain C, O, S, F, etc. that may be indicators of organic contamination of the sample. A high-carbon amorphous shell was found around some HfO2 particles. The data obtained indicate that the formation of these particles is associated with organic contaminations. To prevent the formation of such centers of destruction, it is necessary to improve the purity of the technological processes of production.
89-95
Investigation of thermal conditions of nanosatellite optoelectronic telescopic module for different modes of operation
Abstract
The problem of studying thermal conditions of the optoelectronic telescopic module of a nanosatellite under the influence of operating conditions is considered. To maintain optimal thermal conditions of the telescopic lens, a thermal control system based on electric heaters was chosen. Based on the three-dimensional model, the thermal regime of the lens is calculated taking into account the real operating conditions of the nanosatellite in its orbital motion. As a result of the calculation by the finite element method, the dynamics of the temperature fields of the lens was obtained for different modes of operation of the nanosatellite: access to the established thermal conditions, earth terrain survey in normal and extended modes. It is shown that in different modes of operation the thermal control system maintains a given temperature range of optical elements with moderate energy consumption and provides lens efficiency during the entire time of operation of the optoelectronic telescopic module of the nanosatellite.
96-111
Ensuring permissible level of gas turbine dynamic loading in operation by means of standard engine control devices
Abstract
To solve the fatigue resistance problems of gas turbine engine elements using the existing principles of regulation based on the use of safe load factors for various loading schemes we suggest exercising controlled influence upon the loading sources in operation using a system of automatic control and standard devices for engine monitoring. The article discusses the use of this approach to minimize the dynamic loading of the LPC (low pressure compressor) blades of afterburning turbojet engines installed on supersonic aircraft, as well as to combat oscillatory combustion in combustion chambers with shock actuation of free wheel clutches and self-induced oscillation in the helicopter transmission system. Besides, it is shown that the monitoring of GTE (gas turbine engine) dynamic load should be accompanied by improving the efficiency of the on-board engine diagnostic system. It is impossible to reduce the probability of target drop-out or faulty actuation of the existing standard means and facilities of such systems down to the required level without applying an individual approach to the determination of permissible levels of adjustable diagnostic parameters.
112-120
Reduction of angular velocities of AIST-2D spacecraft using a system of kinetic moment dumping
Abstract
The efficiency of a magnetic system of kinetic moment dumping in solving the problem of stabilizing Aist-2D spacecraft without using information on angular velocity is investigated. We defined the conditions under which the magnetic moment produced by electromagnets constitutes a useful control mechanical moment. Boundary conditions for preventing emergence of the parasitic moment are also defined. The paper presents the solution of the problem of forming the vector of the kinetic moment of the system “spacecraft + control moment gyro” according to the information on the vector of geomagnetic induction of the Earth. We defined the dependence of the time taken by the algorithm of angular speed reduction on the value and direction of the projections of the vector of spacecraft angular speeds at the time of algorithm actuation. The results obtained in the course of mathematical modeling and natural experiment on the spacecraft, the process of dumping angular speeds in providing the solution of the problem of attitude determination with the use of star sensors are compared.
121-127
MECHANICAL ENGINEERING
Prediction of product assembly errors using real part models
Abstract
A method has been developed for calculating the parameters for assembling parts based on the creation of real models of their surfaces. For the construction of actual models, a special method for analyzing the measured surfaces and a software application were developed. Measurement analysis includes smoothing outliers, ordering the grid of points on the surfaces, and additional mathematical referencing. The assembly process is modeled in the ANSYS. The results of calculations for the assembly of two parts joined at their flat surfaces by means of a bolted joint are given. The analysis of the obtained results was carried out. It showed the possibility of using the developed methodology for predicting the parameters of gas turbine engine assembly units. The line of further research related to the study of the relationship between assembly parameters and influencing factors has been determined.
128-137
Problems of modern aircraft maintenance
Abstract
The paper presents a comparison of the legal framework and the legal work carried out in the USSR, the European Union and in the post-Soviet period in Russia. The current state of the Russian civil aviation fleet, the systems of aircraft maintenance and the main problems of civil aviation development in Russia are considered. From this consideration it follows that the number of aircraft in Russia is increasing every year, alongside with the need for their maintenance. However, the construction of maintenance systems in accordance with outdated rules and regulations makes them unviable. On the basis of the analysis, a conclusion is made that it is necessary to search for optimal models of industrial structures of cost-effective aircraft maintenance organizations and the feasibility of using mathematical modeling methods for these purposes.
138-145
Development of a pulsation dampener for hydraulic systems of power plants
Abstract
The article considers the development of a capacitance-type pressure pulsation dampener. The pressure pulsation dampener is used to reduce the noise of hydraulic systems which are subject to increased requirements for vibro-acoustic characteristics. The developed pressure pulsation dampener is a flexible element with negligible hydraulic resistance. This element contains a gas cavity the pressure in which depends on its deformation. Overall dimensions of the dampener under investigation do not exceed the dimensions of a standard pipeline. This property, along with its low hydraulic resistance, is an advantage over its analogues. The article analyzes the known pressure pulsation dampeners and considers two design schemes of the proposed device. The experimental results of analyzing the dampener that showed its high efficiency (5 ... 40 dB) in a wide range of pressure oscillations in the fluid flow (20 ... 3000 Hz) are presented.
146-155
Experimental and theoretical research of continuous motion of rotor on anisotropic gapped elastic support
Abstract
Kinematic and dynamic features of flexible rotor rolling of an unlubricated uneven-stiffness gapped support are shown with the help of a theoretical model and full-scale tests. A combination of original approaches and well-known analytical and experimental methods is used. In particular, the motion equations are Lagrangian, derived in complex and complex-conjugate coordinates, and their solutions are sought in the exponential form, by excluding contact forces from consideration and by introducing a small parameter. Vibration measurements are not made on the rig frame using accelerometers, but at the source of vibration, i.e. by direct tracking of the rotor axle by a pair of eddy-current contactless displacement sensors installed in a XY configuration. Hence, the preciseness of the experimental data does not depend on the mechanical conductivity of the parts between the source rotor and the receiver sensors. As a result, the frequency, amplitude and existence domain of retrograde precession are reliably determined, and a conclusion is drawn that rolling under a certain combination of parameters is impossible in principle.
156-168