Purdue University

Purdue University

Mechanical Engineering
Tribology Laboratory

Ankur Ashtekar

M.S., Purdue University, West Lafayette, 2008
B.S., Engg., University of Pune, India, 2004

Office Address:
585 Purdue Mall
ME Room# G005
West Lafayette, IN 47907

Office Phone: 765-494-0308
email: ankur@purdue.edu





Experimental and Analytical Investigation of Bearing Rotor Systems

The objectives of this investigation were to design and construct a high-speed turbocharger test rig (TTR) to measure dynamics of angular contact ball bearing rotor system, and to develop a coupled dynamic model for the ball bearing rotor system to corroborate the experimental and analytical results.  In order to achieve the objectives of the experimental aspect of this study, a test rig was designed and developed to operate at speeds up to 70,000 rpm.  The rotating components (i.e. turbine wheels) of the TTR were made to be dynamically similar to the actual turbocharger.  Proximity sensors were used to record the turbine wheel displacements while accelerometers were used to monitor the rotor vibrations.  A wireless in-situ MEMS temperature sensor was developed and installed on the bearing cage to monitor the bearing condition.  To achieve the objectives of analytical investigation, a discrete element dynamic ball bearing model was coupled through a set of interface points with a component mode synthesis (CMS) rotor model to simulate the dynamics of the turbocharger test rig.  Displacements of the rotor from the analytical model were corroborated with experimental results.  The analytical and experimental results are in good agreement.  The TTR and the analytical model were used to examine the dynamic response of the turbocharger under normal and extreme operating conditions.  The results were used to develop design guidelines for ball bearings in turbocharger applications.

Bearing Dynamic Modeling using Combined Explicit Finite and Discrete Element Methods

A new approach was developed to investigate the influence of cage flexibility on the forces and motions of bearing components (i.e. inner races, outer race, and balls) and to analyze the cage internal stresses resulting from impacts with bearing components during operation.  In order to achieve the objectives, a 3D explicit finite element cage model was developed and combined with the discrete element dynamic bearing model.  The ball contacts with the inner and outer race are modeled using Hertzian contact theory while a novel contact algorithm was developed to obtain the interaction forces between the cage finite element mesh and discrete bearing components.  The discrete and finite element models interact at each time step to determine the position, velocity, acceleration, and forces of all bearing components.  The model was used to determine the effect of various operating conditions on cage deformations and stresses and their effect on fatigue life.  The Explicit FEM model will replace the CMS model for rotor flexibility in the bearing-rotor analytical model.

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