Critical speed

About: Critical speed is a research topic. Over the lifetime, 2764 publications have been published within this topic receiving 31365 citations.

Free vibration and critical speed of moderately thick rotating laminated composite conical shell using generalized differential quadrature method

Abstract: The generalized differential quadrature method (GDQM) is employed to consider the free vibration and critical speed of moderately thick rotating laminated composite conical shells with different boundary conditions developed from the first-order shear deformation theory (FSDT). The equations of motion are obtained applying Hamilton’s concept, which contain the influence of the centrifugal force, the Coriolis acceleration, and the preliminary hoop stress. In addition, the axial load is applied to the conical shell as a ratio of the global critical buckling load. The governing partial differential equations are given in the expressions of five components of displacement related to the points lying on the reference surface of the shell. Afterward, the governing differential equations are converted into a group of algebraic equations by using the GDQM. The outcomes are achieved considering the effects of stacking sequences, thickness of the shell, rotating velocities, half-vertex cone angle, and boundary conditions. Furthermore, the outcomes indicate that the rate of the convergence of frequencies is swift, and the numerical technique is superior stable. Three comparisons between the selected outcomes and those of other research are accomplished, and excellent agreement is achieved.

Thermohydrodynamic Model Predictions and Performance Measurements of Bump-Type Foil Bearing for Oil-Free Turboshaft Engines in Rotorcraft Propulsion Systems

Abstract: An engineered thermal management is fundamental to the application of gas foil bearings (GFBs) as turboshaft supports in rotorcraft propulsion systems. The paper presents a model for the thermal energy transport in a rotor-GFB system operating at high temperature with typical inner and/or outer cooling flows. Predicted film temperatures agree with published test data, demonstrating the effectiveness of an outer cooling stream to remove heat and to control the operating temperature. The inner flow stream is not as efficient. The analysis shows paths of thermal energy by conduction and convection to assist in the design and troubleshooting of rotor-GFB systems operating hot. Bearing temperatures and shaft motions measurements are obtained in a test rotor electrically heated to 132°C. In speed-up tests to 26 krpm, the rotor motion amplitude drops suddenly just above the critical speed, thus, evidencing the typical hardening of compliant bearings. At the hottest test condition, since air is more viscous, the rotor peak motion amplitude decreases, not showing a jump. The coastdown tests show the critical speed increases slightly as the temperature increases.

Flywheel set for accumulating kinetic energy of rotation

Abstract: Flywheel set for accumulating energy with elastically supported bearings, resulting in a low critical speed, lying at all times under the operational flywheelspeed. The axial thrust taking bearings, or one bearing, may be operating with magnetic forces. Spherical pivot bearings may be fitted both at the bottom and at the top of the rotor.