The study presents evaluation of optical measurements of the air flow field near the fluttering profile NACA0015 with two-degrees of freedom, Mach number of the flutter occurence were M = 0.21 and M = 0.45. Aerodynamic forces (drag and lift components) were evaluated independently on the upper and lower surfaces of the profile. Using the mentioned decomposition, the new information about mechanism of flutter properties was obtained. The forces on the upper and lower surfaces are phase shifted and are partially eliminated as a result of the circulation around the profile. The cycle changes of these forces cause the permanent energy contribution from the airflow to the vibrating system. and Obsahuje seznam literatury
Analysis of two methods used for ascertaining stability of dynamical systems was carried out on a mathematical model of experimental stand of aerodynamic bearings. It was proofed that method of direct eigenvalue calculation gives practically the same results, which are obtained from the solution of equations of motion by means of integral Runge Kutta procedure. and Obsahuje seznam literatury
Paper deals with subject of identification of aerostatic journal bearings dynamic properties with use of Rotor Kit Bently Nevada superstructure. Different bearing types were experimentally investigated and their static and dynamic characteristics were identified. Various methods of identification were used and spectral and modal properties of the system were calculated. Computer program was revised on the basis of experimental data. The influence of non-diagonal stiffness and damping elements was investigated by numeric stimulation. and Obsahuje seznam literatury
A frequently used technological solution of reducing the time varying forces transmitted between the rotor and its casing is represented by application of a flexible suspension with damping devices added to the constraint elements. To achieve their optimum performance their damping effect must be controllable. For this purpose a concept of a hybrid damping device working on the principle of squeezing the layers of normal and magnetorheological oils have been developed. Here in this article, there is investigated influence of the proposed damping element on stabilty of the rotor vibrations induced by its imbalance during the steady state operating regimes. The stability is assessed by the evolutive method which is based on evaluation of eigenvalues of the system linearized in a small neighbourhood of the rotor phase trajectory and calculation of the corresponding damping ratio or logarithmic decrement. and Obsahuje seznam literatury