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Critical speed

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


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Journal ArticleDOI
TL;DR: In this article, a new kind of active magnetic stabilisation is proposed to overcome those limits, which provides an asymptotic dynamic stability of both the forward and backward whirling motions, even in the high supercritical regime.

12 citations

DOI
15 May 2018
TL;DR: The resulting robust optimum design ensures optimum rotor-bearing performance, even at the most severe operating conditions and even if all manufacturing tolerances represent the worst case scenario.
Abstract: In the competitive automotive market, the performance of turbochargers is constantly being pushed towards their theoretical optimum. One of the key components of the turbocharger is the rotor-bearing system, which determines the friction losses and noise output and furthermore affects the overall turbocharger efficiency, reliability and cost. In order to fulfil the demands of the automotive market, developing methods to optimize the rotor-bearing system is the focus of this study, where particular attention is paid to taking into account the product-to-product variations that are inevitable in cost-effective mass-produced parts, as well as the variations in turbocharger operating conditions. First, a model of the rotor-bearing system was developed to predict the rotordynamic response over the operating range. The model is constructed in a step-by-step fashion, starting with a simple test case: a Laval rotor supported by plain journal bearings. As the behavior of the rotor-bearing system varies over its rotation speed range, run-up simulations were performed by a time-transient multi-physical model. In this model, several sub-models are coupled: a rotordynamic sub-model, a thermo-hydrodynamic submodel and a thermal network model. Once a satisfactory correlation was found between numerical simulation results and measurement results, the test case progressed to a Laval rotor with floating ring bearings instead of plain journal bearings. Correspondingly, the bearing model was extended to include the dynamics of the floating ring and its two oil films. The resulting run-ups showed a response consisting of a critical speed, an oil whirl and an oil whip. Analysis of a turbocharger rotor-bearing system was subsequently performed, showing a more complex response, consisting of multiple critical speeds and the co-existence of sub-synchronous whirling modes. The effect of the rotor-bearing operating conditions, unbalance configuration, the thrust bearing and the bearing cylindricity were investigated. Most of the trends are correctly predicted by the model, however the correlation between measurement results and simulation results was clearly inferior to the case of the Laval rotor, most likely due to the uncertainties in the actual turbocharger geometry and the actual unbalance distribution. Lastly, an optimization of a Laval rotor-bearing system was performed. The resulting robust optimum design ensures optimum rotor-bearing performance, even at the most severe operating conditions and even if all manufacturing tolerances represent the worst case scenario. Particularly the uncertainties in rotor unbalance and oil supply temperature were found to have a significant influence on the optimum design.

12 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a critical review on the self-excitation process and steady state analysis of a selfexcited induction generator driven by the wind turbine. But the authors do not consider how the generator relinquishes the initial synchronous mode and enters into the final asynchronous mode.
Abstract: This paper presents a critical review on the self-excitation process and steady state analysis of a self-excited induction generator driven by the wind turbine. The physics of self-excitation is crucial for the interpretation of the voltage build-up process of self-excited induction generators (SEIGs). During the initial phase of build-up the machine behaves as if it be a synchronous machine with weak permanent magnet in the form of remnant magnetization. In this paper the MMF approach as well as the synchronous resonance approach has been proposed to know the fact that how the machine relinquishes the initial synchronous mode and enters into the final asynchronous mode. The process of self-excitation is initiated by the resonating interaction between the terminal capacitor and machine׳s magnetizing reactance. The steady state analysis has been reviewed and proposed based on input/output impedance method to find the steady state reactive VAR need of the SEIG. The minimum and maximum critical capacitance has been evaluated theoretically. Finally the value of critical speed and critical load impedance has been evaluated.

12 citations

Journal ArticleDOI
TL;DR: In this paper, a flexible bladed-disk/rotor bearing system equipped with a dual-ball automatic balancing device was investigated and it was found that the autobalancer effectively compensates for both mass and aerodynamic imbalances produced by a bladed loss condition over a wide revolutions/minute range at speeds above the first lateral natural frequency.
Abstract: Autobalancers for rotor/bearing systems are passive devices consisting of eccentrically mounted balance masses that freely revolve around the rotor's axis of rotation. At certain supercritical speeds, the balancer mass positions naturally adjust to cancel the rotor imbalance. This automatic-balancing phenomena occurs as a result of nonlinear dynamic interaction between the balancer masses and the rotor's lateral vibration. Previous studies have found that autobalancers can effectively compensate for mass imbalance in planar rigid rotors such as hard-disk drives and flywheels, however, their use in bladed-disk and turbomachinery applications has not been previously considered. This study explores the dynamics and stability of a flexible bladed-disk/rotor-bearing system equipped with a dual-ball automatic-balancing device. It is found that the autobalancer effectively compensates for both mass and aerodynamic imbalances produced by a bladed-loss condition over a wide revolutions/minute range at speeds above the first lateral natural frequency. It is also shown that for stable automatic balancing to occur, the ratio of automatic balancer damping to the blade aerodynamic drag coefficient must be above some critical value. The analysis demonstrates that the automatic balancer is able to simultaneously reduce both bearing loads and blade deflections for a simulated blade-loss event.

12 citations

Journal ArticleDOI
TL;DR: In this paper, the aerodynamic coupling effect on natural frequencies and flutter instability of rotating disks was investigated using a vacuum chamber and optical disks, and the results showed that the natural frequency of the disk rotating at ambient atmospheric pressure is equal to that in vacuum at flutter onset speed where the disk experiences aero-induced flutter.
Abstract: Experimental studies on the aerodynamic coupling effect on natural frequencies and flutter instability of rotating disks are investigated in this paper. The experiments performed using a vacuum chamber and optical disks give two main results. One is that the aerodynamic effect by surrounding air reduces the natural frequencies and critical speeds of the vibration modes in pre-flutter regions. The other is that the natural frequency of the disk rotating at ambient atmospheric pressure is equal to that in vacuum at the flutter onset speed where the disk experiences aero-induced flutter. In post-flutter regions, the aerodynamic coupling between the disk and surrounding air increases the natural frequencies of the disk.

12 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20241
202343
2022120
202182
202092
2019102