Annotation of the results obtained in 2022
A series of experimental studies on the active control of the flow behind the cylinder with a slit injection into the stern of the cylinder using a pulsating jet has been carried out. It is shown that the integral drag changes with variations in the pressure creating the pulsating jet and weakly depends on the pulsation frequency. With constant injection, a greater decrease in drag was observed compared to pulsating modes, due to greater air flow through the slit at equal pressures. To study the flow configuration, the high-speed PIV approach and further correlation analysis of particle images were used to estimate instantaneous velocity fields in the separation zone behind the cylinder. Also, active flow control is implemented when the cylinder flows around based on feedback from the sensor of the hot wire anemometer installed in the wake of the cylinder opposite the slit at a distance of two calibers from the trailing edge. The search in the function space was carried out by the method of genetic programming from the class of evolutionary algorithms, where the most adapted control laws are passed from generation to generation. The implemented control method allowed to reduce the resistance by more than 20%. During the work on the project, a model of a trainable neural network based on the PWC-Net architecture was developed to estimate velocity fields from particle images. The results of the evaluation of the instantaneous velocity field by a neural network algorithm and optical flow algorithms and an accurate but slow Dual TV L1 algorithm are presented. This method was also used to analyze the dynamics of the flame front under conditions of external exposure to an alternating electric field. On the basis of vortex-resolving numerical simulation verified on the basis of experimental data, the analysis of the influence of input conditions, the flow swirl rate and the fuel-oxidizer ratio on the distribution of CO and NOx concentrations in the near region of the model combustion chamber was carried out. The efficiency of reducing harmful emissions and reducing pressure pulsations by suppressing natural hydrodynamic modes in the model combustion chamber of a gas turbine engine during methane combustion with a significant excess of air and increased pressure based on multimode exposure and the use of machine learning, including the use of artificial neural networks, is shown. For the cases of the most effective control, the flow dynamics and hydrodynamic modes are analyzed on the basis of planar optical measurements and vortex-resolving numerical modeling using methods of reducing the dimension of stochastic dynamic systems. As a result, scientific and technical background for intelligent control of mixing and combustion in the combustion chambers of real gas turbines was obtained. A method for introducing an azimuthally non-uniform acoustic forcing using a system of four speakers with a signal phase shift for each of the speakers is implemented. The structure of the spray plume of a of a commercially produced centrifugal nozzle under the influence of the specified disturbance in various configurations was analyzed. Data were obtained on the distribution of droplet’s velocity in the spray plume, the geometry of the plume, and the distribution of the relative concentration of liquid in the plume under the influence of an azimuthally nonuniform forcing. The acoustic forcing under the studied conditions did not have a significant effect on the structure of the plume and the distribution of droplet’s velocity, yet a certain influence of the forcing on the average distribution of the liquid concentration and the trajectory of the fine droplets in spray was detected. In general, the effect of acoustic forcing on the spray was weak in tested conditions, and was detected in the averaged characteristics only. The influence of superheated steam parameters on the concentration of toxic combustion products (CO, NOx) during combustion of gaseous (propane-butane mixture) and liquid hydrocarbons (kerosene) under conditions of steam gasification were experimentally studied. It was found that when steam is supplied, a significant reduction in the content of carbon monoxide (by the factor of 1.7 for liquid fuel and the factor of 1.6 for gaseous fuel) and nitrogen oxides in combustion products (by the factor of 2 for liquid fuel and th3e factor of 1.8 for gaseous fuel) is obtained as compared with the hot air supply instead of steam. The obtained results demonstrate that the method of combustion of gaseous and liquid hydrocarbons under steam gasification is preferable for improving environmental performance. The proposed method of fuel combustion in a steam jet can be used in the design of low-emission gas turbine engines. In this section of the project, a pulsed impinging gas-droplet jet was numerically simulated for various pulse shapes (rectangular, sinusoidal and triangular). To describe the dynamics and heat transfer of an unsteady axisymmetric flow, a system of unsteady axisymmetric Reynolds-averaged Navier–Stokes equations was used. To describe gas turbulence, we will use the model of Reynolds stress component transport, which is written taking into account the two-phase character of the flow. The dynamics and heat transfer in the gas-droplet flow were modeled in the Euler approximation. Work to create and generalize a database of numerical studies for non-stationary one- and two-phase turbulent impinging jets was implemented. A set of experimental studies of non-stationary heat transfer during the flow of a pulsed two-phase water-air spray onto a vertical heat transfer surface has been carried out. The spray parameters were varied over a wide range: the duration of a pulse of the liquid phase supply, the pulse repetition rate and the velocity of the co-current air flow, as well as the pressure drops on the liquid and gas nozzles. All experiments were carried out in the regime of constant surface temperature of 70С. It was found that the co-current air flow has a significant effect on heat transfer intensification due to turbulization of the near-wall flow, liquid film destruction, and return of liquid drops reflected from the surface. The individual contribution of the impinging air jet to total heat transfer is not high and hardly affects the thermal energy balance. It is experimentally demonstrated that the regime area of existence of disturbance waves and liquid entrainment in annular-dispersed flow can be expanded by imposing low-frequency pulsations of liquid flow rate. It is possible to reduce critical liquid flow rates at high gas speeds, as well as to decrease the critical gas speed nearly to zero values at large liquid flow rates. An experimental study of an oscillating jet generated by a jet oscillator into a slit channel has been carried out. The results of the study have shown that with equal values of the channel height and the neck width of the jet oscillator outlet nozzle, the flow of the oscillating jet into the slit channel is accompanied by the formation of large-scale quasi-two-dimensional vortex structures at the main frequency of the jet oscillator. For the first time, large-scale longitudinal vortex structures were detected using three-dimensional measurements by PIV. It is shown that the dynamics of these structures is related to the meandering nature of the jet flow and the development of large-scale quasi-two-dimensional vortex structures. The presence of the limiting walls of the slit channel significantly affects the distribution of the averaged velocity and leads to a limitation of the maximum deflection angle of the jet. An experimental database of average and turbulent flow characteristics for the cavitation flow of a hydrofoil under superimposed external consistent disturbances has been obtained. The analysis of the results of the entire complex of experimental data obtained for the modified and original hydrofoil is carried out. The effectiveness of suppression of unsteadiness and cavitation by the implemented method is shown. The POD and spectral characteristics of the cavitation flow near the hydrofoil were analyzed for experimental data and numerical simulation of cavitation. For the problem of film cooling of the plate, a multiparametric optimization of the surface shape was carried out on the basis of the conjugate field method and vortex-resolving numerical modeling to obtain maximum efficiency of thermal protection. The results of modeling the effect of the unsteadiness of the input particle concentration on the wall accumulation of particles in a turbulent flow in a flat channel are also obtained.

 

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Annotation of the results obtained in 2019
Software implementations of model flow control algorithms based on optimal control and management using machine learning with reinforcement are developed. The TFlowsS hydrodynamic calculation package has been modified to allow simulation of flows in a mode with active feedback control. The indicated software was tested on the calculation problem of reducing the drag force when flowing around a cylinder (2D LES, Re = 100). The data are obtained for the drag coefficient and lift for a sinusoidal perturbation in time - rotational vibrations of the cylinder wall around its axis. The high efficiency of this control method for high Reynolds numbers is obtained. The analysis of the propagation coordinate of the jet front was made with the help of the data from the direct numerical simulation. The result was compared with literature. To study the influence of the inlet profile the simulation was carried out, in which an average turbulent profile with zero pulsations was fed into the pipe at each time step. In order to develop a three-fluid continuum model for the transport of concentration, velocity and Reynolds stresses of inertial particles in the near-wall zone of a turbulent flow, a simple method of taking into account the nonequilibrium probability density function of the particle velocity is proposed using an approach using the two-fluid continuum model of the Reynolds stress transport developed by L. I. Zaichik and well-known in computational fluid dynamics (CFD) method of wall functions for the concentration and second moment of particle velocity, taking into account their separation into two groups: diffusion and ballistic particles. A mathematical model has been developed to describe heat transfer in non-stationary gas-droplet jets during their interaction with the impact surface of the obstacle. The turbulent impulse impact gas-droplet jets are simulated, the dependences of the heat transfer coefficient on the flow rate of the liquid phase are obtained with varying pulse duration, droplet diameter and their mass fraction. The agreement between the simulation and experimental data in the modes with a short pulse time and the difference for a long time are shown. The reasons for such a mismatch are established. It has been shown that a transverse pulsating jet is an effective mixer since it captures more liquid than a conventional jet. Experiments on the visualization of a flow with round turbulent jets in a transverse flow showed that the formation of a curved shear layer consisting of separate vortex loops around the jet in the near field predominates in the structure of the transverse jet. Machine learning approach was tested to solve the problem of predicting pre-failure and failure conditions of aircraft engines. Based on the NASA experiment databases, statistical models of multiclass classification of aircraft engine operating regimes and regression of the number of working cycles to failure were investigated. Various families of algorithms were tested: from linear to neural network algorithms. The effectiveness of the proposed approach is shown, optimal predictive models are developed in the form of framework. The distributions of the turbulent characteristics of the isothermal and reacting flow in the GT model chamber are obtained. The instantaneous POD velocity fields were decomposed for various flow regimes, which indicated the presence of a global mode corresponding to a precessing vortex core with strong pressure pulsations. The relationship between this structure and the distribution of CO and NOx in the combustion products with a significant excess of air and atmospheric pressure was studied. Within the project, approaches for qualitative and quantitative diagnostics of fuel atomization by GTE nozzles have been developed and improved. Preliminary studies were carried out was on a gas turbine fuel injection nozzle, a description of the spray cone structure and spray characteristics were obtained. Additionally, schemes for flow rate modulation and spray forcing were proposed for the implementation of control methods at the future stages of the project. A mathematical model and a spray calculation method have been developed, based on the combined Eulerian-Lagrangian approach, based on modeling the fluid flow inside the nozzle and near it based on the Euler VOF method, and the dispersed phase formed at a distance from the nozzle using the Lagrange method of discrete particles. The spray calculation technique was validated using direct numerical experiment data. It is shown that the use of the LES turbulence model allows one to more correctly describe the spray of the liquid phase in comparison with the hybrid RANS / LES turbulence model. Good agreement is observed in the characteristics of the flow and the dispersed phase, as well as in the gas – liquid interface. An experimental study of susceptibility of gas-sheared liquid film to superimposed harmonic perturbations. The range of average gas velocities from 0 to 100 m/s and liquid Reynolds numbers from 30 to 400 was studied; the excitation frequency varied from 20 to 100 Hz. It is shown that superimposed perturbations exist for a certain distance from the inlet and are destroyed due to wave merging. This distance decreases slightly with increasing liquid flow rate and strongly with increasing gas speed. In experiments on an unmodified guide vane model with a blunt trailing edge (without a control device), high-speed visualization of vapor cavities was carried out and two-dimensional distributions of flow velocity were measured by Particle Image Velocimetry for various flow conditions on the attack angle and cavitation number. As a result, a map of cavitating flow regimes was constructed, the inception and development of vapor cavities, their spatial structure and evolution were analyzed, and the influence of the cavitating flow regime on its hydrodynamic characteristics was studied. Based on an in-depth analysis of the literature, an optimal design of the control device in the method of flow control based on periodic forcing by imposing an external electromagnetic field (the number of electrodes, their geometric dimensions and relative position) was determined. Numerical modeling was carried out in the problem of flow around a hydrofoil at high Reynolds numbers for pre- and cavitation modes. We studied the dynamics of the breakdown of the cavitation cloud, the frequency characteristics of which are in good agreement with the visualization data from the experiment. A modification of the nozzle for film cooling of a flat plate is proposed. A cooler supply channel is modified by including a bend and a sharp step. The presence of a recirculation zone in such a nozzle leads to the formation of periodically shedding coherent structures, with the possibility of controlling their frequency. Simulations show that this modification can lead to improvements in a thermal efficiency of film cooling, and improves cooling uniformity in the horizontal plane.

 

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Annotation of the results obtained in 2020
Using modern methods of experimental diagnostics, physical, mathematical and numerical modeling, in 2020 important scientific results were obtained on the efficiency of big-data analysis and machine learning methods for the implementation of effective methods for controlling of heat and mass transfer in flows implemented in power equipment. In particular, the emphasis is placed on the possibility to control the development of hydrodynamic instabilities, to intensity of heat and mass transfer, spraying and mixing of fuel, a significant influence of the control parameters on the local rate of phase transformations (including cavitation) and combustion. - The previously proposed flow control scheme of the wake behind a cylinder, based on the superposition of rotational oscillations of the cylinder, has been developed. The tool is the combination of the computational fluid dynamics code T-Flows and the neural network OpenAI:baselines. This feedback control method was tested for a laminar flow at low Reynolds numbers (Re=100). The criteria for an effective control of the drag using various methods of the superimposition of the external rotational oscillations are determined. - Direct numerical simulation (DNS) of a starting air jet outflowing into an open space filled with helium has been carried out. The influence of the ratio of the densities of the mixing gases on the velocity of the jet front propagation is analyzed. The influence of the initial inlet velocity profile on the flow evolution has been studied. Using modern optical measurement methods, a series of experiments has been performed to study the effect of multimode external perturbation on the dynamics of vortex structures in the initial region of a submerged round jet. The frequency of the periodic oscillations for two harmonics is chosen so that the fundamental harmonic corresponds to the natural frequency of the jet instability - the Strouhal number value 0.5, and the second frequency provides a low-frequency modulation of the signal amplitude. In addition, the efficiency of multimode excitation of the fuel jet mixing and combustion was investigated. - The dynamics of a direct-flow gas jet in a transverse air flow under conditions of periodic disturbance of the flow rate has been investigated experimentally. It is shown that a vertical pulsating jet in a transverse flow is an efficient mixer, since it entrains more surrounding gas than a jet under stationary conditions. The efficiency of the fluidic jet oscillator as a flow control tool was studied. It has been found that in a cross-flow it is an effective device for introducing periodic disturbances into the flow without using mechanical moving parts or the flow modulation. As a result of comparison with the data of the study of the direct-flow jet in a cross-flow, even under conditions of the flowrate modulation, the fluidic jet oscillator demonstrates a significantly higher efficiency in terms of the intensity of heat and mass transfer between the jet and the main flow. A numerical simulation of the effect of a device based on a barrier discharge (DBD-actuator) on a wall-mounted gas near-wall jet has been carried out. It was found that exposure to electric pulses at a selected frequency, close to one of the natural frequencies of the jet, leads to a significant decrease in the recirculation zone and suppression of the jet detachment, when the supplying power is insignificant compared to the kinetic energy of the jet flow. - A hybrid model of the particle concentration transport based on the diffusion-inertial model in the flow core and a three-fluid continual model for the concentration and Reynolds stresses of particles in the near-wall zone has been developed. The model takes into account the power-law singularity of the particle concentration near the wall, manifesting the clustering of inertial particles. A new boundary condition for the Reynolds stresses of particles (wall function) is proposed. The developed model gives more realistic results for high-inertia particles, adequately reproducing the near-wall pile-up of the particle concentration in the viscous sublayer.. - Numerical simulation of the effect of the pulse shape (rectangular, triangular and harmonic) on heat transfer at the stagnation point of the impinging pulsating gas-droplet jet (spray) has been performed. To describe the dynamics and heat transfer of a pulsed axisymmetric flow, an unsteady Reynolds-averaged Navier – Stokes equations (URANS) simulation was used. The turbulence of the carrier phase was described using the model of the transfer of the components of Reynolds stresses. It is shown that in a nonstationary impinging jet, both an increase and a suppression of heat transfer are possible in comparison with a stationary flow for all studied pulse repetition patterns. An increase in the Reynolds number causes a decrease in the heat transfer intensification parameter, and the data for all frequencies approach the steady-state flow regime. The intensification of heat transfer is due to the contribution of evaporative cooling, which in turn depends on the thermal resistance of the liquid film. The interaction of these factors, oppositely affecting the near-wall heat and mass transfer, causes a local extremum in the dependence of the efficiency parameter on the duration of the spray delivery pulse. It is shown that a maximum of the coefficient of thermal efficiency of the spray is observed with a pulse duration of about 10 ms. - Using the PIV / PLIF methods, a detailed study of the mixture formation and combustion in a model gas turbine combustion chamber (with a significant excess of air) under conditions of resonant pressure pulsations causing a modulation of fuel consumption was carried out. To identify coherent structures in flow stream, the data was processed by a POD method. The high-speed visualization of the intensity of chemiluminescence (OH *) in a model gas turbine combustion chamber with the simultaneous recording of the pressure pulsations and measurements of the concentration of CO and NOx in the combustion products at the outlet of the chamber was carried out. It was found that pressure pulsations, which occur in a combustion chamber without an outlet nozzle, are caused by the precession of the vortex core of the flow, coupled with the rotation of large-scale helical vortices around the axis of the combustion chamber. This instability mode corresponds to the first azimuthal mode and the Strouhal number 0.75. Similar results were obtained via mathematical modeling by the LES method: in the absence of a pilot flame, the flow is characterized by the presence of a recirculation zone attached to the swirler center and the presence of a precessing vortex core. Under the conditions of resonant pressure pulsations and fuel supply, appeared for the presence of a narrow outlet nozzle at the combustion chamber exit, intense pulsations of the OH * radiation intensity were recorded in the flow, corresponding to the zero azimuthal mode. They were caused by the modulation of the fuel supply through the fuel channels and, accordingly, the periodic change in the fuel / air ratio of the partially mixed mixture entering the chamber. The feedback in such a resonant combustion mode is caused by pulsations of heat release and, accordingly, pulsations of the density, causing the pressure pulsations. - Within the framework of the project, a stand was developed to study methods for controlling the liquid spraying by acoustic disturbances. Approaches for quantitative panoramic diagnostics of the dispersed composition of a spray based on the laser-induced fluorescence and elastic scattering of radiation by drops are investigated. On a sample of a model fuel injector, preliminary studies of the spray pattern structure under the influence of acoustic disturbances have been carried out. The technique of non-stationary calculation of the spray is developed, based on the combined Euler-Lagrangian approach. The fluid flow in the nozzle and the initial region of the jet is described using the Euler approach (VOF), and the resulting droplets are further modeled using the Lagrange method. The method of non-stationary calculation of the spray with the flow rate modulation mode was validated according to the experimental data of the spray of an annular jet of water with accompanying air flows. The characteristics of droplets of various types of fuel sprayed by a jet of superheated water vapor are studied on the basis of the method of shadow photography, high-speed imaging using a long-focus macroscopic objective. For the first time, visualization of the process of decay of various types of liquid hydrocarbon fuel during interaction with a supersonic gas jet has been carried out. The possibility of efficient dispersion of kerosene with a steam jet has also been shown for the first time; this method can be used in the design of promising gas turbine engines. - A study of changes in the records of the film thickness in a dispersed annular flow near the regime boundary of the onset of droplet entrainment was carried out. It is shown that the steepness of the wave fronts increases sharply near the regime boundary, which leads to the appearance of apparent peaks of high intensity in the Laser-Induced Fluorescence records of the film thickness. Thus, the proximity of the regime boundary can be traced by the behavior of the LIF records before the appearance of high waves. - A series of calculations of the fluid flow at various flow regimes around a hydrofoil was performed. Detailed results, consistent with the experiment, were obtained from the calculations of the pre-cavitation flow regime using the RANS method, as well as for the cavitation regime by the LES method using conditional averaging. The dynamics of the flow is studied in detail using temporal spectral analysis, as well as the POD, which makes possible to identify the most energetic vortex structures. Low-frequency pulsations were identified, corresponding to the detachment of the cavitation cloud from the hydrofoil. The design of the modified hydrofoil with a built-in control element, which is a "sandwich" of electrodes and permanent magnets, has been optimized, its three-dimensional model and a laboratory sample have been created. Based on the ensemble of measured instantaneous velocity fields, turbulent characteristics of a cavitating flow were calculated. Analysis of basic information on the distributions of velocity fluctuations showed that the flow turbulence structure changes significantly when cavitation occurs. The measured power spectra of pressure fluctuations for unsteady flow regimes made it possible to determine the characteristic frequencies and amplitudes of pressure pulsations in the hydrofoil wake associated with periodic variations of the length of an attached cavity and detachments of cloud cavities. The efficiency of the flow control dynamics for a cavitating flow based on the injection of a slot jet on the surface of a hydrofoil is investigated. The possibility of efficient control of the recirculation zone size, the position of the flow separation point and the size of the cavitation cloud is shown. The results of the 2020 research have been published in a number of scientific articles, including in top-ranked first quartile journals.

 

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Annotation of the results obtained in 2021
The DNS of an air jet, flowing into a space filled with carbon dioxide at a fixed Reynolds number of 5300, has been carried out. The front propagation velocity, as well as instantaneous longitudinal velocity fields in the jet front, have been compared for all three gas pairs studied during two previous years of the project, including air-to-air and air-to-helium jets. A real-time PIV measuring system with registration of VGA-sized image pairs and simultaneous GPU data processing at a frequency of 25 Hz has been developed and tested. The resolution of the resulting velocity field corresponds to the size of the input images. The system can be used for quantitative visualization of the flow in real time, for teaching purposes and as a speed sensor in active flow control systems with characteristic process times of at least 0.1 s. The created system has been tested on a number of flows in a liquid, including in a real experiment with a pulsating submerged jet impinging onto a flat horizontal heated wall. A continual model has been developed for the concentration, velocity, and Reynolds stresses of inertial particles in the near-wall zone for the conditions of inelastic rebound and deposition of particles. The model takes into account a power-law singularity of the particle concentration near the wall, associated with both the phenomenon of clustering of inertial particles and the phenomenon of inelastic collapse of inertial particles. The developed model is in good agreement with the data of stochastic Lagrangian modeling for a particle-laden turbulent flow in a channel for the conditions of inelastic rebound and deposition of particles, adequately reproducing the near-wall peak of the concentration of particles in a viscous sublayer. For the studied pulsed jets in a cross-flow the penetration depth has been found to be higher than in the case of a constant flow rate. It has been shown that the pulsating transverse jet is mixed more efficiently. Changing the frequency of the pulsations and the average flow rate of the pulsed jet has shown a possibility of control the penetration length of the jet and efficiency of mixing. A database of high-speed PIV images and spectrozonal images (OH and CH images) have been obtained for a lifted diffusion flame under periodic external forcing. An application of principle component analysis has allowed extracting of the kinetic energy of coherent structures associated with a periodic roll-up and propagation of ring-like vortices in forced jet flows with and without combustion. For the first time it has been shown that for a jet-flame with combustion there is a sharp drop of the vortices shedding frequency (by almost two times) behind the flame front. At the same time the propagation velocity of the vortices increased. This effect has not been previously detected and can explain the fact that the increase of the fuel mixing and combustion efficiency in jet-flames corresponds to the frequency twice greater than the frequency of the fundamental harmonic in jets without combustion. Using the isotropic low Reynolds k-epsilon turbulence model by Hwang and Lin (AIAA J., 1998), the algebraic Girimaji turbulence model (Theoret. Comput. Fluid Dynamics, 1996), and Craft and Launder Reynolds stress transfer model (AIAA J., 1992), investigation of two-phase unsteady impinging jets has been conducted. It has been shown that only Craft and Launder model (AIAA J., 1992) gives good agreement with the measurement data for one- and two-phase regimes. Impinging pulsed gas-droplet jets have been studied using the Eulerian two-fluid and the Lagrangian trajectory approaches. The Eulerian description of the motion and heat transfer in the dispersed phase is more computationally economical. In general, both simulation approaches give similar results. The main difference between the Eulerian and Lagrangian methods is manifested in the droplet concentration profiles, and it reaches 15%. It has been shown that in the central region of the heat exchanger when the spray flows onto the surface, stagnant zones with weak multidirectional flow and regions with intense wave flow directed from the center to the periphery, are formed. Analysis of the data of the flow in the central and peripheral regions of the heat exchanger surface has shown that chaotic shear wave formation with multidirectional radial wave motion prevails in the central region. With an increase in the average film thickness the amplitude of waves in horizontal motion to the periphery of the surface increases, but the wave velocity remains low. An optical single sector combustor for the diagnostics of the velocity field and shape of the flame front has been created and tested. The combustor has been designed to simulate unsteady flames in gas turbine combustion chambers and allows the PIV and OH PLIF measurements. The combustor also provides the monitoring of pressure pulsations level and the content of CO and NOx in combustion products. A series of experiments have been carried out for lean methane-air flame stabilized by a model swirler for pressures up to 4 atm. The emphasis of the study has been put on the analysis of unsteady combustion modes when burning lean mixtures. The LES method for simulating the flames has been verified by using of the PIV/PLIF data. It has been found that unsteady combustion regimes with intensive pressure pulsations in the combustion chamber are characterized by the following processes: periodic lift-off (but not blow-off) of the flame front and downstream displacement of the combustion zone, fuel accumulation inside the central recirculation zone of the flow, a rapid increase in the flame propagation speed and its movement upstream with the intensive turbulent combustion of the fuel, which is accumulated in the central recirculation zone. The latter process is accompanied by the growth of heat release, pressure increase inside the combustion chamber and blocking of the fuel supply channels. This explains a feedback mechanism of thermoacoustic pulsations. A similar mechanism has been found for the flames at elevated pressure. In general, the higher pressure leads to sootier flames and an increase in the level of NOx in the combustion products. Using modern numerical approaches within the framework of Large-Eddy Simulations (LES) method and turbulent combustion models, a series of parametric computations of a model combustion chamber at Re = 15000 have been carried out. For the isothermal and reactive cases there is a good agreement with the experimental data. The distribution of concentrations of CO, CO2, NO, etc. has been analyzed. It has been shown, for example, that CO2 is generated mainly in the recirculation zone, while a high concentration of NO is observed already in the wake of the recirculation zone. The diagnostics of the industrial centrifugal nozzle spray influenced by acoustic forcing has been performed within the current stage of the project. Forcing with a total sound power of up to 1200 W has been induced by means of four symmetrically distributed high-power speakers with the frequency range from 100 Hz to 500 Hz. A spray pattern and droplets velocity distributions have been evaluated in the experiments. The acoustic forcing in the studied conditions had no significant effect on the time-averaged characteristics of the spray. The eigenfrequencies of velocity fluctuations in the spray have been identified from the PIV droplets velocity measurement. It has been noticed that the acoustic forcing may result in a moderate intensification of the selected modes. Based on the previously developed non-stationary Eulerian-Lagrangian approach for modeling of sprays, for an industrial nozzle the results were obtained of the structure of the flame and the dispersion of droplets in the flow modulation mode with disturbance frequency ranging from 20 Hz to 1000 Hz. The influence of the flow rate modulation on the dynamics of the primary decay of the jet has been shown. A study of the effect of superimposed periodic perturbations on the wave structure of a liquid film in a dispersed annular flow has been carried out. The control of the dispersed annular flow by superimposing pulsations of the liquid flow rate is possible in a certain frequency range. Automatic methods for determining the susceptibility based on the spectral approach have been developed. The width of the susceptibility range is 15-20 Hz. The range approximately corresponds to the passing frequency of disturbance waves far from the inlet. In this range flow control consists in: a significant regularization of the flow structure, an increase in the predictability of wave characteristics, the ability to change the frequency, velocity, and amplitude of disturbance waves, as well as in an increase in the dispersed phase flow rate. A comprehensive experimental study of the influence of external disturbances on the evolution of cavitation cavities has been carried out. The power spectra have been obtained based on the measured pressure fluctuations in the wake. The primary analysis of the power spectra of pressure fluctuations for unsteady modes of cavitation flow in the case of external disturbance has been carried out. The possibility of delaying the development of unsteadiness in cloudy regimes of the flow around a model hydrofoil has been demonstrated. A new method for extracting information on the average distribution of vapor in a cavitating flow based on PIV processed data for the liquid phase has been developed and tested (Pervunin et al., 2021). A numerical simulation of the cavitating flow near the hydrofoil at a high Reynolds number has been carried out using the LES method. The obtained data have been verified using the proposed conditional averaging procedure. Analysis of the dimensionless lift coefficient of the hydrofoil together with an averaging over the characteristic points in time have shown that the lift coefficient is minimal in the presence of the largest amount of vapor phase on the surface of the hydrofoil. The previously developed three-dimensional numerical model for flow simulations in the Eulerian approximation has been modified to calculate the interaction of the main single-phase gas flow and a two-phase turbulent near-wall flow. The numerical code for the model has also been implemented. The thermal efficiency of a gas-droplet curtain has been simulated when blowing through inclined cylindrical holes into a transverse trench. A significant increase in the efficiency of the thermal curtain has been obtained with the addition of droplets to the coolant flow (up to 2 times in comparison with the supply of a single-phase coolant through the holes in the trench). The main increase in the thermal efficiency of a two-phase wall curtain has been observed at a distance of x / b = 15–20. Further downstream, due to the evaporation of small droplets, a sharp decrease in the efficiency of the two-phase curtain occurs. An assessment of applying of the electric field to improve the efficiency of thermal protection of the film cooling has been carried out. A modification of the VOF (volume of fluid) solver for two-phase flows from OpenFoam software package has been done to take into account the effect of the electrostatic field. The electric potential distribution was found at each time step by solving the Poisson equation (taking into account the dielectric constant of the liquid cooler). The found distributions of the electric potential were used to construct the force field acting on the cooler (through the polarization of the dielectric). The maximum effect on the dielectric (liquid coolant) is exerted in the region of strong inhomogeneity of the electrostatic field. From the point of view of increasing the efficiency of thermal protection, this effect can be used to prevent the separation of the coolant film from the cooled surface. The problem of film cooling of a flat plate when water is supplied through a cylindrical channel at an angle of 35 degrees has been considered. A modification of this configuration is proposed by introducing a longitudinal protrusion running along the lower surface of the channel downstream, with a sharp edge as an electrostatic field concentrator. When a constant potential difference is applied between the upper and lower walls of the channel, the electric field concentrating on the protrusion tends to keep the coolant jet on the wall surface, while not interfering with its movement in the longitudinal direction. An installation has been developed for creating a gas-droplet suspension in order to control the flow of a film cooling using an electric field. The size distribution of the dispersed phase was investigated using a laser Doppler particle analyzer. The first PIV-PLIF measurements has been carried out to analyze the change in the particle velocity under the influence of a constant electric field and to assess the possible influence of the electric field on the efficiency of thermal protection, taking into account the effects of the electric polarization of the droplets.

 

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