In this article, a theoretical analysis of the flows arising in the cross sections of fluid and gas flows is performed. Such flows are subdivided into secondary flows and coherent structures. From experimental studies it is known that both types of flows are long-lived large-scale movements (LSM) stretched along the flow. The relative stability of the vortices is traditionally explained by the fact that the viscous friction forces that inhibit the rotation are compensated by the intensification of the swirl when moving slowly rotating peripheral layers to the center of the vortex due to longitudinal tension. An analysis of this mechanism made it possible to develop a relatively simple model of vortex structures in which the viscous friction forces and axial expansion are considered to be infinitesimal. Under these assumptions, one can use the equations of motion of an ideal fluid in the variables “stream function - vorticity”. It is shown that under certain assumptions these equations take the form of a wave equation, and the boundary conditions are the condition that the stream function on the solid walls of the flow equals zero. The obtained solutions of the wave equation describe the following special cases: Goertler’s vortices between rotating cylinders, secondary flows in a pipe with a square cross section, swirling flow in a round pipe, paired vortex after bend of the pipe. The physical sense of more complex solutions of the wave equation has become clear relatively recently. Very similar structures were found in experimental studies using orthogonal decomposition (POD) of a turbulent pulsations field. This may mean that the eigenfunctions in the POD correspond to coherent structures that really arise in the flow. The results obtained confirm the hypothesis that secondary flows and coherent structures have a common nature. The solutions obtained in this paper can be used in processing the experiment as eigenfunctions for the orthogonal decomposition method. In addition, they can be used in direct numerical simulation (DNS) of turbulent flows

The containment system (CS) is the last barrier to the release of radioactive substances into the environment in the event of a nuclear accident. After each overload, this system is tested for its ability to perform its functions by determining the integral leakage, which should not exceed a certain value. The tests are performed at an overpressure in the CS of 0.72 kgcm–2, which is achieved by injecting air with a compressor. The paper considers the use of an ejector to accelerate the injection process, which has a positive effect on the technical and economic performance of a nuclear power plant (NPP) power unit by increasing the amount of electricity generated, which is very important today, when the NPPs provide the maximum share of electricity generated in the country. Previous studies have evaluated the use of an ejector for this purpose, but they did not consider the need to install filters on the intake air stream. In addition, they used numerical methods that generate an error. The present work uses a mathematical apparatus that provides a more accurate result. The obtained calculated compressor injection time coincides with the actual injection time for the Rivne NPP power units. The design of the ejector ensures the minimum injection time is determined. The optimal ejector module is equal to 8.6 (the ratio of the cross-sectional area of the cylindrical mixing chamber to the critical cross-sectional area of the working air nozzle). This reduces the injection time by 38.8%. The suction air must be free of dust and moisture. Suitable filters have a total aerodynamic resistance of 0.2 bar. Taking these air filters into account slightly reduces the efficiency of the ejector. The final time of air injection using the ejector is 2.56 h, which reduces the time of air injection for testing by 35.5%.

The article is devoted to solving a practical problem: the choice of equipment for pre-treatment of salt water that feeds the desalination plant. The preliminary stage of desalination is the purification of water from sand particles, which can significantly reduce productivity and even damage the desalination plant, which is situated at the next stage. For pre-treatment, settling tanks, hydrocyclones, sand filters, etc. are used. The main dimensions of hydrocyclones of standard designs are calculated based on well-known recommendations. Modern computer simulation systems allow you to create three-dimensional models of the apparatus being studied, and then calculate the velocity and pressure fields in them. It was necessary to estimate the amount of sand contained in the feed water. To solve this problem, an experimental hydrocyclone was developed and manufactured. The hydrocyclone was numerically simulated and the sand capture coefficient was estimated under various operating conditions. It has been established that an experimental hydrocyclone reliably captures grains of sand 50 microns in size and above. The average daily mass of trapped sand was experimentally determined. Numerical modeling made it possible with reasonable accuracy to estimate the sand capture coefficient by an experimental hydrocyclone. During the tests, the mass of sand entering the pipeline per day was determined. The hydrocyclone reliably captures sand particles of 50 microns or more. At the same time, a significant part of particles less than 50 microns is not captured by the hydrocyclone, which is why a sand filter was chosen for industrial use. In the future, it is advisable to use a serial connection of a hydrocyclone and a sand filter, but such a solution requires additional technical and economic calculation. It is concluded that in the case under consideration, it is advisable to use a sand filter for preliminary water treatment

The object of research is methods for reducing the level of air pollution in working areas with industrial dust. The problem of reducing the impact of dustiness of production premises on the workers' health is solved by improving the aspiration air purification system. A new approach is proposed that provides the blower (fan) with an additional purification function by attaching a dust collector to its housing. By organizing the circulation movement of the dust-gas flow, part of the dust settles in the dust collector before it enters the main dust collector. Such a combined dust collector can be used as an independent device in closed aspiration systems or as part of complex dust removal systems, reducing the load on the main device. A methodology for calculating purification indicators has been developed, which is based on the discretization of the differential dust mass distribution curve by particle size. The method allows to assess the efficiency of the process, determine the dimensions of the dust collection container and the frequency of dust discharge from it. The technology was used for the air aspiration system of the working area of the building materials processing facility to reduce the risk to workers' health from air pollution. The calculations have established the conditions of acceptable non-carcinogenic risk at the level of construction dust concentration not higher than 61.42 mg/m3, and with the introduction of the proposed combined dust collector, it is possible to increase the dust level to 99.1 mg/m³ without exceeding the risk threshold. The proposed technology is cost-effective, requires minimal design changes and can be implemented at most industrial facilities, especially in conditions of high dustiness of production premises.