Chernyshov M. V.
The interaction of a simple or centered Prandtl–Meyer expansion or compression wave with a subsequent same-family oblique shock is studied theoretically. Two analytical models describing the interaction results (the resulting shock-wave structure) are proposed. One of the proposed models is based on the condition of equal static pressures and parallel flow directions behind the outgoing shocks and isentropic waves. The other model, using differential dynamic compatibility conditions at gas-dynamic discontinuities in the form proposed by V. N. Uskov and his students, assumes zero curvature of the shock emerging from the fan of straight characteristics of the overtaking wave. In this case, the shape of the interacting shock, the flow properties behind it, and the parameters of the reflected wave are determined either from finite relations that can be easily analyzed, or by solving an ordinary differential equation. Using these analytical models, criteria are established for: a change in the reflected wave type (rarefaction or compression, possibly repeated during a single interaction), a change in shock-surface curvature sign in the active interaction zone, degeneration of the shock into a weak disturbance, and the occurrence of subsonic flow regions immediately behind the interacting shock, as well as in the reflected wave. The effect of the specific heat ratio of the supersonic gas flow on the interaction results is studied. The analytical and numerical results can be useful in the gas-dynamic design of supersonic aerodynamic configurations (including supersonic air inlets), nozzle devices (including rocket engine nozzles effective over a wide range of flight altitudes), jet-technology equipment, and other devices using supersonic gas flows. An important feature of such problems is the possibility of applying the solutions to the development of approximate analytical models of supersonic gas flows with irregular reflection of oblique shocks, estimation of the Mach stem size, other elements of the emerging shock-wave structure, and the integral characteristics of the flow field as a whole.
Kurkova M. K., Mikhaylov D. S., Tishchenko D. Yu., Lapteva L. A.
Methods for determining the maximum lift coefficient and critical angle of attack of a subsonic airfoil are considered to refine an empirical-analytical method for calculating the aerodynamic characteristics of an isolated wing of a subsonic aircraft. Determining these quantities is an important design stage, as they limit the operational angle-of-attack range and determine aircraft maneuverability. The aerodynamic characteristics of subsonic airfoils of various thicknesses and cambers from the NACA series, as well as the NASA GA(W)-1 airfoil, were calculated at different Reynolds numbers using specialized programs implementing computational aerodynamics methods and CFD software packages for flow simulation. The use of these methods for determining aerodynamic characteristics will reduce the volume of costly experimental testing in aircraft design. The computational tools used included programs based on the panel method with an integral boundary-layer model accounting for viscous-inviscid interaction, and the CFD software package, which implements solutions to the Reynolds-averaged Navier–Stokes equations using differential turbulence models. During the numerical simulation of flow over a subsonic airfoil, a grid convergence study was performed to justify the choice of computational grids ensuring stable and accurate results. The results obtained were compared with experimental wind-tunnel data reported in the scientific and technical literature. The analysis included a comparison of lift-coefficient versus angle-of-attack curves, identification of flow-separation points, and assessment of the accuracy of critical-angle-of-attack predictions. It is concluded that the programs are applicable to calculating the aerodynamic characteristics of a subsonic airfoil for estimating its maximum lift coefficient and critical angle of attack. Based on the results of the study, recommendations are formulated for selecting software to determine these parameters, offering the optimal combination of accuracy and computational efficiency for preliminary assessment at early stages of aircraft design.
Yarygin V. N., Prikhodko V. G., Yarygin I. V.
Results of comprehensive experimental studies on modeling jets of low-thrust liquid-propellant rocket engines (LPREs) under vacuum conditions are presented; the studies were conducted at the Kutateladze Institute of Thermophysics, Siberian Branch of the Russian Academy of Sciences (IT SB RAS). Engines of this class, with thrust in the range from 5 to 4000 N, serve as a key element in attitude control and orbit correction systems of spacecraft and orbital stations. The research was carried out using the unique scientific facility – the Vacuum Gasdynamic Complex of IT SB RAS – which includes the large-scale vacuum gasdynamic chamber VIKING. This facility enables the study of rarefied gas jets under conditions simulating the real space environment. The methodological foundations of modeling are examined in detail; they are based on preserving the integral gasdynamic characteristics of jets, including the characteristic expansion angle and relative impulse. Special attention is given to three main types of jet impact on spacecraft structures: force, thermal, and physicochemical (contamination). Modeling criteria have been developed and validated, accounting for both gas and droplet phases of the flow. The results have been systematized for various thruster configurations used in Russian and international space programs. The fundamental mechanisms of plume backflow formation were identified, and effective gasdynamic protective devices were developed to minimize them. The research methodology included modern diagnostic techniques, among them electron beam diagnostics and laser stroboscopy. The results of the model studies were successfully compared with data from full-scale on-orbit experiments at the International Space Station, confirming the reliability of the applied methodology and the effectiveness of the proposed technical solutions. The developed protective devices reduced the contamination of the station’s external surfaces by products of incomplete propellant combustion by several orders of magnitude, increasing its operational reliability. The results contribute to the development of fundamental science in the field of rarefied gas dynamics and gas-liquid flows, as well as to addressing practical problems of modern astronautics.
Krainov A. Yu., Minkov L. L., Moiseeva K. M.
Mathematical modeling of gas-dynamic processes in a model solid rocket motor (SRM) chamber for the entire combustion period of an axisymmetric case-bonded solid propellant grain is presented. The mathematical formulation is described by the mass, momentum, and energy conservation equations for an ideal gas in an axisymmetric approximation. The numerical solution was obtained using the Godunov method on a computational mesh accounting for the grain shape and nozzle section. An algorithm to reduce the computation time for gas dynamics in the SRM chamber over the entire combustion period is presented. The algorithm assumes quasi-steady behavior of the grain burning rate over a time interval much shorter than the total grain burning time and much greater than the time step of the numerical scheme. To accelerate convergence to a steady state in the chamber after each grain geometry change during combustion, the mean pressure was specified using the steady-state pressure equation (Bory’s formula). The gas dynamics are calculated until steady flow is established in the SRM chamber. Gas-dynamic processes in the chamber of a model SRM were simulated for the entire combustion period of an axisymmetric case-bonded solid propellant grain of two configurations: with a gap between the case head end and the grain, and with an umbrella-shaped grain. The time dependencies of the mean pressure in the combustion chamber over the grain burning period were obtained.
Volkova T. V., Zherebtsov V. L., Levikhin A. A.
Domestically, microthrusters operating based on the catalytic decomposition of a high-energy chemical compound – hydrazine (N2H4) – are used for the attitude control systems of several spacecraft (SC). Both compact briquetted metal catalysts, such as K-53, and supported catalysts, such as K-201, are used in these engines. The K-53 metal catalyst is used in thermocatalytic thrusters. However, due to the low activity of this catalyst at temperatures below 100 °C, its preheating temperature before thruster startup must be above 350 °C. This requires high power consumption aboard the spacecraft. Highly active iridium-based catalysts offer advantages in terms of activity and bed loading capacity. The K-201 catalyst is used in Russia. Like all highly active catalysts, it utilizes iridium (29–33 %) as an active component, as it is the most active metal in the hydrazine decomposition reaction. The feasibility of creating a combined catalyst that integrates the best qualities of both types is investigated. Additive manufacturing, also known as 3D printing, aids in resolving the issue of the creation and manufacturing methods of a new metal catalyst. The advent of 3D printing has opened new possibilities for manufacturing reactor parts, organizing propellant combustion processes in power systems, and creating complex internal structures of chemical reactors. The most attractive aspect of additive manufacturing is that it enables the production of parts with any desired configuration. The layer-by-layer melting of powders involves a stage of porous structure formation, which can be investigated as a support for a porous catalyst. These possibilities are explored.
Pravidlo M. N., Biryukov P. A., Kiselev A. P.
An algorithm for generating the trajectory of an aerial target based on flight data recorder information is described. The algorithm allows generating reliable trajectory data of aerial target motion if the flight data of the aerial target motion is incomplete. One of the problems associated with simulating the trajectories of objects in 3D space during computer simulation is considered using the example of modeling guidance algorithms for aviation weapons in various tactical conditions. Simulating the motion of an aerial target in the atmosphere is one of the significant problems in using computer models. To evaluate the functioning of aerial target guidance systems, it is necessary to simulate the motion of a real target as realistically as possible, including instantaneous changes in trajectory coordinates and all random variables accompanying motion in the real atmosphere, such as trajectory instabilities, fluctuations in angular orientation parameters, etc. The difficulty of solving this problem lies in the lack of sufficient information about the statistical motion parameters, flight characteristics, and tactical maneuvers of real targets. Modern combat aircraft are equipped with flight data recording systems that allow recording the parameters determining the functioning of the targeting and navigation complex, including the motion parameters of observed aerial targets. Based on this, an approach to simulating the motion of a real target in a computer model is proposed, which consists in generating the trajectory of an aerial target based on data from a flight data recording system capable of registering the motion parameters of the observed target. An analysis of records from modern recording systems indicates the presence of severe noise and distortion in the recorded data. To eliminate them, well-known data recovery methods described in the literature are used. However, traditional data recovery methods prove inapplicable in the presence of anomalous jumps and gaps in the data. The proposed algorithm for recovering the acquired data uses well-known filtering methods and an original algorithm for eliminating anomalous distortions in the recorded data, which together makes it possible to obtain a dataset describing the trajectory and motion parameters of the target, serving as the basis for reproducing motion in a computer model of a maneuvering target. Since the proposed data recovery method does not impose high requirements on processing system performance, its use makes it possible to automate the high-quality processing of large volumes of data for the subsequent analysis of aviation weapons employment conditions in real tactical situations.
Ponomarenko A. V., Ustyuzhantsev A. M., Starkov V. D., Dryagin V. A.
A methodology for conducting aerial radiation reconnaissance using a rotary-wing unmanned aerial vehicle (UAV) is presented. Aerial radiation reconnaissance is an effective monitoring tool enabling rapid assessment of contamination extent, determination of the volumetric concentration of radioactive materials in the atmosphere, and tracking of the spatial distribution of radionuclides. The developed methodology automates parameterizing the spatiotemporal distribution of radioactive materials in the atmosphere, minimizing time requirements while maintaining a specified confidence level in determining contamination boundaries and total released activity. Identifying the boundaries of a dispersing radionuclide plume via dynamic route optimization at waypoints involves the integrated use of a priori, a posteriori, and predictive data when solving the assimilative-adaptive problem of refining the route at UAV turning points (decision nodes). Determining atmospheric radioactive contamination parameters involves sequentially intersecting the released plume, measuring radiation intensity along the track, and constructing an atmospheric radioactive contamination profile with dynamic assimilative adaptation. Utilizing a pre-trained model enables rapid generation of a predicted concentration field of radioactive materials at each decision node, including uncertainty quantification of the system and reconnaissance route optimization, while preserving the specified confidence level in determining contamination parameters. Integrating a pre-trained predictive model with a bootstrap ensemble significantly improves the quality of the a priori assessment of the state of the contamination area and reduces computational costs when solving the problem under time constraints and limited measurement data. The bootstrap ensemble ensures robust reconstruction of a hypothetical contamination area with insufficient actual measurement data. The proposed approach provides a statistically sound determination of atmospheric radioactive contamination parameters.
Molchanov D. A., Tretyakov A. V.
A system is being developed to counter UAVs and drones by monitoring the airspace and identifying aerial objects and their flight paths. The main component of the proposed system is a UAV identification unit that classifies photographic images using an embedded computer vision neural network. The problem of designing this neural network for ground-based observation of aerial objects in the optical band is considered in order to determine the main geometric parameters of these objects for their subsequent classification and the formation of corresponding information signals and features at the network output. These features are expected to be used as input data for analyzing behavioral algorithms and generating the trajectory of the observed objects. A neural network architecture optimized for the problem at hand and consisting of convolutional and fully connected layers has been designed. To obtain a more flexible logical inference, the program implements elements of fuzzy logic. Various source image augmentation methods based on Gaussian blur filters, as well as rotation and reflection algorithms, are implemented using a stochastic algorithm. Special attention is paid to neural network training algorithms, solving optimization issues, and adapting the training process to the problem being solved. A method based on the Adam optimizer is proposed for adaptively adjusting the gradient descent step size at each calculation stage within the considered training batch, taking into account the change history of the activation function and cost function gradients. A computer program for neural network deployment and training has been developed. Multi-stage training and testing of the program on images of aerial objects from seven different classes were successfully conducted. Special attention was paid to the reproducibility of the training results. Along with the final classification accuracy, the stability of the probability distribution across classes was monitored, as well as the repeatability of the results during repeated training runs on identical datasets.
Bocharov P. V., Libman M. S.
A comparative experimental study of two algorithms for the automatic classification of surface targets using passive radar data is presented: two-stage probabilistic classification and multiple-hypothesis probabilistic classification. The study is motivated by the need to improve the reliability of passive target recognition in airborne, coastal, and distributed passive radar surveillance systems for maritime situational awareness, where decisions must be made under incomplete, ambiguous, and partially contradictory information. The objective is to compare these algorithms in terms of classification accuracy and relative computational complexity in typical radio-frequency scenarios of interest for passive surveillance systems. For a valid comparison, both algorithms were tested within a unified computational framework on a common synthetic database modeling platform composition, onboard emitter suites, and their operating ranges. All features were mapped to a normalized feature space, which made it possible to eliminate the effect of specific signal parameterization and to focus the analysis on the algorithmic differences between the methods. The experiments were conducted under a full-factorial variation of key scenario parameters, including emitter operating probability, observed emission coverage, the average number of emitters per platform, the average number of platforms per emitter, and operating range width. It is shown that multiple-hypothesis probabilistic classification makes more complete use of available information and is safe more robust to uncertainty, which in a number of scenarios yields an absolute accuracy gain of up to 57 percentage points compared with the two-stage algorithm. At the same time, this gain is achieved at the cost of a substantial increase in computational burden caused by the growth in hypothesis-tree depth. The two-stage algorithm, in contrast, while being less accurate in ambiguous situations, retains substantially higher computational efficiency. The practical significance of the results lies in supporting the choice of classification architecture for passive radar and related surveillance systems used for maritime situational awareness, as well as in confirming the feasibility of adaptive or hybrid use of the compared algorithms depending on the observation mode and available computational resources.
Andryushkin A. Yu., Pivovarov A. A., Yablokov D. V.
The paint coating protects the metal structure of an aircraft from corrosion and consists of several functional layers (primer, filler, lacquer, enamel, paint, and others). The protective properties and durability of the paint coating are determined by its thickness, which is the primary quality indicator. Automated pneumatic spraying is used to apply coating materials to aircraft surfaces. Ensuring uniform paint coating thickness in automated pneumatic spraying is an important practical problem. The uniformity of paint coating thickness is determined by a combination of process parameter values that define the operating conditions of automated equipment over a prescribed time. A method is proposed for calculating the interrelated process parameters of automated pneumatic spraying to achieve a uniform-thickness paint coating. The effect of the spray regime on the thickness and uniformity of the paint coating is shown. Expressions are presented for estimating the air flow velocity along the spray cone axis, the air flow rate, the coating material flow rate, and the size of atomized droplets. The formation of a coating material layer on the surface being coated is considered; the layer consists of partially overlapping passes, each having a normal thickness distribution in cross-section. Expressions are given for estimating the waviness of the coating material layer surface. Expressions are presented for determining the optimal sprayer feed rate and the sprayer traverse speed along the applied pass that ensure minimal waviness of the coating material layer surface. An overlap coefficient for adjacent coating material passes is introduced, relating the optimal sprayer feed rate to the standard deviation that characterizes the spray spot diameter of the spray cone. An example is presented showing the effect of spray distance on the spray spot diameter, the optimal feed rate, and the sprayer traverse speed in automated pneumatic spraying of a uniform-thickness paint coating. The coating material layer thicknesses at the peaks and valleys of its surface are determined. The uniformity of paint coating thickness in automated pneumatic spraying is ensured by a combination of process parameter values; their interdependence is established.
Vilkina M. V.
The technological features of the mechanical machining of complex aerospace components, which are characterized by intricate three-dimensional geometry, thin-walled elements, deep cavities, and stringent requirements for the quality of formed surfaces, are examined in this study. Such products include compressor impellers, integrally bladed disks (blisks), and structural housing components of aircraft and space systems. It is demonstrated that the increasing geometric complexity of modern aerospace parts limits the efficiency of conventional milling methods based on 2.5-axis and positional machining strategies, which is manifested in increased tool overhang, reduced stiffness of the technological system, higher vibration levels, and deterioration of the machined surface quality. The aim of this work is to provide an analysis of modern CAM approaches to toolpath generation for machining parts with complex spatial forms and to substantiate the feasibility of implementing multi-axis machining strategies. Within the framework of the research, the design features of aerospace components are considered and the technological factors affecting cutting process stability, shaping accuracy, and machining productivity are identified. Particular attention is paid to current methods of toolpath calculation in CAM systems, including residual stock consideration, the application of adaptive and multi-pass strategies, and the use of updated stock models based on three-dimensional representations. The capabilities of five-axis machining are separately analyzed, including the use of “3+2” positional schemes and simultaneous five-axis strategies that allow for the optimization of tool orientation relative to the machined surface, a reduction in tool overhang, and an increase in the stability of the cutting process. The efficiency of using circle-segment end mills (barrel tools) is demonstrated, as they allow for an increase in the effective contact radius, a reduction in the number of machining passes, and an improvement in surface roughness parameters during finishing operations. The results obtained can be utilized in the development and optimization of technological processes for machining complex aerospace components on multi-axis machining centers using CAM systems. The presented approaches to the selection of machining strategies, consideration of residual stock, and the use of tools with complex geometry make it possible to increase machining productivity, ensure the stability of the cutting process, and improve the quality parameters of the formed surfaces. The proposed solutions can be applied in the technological preparation of production for aircraft and space hardware, as well as in improving the methods for designing NC programs for the multi-axis milling of complex-profile products.
Filin D. S., Tihonova E. S., Kunitsyn K. A., Khorevsky K. K.
Hollow axisymmetric parts made from round bar stock are widely represented among the products of general and special mechanical engineering. In most cases, simple bulk forming schemes are used in their manufacture, in particular reverse extrusion. The main disadvantage of a simple scheme is the extremely high working pressure on the punch, which severely limits the process capabilities of the operation. At the same time, the mean strain of the workpiece material is relatively small, which does not allow the workpiece structure to be adequately worked. One approach to solving this problem may be a transition to combined extrusion schemes, such as longitudinal-transverse extrusion. When introducing new metal forming schemes, it is important not only to maintain the integrity of the workpieces, but also to determine the maximum forming force in advance and maintain the strength of the tooling. Data are presented on the influence of characteristic geometric parameters of the combined longitudinal-transverse extrusion scheme on the magnitude of the forming force and the working pressure on the punch and counterpunch. A comparison of the results obtained using the previously proposed equation and the power balance method (PBM) revealed large errors in the existing recommendations for selecting tool and workpiece dimensions. The need to calculate the forming force for the counterpunch is also noted. Based on computer simulation results, correction factors are proposed for calculating the forming force on the punch and counterpunch using the derived equation and the power balance method, which allow results to be obtained with acceptable accuracy within the previously formulated recommendations for selecting tool and workpiece geometry.
Artemenko D. E., Oleinikov A. Yu.
A problem of selecting rational submodeling zones in finite element analysis of sandwich structures with a honeycomb core is considered. The use of numerical methods in modern design inevitably faces a trade-off between analysis accuracy and computational cost. Simple mesh refinement across the entire structure is inefficient; therefore, the submodeling technique is a promising approach, allowing detailed examination of local zones only, with boundary conditions taken from the global analysis. A sandwich panel with aluminum face sheets and a honeycomb core, bolted and subjected to a uniformly distributed load, is taken as the object of study. The aim of the work is to select submodeling zones and determine their optimal dimensions, accounting for the loading pattern, boundary conditions, and underlying physics. In the theoretical part, two key zones are identified: the panel center (the region of maximum displacement) and the bolted joint zones (regions of elevated local stresses). A method for determining the dimensions of these zones is proposed. For the center zone, the criterion is suppression of edge effects (inclusion of at least 3–5 periodic unit cells). For the attachment zones, the in-plane dimension is determined by the half-wavelength of the deformation (from the bolt to the midspan), and the through-thickness dimension is determined by the decay length of local stresses according to the Saint-Venant principle (1,5–2,5 of the characteristic body dimension). Practical calculations were performed in two stages: global analysis with an orthotropic equivalent core and subsequent submodel analysis with explicitly modeled discrete cell geometry. Comparison of the results confirmed the effectiveness of the approach. The discrepancy in displacements between the global model and the submodels did not exceed 10%, indicating correct transfer of boundary conditions. At the same time, the maximum von Mises stresses in the attachment zone of the long side and at the panel center, obtained from the submodels, exceeded the global analysis results by 138 % and 695 %, respectively. This demonstrates that accounting for the actual core geometry is essential for strength assessment, as it reveals stress redistribution from the face sheets to the honeycomb core members. The developed recommendations for selecting submodeling zone dimensions allow efficient analysis models to be constructed, ensuring high fidelity of local strength analysis at acceptable computational cost, which is of particular importance for aerospace applications.