Critical speed

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

Nonparametric Stochastic Modeling of Structural Uncertainty in Rotordynamics: Unbalance and Balancing Aspects

Abstract: This paper focuses on extending an earlier investigation on the systematic and rational consideration of uncertainty in reduced order models of rotordynamics systems. The current effort concentrates on the consistent introduction of uncertainty in mass properties on the modal mass and gyroscopic matrices as well as on the unbalance force vector. The uncertainty in mass is separated into uncertainty that maintains the rotor symmetry and the one which disrupts it. Both types of uncertainties lead to variations in the system modal matrices but only the latter induces an unbalance. Accordingly, the approach permits the selection of separate levels on the uncertainty on the system properties (e.g. natural frequencies) and on the unbalance.It was first found that the unbalance response is increased by considering the uncertainty in the rotor modal mass matrices. It was next noted that the approach presented not only permits the analysis of uncertain rotors but it also provides a computational framework for the assessment of various balancing strategies. To demonstrate this unique feature, a numerical experiment was conducted in which a population of rotors were balanced at low speed and their responses were predicted at their first critical speed. These response predictions were carried with the uncertainty in the system modal mass matrices but with or without the balancing weights effects on these matrices. It was found that the balancing at low speed may in fact lead to an increase in both the mean and 95th percentile of the response at critical speed.Copyright © 2013 by ASME

Permanent automatic rotor balancer for shafts operating above critical speed

Abstract: A pair of balancing weights are mounted on opposite sides of the center line of the rotor for movement about the axis of the rotor. The weights are automatically locked against movement about the axis of the rotor when the rotor is rotating below critical speed and automatically released for free movement about the axis of the rotor when the rotor is rotating above critical speed. The weights are exemplified as roller cages. The balancing weights are variously locked by mechanical clutches actuated at critical speed. The clutching for the weights is either individual or such that the weights are necessarily locked against movement and released simultaneously. Centrifugal force is used to control the clutches.

The Analytical Imbalance Response of Jeffcott Rotor During Acceleration

Abstract: The characteristics of the transition vibration of a rotor system when it passes its critical speeds during acceleration are of great interest for active vibration control, active real-time balancing @1#, and rotor design. In the past, a few analyses @2‐8# have dealt with speed varying transient rotor dynamics. These researchers used numerical integration techniques to calculate numerical solutions to the transient dynamic model. Although these models can be used to predict the transient vibration for a complicated rotor system, it remains hard to obtain the quantitative characteristics of the transient vibration. Lewis @9# and Dimentberg @10# presented an analytical solution of the problem of running a rotor system through its critical speeds at a uniform acceleration. The basic characteristic of the ‘‘envelope’’ ~amplitude! of the transient vibration was studied by an approximation method. In this paper, their work is extended. An analytical expression of the motion of the geometric center of a simple Jeffcott rotor is derived. The exact ‘‘envelope’’ and ‘‘phase’’ of the transient vibration are presented. As stated in Dimentberg @10#, it is found that the transient vibration through critical speeds consists of free vibration and synchronous vibration. Explicit expressions of these two components are presented in this paper.

Experimental Investigation of Surge and Stall in a High-Speed Centrifugal Compressor

Abstract: Flow instability, known as surge and stall, limits the stable operating range of compressors. In this paper, a panoramic map of instability evolution across all typical operations is experimentally demonstrated for the first time in a high-speed centrifugal compressor with a maximum speed of 185,000 r/min and a corresponding rotation velocity at the impeller outlet of 593 m/s. Twelve high-response Kulite pressure probes are mounted on the internal surface of the compressor’s casing. The experimental results show that the instability phenomena are quite complex and diverse at different operations. At low speed (<70% of the maximum speed), high-frequency and low-frequency stall successively occurs at the impeller, and is followed by surge as mass flow rate reduced. The transient process of surge is a transient stall/unstall self-loop, with the “self-similarity” to the sustainable stall/unstall conditions. At 70% of the maximum speed, the system exhibits two types of surge, a minor-amplitude periodic surge...