A technique has been developed for thermal-vacuum strength tests of heat-shielding structural elements for temperatures up to 1400 K. Heating and vacuum equipment for these tests has been developed and the accuracy of measuring the temperature on the surface of the heat-shielding coating has been studied. Recommendations are given on the use of K-type thermocouples for these tests.
The possibility of occurrence of near-resonant rotation modes during uncontrolled descent of spent first-stage boosters of launch vehicles in the atmosphere due to small mass-inertial asymmetry is considered. The stability of near-resonant rotation modes is analyzed using a quasistatic approach.
Results of experimental investigation of steady aerodynamic characteristics and heat flux distribution over the surface of the DM-18 lander of the "ExoMars" project at hypersonic flow regimes are presented.
Results of comprehensive numerical and experimental investigations of isolated bypass nozzles with separate exhaustion of the flows in the first (gas generator) and second (fan) circuits of the turbofan engine with different bypass ratios are reported. Rational geometric parameters of the nozzles, which ensure the minimum thrust losses, are determined. The effects of the Mach number of the external flow, pressure ratio in the circuits, and presence of a pylon are investigated. The characteristics of bypass engine nozzles with separate exhaustion of the flows and with their mixing are compared with due allowance for friction, pressure drag, and internal thrust losses.
This paper describes experimental studies of nozzles in a distributed power plant with separate exhaust configurations of gases from the first and second circuits of a bypass turbojet engine. The nozzles are located in the trailing edge of the wing of a quiet aircraft and have a sonic exit section of a trapezoidal shape. Only the aerogasdynamic characteristics of the nozzles are considered. It is demonstrated that the thrust loss of trapezoidal nozzles is close to that of the well-known round and plane nozzles. The influence of the airframe elements (wing and fuselage) on the effective thrust loss is examined, and the conditions for minimum negative interference of the jet and the external flow with closely spaced airframe elements are determined. A comparative analysis of the integrated layout of trapezoidal nozzles located in the wing with the layout of typical round nozzles of a bypass turbojet engine above or under the wing allows us to conclude that it is possible to provide approximately the same level of effective thrust loss.
The method of calculating panel flutter of a flat plate is proposed in two-dimensional formulation. It is assumed that the upper surface of the plate is passed by a subsonic flow and the lower surface contacts with still air. Unsteady velocity potential is used to calculate aerodynamic pressure values. An integral-differential equation of plate oscillations in air flow is derived. Its discretization is fulfilled using finite element method. Several examples of numerical calculations of panel flutter are considered.
One of the key challenges in developing next-generation civil supersonic aircraft is to ensure a safe noise level in airport areas in accordance with modern requirements for subsonic aircraft. The use of a mixer-ejector flat nozzle with a noise suppression system is proposed as a possible solution to reduce the jet noise of a low-bypass ratio engine. In this nozzle, there is an active effect on the jet to intensify its mixing with the approaching flow. The investigation results of the flow characteristics in such a nozzle are presented. Solutions are proposed to eliminate the disadvantages of the nozzle geometry detected during numerical flow simulation using the ANSYS CFX software program. The effect of the shape and deflection angles of the nozzle flaps on their characteristics and the velocity profile structure in the outlet cross section is determined.
Along with achievements in relation to the high aerodynamic characteristics during the supersonic cruising mode one of the main problems of creating new generation supersonic transport aircraft is providing acceptable sonic boom levels. This requires the development of reliable methods for obtaining the near field under the plane by taking into account the influence of the boundary layer in order to calculate the overpressure on the ground and evaluate the loudness of the sonic boom. In this work, a methodology used at TsAGI to calculate the sonic boom overpressure was adapted in the ANSYS CFX software package to solve the Reynolds-averaged Navier-Stokes equations. A macro to calculate the overpressure on the ground for the distribution of disturbances in the near field under the aircraft and a code to evaluate the sonic boom loudness in various metrics were developed. Computational mesh verification of the results was carried out and the methodology was validated using American Institute of Aeronautics and Astronautics Sonic Boom Prediction Workshop materials. Four variants of the equivalent body of revolution of the minimum sonic boom using nose part sharpening variations were investigated. The obtained overpressure curves were compared with the theoretical data and calculation results using Euler equations. The effect of sharpening the nose part on the aerodynamic drag and sound boom characteristics is shown.
A main problem in creating next-generation civil supersonic passenger aircraft is providing a sonic boom (SB) level that is acceptable for flights over inhabited areas. To evaluate the SB impact on humans, the loudness in different metrics is examined. Due to an insufficient amount of experimental data on low-intensity SB flights, computational methods are widely used in order to evaluate SB overpressure and loudness. In this work, a method is presented for calculating SB loudness in the A, B, C, and perceived level metrics, validated by test overpressure signatures from the European-Russian regulation and norm for low sonic boom levels (RUMBLE) project. A technique for pressure rise time taking into account the overpressure signature is proposed. The influence of modifications made to the overpressure signature shape on the SB loudness level is shown.
The processes of disturbance propagation in laminar boundary layers at high external flow velocities are studied. For the first time, solutions to the Faulkner−Skan equation for compressible flows are obtained, in addition to those found by Stewartson. The dependence of the propagation velocity of disturbances upstream on the pressure gradient parameter is determined for various values of the temperature factor.
The methodology and the testing results on investigation of the effect of the stabilizers located in the aft part of aircraft as a function of the parameters of the aircraft motion and their aerodynamic characteristics are presented. The paper describes the experiments in an aeroballistic dash as well as the methodology of optical registration of flight parameters and shadow spectra of the flow around the model of a blunted cylinder with stabilizers and the results obtained.
A standard KME-4, -6 heating block with four and six heat radiant emitters made of Uglekon-T composite material has been developed, which provides heating of heat-shielding elements at a high growth rate up to a temperature of 2100 K. A description and general view of this block, the experimental characteristics of one of the emitters, and the results of block tests are presented. The current-voltage characteristics of the block up to U = 22.9 V are given; the attained temperature in the stationary mode was 2056 K. Further research was limited by the heat resistance of the shield, which was made of Ultra Board material. A temperature of 2670 K was reached on a single heat insulating radiant emitter with a 2 mm radiating plate thickness, while the emitter remained under normal operating conditions.
The results obtained using standard and improved (modified) calculation methods for load distribution on fasteners and joints strength are analyzed on the examples of four types of multiple-row metal-composite joints with cover plates of various thickness and various diameters of fasteners. A modified technique based on the Nuismer criterion is used to determine the load-bearing capacity. It was determined that for all joints the difference between the calculation results and the experiment is 14 - 26% using this criterion. It’s desirable to use a modified scheme of the Nuismer criterion to improve a calculation convergence of the load-bearing capacity with experimental data. In this case, the maximum difference between the calculation results and the experimental data for the considered joints was 12.9%.
Kirill Ivanovich Sypalo, General Director of TsAGI, corresponding member of the Russian Academy of Sciences, celebrated his 50th birthday on December 18, 2020. He began his career in aviation science with admission to the Moscow Aviation Institute, majoring in Flight Dynamics and Motion Control of Rockets and Spacecraft. After graduating from the Moscow Aviation Institute in 1993, Kirill Ivanovich remained loyal to his alma mater, holding positions ranging from assistant to professor and lecturing courses for future generations of scientists, designers, and engineers. He acted as a leader and responsible executor for research and development projects funded by the RFBR, ESA, and AIAA, as well as within the framework of Russian and international contracts. Kirill Ivanovich came to the Central Aerohydrodynamic Institute in October 2012, heading the Complex for Perspective Development. Under his leadership, a number of important documents were issued that determined the key goals and tools for the strategic development of
The study of the model of a developed turbulent flow of incompressible fluid in a boundary layer on a plate is based on the analysis of the Navier-Stokes equations that describe the behavior of the amplitudes of the Tollmien-Schlichting wave in single-mode approximation. A weakly nonlinear version of the wave model of a developed turbulent boundary layer is considered. The dispersion characteristics of the waves of the least decaying mode are determined, and the conditions of multiple three-wave resonances of this mode of the Tollmien-Schlichting waves are analyzed. The equations for a coherent part of the pulsations are obtained based on the method of multiple scales. The discrete representation of a coherent structure shows that the sum of the squares of the absolute values of the wave amplitudes in the state of multiple three-wave resonances, multiplied by the real weight factors, is an invariant of the original dynamical system. This invariant allows applying the Birkhoff-Khinchin theorem on the existence of time-averaged squares of absolute values of the amplitudes of waves, which confirms the existence of the structures under consideration.
A method is proposed to determine the thermodynamic properties of combustion products of a mixture of several fuels using approximating polynomials. Formulas are given to calculate the thermodynamic properties of the combustion products of a mixture of fuels based on the properties of each individual fuel. The accuracy of determining the heat capacity and enthalpy change is assessed.
A significant number of air accidents occur during flight under high mountain conditions. This is due, in particular, to the underestimation of the danger of coherent vortex structures arising when the wind boundary layer flows around a mountainous relief. In this study, within the framework of the boundary value problem for the Reynolds-averaged Navier-Stokes equations, the flow around a landscape fragment is simulated. To set the boundary conditions correctly, model problems are solved, the correctness of which is proven. To verify the calculations, the maximum pressure principle and criteria proposed on its basis have been used.
The flow in a laminar boundary layer on a flat wing with a point of inflection on the leading edge in the regime of strong viscous-inviscid interaction is considered. The flow functions are presented in the form of a power series in the angular coordinate in the vicinity of the leading edge and the plane of symmetry. The method of matched asymptotic expansions is applied to determine the induced pressure on the wing surface. It is shown that the solutions obtained in the study are in good agreement with the solution to the full equations of the boundary layer on a thin wing.
A methodology is presented for conducting a model wind tunnel test aimed at investigating a helicopter main rotor equipped with elastically scaled blades of a given full-scale prototype. Various model test conditions are considered, including aerodynamic and aeroacoustic studies. Key principles of developing the methodology are described based on analysis of the aerodynamic, strength, and frequency characteristics of a full-scale main rotor.
Numerical simulations of the propagation of three-dimensional disturbances induced by a row of underexpanded microjets injected across a supersonic flow in a flat-plate boundary layer at Mach 5.4 were performed. The Navier-Stokes equations for 3D flows of a compressible perfect gas were integrated using the in-house code that implements an implicit shock-capturing scheme. The numerical solution shows that injection of supersonic microjets normal to the wall effectively disturbs the boundary layer and causes an early laminar-turbulent transition.
