ACOUSTIC JOURNAL BEARING – A SEARCH FOR ADEQUATE CONFIGURATION Tadeusz Stolarski Rafal Gawarkiewicz Krzysztof Tesch ITC 2015, Tokyo, Japan Gdansk University of Technology Faculty of Mechanical Engineering, Poland

AIM OF PROJECT Aim of project was to find appropriate geometry to maximise acoustic pressure generation. This was done by using FEM method 2 In order to select the most appropriate configuration (geometry) experimental testing was carried out using specially designed rig There were many different geometries analysed. Finally three configurations were considered for experimental testing

1-st CONFIGURATION CHOSEN FOR EXPERIMENTAL RESEARCH – SOLID MODEL IMAGE 3 v. 1: bearing surface vibrating and elastically deforming location for PZT arm for full constraining of the bearing

1-st CONFIGURATION – RESULTS OF NUMERICAL ANALISYS OF DEFORMATION PRODUCED BY PZTs v. 1: 4 Radial deformation [mm] (3300x magnification of deform.) Radial deformation [mm] of inner surface of bearing (3300x magnification of deform.) There was search for radial deformation generated symmetrically relative to the main axis of the bearing. A minimum three lobes were required to secure aerodynamic effects 4

Acceptable modal shape – total deformation [-] 1-st CONFIGURATION – EXAMPLE RESULT OF NUMERICAL ANALISYS FOR PROPER MODAL SHAPE v. 1: Acceptable modal shape – radial deformation [-] 5

2-nd CONFIGURATION CHOSEN FOR EXPERIMENTAL RESEARCH – SOLID MODEL IMAGE v. 2: 6 bearing surface vibrating and elastically deforming location for PZT arm for full constraining of the bearing

2-nd CONFIGURATION – RESULTS OF NUMERICAL ANALISYS OF DEFORMATION PRODUCED BY PZTs Radial deformation [mm] (1200x magnification of deform.) Radial deformation [mm] of inner surface of bearing (1200x magnification of deform.) 7

2-nd CONFIGURATION – EXAMPLE RESULT OF NUMERICAL ANALISYS FOR PROPER MODAL SHAPE 8 Total deformation practically defined by radial deformation Acceptable modal shape – total deformation [-]

3-rd CONFIGURATION CHOSEN FOR EXPERIMENTAL RESEARCH – SOLID MODEL IMAGE 9 v. 3: slot for PZT fully constrained outer surface vibrating bearing surface elastically deforming into three-lobe configuration multiple elastic hinges

3-rd CONFIGURATION – RESULTS OF NUMERICAL ANALISYS OF DEFORMATION PRODUCED BY PZTs Radial deformation [mm] (500x magnification of deform.) Radial deformation [mm] of inner surface of bearing (500x magnification of deform.) 10

3-rd CONFIGURATION – EXAMPLE RESULT OF NUMERICAL ANALISYS FOR PROPER MODAL SHAPE Acceptable modal shape – total deformation [-] Acceptable second modal shape – total deformation [-] 11

SOLID MODEL IMAGE OF THE TEST RIG 12 air turbine drive shaft's speed sensor end part of housing fixed to the tilting table special torque meter attached here shaft test aparatus housing aerostatic thrust bearing thrust bearing air supply test bearing shaft's position sensor

MODEL OF DEVICE FOR TORQUE MEASUREMENTS 13 supporting plate fixed to the housing of the apparatus strain gauge beam tube attached to the rotating shaft shaft loaded by friction torque developed in tested bearing

DEVICE FOR TORQUE MEASUREMENTS 14

TEST RIG (with device for torque measurements) 15

TEST RIG (without device for torque measurements) 16

THE TEST RIG (with bearing of 3-rd configuration) 17

PICTURES OF TESTED BEARINGS

RESULTS OF EXPERIMENTAL RESEARCH – 1-st CONFIGURTION DRIVING TORQUE 19 v. 1: Driving torque as a function of the load applied to the bearing operating at 58.7 kHz By tilting the base of the rig, load was applied on the test bearing. For a given tilt angle torque required to initiate rotation of the shaft was measured. This procedure was repeated for a number of the tilt angles (loads)

RESULTS OF EXPERIMENTAL RESEARCH – 2-nd CONFIGURTION DRIVING TORQUE 20 v. 2: Driving torque as a function of the load applied to the bearing operating at 36.7 kHz

RESULTS OF EXPERIMENTAL RESEARCH – 3-rd CONFIGURTION DRIVING TORQUE 21 v. 3: Driving torque as a function of the load applied to the bearing operating at 8.4 kHz

RESULTS OF EXPERIMENTAL RESEARCH – 3-rd CONFIGURTION DRIVING TORQUE (cont.) 22 v. 3: Driving torque as a function of the load applied to the bearing operating at 27.2 kHz Two resonance frequencies because the 3-rd configuration was much more flexible than the other two

1.Results testify to the feasibility of the idea of a journal air bearing operating on a squeeze film acoustic levitation principle 2.Geometric configuration of an acoustic bearing proved to be a very important factor governing the load supporting capacity 3.Bearing possessing low overall stiffness which is provided by geometric configuration attested to much higher load capacity comparing to the other two configurations tested 4.Increased flexibility of the bearing directly translates into bigger elastic deformation amplitude of the initially circular bore and hence improved ability to separate interacting surfaces. This is only valid with the assumption that the force generated by PZT and responsible for elastic deformation of the bearing is kept constant 5.The most appropriate geometry was found to be 3-rd configuration CONCLUSIONS OF THE TESTING Gdansk University of Technology Faculty of Mechanical Engineering, Poland 23

THE MOST APPROPRIATE GEOMETRY (3-rd CONFIGURATION) 24

ACKNOWLEDGEMENTS Gdansk University of Technology Faculty of Mechanical Engineering, Poland 25 The authors would like to acknowledge the financial support for the research reported in this paper by the grant from the National Centre of Science, Poland (Grant no.: 2012/07/B/ST8/ 03683)

Thank you for your attention 26 Gdansk University of Technology Faculty of Mechanical Engineering, Poland