Abstract
In order to protect rotors and foil bearings operating at high temperatures from being overheated and damaged, these components are often cooled by air. In addition, such a cooling method is accompanied by an axial temperature gradient that changes the shape of the lubrication gap in a way likely to affect the operation of a foil bearing. This article presents the research on various methods for cooling a foil bearing and discusses the impact of these methods on dynamic parameters of the rotor-bearings system. To be able to assess the temperature inside such a bearing, there is a need for a reliable measurement method. The authors of the article measured the temperature of the top foil using thermocouples and showed that their measurement method does not exert any significant impact on the operation of the rotor-bearings system. The article also describes a novel method for compensating the axial temperature gradient occurring in the bearing bush using Peltier modules.
Highlights
New requirements which any microturbine must meet are related to the need to find bearings that can withstand such harsh conditions
The air blower is not suitable for decreasing temperature of the bearing operating at room temperature since forced air streams had a higher temperature than the air in the lubricating gap
A supposition can be made that air streams affect the dynamic performance of the system by changing the conditions existing in the lubricating gap
Summary
New requirements which any microturbine must meet (such as low weight, the ability to operate at high temperatures and/or rotational speeds) are related to the need to find bearings that can withstand such harsh conditions. The bearing and the seal operated successfully at temperatures up to 560 °C and speeds up to 55,000 rpm. The tested foil bearing exhibited very good damping properties (even at high temperatures) and there was no evidence of wear on the journal or seal surface. 400 g, the rotor was tested at speeds up to 150,000 rpm After numerous tests at speeds up to 60,000 rpm and temperatures up to 650 °C, the bearing and journal showed no evidence of rubs or surface degradation. A test rotor was supported by two foil bearings operating with a heated shaft. The parameters that were changed are as follows: rotational speed and the amount of cooling air supplied to the bearings. The authors discuss the issues related to operating parameters of the rotor-foil bearings system and the impact of the ambient temperature of its functioning
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