Journal of Dynamics and Vibroacoustics

The article considers the influence of unstady processes on the calculated estimate of the surface temperature of the hub cavities and the degree of hot gas inflow using a two-stage axial turbine of a gas turbine engine as an example. A distinctive feature of the study is the use of a CFD model that simultaneously includes the domains of all turbine blades (nozzle and working) and three inner hub cavities. The modeling was performed both in stationary and non-stationary settings in the ANSYS CFX program. The paper describes in detail the requirements necessary for performing high-quality non-stationary modeling. It was found that due to the circumferential unevenness of the flow behind the blade rows, hot gas flows into the liner hub cavities of the turbine, which causes additional heating of the turbine structural elements. It was also found that the gas temperature in the tract cavities obtained in the non-stationary calculation is significantly (by up to 18%) higher than that determined in the stationary calculation. The reason for such a discrepancy is the peculiarity of the rotor-stator interface operation in a stationary calculation. A significant (up to 7%) fluctuation in gas temperature in the cavities per one rotor revolution was also revealed. The paper concludes that correct determination of the temperature of turbine rotor elements in the hub cavities is possible only in a non-stationary calculation.

The article determines the degree of influence of laser shock peening parameters (power density, number of passes and percentage of laser spot overlap) on the depth of residual compressive stresses. An empirical dependence of the depth of compressive residual stresses on the parameters of laser impact treatment is obtained. It is found that the number of passes and power density have the greatest influence on the depth of residual stresses. A graph of the dependence of the depth of residual stresses on the parameters of laser shock peening is presented. It is found that by varying the parameters of laser shock peening it is possible to achieve a depth of residual compressive stresses up to 0.8 mm. A microstructural study was conducted on samples both with and without a protective layer. It was found that laser impact treatment without a protective layer resulted in numerous cracks in the surface layer at a depth of 3-6 µm. Using a protective layer eliminates this. It was shown that laser impact treatment resulted in the formation of several layers with different orientations: a surface layer up to 130 µm deep, a transition layer up to 240 µm deep, and then a base layer. Laser shock peening of flat samples made of titanium alloy 2 mm thick was performed on one side by a solid-state Nd:YAG laser with a wavelength of 1064 nm. Aluminum foil 80 μm thick was used as a protective layer.

The article presents the results of experiments investigating the observed effect of significant force interaction between a rotating unbalanced disk and screens (or frames) located nearby under conditions of the transmission of circular vibration from the disk to them. It is demonstrated that this additional force effect on the limited-mobility elements of devices during the excitation of circular vibration is not a simple mechanical effect of vibration acceleration. It has been experimentally established that in this case, either dynamic repulsion or high-amplitude oscillations of the limited-mobility structural elements occur at a frequency that does not coincide with the rotational frequency of the unbalanced disk. The significant cyclic (impulse) forces that arise in this case are always directed along the axis of the rotating unbalanced disk (rotor). The manifestation of the additional force interaction effect qualitatively depends on the relative positions of the structural elements. Additional forces and torques arose only when the screens (frames) were located above the disk contour at a distance of no more than 4–5 mm and at a rotational frequency of the unbalanced disk itself exceeding 120–140 Hz. In the absence of circular vibration transmitted from the disk to these structural elements of the devices, no additional force loading was observed. Additional force effects arising under these conditions can cause deformation or failure of mechanical components located close to the rotor if intense circular vibration occurs due to rotor imbalance.

The motion of a spacecraft with a gravitational attitude control and stabilization system relative to its center of mass in the plane of its circular orbit is studied. The spacecraft contains a damper body, which has a triaxial ellipsoid of inertia but is geometrically spherical. The interaction between the spacecraft body and the damper body occurs through a thin layer of lubricating fluid with known kinematic viscosity. A mathematical model is constructed for the planar motion of the system under the action of a gravitational moment on both bodies (body and damper). The dissipative effect of the damper, consisting of a decrease in oscillation amplitude over time, is demonstrated numerically and analytically. Based on the results of numerical calculations and approximate analytical solutions obtained using asymptotic methods, the oscillation damping time is estimated for the case of small oscillations.