RELEVANCE of the study is determined by the fact that non-stationary gas-dynamic phenomena in pipelines of complex configuration are widespread in heat exchange and power equipment. Therefore, the study of the level of heat transfer of pulsating air flows in round and triangular pipes with different degrees of turbulence is an urgent and significant task for the development of science and technology. THE PURPOSE. The influence of gas-dynamic nonstationarity (flow pulsations) on the degree of turbulence and the intensity of heat transfer of air flows in straight pipes with different cross-sectional shapes had to be assessed. METHODS. The studies were conducted on a laboratory bench based on the thermal anemometry method and an automated system for collecting and processing experimental data. Rectilinear round and triangular pipes with identical cross-sectional areas were used in the work. Flow pulsations from 3 to 15.8 Hz were generated by means of a rotating damper. The degree of turbulence of pulsating flows varied from 0.03 to 0.15 by installing stationary flat turbulators. The working environment was air with a temperature of 22-24 о C moving at a speed of 5 to 75 m/s. RESULTS. Experimental data on instantaneous values of velocity and local heat transfer coefficient of stationary and pulsating air flows with different levels of turbulence in straight pipes with different cross-sectional shapes were obtained. CONCLUSION. It has been established that the presence of gas-dynamic non-stationarity leads to an increase in the degree of turbulence by 47-72% in a round pipe and by 36-86% in a triangular pipe. The presence of gas-dynamic non-stationarity causes an intensification of heat transfer in a round pipe by 2635.5% and by 24-36% in a triangular pipe. It has been shown that a significant increase in the degree of turbulence leads to an increase in the heat transfer coefficient of pulsating flows in a round pipe by 11-16% and, conversely, a decrease in the heat transfer coefficient by 7-24% in a triangular pipe. The obtained results can be used in the design of heat exchangers and gas exchange systems in power machines, as well as in the creation of pulsed action devices and apparatus.

The gas-dynamic and heat-exchange behaviours of air flows in gas-dynamic systems have a significant impact on the efficiency and environmental performance of most technical equipment (heat engines, power plants, heat exchangers, etc.). Therefore, it is a relevant task to obtain reliable experimental data and physical laws on the influence of cross-sectional shape and initial turbulence intensity on gas dynamics and the level of heat transfer. In this study, data were experimentally obtained on the instantaneous values of the local velocity and local heat transfer coefficients of stationary air flows in straight pipes with circular, square, and triangular cross-sections at different initial values of the turbulence intensity. The measurements were carried out with a constant temperature hot-wire anemometer, thermocouples, and pressure sensors. Based on the research results, data on the turbulence intensity and averaged local heat transfer along the length of pipes with different cross-sections were summarised. It has been established that turbulence intensity in a square pipe is up to 40% higher than in a round channel; in a triangular channel, on the contrary, it is up to 28% lower. After the air flow's initial turbulence, the relaxation of the flow in square and triangular pipes occurs faster than in a round channel. It is found that the initial intensity of turbulence leads to an increase in the averaged local heat transfer, which is typical of all investigated pipe configurations and initial conditions.

Improving the process of cleaning the cylinder from exhaust gases has a significant impact on the operational and environmental performance of a piston engine. The purpose of the work was to assess the influence of the exhaust pipeline design on the gas dynamics and heat transfer of a stationary flow in the cylinder and exhaust system. The article obtained data on the flow structure in the cylinder and exhaust pipelines with different cross-sectional shapes. Additionally, the values of the turbulence number and heat transfer coefficient in the profiled exhaust pipelines were determined. Cross sections in the form of a circle (base), square and equilateral triangle were used. The thermal imaging method and the thermal anemometry method were used to determine the gas-dynamic and heat transfer characteristics of stationary flows. The studies were carried out on full-scale experimental stands. It has been established that the cross-sectional shape of the exhaust pipeline has virtually no effect on the flow structure in the cylinder. Differences in flow patterns in exhaust pipes with different cross-sections for different air flow rates through the system were shown. It was revealed that there was a decrease in the flow turbulence number in the exhaust system for profiled pipelines by an average of 25

RELEVANCE. Vertical cone diffusers are used in various technical applications: heat exchangers, gas cleaning units, boilers, industrial furnaces, dryers, ventilation devices, nozzle systems and others. For their efficient operation, it is necessary to ensure a uniform supply of the working medium to the device, which is determined by the characteristics of the flow in thediffuser. Thus, the study of the aerodynamics of technological devices with conical diffusers is an urgent task for gas-dynamic improvement and the search for ways to control flow characteristics. THE PURPOSE. To establish the evolution of the velocity field along the height of the cylindrical part of the diffuser for different configurations of the supply tubes, and also to determine the magnitude of the change in the intensity of turbulence along the height of the diffuser under different initial conditions based on experimental data on the instantaneous values of the air flow velocity. METHODS. Measurement of instantaneous values of air flow velocity is carried out using a constant temperature hot-wire anemometer. The article provides data on velocity fields and turbulence intensity along the height and along the diameter of the cylindrical part of the diffuser when air is supplied through tubes of different configurations. Feed tubes with cross sections in the form of a circle, a square and an equilateral triangle were used. RESULTS. The article provides a detailed description of the experimental stand (including key geometric dimensions), instrumentation and measurement system, and data processing techniques. The ranges of changes in the initial conditions for the experiments are presented. A comparison of the aeromechanical characteristics of flows in a vertical diffuser when air issupplied through different tube configurations is carried out. CONCLUSION. It is shown that in the diffuser there is a drop in the average velocity upstream, which is typical for all configurations of the supply tubes. It has been established that profiled tubes influence the shape of the velocity field. It was found that the values of turbulence intensity vary from 0.05 to 0.39 (the highest values were typical when air was supplied through profiled tubes). It is shown that the intensity of turbulence has its maximum values at a height of 300-350 mm, which is typical for all investigated tube configurations.

Reciprocating engines are actively used in small-scale power engineering for heat and power supply to various consumers. Reciprocating engines are also used as emergency energy sources in critical facilities and organizations. Therefore, improving the working process and design of the engine gas exchange system is an urgent task in the development of power engineering. The article is based on mathematical modeling of the working process of a reciprocating engine with a piston diameter of 82 mm and a stroke of 71 mm. The main idea of the article was to modernize (by changing the design) the gas exchange system (intake and exhaust systems) of the engine in order to improve the technical and economic indicators. A brief overview of modern scientific and technical results on this topic is presented. A description of the technical characteristics of the engine under study is given. Mathematical modeling was carried out in the Diesel-RK software (Moscow State Technical University). The main methods (algorithms) of modeling are discussed in the article. The influence of the geometric configuration of the intake and exhaust systems on the quality indicators of gas exchange and engine performance is shown. For example, it is possible to increase power up to 11

An indirect method and procedure for determining the local heat transfer coefficient in experimental studies on the intensity of heat transfer at a gas–surface interface is described. The article provides an overview of modern approaches and technical devices for determining the heat flux or friction stresses on surfaces in the study of thermophysical processes. The proposed method uses a constant-temperature hot-wire anemometer and a sensor with a thread sensitive element fixed on the surface of a fluoroplastic substrate. A substrate with the sensor’s sensitive element was mounted flush with the wall of the investigated pipeline. This method is based on the Kutateladze–Leontiev approach (the laws of friction and heat transfer) and the hydrodynamic analogy of heat transfer (the Reynolds analogy): this is an assumption about the unity of momentum and heat transfer in a turbulent flow, which establishes a quantitative relationship between friction stresses on the heat exchange surface and heat transfer through this surface. The article presents a method for determining the speed of the developed measuring system. An example of a successful application of the proposed method in relation to the study of thermomechanical processes in the gas exchange systems of reciprocating internal combustion engines is described.

THE PURPOSE. To On the basis of spectral analysis, to evaluate the effect of installing a turbocharger turbine on the aeromechanics of pulsating gas flows in the engine exhaust system and to propose a method for controlling the aerodynamic and heat transfer characteristics of unsteady gas flows by creating an ejection effect in the exhaust system.METHODS. A laboratory experiment on a full-scale piston engine model was chosen to achieve this goal. Spectral analysis of harmonic dependences was used to assess changes in the structure of gas flows in the exhaust system. Mathematical modeling of the operating cycle of diesel engines was used to assess the potential positive effects of the use of an ejection system in the exhaust tract of a diesel engine. Three-dimensional solid modeling systems were used for sketch (engineering) studies of new (modernized) exhaust system designs.RESULTS. The article describes laboratory equipment, measuring system and data processing methods. A description of the boundary conditions in the course of experimental research is given. Comparison of aeromechanical and heat exchange characteristics of unsteady flows in the exhaust system of an engine with and without a turbocharger is carried out in the article. The qualitative and quantitative differences in aeromechanics and thermal physics of processes are shown. The proposed method of aeromechanical improvement of the exhaust system by creating an ejection.CONCLUSION. It was revealed that the turbine of a turbocharger has a significant effect on the aeromechanical characteristics of flows in the exhaust system. A significant decrease in the maximum flow rate in the exhaust tract (up to 3 times) is observed when installing a turbocharger. There is a decrease in flow characteristics through the turbocharged exhaust system (within 30%). It was found that the ejection effect in the engine exhaust system leads to stabilization of the flow, an increase in gas consumption by 6-12%, a decrease in specific fuel consumption by an average of 1% and an improvement in reliability indicators by 1.11-1.74%.

Numerical simulation is often used in the study of physical and chemical processes in order to increase the efficiency and reduce the level of harmful emissions in reciprocating engines. Changing the combustion chamber geometry is one of the ways to reduce the concentration of toxic components in exhaust gases. The combustion chamber shape determines the characteristics of the movement of air and fuel in the cylinder, the features of mixing and the quality of combustion. The article is related to the study of the influence of the combustion chamber shape on the environmental performance of a diesel engine. The article provides an analysis of scientific and technical results on this topic. Four forms of combustion chambers with different geometries were investigated for a diesel engine. The research was carried out in the program "Diesel-RK" through mathematical modeling. It is shown that the combustion chamber design leads to a significant change in the content of harmful substances in the exhaust gases of the engine. The range of NOx change in the exhaust gases was 15%, СО2 – 5%, particulate matter – 70%, smoke – 60%. The article also provides recommendations for improving the environmental friendliness of an engine.

Disclosure of the physical mechanism of the influence of the turbulence intensity of gas flows on the heat transfer level in pipes of different configurations is an urgent task in the field of heat and power engineering. A brief overview of the literature on this topic is given in the article. A description of the boundary conditions for modeling is presented. The main characteristics of the experimental stand and measuring instruments are described. The purpose of this study is to study the effect of the initial turbulence level of a stationary gas flow on the heat transfer intensity in long pipes with different cross sections. The study is carried out using numerical simulation. The simulation results are qualitatively confirmed using experimental data. The values of the local heat transfer coefficient are shown to increase from 5 to 17% with increasing turbulence intensity (from 2 to 10%) in pipes with different cross sections. The heat transfer intensity in a triangular pipe is found to increase up to 30% compared to a round pipe. It is revealed that there is an up to 15% suppression of heat transfer in a square pipe compared to a round pipe. The data obtained may be useful for the design of flow paths and gas exchange systems for power machines and installations.

It is known that the initial level of gas flow turbulence has a noticeable effect on the development and structure of the boundary layer and on the intensity of heat transfer, respectively. Many scientists have evaluated the influence of the flow turbulence number on the level of heat transfer for various applications, among them Dyban E.P., Kestin J., Simonich JC, Isomoto K., Dreitser G.A., Terekhov V.I., MacMullin R. and etc. In all cases, the turbulence of the flow led to the intensification of heat transfer. However, insufficient attention is paid to studies of the effect of turbulence on the heat transfer of flows in pipes. The studies were carried out on the basis of numerical modeling of gas dynamics and heat transfer of stationary flows based on the CFD method. The results of numerical modeling to assess the influence of the turbulence scale of gas flows on heat transfer in a long smooth pipe are presented in the article. It has been established that a growth in the heat transfer coefficient by about 3% occurs with an increase in the turbulence scale from 10 to 30% with a Reynolds number equal to 250,000.

Introduction: We discuss the problem of correlated noise suppression by adaptive complex notch filters of various orders. In order to eliminate the dependence of the transmission coefficient of the useful signal on its frequency, the pulse repetition period is modulated. Purpose: Studying the influence of pulse repetition period modulation on the correlated noise suppression coefficient. Methods: The notch filter parameters were optimized with the criterion of minimum average dispersion of correlated noise at the output of the filters during the repetition period modulation. Results: Expressions are obtained for the variance of correlated noise at the output of complex adaptive filters of various orders when the repetition period is modulated. Relationships are given for finding the optimal values ​​of the tuning frequency and coefficients of the notch filters which minimize the correlated noise level at their output. Expressions are obtained for the coefficients of correlated noise suppression by notch filters in the context of pulse repetition period modulation. The graphs are presented showing how the correlated noise suppression coefficient depends on the relative value of the probing signal repetition period deviation for various values ​​of the correlated noise spectral density width at optimal or non-optimal values ​​of the tuning frequency and coefficients of the notch filters. It is shown that the use of probing pulse repetition period modulation leads to a decrease in the correlated noise suppression coefficient. On the other hand, the adaptation of the weighting coefficients for the adopted models of notch filters and correlated interference provides an increase in the suppression coefficient. Practical relevance: When developing or studying correlated noise suppression systems, the obtained results make it possible, taking into account the permissible losses of the suppression coefficient, to reasonably choose the input pulse repetition period deviation value in order to eliminate the effect of “blind” frequencies.

The article presents the results of bench tests of a single-cylinder diesel engine (dimension 7.5/6.0) with different configurations of the intake manifold. A brief description of the stand is given. The modernization consisted in the use of a section in the manifold with cross-sections in the form of a square or a triangle. The power characteristics of the diesel engine in two operating modes are presented. It was shown that the profiling of the intake manifold leads to an increase in the diesel engine power up to 17%.

The efficient operation of power machines and installations is largely determined by the initially set value of flow turbulence in gas-air systems. Consequently, the level of flow turbulence affects the formation of the boundary layer and the quality of heat transfer in the channels. The main goal of this study was to examine the effect of the turbulence scale on the heat transfer intensity from s...

THE PURPOSE. To carry out a comparative analysis of the spectra of gas-dynamic characteristics of flows in the intake systems of piston engines with and without turbocharging, to assess the degree of influence of the turbocharger on the flow structure in such systems, and also to propose a method for the gas-dynamic improvement of processes in the system under consideration. METHODS. Due to the complexity of the object of research, an experimental approach was taken as a basis. The experiments were carried out on a single-cylinder piston engine model, which could be equipped with a turbocharger. A system for collecting and processing experimental data based on an analog-to-digital converter was used in the study. Data on changes in local values of velocity and static pressure of pulsating flows in the intake system during the engine's operating cycle were obtained using a constant temperature hot-wire anemometer and a fast-acting pressure sensor. Spectral analysis of functions of flow velocity and pressure versus time was carried out on the basis of the fast Fourier transform algorithm. RESULTS. The article presents a comparative analysis of the spectra of the amplitudes of the velocity and pressure pulsations in the intake system of an engine with and without turbocharging. Also proposed is a method for stabilizing the pulsating flow in the intake system by installing a leveling grid in the outlet channel of the turbocharger compressor. CONCLUSION. It is shown that the installation of a turbocharger leads to a significant change in the structure of gas flows in the intake system of the engine. It has been established that the presence of a leveling grid in the intake system of a turbocharged piston engine leads to a decrease in the low-frequency amplitudes of the flow velocity and pressure pulsations up to 30%. It is shown that the probability of failure-free operation of an automobile engine (cylinder diameter – 82 mm, piston stroke – 71 mm) increases by almost 1% when a leveling grille is used in the intake system.

The article describes the technical characteristics for two gasoline engines that are converted to methane fuel. The study was carried out on the basis of mathematical modeling in the Diesel-RК program. It is shown that the conversion of gasoline engines to methane leads to a power reduction in the range of 7.5% with a decrease in specific fuel consumption to 12%, as well as a reduction in NOx emissions by 2–3 times. It is revealed that an increase in the compression ratio to 15 leads to an increase in the power and environmental friendliness of the gas piston engine.

THE PURPOSE. To carry out a comparative analysis of the spectra of gas-dynamic characteristics of flows in the intake systems of piston engines with and without turbocharging, to assess the degree of influence of the turbocharger on the flow structure in such systems, and also to propose a method for the gas-dynamic improvement of processes in the system under consideration. METHODS. Due to the complexity of the object of research, an experimental approach was taken as a basis. The experiments were carried out on a single-cylinder piston engine model, which could be equipped with a turbocharger. A system for collecting and processing experimental data based on an analog-to-digital converter was used in the study. Data on changes in local values of velocity and static pressure of pulsating flows in the intake system during the engine's operating cycle were obtained using a constant temperature hot-wire anemometer and a fast-acting pressure sensor. Spectral analysis of functions of flow velocity and pressure versus time was carried out on the basis of the fast Fourier transform algorithm.RESULTS. The article presents a comparative analysis of the spectra of the amplitudes of the velocity and pressure pulsations in the intake system of an engine with and without turbocharging. Also proposed is a method for stabilizing the pulsating flow in the intake system by installing a leveling grid in the outlet channel of the turbocharger compressor. CONCLUSION. It is shown that the installation of a turbocharger leads to a significant change in the structure of gas flows in the intake system of the engine. It has been established that the presence of a leveling grid in the intake system of a turbocharged piston engine leads to a decrease in the low-frequency amplitudes of the flow velocity and pressure pulsations up to 30%. It is shown that the probability of failure-free operation of an automobile engine (cylinder diameter – 82 mm, piston stroke – 71 mm) increases by almost 1% when a leveling grille is used in the intake system.

Reciprocating internal combustion engines are the most common heat engines in the world. Therefore, improving the performance of reciprocating engines is an urgent task in the development of engine building and energy. The quality of gas exchange processes largely determines the efficiency of engines. The article shows that there are practically no studies on the effect of hydraulic resistance on the gas-dynamics of pulsating flows in the inlet and final systems of engines. In this article, the results are based on experimental studies. The experimental installation and measuring base are described in the article. It is established that the presence of increased resistance in the inlet system smooths the dependences wx = f(φ) and px = f(φ). In this instance, the maximum air flow velocity and average air flow velocity in the system are reduced; this impairs the filling of the cylinder with air and, accordingly, the efficiency of the engine. It is established that a growth in the hydraulic resistance of the final system in the engine leads to a growth in pulsations of the air flow velocity during the final process. The effect of the hydraulic resistance of the final system on the flow characteristics is multidirectional. The presented results can be used in engineering practice in order to optimally select the characteristics of inlet and final silencers.