Today, with the increases in organic fuel prices and growing legislative restrictions aimed at increasing environmental safety and reducing our carbon footprint, the task of increasing thermal power plant efficiency is becoming more and more topical. Transforming combusting fuel thermal energy into electric power more efficiently will allow the reduction of the fuel cost fraction in the cost structure and decrease harmful emissions, especially greenhouse gases, as less fuel will be consumed. There are traditional ways of improving thermal power plant energy efficiency: increasing turbine inlet temperature and utilizing exhaust heat. An alternative way to improve energy efficiency is the use of supercritical CO₂ power cycles, which have a number of advantages over traditional ones due to carbon dioxide’s thermophysical properties. In particular, the use of carbon dioxide allows increasing efficiency by reducing compression and friction losses in the wheel spaces of the turbines; in addition, it is known that CO₂ turbomachinery has smaller dimensions compared to traditional steam and gas turbines of similar capacity. Furthermore, semi-closed oxy–fuel combustion power cycles can reduce greenhouse gases emissions by many times; at the same time, they have characteristics of efficiency and specific capital costs comparable with traditional cycles. Given the high volatility of fuel prices, as well as the rising prices of carbon dioxide emission allowances, changes in efficiency, capital costs and specific greenhouse gas emissions can lead to a change in the cost of electricity generation. In this paper, key closed and semi-closed supercritical CO₂ combustion power cycles and their promising modifications are considered from the point of view of energy, economic and environmental efficiency; the cycles that are optimal in terms of technical and economic characteristics are identified among those considered.

Currently, software products for numerical simulation of fluid dynamics processes (Ansys, Star CCM+, Comsol) are widely used in the power engineering industry when designing new equipment. However, computer simulation methods embedded in proprietary software products make specialists choose grid settings, boundary conditions, and a solver providing the minimal deviation from experimental data with the maximal calculation speed. This paper analyzes the influence of the main grid settings and boundary conditions in the Ansys software package on the error in the computer simulation of flows in standard elements of power equipment and gives recommendations for their optimal choice. As standard elements were considered blade turbine channels formed by C-90-22 A profiles.

At present, software products for numerical simulation of fluid dynamics problems (ANSYS Fluent, Ansys CFX, Star CCM, Comsol, etc.) problems are widely used. These software products are mainly based on the numerical solution of the Navier–Stokes equations, the most common and computationally easy method of solving, which is Reynolds averaging (RANS), and further closing the system using semi-empirical turbulence models. Currently, there are many modeling methods and turbulence models; however, there are no generalized recommendations for setting up grid models for modeling flows, while for practical use both the correct mathematical models and the setting of the computational grid are important. In particular, there are no generalized recommendations on the choice of scale of global elements of grid models for typical single channels. This work is devoted to the development and study of relations for a priori estimation of the parameters of a grid model in relation to solving hydrodynamic problems with fluid flow in channels. The paper proposes the introduction of a generalized grid convergence criterion for single channels at high Reynolds numbers. As single channels, a channel with a sudden expansion, a channel with a sudden contraction, and diffuser channels with different opening angles are considered. Based on the results of variant calculations of typical single channels at various Reynolds numbers and various geometric parameters, generalized criterion correlations were obtained to find dimensionless linear scales of grid elements relative to the hydrodynamic characteristics of the flow in the channel. Variant calculations of the compound channel were investigated, which showed the adequacy of correlations proposed.

A numerical study was carried out of thermohydraulic processes in slot channels with heat transfer intensifiers in the form of staggered arrays of drop-sha

The study examines the fundamental technical characteristics of bladeless propulsors intended for advanced turbofan propulsion systems in multicopter unmanned aerial vehicles. The research identifies optimal aspect ratios that maximize thrust and thrust efficiency while analyzing the impact of fan radius and annular gap thickness on propulsion efficiency under constant flow rate and length conditions. The findings indicate that the most efficient configuration features a fan radius of 175 mm, a length of 150 mm, and an air mass flow rate of 0,3 kg/s, yielding an exit Mach number of 0,42. This configuration generates a thrust of 44 N while maintaining high-speed jet momentum conservation at 92 %, under a total inlet pressure of 17,800 Pa

The article presents the results of an experimental study of the flow structure and temperature field in a plume formed above a low-power burner flame. The pulsation and spectral characteristics of the flow at key sampling points were analyzed, which allowed us to draw a conclusion about the nature of the flow at the main points of the jet. It is proposed to use time series of changes in the point displacement field to analyze the spectral characteristics of the flow. In this work, the Background Oriented Schlieren method was used to visualize the flow and determine temperatures followed by post-processing in the program developed during the study. The advantage of this approach compared to the traditional optical Schlieren method is that there is no need for parabolic mirrors as well as the ability to obtain results in digital form convenient for further processing. During the experiment, a special background with randomly located bright dots was placed behind the object of study which was filmed by a video camera. Fluctuations in the medium density caused changes in the refractive indices of the medium, as a result of which the points on the background of the video frames displaced, and the displacements of the points was proportional to the change in the refractive index which in turn is proportional to the density gradient and, accordingly, to the temperature gradient of the medium. The displacement of the points was determined by cross-correlation analysis of each frame in comparison with the frames in the absence of disturbances. Then the displacement field was filtered by a median filter in order to minimize noise and statistical outliers. The filtered displacement field was used to calculate the temperature field, while solving the Cauchy problem for temperature with a known derivative at a point and specified boundary conditions. A set of instantaneous point displacement fields, instantaneous and time-averaged temperature fields was obtained, which allowed us to draw conclusions about the flow structure. At characteristic points of the jet, oscillograms of the displacement value were obtained as well as pulsation spectra with an inertial interval corresponding to the “–5/3” law. The approach proposed in the work allows, in addition to contactless study of the temperature field, also studying turbulent flow pulsations in the case of close to two-dimensional or axisymmetric flows.