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1 A FE Model for Static Load in Tilting Pad Journal Bearing with Pad Flexibility Year III May 2013 Yingkun Li Graduate Research Assistant 33 rd Turbomachinery.

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Presentation on theme: "1 A FE Model for Static Load in Tilting Pad Journal Bearing with Pad Flexibility Year III May 2013 Yingkun Li Graduate Research Assistant 33 rd Turbomachinery."— Presentation transcript:

1 1 A FE Model for Static Load in Tilting Pad Journal Bearing with Pad Flexibility Year III May 2013 Yingkun Li Graduate Research Assistant 33 rd Turbomachinery Research Consortium Meeting Luis San Andrés Mast-Childs Professor TRC-B&C Computational Model for Tilting Pad Journal Bearings TRC Project 32513/15196B

2 2 Past TRC work Pivot flexibility reduces the force coefficients in heavily loaded tilting pad journal bearings (TPJBs). W, static load Y X Housing Pad Pivot Fluid film Journal , Journal speed , Pad tilt angle   Developed XLTPJB®, benchmarked by test data, to predict K- C-M coefficients of TPJBs. Code accounts for thermal energy transport and the (nonlinear) effects of pivot flexibility. TRC-B&C

3 funded by TRC (2 years) Hydrodynamic pressure P Hot oil flow Pivot constraint Pad surface elastic & thermal deformations change bearing & pad clearances K  = P + C∆T K, Pad stiffness matrix P, Fluid film pressure vector C, Mechanical-thermal stiffness matrix , Pad displacement vector Objective: Enhance TPJB code to accurately predict pad surface deformations $ 40,984

4 4 Proposed work Build a 3-D FE ANSYS® model to obtain pad stiffness matrix. Reduce model with active DOFs. Implement oil feed arrangements (LEG, spray bar blockers etc.) in the FE model Construct new Excel GUI and Fortran code for XLTRC 2 Digest test data and continue to update predictions using enhanced code. $ 40,984

5 5 TRC funded Under moderate to heavy loads, pivot and pad flexibility affect the static and dynamic forced response of TPJBs. XLTPJB© includes pivot flexibility and delivers improved predictions but does not account for pad flexibility. Research objective: Extend TPJB© code with effects of pad flexibility. Pad elastic deformation Pressure field $ 40,984

6 6 Tasks completed Built FE structural models and extracted reduced stiffness matrices from ANSYS® Included pad flexibility into XLTPJB© code for static force case Compared predictions from the TPJB code against test data Composed a guide for pad FE analysis with ANSYS ®

7 7 FE pad model with ANSYS® FE Model built in ANSYS® Cylindrical coordinate (r,θ,z) Circumferential direction, θ Axial direction, z Radial direction, r noded, isoparametric element Degrees of freedom (DOFs) of each node: u r, u θ, u z NO ROTATIONS K, stiffness matrix u, Displacement load vector Q, Load vector S, Vector of surface tractions Assemble over whole domain

8 8 Pad reduced stiffness matrix Reduce K matrix to active DOFs [1] Desbordes. H., Fillon, M., Frene, J. and Chan, C., 1995, ASME J. Tribol, 117, 380 z=0 z=L/2 z=-L/2 Constraints along two lines: u r =0 Constraints at a point (pivot): u r =u θ =u z =0 Loads: pressure field acting on pad upper surface Boundary conditions: Desbordes’s model [1] Pressure field K, Reduced stiffness matrix u p, Displacements load vector f, Loads vector

9 9 Cholesky decomposition K is symmetric positive definite, then Cholesky decomposition is applicable: System of linear equations Back substitution L is calculated prior to running XLTPJB®. Savings in processing time! L: lower triangular matrix

10 10 Fluid film thickness in a pad Ω Y X WYWY WXWX RBRB RJRJ θPθP θ θLθL h upup Fluid Film Bearing Center O B Pad Center O P η ξ ξ piv η piv δpδp Unloaded Pad ΘPΘP Loaded Pad Pivot C p : Pad radial clearance C B = C p -r p Bearing assembled clearance R d = R p +t : Pad radius and thickness r p : Pad dimensional preload  p : Pad tilt angle  piv  piv  Pivot radial and transverse deflections u p : Pad upper surface deformation

11 11 Predictions for a four-pad TPJB (Tschoepe) Four pad, Rocker-back tilting pad bearing (LOP) Tschoepe, D.P., 2012, Master Thesis, Texas A&M University. Number of pads, N pad 4 ConfigurationLOP Rotor diameter, D mm (4 inch) Pad axial length, L60.33 mm (2.4 inch) Pad arc angle,  P 72 o Pivot offset57% Preload, 0.589(pad1)0.457(pad2) 0.559(pad3)0.460(pad4) Pad clearance, C P 112 µm (4.4mil) Pad inertia, I P 1.81kg.cm 2 (0.618lb.in 2 ) Oil inlet temperature~43.3 o C (110 o F) Lubricant typeISO VG32 Supply viscosity,  Pa.s Specific load, W/LD 0 MPa MPa (421 psi) Journal speed,  6.8krpm-13.2krpm X Y Pad 3 Pad 2 Pad 4 W Pivot offset = 0.57 Journal Fluid film  P = 72 o Pad 1

12 12 Light load Tschoepe, D.P., 2012, Master Thesis, Texas A&M University. Rotor speed  =6.8 krpm Specific load W/LD=726kPa X Y  Pad 2 W Pad 1 Pad 3 Pad 4 Pad 3 Pad 1 Pad 2 Film thickness Pad deformation Pad 1Pad 2 Pad 4 Pad 3 Film thickness and pad deformation: Deformation of loaded pad (#1) is very small compared to film thickness.

13 13 Rotor speed  =6.8 krpm Specific load W/LD=2.9MPa X Y  Pad 2 W Pad 1 Pad 3 Pad 4 Pad 3 Pad 1 Pad 2 Film thickness Pad deformation Pad 1Pad 2 Pad 4 Pad 3 Deformation of loaded pad (#1) is 30% of the minimum film thickness Tschoepe, D.P., 2012, Master Thesis, Texas A&M University. Film thickness and pad deformation: Large load

14 14 Journal eccentricity vs. static load Tschoepe, D.P., 2012, Master Thesis, Texas A&M University. Rotor speed  =6.8 krpm -e X -e Y : test data : prediction for rigid pad : prediction for flexible pad Max. 421 psi Journal eccentricity agrees well with test data. Pad flexibility affects little the journal eccentricity. X Y  Pad 2 W Pad 1

15 15 Predictions agree well with temperature in loaded pad X Y  Pad 2 W Pad 1 : test data : prediction for rigid pad : prediction for flexible pad Pad 1Pad 2 Pad 4 Pad 3 Oil Inlet temperature Loaded pad Tschoepe, D.P., 2012, Master Thesis, Texas A&M University. Light load Rotor speed  =6.8 krpm Specific load W/LD=726kPa Pad temperatures

16 16 Predictions underestimate the temperature X Y  Pad 2 W Pad 1 Rotor speed  =6.8 krpm Specific load W/LD=2.9MPa : test data : prediction for rigid pad : prediction for flexible pad Pad 1 Pad 2Pad 4Pad 3 Oil Inlet temperature Loaded pad Tschoepe, D.P., 2012, Master Thesis, Texas A&M University. Rotor speed  =6.8 krpm Specific load W/LD=2.9MPa Large load Pad temperatures

17 17 Predictions for a five-pad TPJB Five pad, Rocker-back tilting pad bearing (LBP) Hagemann, T., Kukla, S., and Schwarze, H., 2013, ASME GT Number of pads, N pad 5 ConfigurationLBP Rotor diameter, D500mm (19.7 inch) Pad axial length, L350mm (13.7 inch) Pad arc angle,  P 56 o Pivot offset60% Preload,0.23 Bearing clearance, C B 300µm (11.81mil) Pad inertia, I P 0.438kg. m 2 (1496.7lb.in 2 ) Oil inlet temperature~50 o C (122 o F) Lubricant typeISO VG32 Oil supply viscosity,  Pa.s Specific load, W/LD 1MPa-2.5MPa (363 psi) Journal speed,  500rpm-3krpm X Y Pad 3 Pad 2 Pad 4 W =0.23, C B =300  m, Pivot offset = 0.6 Journal Fluid film  P = 56 o Pad 5 Pad 1

18 18 Film thickness Hagemann, T., Kukla, S., and Schwarze, H., 2013, ASME GT X Y  Pad 3 Pad 2 Pad 4 W Pad 5 Pad 1 Rotor speed  =3krpm Specific load W/LD=2.5MPa Predicted film thickness correlates poorly with measurements Pad 1 Pad 2 Pad 4 Pad 3 Pad 5 Pad 4 Pad 2 Pad 3 Pad 1 : test data : prediction Film thickness Pad deformation

19 19 Film pressures Hagemann, T., Kukla, S., and Schwarze, H., 2013, ASME GT X Y  Pad 3 Pad 2 Pad 4 W Pad 5 Pad 1 Rotor speed  =3krpm Specific load W/LD=2.5MPa Predicted film pressure < test data. ~20bar difference on loaded pads (#1 & #2). Pad 1Pad 2 Pad 4 Pad 3Pad 5 : test data : prediction for rigid pad : prediction for flexible pad Oil jacking ports located in pads #1 & #2. Notes: flow in bearing is turbulent & test data shows much larger pad deformations (mechanical and thermal)

20 20 Conclusions Selected examples for comparison do not show pad flexibility affects TPJB static load performance. Considerable discrepancies exist between predictions and measurements for large size TPJBs. FE pad model is too stiff leading to underestimation of the pad surface elastic deformation. XLTPJB® models laminar flow bearings. Large size TPJBs operate in both the laminar & turbulent flow regions.

21 21 Enhanced Computational Model for Tilting Pad Journal Bearing with Pad Flexibility 2013 Continuation Proposal to TRC Year IV May 2013 Yingkun Li Graduate Research Assistant Luis San Andrés Mast-Childs Professor

22 22 Validate the constructed pad FE structural surface deformation model with comparisons to test data. Include pad flexibility on the prediction of frequency reduced TPJB dynamic force coefficients. Construct the FE model that relates pad elastic deformation to thermally induced stresses. Compare predictions from code to test data. Proposed work Enable model for operation with laminar/transition & turbulent flow conditions Year IV

23 TRC Budget Year III Support for graduate student (20 h/week) x $ 2,050 x 12 months$ 24,600 Fringe benefits (0.6%) and medical insurance ($185/month)$ 2,368 Travel to (US) technical conference$ 1,200 Tuition & fees three semesters ($362/credit hour)$ 8,686 Other (Mathcad® and portable data storage HD)$ 220 Total Cost:$ 37,073 XLTPJB® will continue to assist TRC members in modeling accurately TPJBs for specialized applications. The model and GUI reduce the burden on the unseasoned user by minimizing the specification of empirical parameters and guessing the correct boundary conditions for a proper analysis with thermal effects Year IV


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