CFD-researches of centrifugal compressor stage vane diffusers

The paper presents result of CFD simulations of a series of centrifugal compressor stage vane diffusers in the Ansys CFX. Objects of research are vane diffusers with external relative diameter (relative to the diameter of the impeller) equal to 1.5, vane inlet angle of 20 degrees, relative vane heights of 0.025, 0.034, 0.045, 0.06, 0.08, vane profile curvature angles of 10, 15, 20 degrees. The characteristics of polytrophic efficiency, loss coefficient, recovery coefficient, ratio of inlet and outlet velocities, flow deviation angle versus incidence angle are set. The analysis of the flow structure in the vane diffuser channels is presented. Unlike with a straight vane cascade, the deviation angle in the circular rows of vane diffusers tends to increase with increasing row density. This may be due to the complex nature of the interaction of the active part of the flow with separation zones. In rows with almost straight vanes at a lower density, the separation zone on the pressure side decreases, and even shifts to the very end of the suction side.

Efficient Multi-Objective CFD-Based Optimization Method for a Scroll Distributor

An efficient approach to the geometry optimization problem of a non-axisymmetric flow channel is discussed. The method combines geometrical transformation with a computational fluid dynamics solver, a multi-objective genetic algorithm, and a response surface. This approach, through geometrical modifications and simplifications allows transforming a non-axisymmetric problem into the axisymmetric one in some specific devices i.e., a scroll distributor or a volute. It results in a significant decrease in the problem size, as only the flow in a quasi-2D section of the channel is solved. A significantly broader design space is covered in a much shorter time than in the standard method, and the optimization of large flow problems is feasible with desktop-class computers. One computational point is obtained approximately eight times faster than in full geometry computations. The method was applied to a scroll distributor. For the case under analysis, it was possible to increase flow uniformity, eradicate separation zones, and increase the overall efficiency, which was followed by energy savings of 16% for the scroll. The results indicate that this method can be successfully applied for the optimization of similar problems.

IMPACT OF DEFORMABLE STAMP WITH A MULTILAYERED WALL

In this paper, was performed by numerical work according to the difference scheme. Analysis of the numerical results showed: one of the important issues of contact interaction is to determine the duration of the impact of the colliding bodies. Obviously, under the condition of a hard clutch, sticking of the striker from the barrier will not occur. To study the process of complete breakage of mechanical contact (appearance of separation zones), we will use boundary conditions that simulate a perfectly smooth impact. Analysis of the dynamics of contact resistance has shown that its magnitude and features of evolution over time substantially depend on the geometric and physicomechanical parameters of the deformable system, as well as on the type of boundary conditions. An increase in the acoustic rigidity of the impactor leads to an increase in the amplitude and duration of the impact. The impact of a less rigid punch or the presence in the barrier of a shielding layer of a polymeric material reduces the contact resistance of the plate, but the force interaction between the impacted bodies is longer. As the analysis of the results shows, the evolution of contact stresses is characterized by a number of specific features. For example, there is a direct correlation between the height of the cylinder and the time of its complete detachment from the obstacle, which corresponds to the vanishing of the function   tk  . An increase in the acoustic rigidity of the impactor leads to a sharp increase in the amplitude of the total resistance and an increase in the duration of the contact interaction. Thus, the contours of the isolines provide a visual representation of the configuration of the areas at which points the stresses develop, immediately preceding the appearance of elastoplastic deformations for spall fractures (for brittle materials).

Numerical Analysis of Cavitation Inception and Desinence Behind Orifices

Experimental results and trends for cavitation inception and desinence behind orifices in microchannels are quite different from the data obtained during previous experiments in much larger facilities. The objective of this paper is to explain these differences via a numerical analysis. The employed computational procedure is divided into two parts. The first part is computation of an axisymmetric separated flow around the orifice. The second part is determination of characteristics of cavities appearing within separation zones. The provided analysis of the experimental data of other researchers pointed out two sources of the above-mentioned differences. First, for larger orifices, the cavities appear in the cores of drifting vortices. For such a situation, cavitation inception and desinence number increases with the inflow speed due to an impact of turbulence, but there is no such an increase for microbubbles with laminar flows. Second, because of the difficulty to measure the cavity pressure in microbubbles, cavitation number is usually defined with employment of the vapor pressure, and this leads to misinterpretation of the measurements and their trends.

NUMERICAL STUDY OF THE EXHAUST GAS FLOW OF TV3-117 TYPE ENGINES IN COMPOSITION WITH A SCREEN - EXHAUST DEVICE

The object of research is a screen-exhaust device in the TV3-117 engine of the Mi-8 helicopter. Investigated problem: The problem of equalizing the flow in the exhaust nozzle is solved. As a result of the numerical study, the total pressure losses are calculated and the flow structures in the structural elements of the exhaust nozzle and the screen-exhaust device (SED) are analyzed. Main scientific results: Obtained Gas-dynamic parameters of the flow in the SED flow path are obtained and the verification of injection processes between the working circuits along the path in the SED design is done. Numerical modeling of gas flows in the SED flow path makes it possible to study in detail the characteristics of the flow at any of its points, as well as to determine the values of hydrodynamic losses associated with the formation of a boundary layer and the emergence of separation zones. A constructive method for leveling the gas-dynamic flow is proposed by installing a blade in the form of an aerodynamic profile in a standard engine exhaust nozzle. Two variants of engine nozzles are investigated under the same boundary conditions using a standard exhaust nozzle with and without a blade. The influence of uneven flow in the exhaust nozzle on the nature of the flow in the SED is shown. An insignificant equalization of the flow in the exhaust nozzle using the installed blade led to a decrease in the total pressure loss in the SED by more than 1 %. The area of practical use of the research results: The results of calculations and modeling can be used for computational and experimental studies aimed at improving the flow path of the exhaust nozzle and the screen-exhaust device by the developers of new military aviation equipment or when modernizing the existing helicopter fleet. Scope of application of the innovative technological product: a new screen-exhaust device has been proposed for left and right TV3-117 engines of all types, which can be installed on the Mi-8MSB-V, Mi-8MT, Mi-14, Mi-24 helicopters. It is competitive and has significantly higher technical and economic indicators compared to known analogues.

Confined multiphase swirled flows in chemical engineering

Exploration of confined swirled flows in the former USSR and present-day Russia has a long history and is presented by numerous publications, mostly written in Russian. The obtained results have been put to practical use in different areas of chemical, energy, and processing industries. In view of the process intensification concept, such characteristics of confined swirled flows may be considered unique: high centrifugal gravity, elongation of trajectories, the presence of internal separation zones, energy separation phenomena, and efficient mass/heat transfer in the absence of any moving parts. For instance, high gravity provides an excellent opportunity for multiphase flow stabilization, preventing the appearance of nonuniformities and stability loss, while enhancement of various driving forces acting on the reaction medium takes place. This review is devoted to outlining the main research trends and to discuss the most essential practical implementations in the subject matter done up until now. It is not foreseen to embrace the whole area of swirled flow investigations in the world, but only covers most of the significant ideas and applications contributed in by former Soviet and Russian scientists and engineers. Shortcomings and difficulties of using swirled flows are also briefly discussed.

Наносекундная ионизация области обтекания прямоугольного уступа высокоскоростным потоком

The phenomenon of pulsed volume discharge plasma and current redistribution based on self-localization in an unsteady flow in a shock tube with 48 x 24 mm cross section is described. It is shown that in the gas-dynamic channel with a parallelepiped-shaped step in the flow behind theshock wave with Mach numbers of 2.8 - 3.5, short-lived plasma channels are formed in the separation zones near the step within 2800 μs.

Numerical and Wind Tunnel Simulation Studies of the Flow Field and Pollutant Diffusion around a Building under Neutral and Stable Atmospheric Stratifications

In this paper, the k–ε renormalization group (RNG) turbulence model is used to simulate the flow and dispersion of pollutants emitted from a source at the top of a cubic building under neutral and stable atmospheric stratifications, the results of which were compared with corresponding wind tunnel experiment results. When atmosphere stratification is stable, the separation zones on the sides and at the top of a building are relatively smaller than those under neutral conditions, and the effect of the building in the horizontal direction is stronger than that in the vertical direction. The variation in turbulent kinetic energy under stable conditions is significantly lower than that under neutral conditions. The effect of atmospheric stratification on the turbulent kinetic energy becomes gradually more prominent with increased distance. When atmosphere conditions are stable, the vertical distribution of the plume is smaller than that of neutral conditions, but the lateral spread and near-ground concentration are slightly larger than those of neutral conditions, mainly because stable atmospheric stratification suppresses the vertical motions of airflow and increases the horizontal spread of the plume.