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AffiliationFederal Autonomous Enterprise the Central Aerohydrodynamic Institute named after Professor N.E. Zhukovsky,

Research area 09 - ENGINEERING SCIENCES, 09-104 - Motion of objects and apparatuses within different media

Annotation
A large number of works on improving the aerodynamic characteristics of civil aircraft in cruising and takeoff-landing regimes are caried out in Russia and abroad. Aviation regulations allow the use of regimes for this, which have a certain amount of lift force in comparison with the maximal lift force regimes or in comparison with the buffet onset regimes. However the flow around aircraft in maximal lift force regime and in buffet onset regime is detached and fundamentally unsteady. Aerodymanic characteristics can change significantly over time in this case, which can lead to large unsteady loads on the aircraft elements and to structural damage and other unfavorable effects. Modelling this unsteady process is a difficult unresolved problem at present time. Among other things, difficulties are associated with the fact that the flow around the aircraft is turbulent and occures at high Reynolds numbers. The existing semi-empirical turbulence models for the Reynolds equations do not describe this process weel enough. Therefore, for a more accurate description of the turbulent separated flow around the aircraft, it is necessary to use more complex models, for example large eddy simulation method or hybrid approaches (the so-called vortex-resolving methods), the use of which for complex geometries are limited by large computational costs. However the growth of computational performance allows us to hope to obtain new results in this project using complex turbulence models and compare them with the numerical results of Reynolds equations. It should be noted that asymetric flow separation can be realized on a symmetric aircraft layout at large angles of attack, which leads to an additional roll moment and other difficulties that must be taken into account for the safe operation of the aircraft. This phenomenon is well known for maneuverable aircraft with a sharp nose section of the fuselage and has hardly been studied for long-haul aircraft. Therefore, it will be considered in this project. From the point of view of flight safety, it is necessary to know the behavior of the aircraft in case of unsteady changes in the main-stream flow parameters. In particular, with fluctuations in the angle of attack of the aircraft, a hysteresis of the aerodynamic characteristics can be observed. Numerical simulations of this phenomenon for the long-haul aircraft layout is still complex unexplored problem, which will also be considered in this project. The main goal of the project is to study and learn how to simulate new unsteady effects in an extended range of flow regimes around a civil aircraft layout.

Expected results
The project will make it possible to study new unsteady effects associated with unsteadyness of flow around civil aircraft assembly elements. At present time, numerical simulations and experimantal research are mainly carried out in a steady consideration. Only a very small part of works is devoted to the study of unsteady characteristics. The project will consider numerical simulations of separated unsteady flow regimes around the aircraft layout at low main-stream velocities using both vortex-resolving approach and more standard approch to solving the Reynolds equations. The results of vortex-resolvin g approaches will be compared with the results of numerical simulations with the Reynolds equations with different semi-empirical turbulence models. At the same time, the limitations of the models will be assessed for this type of problems and the capabilities of using such methods for modern aircraft will also be studied. Unsteady flow characteristics at large angles of attack and unsteady motion will be obtained and analyzed. The significance is determined by the fact that the problems studied in the project are key in the development of the next generatoin civil aircraft. The study of unsteady characteristics is necessary to improve the flight safety, as well as to determine the parameters of aircrsft control system. The planned results of the project will correspond to the world level, they will be published in leading peer-reviewed world journals such as Aerospace Science and Technolofy (Q1), Computers and Fluids (Q1), Fluid Dynamics (Q2), Thermophysics and Aeromechanics (Q2), Technical Physics Letters (Q2) and to present at major international conferences, such as ICAS (conference proceedings are included in Scopus), CEAS, EUCASS, ICMAR (conference proceedings are included in Scopus).

Annotation of the results obtained in 2023
Within the framework of the DDES eddy-resolving approach, calculations of the flow around a model of a straight wing with an NACA 0018 airfoil at near-critical and supercritical angles of attack were continued. The results were compared with the results of solving the Reynolds equations in three-dimensional and two-dimensional (for the wing airfoil) formulation. In these calculations, the DDES results are close to the experimental data with a very good accuracy of 1-3%. Calculations within the framework of the DDES eddy-resolving approach showed results that are in the best agreement with experiment. The results within the three-dimensional Reynolds equations agree with experiment within 10%. A two-dimensional formulation of the problem for a wing airfoil without correcting the results gives overestimated values of the normal force coefficient. A comparison of the results of the dynamic hysteresis loop of this model of a straight wing during oscillations along the angle of attack with the harmonic law showed that there are the same features as for the stationary case. The results of the two-dimensional problem (without correction) have a stronger slope of the linear part of the normal force coefficient with a noticeable difference in the value of the maximum normal force coefficient from the experiment. The calculation results for a three-dimensional model of a straight wing are significantly closer to the experimental dynamic hysteresis loop. Computational studies of unsteady flow around a typical model of a civil aircraft at a high angle of attack, corresponding to the spin mode, have been carried out. The calculation was carried out using the eddy-resolving DDES approach for both halves of the configuration without the assumption of the presence of a symmetry plane. The experimental results are compared with the results of RANS and DDES. The DDES results turned out to be very close to the RANS results and differ by 5% from the experiment in terms of the normal force. This agreement of results for such a complex geometry and complex flow can be considered good. Numerical modeling of the flow around an aircraft layout in a three-dimensional unsteady formulation was carried out for the Reynolds equations, where the layout oscillates along the angle of attack. Different oscillation frequencies and oscillation amplitudes were considered. It is shown that the calculated dynamic hysteresis loop is in fairly good agreement with the available experimental results. As the oscillation frequency increases, the dynamic effects become more pronounced, especially in cases with developed flow separation. Increasing the frequency leads to greater hysteresis. The separation is mainly formed in the area where the pylon and engine nacelle are located and the root part of the wing at the junction of the wing and the fuselage. Based on two-dimensional calculations of the wing airfoil, an approximate phenomenological mathematical model of aerodynamics (phenomenological model of normal force and pitching moment) has been developed, suitable for use in problems, for example, dynamics. It is shown that with this approach it is possible to more accurately model longitudinal aerodynamic characteristics compared to the traditional use of a linear model. Calculations in a two-dimensional formulation for the wing profile using a laminar-turbulent transition model made it possible to visualize a short separation bubble in the vicinity of the middle of the airfoil and establish the coincidence of the location of the separation bubble and the plateau pressure behaviour, as well as the coincidence of the location of the closing part of the cavity and the zone with the highest noise level. Calculations in this formulation made it possible to explain features of experimental data that were previously incomprehensible.

Publications

1. Abramova K.A., Alieva D.A., Soudakov V.G., Khrabrov A.N. Моделирование нестационарных аэродинамических характеристик профиля NACA 0015 по данным численного расчета обтекания Fluid Dynamics, № 1 (year - 2024)

2. Alieva D.A., Grishin I.I., Kolinko K.A., Khrabrov A.N. Аэродинамические характеристики модели CRM при вынужденных колебаниях большой амплитуды и их математическое моделирование Ученые записки ЦАГИ, Т. 54. № 5. С. 30-43. (year - 2023)

3. Alieva D.A., Grishin I.I., Kolinko K.A., Khrabrov A.N. Экспериментальные исследования динамических производных модели CRM при малых дозвуковых скоростях Ученые записки ЦАГИ, Т. 54. № 2. С.67-82. (year - 2023)

4. Kirillov O.E., Petronevich V.V., Soudakov G.G. Особенности обтекания покоящегося и колеблющегося по углу тангажа профиля при низких числах Рейнольдса Ученые записки ЦАГИ, № 1 (year - 2024)

5. Voyevodin A.V., Petrov A.S., Soudakov G.G. Аналитическая модель импульсного режима работы эжектора Ученые записки ЦАГИ, Т. 54. №2. С. 3-15. (year - 2023)

Annotation of the results obtained in 2021
Elements of aircraft (airfoil, wing, delta-wing, cruise configuration of a civil aircraft) are considered under the current project on regimes with high angles of attack and high Reynolds numbers, where unsteady detached turbulent flow is realized. The analysis of the scientific approaches for modeling the turbulence for cases of detached flows around airfoils, wings and wing-body configurations of civil aircraft was carried out. Special test cases were chosen for validation of the results of numerical simulations and estimation of the applicability of the turbulence models: • flow around the airfoil (straight wing model) at high angles of attack; • flow around the delta-wing at high angles of attack; • flow around the oscillating airfoil (straight wing model); • flow around the oscillating delta-wing; • flow around the oscillating cruise configuration of civil aircraft. The problem setup for different turbulence modeling approaches was defined. At first stage the two-dimensional (2D) and three-dimensional (3D) steady and unsteady (URANS - unsteady RANS) Reynolds averaged Navier-Stokes equations are utilized. One of the hybrid LES approaches will be considered during second and third stages of the project. The flows with subsonic Mach numbers are considered. The range of angles of attack for each geometry covers regimes with maximal value of lift coefficient (the stall angle of attack) and lies from 0 to 90 degrees. The structured numerical meshes were generated for the numerical simulations. Additional meshes with approximately 2 times increased nodes along each direction were generated for verification of the numerical simulation. In addition to that the calculations were performed with 5 times reduced value of the time step. The unsteady characteristics may vary within 5-10% range (the average values vary weakly). The numerical investigation of the flow around the airfoil at high angles of attack was carried out using two-dimensional and three-dimensional RANS and URANS approaches. The subsonic regime with Mach number M=0.4 and Reynolds number Re=2.5M was investigated for the VERTOL23010 airfoil. The averaged characteristics obtained during three-dimensional simulations were found to be approximate equal to the results of simulations for two-dimensional airfoil. However, the separation curve becomes three-dimensional with periodical structures in span-wise direction in 3D simulations. The analysis shows that RANS and URANS approaches allow one to estimate aerodynamic characteristics of the airfoil at stall and post-stall angles of attack with enough accuracy. In particular, the comparison with existing experimental data shows the agreement of the maximal normal force coefficient value within the range of 2-7%. The preliminary simulations were carried out for the same airfoil oscillating in angle of attack with the same free-stream flow parameters. The airfoil oscillations were harmonic. The simulation using URANS approach was shown to cover main trends of dynamic hysteresis of aerodynamic characteristics. The agreement between numerical simulation and the experimental data for small values of the Strouhal number (less than 0.25) is suitable – within the range of 10-13%. With an increase in the Strouhal number the agreement deteriorates. The new empirical method for mathematical modeling of airfoil lift coefficient in arbitrary unsteady motion at regimes with hysteresis was proposed on the basis of of the existing experimental data. The proposed nonlinear mathematical model based upon the solution of the empirical ordinary differential equation provides qualitative and quantitative correct description of the observed hysteresis of the aerodynamic characteristics at quasi-steady variations of the angle of attack. Numerical simulations for the delta-wing at high angles of attack were carried out using thee-dimensional RANS and URANS approaches. The comparison of the aerodynamic characteristics obtained in simulation with experimental data shows that the calculations might covers leading trends of the aerodynamics. However, the numerical values of the normal force coefficients tends to be higher than the experimental one (up to 20% higher on angles of attack greater than 50 degrees). The preliminary simulations were performed for delta-wing with sweep angle of 65 degrees harmonically oscillating in angle of attack with free-stream flow velocity of 40 m/s. The simulations were carried out for Strouhal numbers 0.034, 0.069, 0.104. The calculation was shown to reflect the dynamic hysteresis loop on relatively small oscillation frequencies. Average deviation of the calculated aerodynamic characteristics from the experimental ones was approximately 10%. The preliminary numerical simulations were carried out for cruise configuration of civil aircraft at high angles of attack using three-dimensional RANS and URANS approach. It can be noted, that this approach provides suitable results for average integral aerodynamic characteristics. The calculated normal force coefficient differs from the experimental one less than 10% even at angles of attack from the range 40-80 degrees. The simultaneous flow field was found to be asymmetrical at angles of attack in the range 15-40 degrees (the flows around the left and the right sides of the configuration are different). However the average values of side force and momentum are approximately zero. The asymmetric regimes with noticeable non zero side characteristics were found to occur for angles of attack higher than 50 degrees.

Publications

1. Alieva D.A., Kolinko K.A., Khrabrov A.N. Гистерезис аэродинамических характеристик профиля NACA 0018 при малых дозвуковых скоростях Thermophysics and Aeromechanics, - (year - 2022)

2. Gaifullin A.M.,Khayrullin K.G.,Sviridenko Yu.N. Designing an Aerofoil with a Fowler Flap Using Artificial Neural Networks Lobachevskii Journal of Mathematics, No.9, Vol.42, pp.2118-2128 (year - 2021) https://doi.org/10.1134/S1995080221090092

Annotation of the results obtained in 2022
The project considers the flow past the elements of the aircraft (wing profile, wing, delta wing, layout of the main aircraft) at high angles of attack, where a detached unsteady turbulent flow occurs, as well as the pitching motion of these elements. Detailed numerical simulations have been carried out in the range of angles of attack from 0 to 90°, as well as the analysis of the flow fields and physical features of the flow past a typical layout of a civil aircraft at subsonic velocities of the oncoming flow for a three-dimensional Reynolds equations. The SST turbulence model is used. The assymetry of the flow past the symmetric layout is studied in detail. It is shown that with the increase in the Reynolds number from wind tunnel values to the flight ones, all trends in the aerodynamic characteristics of the model are preserved and no additional features appear. However, the quantitative behavior of the characteristics changes somewhat. Similar numerical simulations have been carried out for a model rotating at a constant angular velocity about an axis parallel to the velocity vector. Such flow regimes correspond to spin ones. It is shown that the longitudinal characteristics Cx, Cy and mz for the case with rotation have the same qualitative behavior as for the case without rotation. The quantitative discrepancy is also small and is less than 4% of the maximum value. At the same time, due to the presence of rotation, the lateral characteristics differ noticeably from the case without rotation. The deviation of average Cz values from zero starts at the angle of attack of 15 degrees. It should be noted that here the maximum value of Cz depends on the asymmetry of the flow caused by the rotation of the model, in contrast to the case without rotation, where the value of Cz depends on the asymmetry of the flow caused by the instability of the symmetric flow. It is shown that the maximum values of Cz for the cases with and without rotation differ by a factor of ~1.5. In the presence of rotation, an area of noticeable change in mx appears at the angles of attack less than 10 degrees. This change is associated with the fact that due to rotation the separation on one of the consoles begins earlier than on the other. With an increase of the angle of attack to 10 degrees, the flow past both consoles is detached and the value of mx decreases. Computational studies of the flow past various bodies at high angles of attack and bodies undergoing pitching motion have been carried out by solving Reynolds equations with the use of various semi-empirical turbulence models. These studies are carried out in a two-dimensional formulation for a wing airfoil, as well as for a delta wing in a three-dimensional formulation. It is shown that the SA turbulence model gives overestimated Cy results, the SST model and the RSM-class model give satisfactory results in terms of the maximum normal force and for the qualitative behavior of the Cy dependence on the angle of attack. Comparison of the numerical results with experimental data for the model of a straight wing at high angles of attack showed that the two-dimensional formulation of the problem for the wing airfoil gives overestimated values of Cy (the value of Cy max is ~0.2 higher) and a higher slope of the dependence of Cy on the angle of attack. The calculation of the three-dimensional Reynolds equations showed results much closer to the experiment: the slope of the curve in the calculation is close to the experiment, and the Cymax value differs by less than 0.1. The calculation within the framework of the DDES eddy-resolving approach shows the results that are in the best agreement with the experiment. The difference between the DDES calculation and the experimental data at a supercritical angle of attack of 30 degrees is 0.004 for the Cy value. The numerical simulations of the pitching airfoil taking into account the laminar-to-turbulent transition have been carried out. Comparison with the experimental data shows that the level of discrepancy when the transition is taken into account remains the same as for the case of a fully turbulent boundary layer. The pitching motion of the straight wing model is calculated, which shows three-dimensional flow features that are not modeled in a two-dimensional formulation of the problem. The analysis of these three-dimensional structures will be continued at the next stage. Numerical simulation of flow control around a delta wing has been carried out by blowing a gas jet from local nozzles located on the upper surface of the wing. It turned out that the influence of the jet blowing can be described by three factors: the appearance of reactive forces of the nozzles, the appearance of the ejection of the surrounding gas into the jet, and the influence of the jet momentum on the position and size of the regions with negative streamwise velocity that arise above the upper surface of the wing as a result of the vortex “burst”. The effect of jet ejection is reduced to a relatively small increase in the normal force coefficient and takes place for all the values of the angle of attack. The jet momentum influences on the position and size of the separation zones only for the angles of attack near and above the critical one, where the vortex "burst" occurs above the wing surface. In this case, the jet enters the peripheral region of the vortex, “wraps” around the vortex without getting into its center, and shifts the vortex "burst" downstream. During the oscillatory motion of the delta wing, the influence of the jet leads to an increase in the normal force for the entire range of the angle of attack of the wing and to a narrowing of the area of the dynamic hysteresis loop. The direction of the jet blowing has a little effect on the aerodynamic characteristics of the wing; only the fact that the jet enters the vortex region is significant.

Publications

1. Alieva D.A., Grishin I.I., Kolin’ko K.A., Khrabrov A.N., Shukhovtsov D.V. Hysteresis and Asymmetry of the Aerodynamic Characteristics of Aircraft Model with High Aspect Ratio Straight Wing under the Flow Separation Fluid Dynamics, V. 57, No 6, pp.729-735 (year - 2022) https://doi.org/10.1134/S0015462822601280

2. Soudakov V.G., Soudakov G.G. Управление обтеканием треугольного крыла с помощью выдува струи газа при колебаниях по углу атаки Ученые записки ЦАГИ, - (year - 2023)

3. Vorozhbit E.E., Petrov A.V., Soudakov V.G. Experimental Investigation of Local Jets Blowing for Flow Control in the Stream Past the Civil Aircraft Wing Fluid Dynamics, V. 57, No 6, pp.710-719 (year - 2022) https://doi.org/10.1134/S001546282260095X

4. Voyevodin A.V., Efremov A.A., Soudakov V.G. Numerical and experimental investigation of aerodynamics of civil aircraft model on high angles of attack and with rotation Thermophysics and Aeromechanics, - (year - 2023)