Central Aerohydrodynamic Institute

Within the framework of lubrication theory, numerical studies of thin film movement along the surface of a wing with the NACA0012 airfoil were carried out. The film is created by incoming drops of water and drifted by the external air flow. A model problem of one-dimensional film motion in the presence of a retarding longitudinal stress caused by disjoining pressure is considered. A cubic equation was obtained to determine the film thickness. If the contact angle exceeds a certain critical value, then the solution of this equation loses its physical meaning at some distance from the front critical point (the film thickness becomes negative). This means that the one-dimensional flow assumption is no longer satisfied. The maximum coordinate for existence a one-dimensional solution can be considered approximately as the beginning for the film disintegration into rivulets. Theoretical results are compared with the available experimental data.

Interest in various active and passive methods of flow control over an airfoil, aimed at increasing the maximum lift coefficient of a wing, is driven by the relevance of reducing take-off and landing distan- ces. Unlike active flow control methods, which require energy input, passive methods use the energy of the external airflow in such a way as to produce an overall beneficial effect. Passive flow control methods are simpler than active ones, have more reliable designs, and generally add little extra weight. This work presents a passive method for controlling the flow over a high-lift wing airfoil with a flap by means of specially profiled flow channels. The described control method is effective both with the flap undeflected (cruise flight mode) and with the flap deflected. It is shown that in the profiled channel the airflow accelerates and exits tangentially onto the upper surface of the flap, increasing suction and shifting the boundary-layer separation line on the deflected flap downstream. Humid air with increased moisture concentration raises the momentum coefficient of the blown jet.

A closed-loop control was implemented to mitigate stationary cross-flow instability vortices in the boundary layer of a swept wing. Control was achieved using a multichannel plasma actuator and a flow velocity sensor based on a particle image velocimetry system. The optimal control strategy was determined using a gradient descent method, which minimized the root mean square of the steady velocity modulation. The excitation of the boundary layer by a single section of barrier discharge was investigated, with key actuator characteristics, such as linearity limits and noise levels, measured during the experiment. The system's performance was evaluated in a wind tunnel experiment, with various roughness patterns used to force the initial vortices. For isolated roughness elements, substantial transition delay was achieved.

A new approach has been developed and implemented to determine the main components of residual stresses that arise as a result of the contact interaction of a spherical indenter and a flat surface of composite plate made. The experimental technique includes drilling a probe hole and measuring the increments of the diameters of this hole in the direction of the principal residual deformations by speckle interferometry. The high-quality interference fringe patterns essential for the implementation of this procedure are visualized both inside and outside the contact dimple. Data from interference measurements of in-plane displacement components are used to determine the principal components of residual stresses based on the unequivocally solution to the properly posed inverse problem. This procedure provides minimal possible errors inherent in a determination of residual stress components by measurements of local deformation response to small hole drilling in orthotropic plate. The presented studies were carried out both for static and dynamic application of contact indentation of a spherical indenter into a flat surface of samples made of laminated carbon fiber material with cross-ply stacking sequence. It is shown that the values of residual stresses, unlike indirect parameters, are a parameter that can be used to establish a correlation between the results of residual strength tests and the quantitative characteristics of the residual stress field in the vicinity of the contact dimple.

The disturbances generated by external turbulence in the shear layer on a flat plate suddenly set in motion are found. As the initial conditions, turbulent flow found using direct numerical simulation of the development of isotropic homogeneous turbulence is used. The solution obtained models laminar-turbulent transition in the boundary layer on a flat plate under relatively low free-stream turbulence when the transition is caused by Tollmien–Schlichting waves. The solution makes it possible to describe the process of generating various disturbances, namely, low-frequency streaky structures and instability waves and also their development in the initial stage of laminar-turbulent transition. Based on the processing of the obtained results, a simple model is proposed that relates the spectra of instability waves in the boundary layer and turbulent pulsations in free-stream flow. The dependences of the initial amplitude of instability waves and their critical amplification factors (N-factors) on the degree of flow turbulence are also obtained.

Optimization of tangential jet blowing on the upper surface of a supercritical transonic airfoil under buffet conditions was carried out. Two-dimensional unsteady Reynolds-averaged Navier–Stokes equations were solved to simulate the flow past the airfoil. The Spalart–Allmaras turbulence model was used to close the equations. The location of the slot nozzle and the intensity of the jet blowing from it were varied. The optimal location for blowing with minimum jet intensity to suppress buffet was determined.

A regularized problem of describing an irregular nonequilibrium flow of a homogeneous molecular gas in a hypersonic kinetic thin viscous shock layer (TVSL) near the leading edge of the windward side of a thin rotating disk flowing around it with a finite angle of attack is formulated. It is shown that the friction and heat flow at the leading edge of the rotating disk in the kinetic TVSL coincide, respectively, with similar values in the Navier–Stokes TVSL. A formula for calculating the kinetic pressure at the leading edge of a rotating disk in a kinetic flow is obtained. It is shown that the pressure at the leading edge of the rotating disk in the kinetic TVSL exceeds the pressure at the edge in the Navier–Stokes version of the TVSL. It is shown that taking into account the kinetics of the flow in the flow under study by means of the kinetic approximation of the TVSL affects the pressure (pressure increase) in the region under consideration and does not affect friction and heat exchange on the wall in any way. The proposed mathematical model of the flow in a kinetic TVSL near the edge allows us to obtain an analytical solution of a regularized problem in this area of strong irregularity, which is also an important attribute of the numerical modeling of the TVSL downstream.

Recently, aircraft engine manufacturers have shown increased interest in developing hybrid powerplants, which are a combination of gas turbine engines (GTE) with electric motor-generators. The use of the hybrid powerplant makes it possible to increase the fuel efficiency of an airplane, as well as to create new configurations with improved aerodynamic and thrust characteristics. The fuel efficiency improvement is achieved as a result of optimizing the powerplant operation mode to meet the cruising flight requirements, compensating insufficient power during the takeoff and go-around procedures by activating battery-powered electric motors. The creation of new configurations with improved performance can be ensured due to the synergetic effect of the propeller-airframe interaction. Successful flight tests of the hybrid powerplant prototypes in light aircraft configurations allow us to rely on their possible application in the future regarding the projects of new propeller-driven aircraft. The potential benefits of using new powerplants on local airlines can lead to both fuel savings and carbon emission reduction. Short-term maintaining a safe flight mode is also practical in case of one engine failure when using multiple power sources. The power, generated by an electric generator connected to the running engine, can be used both for the electric motor drive of the tip propellers and for rotating the thrust producer of the failed engine. The paper presents the study results of the critical engine failure effect on the aerodynamic performance of the light transport aircraft model obtained as under available electrical transmission as under non-available one between a running and a failed engine. Experimental studies were carried out in a low-speed wind tunnel T-102 TsAGI. The simulation of the electric transmission operation was carried out by setting the operation mode of two power-plant simulators corresponding to the half value of the load factor of one engine propeller Bo in the take-off mode.