GT 2009 59199 Flexure Pivot Hybrid Gas Bearings

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings ASME TURBO EXPO 2009 , Orlando, Fla Dynamic Forced Response of a Rotor-Hybrid Gas Bearing System due to Intermittent Shocks Dr. Luis San Andrés Keun Ryu Mast-Childs Professor Fellow ASME Research Assistant TURBOMACHINERY LABORATORY TEXAS A&M UNIVERSITY ASME paper GT 2009 -59199 Supported by TAMU Turbomachinery Research Consortium

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Micro Turbomachinery (< 0. 5 MW) ADVANTAGES • High energy density • Compact and fewer parts • Portable and easily sized • Lower pollutant emissions • Low operation cost ASME Paper No. GT 2002 -30404 http: //www. grc. nasa. gov/WWW /Oilfree/turbocharger. htm Gas bearings Gas Foil Bearing • Oil-Free bearing • High rotating speed (DN value>4 M) • Simple configuration • Lower friction and power losses • Compact size Flexure pivot Bearing AIAA-2004 -5720 -984 GT 2004 -53621

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Ideal gas bearings for micro turbomachinery (< 0. 5 MW ) must be: Simple – low cost, small geometry, low part count, constructed from common materials, manufactured with elementary methods. Load Tolerant – capable of handling both normal and extreme bearing loads without compromising the integrity of the rotor system. High Rotor Speeds – no specific speed limit (such as DN) restricting shaft sizes. Small Power losses. Good Dynamic Properties – predictable and repeatable stiffness and damping over a wide temperature range. Reliable – capable of operation without significant wear or required maintenance, able to tolerate extended storage and handling without performance degradation. +++ Modeling/Analysis (anchored to test data) readily available

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Thrust of research program: Investigate conventional bearings of low cost, easy to manufacture (common materials) and easy to install & align. Combine hybrid (hydrostatic/hydrodynamic) bearings with low cost coating to allow for rubfree operation at start up and shut down Major issues: Little damping, Wear at start & stop, Instability (whirl & hammer), & reliability under shock operation

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Test rig Max. operating speed: 100 kpm 3. 5 k. W (5 Hp) AC integral motor Rotor: length 190 mm, 28. 6 mm diameter, weight=0. 826 kg Rig housing Bearing shell and Load cells Bearing cover Gas bearing Shaft and DC motor Components of high-speed gas bearing test rig

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Test rig Rotor/motor Load cell Sensors Bearing Positioning Bolt Thrust pin Air supply LOP

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Flexure pivot tilting pad hybrid bearing Promote stability: no cross-coupled stiffnesses Eliminate pivot wear, contact stresses, pad flutter Minimize manufacturing and assembly tolerances’ stack-up worn pads surfaces Clearances Cp =38 & 45 mm, Preload =7 & 5 mm (~20%) Web rotational stiffness=20 Nm/rad

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings TAMU work on flexure pivot tilting bearings GT 2004 -53621 Zhu & San Andres (2004) GT 2004 -53621 Gas bearing for oil-free applications. Good comparisons with: 60 KRPM Delgado & San Andres (2004) Stable to 99 krpm Computational model for GT 2004 -53614 hydrodynamic operation, with application to hybrid brush seals San Andres (2006) Journal of Tribology, 129 Computational model for hybrid operation validated by Zhu (2004) measurements. Code used by 20+ companies San Andres & Ryu (2007) J. Eng. Gas Turbines and Power, 2008, 130 Operation with worn clearances and LOP/LBP configuration

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings J. Eng. Gas Turbines and Power, 2008, v. 130 2008: Control of bearing stiffness / critical speed 5. 08 bar 2. 36 bar Displacements at RB(H) 2. 36 bar Blue line: Coast down Red line: Set speed Controller activated system Peak motion at “critical speed” eliminated by controlling supply pressure into bearings

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Objectives: Demonstrate the rotordynamic performance, reliability, and durability of hybrid gas bearings • Rotor motion measurements for increasing gas feed pressures and speed range to 60 krpm. • Install electromagnetic pusher to deliver impact loads into test rig. • Perform shock loads (e-pusher & lift-drop) tests to assess reliability of gas bearings to withstand intermittent shocks without damage.

2008 Gas bearing test rig layout GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings E-pusher : Push type solenoid 240 N at 1 inch stroke

Electromagnetic pusher tests GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Multiple impact Impact duration ~20 ms E-force ~400 N (pk-pk)

Manual lift & drop tests GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Multiple impact Lift off to 5~15 cm (10~30° rotation)

Coast down: E-pusher tests GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Ps=5. 08 bar (ab) Displacements at LB(H) Intermittent shocks Impact force 100~400 N 46 krpm Shock ~15 g Transient rotor response ~ 40 µm

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Coast down: manual lift & drop tests Shock induced acceleration At base 5~20 g At housing 5~10 g Ps=3. 72 bar (ab) Beyond critical speed: Synchronous frequency is isolated from shocks Below 20 krpm: Large fluctuation of synchronous response Displacements at LB(H)

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Waterfall: manual lift & drop tests Ps=2. 36 bar (ab) Displacements at LB(H) Rotor speed decreases Excitation of rotor natural frequency. NOT a rotordynamic instability!

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Rotor response: manual lift & drop tests Ps=2. 36 bar (ab) Shock loads applied Overall rotor amplitude increases largely. Subsynchronous amplitudes larger than synchronous

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Rotor response: manual lift & drop tests Ps=2. 36 bar (ab) Natural frequency of rotor-bearing system (150~190 Hz) Natural frequency of test rig (~40 Hz) Rotor-bearing natural frequency increases with rotor speed. Natural frequency of test rig also excited.

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Rotor response: manual lift & drop tests 15 krpm Ps=2. 36 bar (ab) Drop induced shocks ~30 g Transient response Full recovery within ~ 0. 1 sec.

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Rotor speed vs time (No shocks) Dry friction (contact) With feed pressure: long time to coast down demonstrates very low viscous drag!

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Rotor speed vs time ( manual lift-drop tests) Overall coast down time reduces with shock loads (~ 20 sec) No shocks Exponential decay (No rubs) even under severe external shocks No shocks

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Conclusions: • Under shock loads ( up to ~30 g), natural frequency of rotorbearing system (150 -200 Hz) and test rig base (~ 40 Hz) excited. However, rotor transient motions quickly die! • For all feed pressures (2 -5 bar), rotor transient responses from shocks restore to their before impact amplitude within 0. 1 second. Peak instant amplitudes (do not exceed ~50 µm) • Even under shock impacts, viscous drag effects are dominant, i. e. , no contact between the rotor and bearing. • Hybrid bearings demonstrate reliable dynamic performance even with WORN PAD SURFACES

Dominant challenges in gas bearing technology GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings – Bearing design & manufacturing process better known. Load capacity needs minute clearances since gas viscosity is low. – Damping & rotor stability are crucial – Inexpensive coatings to reduce drag and wear at low speeds and transient rubs at high speeds – Engineered thermal management to extend operating envelope to high temperatures Current research focuses on coatings (materials), rotordynamics (stability) & high temperature (thermal management) Need Low Cost & Long Life Solution!

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings 2009 Gas bearing test rig layout connecting rod pushes base plate!

GT 2009 -59199 Flexure Pivot Hybrid Gas Bearings Rotor speed coast down tests Ps = 2. 36 bar (ab) Shaker input frequency: 12 Hz Subsynchronous response: 1) 24 Hz (Harmonic of 12 Hz) 2) Natural frequency 193 Hz Synchronous Dominant! excitation of system natural frequency is NOT an instability!