Vol 20, No 4 (2021)

The paper presents the results of a stage of development of an analytical model for assessing the impact of various defects on the operation of an axial-flow compressor. Some recommendations on setting the numerical models for carrying out gas dynamic and strength analysis of compressor stages and blades with account for various defects are proposed. Verification was carried out for the models presented: the results are also presented in the paper. On the basis of the verification results some special aspects of CFD-modeling are discussed. The requirements for the defects under investigation are defined. A classification of the defects that can be analyzed with the use of the developed mathematical description of the geometry of airfoils and blades with account of all proposed recommendations for the setting of the numerical model is presented.

Some data on the knowledge base to support the development of low-thrust liquid-propellant rocket engines using computer technologies are presented. The structure of the base is proposed on the basis of characteristic features of engines, including the purpose, fuel components, physical principles of organizing the work process of the engines, etc. The presence of electronic versions of schematic diagrams, configuration and the main achieved characteristics in the database will make it possible to choose effective design solutions at the design stage of new products.  In the future these solutions will lead to the required parameters and characteristics of the low-thrust rocket engines being developed. The description of the engine used in the database allows assessing the capabilities of the engineering solution used in the design, as well as tracing the development trends of a particular direction in rocket propulsion. The peculiarity of the base being created is that, in parallel with the information about low-thrust rocket engines, the data on their components and accessories is accumulating, which can also be used in new developments. Given the growing volume of the knowledge base on low-thrust rocket engines, some forms of communications are presented that make it possible to quickly find the required information, but requires certain ordering of the design data already at the initial stages.

Modern aircraft need increased maneuverability to maintain a competitive position. One way to improve this characteristic is to use methods to adjust the thrust vectors of a jet engine nozzle. One method of controlling nozzle thrust is the use of nozzle interceptors – devices of various shapes that extend into the nozzle channel and cause an uneven distribution of pressure along the walls of the channel. The extension of the rod interceptor near the critical section of the nozzle creates a greater lateral force than the extension of the rod near the exit section. The dependence of the lateral force on the extension height is nonlinear. The article presents a description of a nozzle interceptor of a cylindrical shape extended from the channel wall. Numerical simulation of gas flow in the nozzle with a cylindrical interceptor was carried out. The patterns of gas flow in the channel and in the environment outside the nozzle are presented. The plots of the lateral and axial components of the thrust force against the interceptor rod length are also presented for both cases of the rod location. Rod interceptors can be used in combination with other correcting devices. 

The article describes a method for experimental evaluation of the stiffness of an elastic damper ring.   A thin-walled low-stiffness ring with uniformly distributed smooth protrusions on the inner and outer surfaces acts as a damper ring. Despite the widespread use of such a design in domestic and foreign mechanical engineering, control of the characteristics of this element and, accordingly, of the support as a whole remains quite difficult. A numerical model was developed, the reliability of which is confirmed by analytical calculations. To check the data obtained by numerical calculations, a special device was designed, which was installed on the “galdabini” tensile testing machine, where a series of measurements was carried out. Analysis of the data obtained showed a significant difference between the numerical, analytical and experimental data, which can be explained by the discrepancy between the equipment used and the boundary conditions of the theoretical model. The parameters of the device were selected in such a way that its rigidity was much higher than the rigidity of the elastic ring under study. The paper describes the improvement of both the design of the device and the method for determining the stiffness of the elastic ring of the damper using the specified measuring equipment. After making corrections, the obtained data on the scatter of the stiffness of the elastic ring are in good agreement with the analytical and numerical dependence, which makes it possible to use the data of the latter to refine the analytical methods in the future

The reason for the failure of carbide end mills is the chipping of the cutting edges at the transition from the radius edges to the helix edges on the cylindrical part of the cutter. One of the reasons for the chipping of the cutting edges are the vibrations of the end mills which arise due to the intermittent cutting process and the variability of forces acting on the end mill. The principle of operation of a vibration measuring device is considered which allows vibration measurements to be carried out when milling with an end mill. The main measuring elements of the device are two eddy current sensors that allow measuring the vibration displacement of the milling cutter in two directions – perpendicular and parallel to the movement of the longitudinal feed. The device has a compensation sensor that takes into account the influence of related factors, and a sensor for fixing the instantaneous rotation speed of the machine spindle. The milling cutter itself, fixed in a collet chuck, was used as an elastic element of the oscillating system. The data of measuring the amplitude of vibrations during milling of titanium alloy VT9 with a four-tooth and six-tooth end mill are presented. The study of vibrations of end mills included two stages. At the first stage, the influence of milling parameters and modes, as well as milling schemes (up and down milling) on the frequency and amplitude was investigated. At the second stage, measures were worked out to reduce the intensity of vibrations and increase the reliability and durability of the milling cutters. The research results showed lower amplitude values when working with a six-tooth cutter.