Ultrasonic Measurement Of Foil Deformation And Air Film Thickness In Bump Foil Gas Bearing

Gas foil bearing(GFB)is gradually playing a more important role in high-speed rotating machinery due to their advantages of high speed,high temperature resistance,long life,environmental protection and energy saving.GFB have been successfully applied to oil-free air circulation machines,turbochargers,High-speed and highefficiency motors,supercritical carbon dioxide power systems and other high-speed equipment,and become the key technologies that lead turbomachinery to high power density.GFB is also limited in application due to their low load,low damping and other characteristics.Scholars at home and abroad try to improve the performance of GFB through theories and experiments.However,the current experimental and detection technology for GFB can only be used to detect the comprehensive performance of foil bearings,but lacks real-time parameters detection,such as foil deformation and gas film thickness.On the other hand,as a new direction for the development of GFB,active foil bearings also lack features that can better characterize the state of the bearing relative to the amount of rotor vibration as a feedback quantity,and it is difficult to further improve its control efficiency and effect.In the field of oil bearings,the ultrasonic method has achieved great success in real-time oil film thickness detection,which brings new ideas to the real-time state detection of GFB.Therefore,this paper firstly proposes an ultrasonic-based real-time detection method for the deformation and gas film thickness of the bumb foil bearing and studies the ultrasonic signal processing technology,and then builds a verification test bench,lastly applies the detection method in the start-stop experiment of foil bearing,the main work of this paper is as follows:The gas film thickness detection method based on the thin sandwich thickness ultrasonic detection theory was designed and the acoustic impedance matching layer in the bearing was introduced.The echo signal of the ultrasonic wave propagating in the foil bearing was obtained,and it was used to obtain the foil deformation based on the waveform correlation analysis method.The software and hardware systems for ultrasonic measurement of the foil deformation was built,and the factors affecting the signal-to-noise ratio of ultrasonic echo signals was studied;ultrasonic signal processing technology was studied,and appropriate wavelet denoising and signal up-sampling methods was selected through numerical simulation experiments to improve the resolution of ultrasonic measurement for bump foil deformation.An experimental platform for the verification of the bump foil static deformation and the radial bump foil static deformation was built to compare the elastic deformation obtained by the ultrasonic measurement method with the structural value.A radial foil bearing dynamic deformation structure verification test bench was set to construct the elastic deformation at different frequencies.The structure values were compared with the ultrasonic measurement value.The results show that the difference between the static and dynamic detection value and the structure value of the ultrasonic detection method is within 5 μm.A gas foil bearing start-stop test bench on which ultrasonic measurement was applied was set up.The start and stop experiments with variable load and variable rotating speed for the bearing was performed.The time domain value of foil deformation and air film thickness of the bearing at steady rotaing speed were obtained.The characteristics of the measurement results were analyzed.The results show that the deformation of the foil increases with the increase of the load,but is less affected by the rotation speed;the thickness of the gas film decreases with the increase of the load,and has a tendency to increase with the rotation speed;The peak-to-peak value has no obvious trend with the change of the rotating speed and the load.