Many automotive turbochargers operate in the self-excited unstable region. In the past these instabilities have been accepted as unavoidable, but recent developments in analysis and instrumentation may make it possible to reduce or eliminate them. A test stand being developed at Virginia Tech has been used to measure the vibrations of a 3.9 liter diesel engine stock turbocharger with floating bushing journal bearings. Vibration spectrum content clearly identifies the shaft instabilities and provides the basis for additional evaluation of future bearing design modifications. This paper provides additional experimental vibration data reduction that will be useful for future research direction to fully understand the turbocharger dynamic instability.
Automotive turbochargers are known to have operation into the self-excited unstable vibration region. In the past these instabilities have been accepted as unavoidable, but recent developments in analysis and instrumentation may make it possible to reduce or eliminate them. A test stand has been developed at Virginia Tech to measure the vibrations of a 3.9 liter diesel engine stock turbocharger with both stock floating bushing journal bearings and also custom design fixed geometry bearings. Vibration spectrum content clearly identifies the shaft instabilities and provides the basis for additional evaluation of current and future improved bearing design modifications. The current results, for a series of custom fixed geometry journal bearings, show a shift in the frequencies of the two unstable modes for the no load operating condition. These results can be compared to the linear analysis predicted instability frequencies to better understand the actual response of the high speed turbocharger. This paper documents the spectrum content for three different bearing designs and compares the results to a stock floating bush journal bearing result for the same no load operating condition.
The aim of this study is to analytically design flexible damped bearing-supports in order to improve the dynamic characteristics of the rotor-bearing system. The finite-element model of the turbocharger rotor with linearized bearing dynamic coefficients is used to solve for the logarithmic decrements and hence the stability map. The design process attempts to find the optimum dynamic characteristics of the flexible damped bearing-support that would give best dynamic stability of the rotor-bearing system. The method is successful in greatly improving the dynamic stability of the turbocharger and may also lead to a total linear stability throughout the entire speed range when used besides the enhanced-performance hydrodynamic bearings.
This study investigates the radial aerodynamic forces that may develop inside the centrifugal compressor and the turbine volutes due to pressure variation of the circulating gas. The forces are numerically predicted for magnitudes, directions, and locations. The radial aerodynamic forces are numerically simulated as static forces in the turbocharger finite element model with floating ring bearings and solved for nonlinear time-transient response. The numerical predictions of the radial aerodynamic forces are computed with correlation to earlier experimental results of the same turbocharger. The outcomes of the investigation demonstrate a significant influence of the radial aerodynamic loads on the turbocharger dynamic stability and the bearing reaction forces. The numerical predictions are also compared with experimental results for validation.
The high-speed diesel engine turbocharger is known to have subsynchronous vibrations for a wide speed range. The bearing fluid-film instability is the main source of the vibration. The nonlinear forces inside the bearings are causing the rotor to whirl in a limit cycle. This study presents a new method for improving the dynamic stability by inducing the turbocharger rotor unbalance in order to suppress the subsynchronous vibration. The finite-element model of the turbocharger with floating-ring bearings is numerically solved for the nonlinear time-transient response. Both compressor and turbine added unbalance are induced and the dynamic stability is computed. The turbocharger model with linearized floating-ring bearings is also solved for eigenvalues to predict the modes of instability. The linear analysis demonstrates that the forward whirling mode of the floating-ring at the compressor end also becomes unstable at the higher turbocharger speeds, in addition to the unstable forward conical and cylindrical modes. The numerical predictions are also compared to the former experimental results of a similar turbocharger. The results of the study show that the subsynchronous frequency amplitude of the dominant first mode is reduced when inducing either the compressor or the turbine unbalance at a certain level.
BackgroundMalaria transmission was stopped on most of the vast area of the Kingdom of Saudi Arabia. However, the pandemic of coronavirus disease (COVID-19) has negatively affected the efforts to control malaria. For instance, COVID-19 was reported to induce a relapse of malaria that is caused by Plasmodium vivax. Furthermore, physicians' attention toward COVID-19 can only result in neglect and delayed diagnosis of complicated malaria cases. These factors, among others, might have contributed to an increase of malaria cases in Dammam, Saudi Arabia. Thus, this study was conducted to examine the effects of COVID-19 on malarial cases.
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