Critical speed

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

Small Gas Turbine Engine Operating With High-Temperature Foil Bearings

Abstract: A 134 Newton thrust class, 120,000 rpm turbojet was redesigned to incorporate a high-temperature compliant foil bearing aft of the turbine rotor and a compliantly mounted ball bearing forward of the centrifugal compressor–cold section. Two rotor-bearing system configurations were evaluated, one for operation above the bending critical speed and one for rigid rotor operation. Required characteristics for the foil bearing and ball bearing equipped with compliant foil damper mount were determined through a series of design tradeoff studies evaluating critical speeds and system stability. Following the design studies, the necessary hardware was fabricated, the engine assembled and operation to full speed achieved. Engine speed, rotor vibrations, compressor discharge pressure, exhaust gas temperature, thrust and fuel consumption were all recorded for both a baseline fluid lubricated ball bearing supported engine and the new turbojet engine using the hybrid foil bearing support system. Issues related to high-speed operation above the bending critical speed are identified and recommendations offered. Engine test data show that approximately 10% less fuel is consumed by the hybrid foil bearing mount system than the baseline conventional design. It is also shown that the foil bearing life was longer than the ball bearing life even though the foil bearing operated in the exhaust gas stream at temperatures exceeding 800°C. The results of this program demonstrate the feasibility of developing a completely oil-free foil bearing gas turbine engine.Copyright © 2006 by ASME

An analysis of the electric spindle's dynamic characteristics of high-speed grinder

Abstract: Structural parameters are important factors that affect the dynamic performance of the electrical spindle of high-speed grinder. In this study, the influences of the electric spindle's major structural parameters on its dynamic characteristics are investigated. Based on the transfer-matrix method and taking into consideration the gyroscopic couple, the shear, the variable cross-section, and other influential factors, a dynamic model is established for the multidisk rotor of the rotor-bearing system of the electric spindle. The critical speeds of first three orders, the modes of variation, and other dynamic characteristic parameters of the electric spindle are programmed and calculated. The influences of the axial pre-tightening force of the bearing, the span of the fulcrum bearing as well as the changes in the front and rear overhangs on the critical speed of the rotor-bearing system on the electric spindle and their pattern of changes are analyzed. The results show that the span of the fulcrum bearing and the overhang have significant influences on the critical speed within a certain range, and the study provide the basis and guidance for the structural design and performance optimization of the electric spindle.

Vibration Suppression of Rotating Machinery Utilizing Discontinuous Spring Characteristics (Stationary and Nonstationary Vibrations)

Abstract: In rotating machinery, resonance phenomena occur with large amplitude in the vicinities of the major critical speeds. In this paper, a new vibration suppression method utilizing a discontinuous spring characteristic is proposed. This spring characteristic is achieved using additional springs with preload. This method has the following advantages. (1) In designing these additional springs, we need not adjust their parameter values to the optimal ones, which are determined by rotor stiffness and the system damping. (2) The amplitude of vibration can be suppressed to any desired small level. (3) This method is also effective for nonstationary vibration. Although the method has a disadvantage that an almost periodic motion occurs above the major critical speed, two countermeasures are proposed to diminish it. The characteristics of the vibration suppression are demonstrated theoretically and experimentally.

Speed limiting method for vehicle, involves modifying pedal deflection velocity curve such that vehicle's reaction to velocities within speed tolerance range is less sensitive than velocities outside of speed tolerance range

Abstract: The method involves predetermining a critical speed (101) containing speed tolerance range. A pedal deflection velocity curve is modified (103) in such a manner that a vehicle's reaction to velocities within a speed tolerance range is less sensitive to pedal deflections than the velocities outside of the speed tolerance range. The critical speed is determined by a road sign recognition system or by a position determination system based on critical speed stored in the vehicle. The critical speed is canceled by a kick-down with pedals. An independent claim is also included for a velocity delimiter for a vehicle.