Presentation on theme: "33rd Turbomachinery Research Consortium Meeting"— Presentation transcript:
1 33rd Turbomachinery Research Consortium Meeting A FE Model for Static Load in Tilting Pad Journal Bearing with Pad FlexibilityTRC-B&CLuis San AndrésMast-Childs ProfessorYingkun LiGraduate Research AssistantMay 2013Year IIITRC Project 32513/15196BComputational Model for Tilting Pad Journal Bearings
2 Past TRC work 2010-12 TRC-B&C-01-2013 Pivot flexibility reduces the force coefficients in heavily loaded tilting pad journal bearings (TPJBs).W, static loadYXHousingPadPivotFluid filmJournalW , Journal speedd, Pad tilt anglexhTRC-B&CDeveloped 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.2
3 2013 funded by TRC (2 years) Kd = P + C∆T $ 40,984Objective: Enhance TPJB code to accurately predict pad surface deformationsPad surface elastic & thermal deformations change bearing & pad clearancesHydrodynamic pressure PKd = P + C∆THot oil flowK, Pad stiffness matrixP, Fluid film pressure vectorC, Mechanical-thermal stiffness matrixd, Pad displacement vectorPivot constraint3
4 Proposed work$ 40,984Build 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 modelConstruct new Excel GUI and Fortran code for XLTRC2Digest test data and continue to update predictions using enhanced code.4
7 FE pad model with ANSYS® 56781234FE pad model with ANSYS®Circumferential direction, θAxial direction, zRadialdirection, r8-noded, isoparametric elementFE Model built in ANSYS®Cylindrical coordinate (r,θ,z)Degrees of freedom (DOFs)of each node: ur, uθ, uzNO ROTATIONSAssemble over whole domainK, stiffness matrixu, Displacement load vectorQ, Load vectorS, Vector of surface tractions
8 Pad reduced stiffness matrix z=0z=L/2z=-L/2Boundary conditions: Desbordes’s model Loads: pressure field acting on pad upper surfacePressure fieldReduce K matrix to active DOFsConstraints along two lines:ur=0Constraints at a point (pivot):ur=uθ=uz=0K, Reduced stiffness matrixup, Displacements load vectorf, Loads vector Desbordes. H., Fillon, M., Frene, J. and Chan, C., 1995, ASME J. Tribol, 117, 380
9 System of linear equations Cholesky decompositionK is symmetric positive definite, then Cholesky decomposition is applicable:L: lower triangular matrixSystem of linear equationsBack substitutionL is calculated prior to running XLTPJB®. Savings in processing time!
10 Fluid film thickness in a pad YCp : Pad radial clearanceCB= Cp-rp Bearing assembled clearanceRd= Rp+t : Pad radius and thicknessrp : Pad dimensional preloaddp : Pad tilt anglexpiv, hpiv : Pivot radial and transverse deflectionsup: Pad upper surface deformationPad Center OPFluid FilmΩRBBearing Center OBWYXWXθPRJηθθLξpivhδpUnloaded PadupηpivLoaded PadξPivotΘP
12 Light load Film thickness and pad deformation: Film thickness Rotor speed W =6.8 krpmSpecific load W/LD=726kPaFilm thickness and pad deformation:XYqPad 2WPad 1Pad 3Pad 1Pad 2Pad 4Pad 3Film thicknessPad 4Pad deformationPad 4Pad 3Pad 1Pad 2Deformation of loaded pad (#1) is very small compared to film thickness.Tschoepe, D.P., 2012, Master Thesis, Texas A&M University.
13 Large load Film thickness and pad deformation: Film thickness Rotor speed W =6.8 krpmSpecific load W/LD=2.9MPaFilm thickness and pad deformation:XYqPad 2WPad 1Pad 3Pad 1Pad 2Pad 4Pad 3Pad 4Film thicknessPad deformationPad 4Pad 3Pad 1Pad 2Deformation of loaded pad (#1) is 30% of the minimum film thicknessTschoepe, D.P., 2012, Master Thesis, Texas A&M University.
14 Journal eccentricity vs. static load XYqPad 2WPad 1Max. 421 psi-eY-eX: test data: prediction for rigid pad: prediction for flexible padRotor speed W =6.8 krpmJournal eccentricity agrees well with test data. Pad flexibility affects little the journal eccentricity.Tschoepe, D.P., 2012, Master Thesis, Texas A&M University.
15 Light load Pad temperatures Rotor speed W =6.8 krpmSpecific load W/LD=726kPaPad temperaturesXYqPad 2WPad 1Pad 1Pad 2Pad 4Pad 3Oil Inlet temperature: test data: prediction for rigid pad: prediction for flexible padLoaded padPredictions agree well with temperature in loaded padTschoepe, D.P., 2012, Master Thesis, Texas A&M University.
16 Large load Pad temperatures Predictions underestimate the temperature Rotor speed W =6.8 krpmSpecific load W/LD=2.9MPaPad temperaturesXYqPad 2WPad 1Pad 1Pad 2Pad 4Pad 3Oil Inlet temperature: test data: prediction for rigid pad: prediction for flexible padLoaded padRotor speed W =6.8 krpmSpecific load W/LD=2.9MPaPredictions underestimate the temperatureTschoepe, D.P., 2012, Master Thesis, Texas A&M University.
18 Film thickness Film thickness Pad deformation Rotor speed W =3krpm Specific load W/LD=2.5MPaXYqPad 3Pad 2Pad 4WPad 5Pad 1Pad 1Pad 2Pad 4Pad 3Pad 5Film thicknessPad deformationPad 5Pad 4Pad 2Pad 3Pad 1: test data: predictionPredicted film thickness correlates poorly with measurementsHagemann, T., Kukla, S., and Schwarze, H., 2013, ASME GT
19 Film pressuresRotor speed W =3krpmSpecific load W/LD=2.5MPaXYqPad 3Pad 2Pad 4WPad 5Pad 1Pad 1Pad 2Pad 4Pad 3Pad 5: test data: prediction for rigid pad: prediction for flexible padPredicted film pressure < test data. ~20bar difference on loaded pads (#1 & #2).Oil jacking ports located in pads #1 & #2.Notes: flow in bearing is turbulent & test data shows much larger pad deformations (mechanical and thermal)Hagemann, T., Kukla, S., and Schwarze, H., 2013, ASME GT
20 ConclusionsSelected 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 2013 Continuation Proposal to TRC Enhanced Computational Model for Tilting Pad Journal Bearing with Pad FlexibilityMay 2013Luis San AndrésMast-Childs ProfessorYingkun LiGraduate Research AssistantYear IV
22 Proposed workYear IVEnable model for operation with laminar/transition & turbulent flow conditions.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.
23 TRC BudgetYear IVYear IIISupport for graduate student (20 h/week) x $ 2,050 x 12 months$ 24,600Fringe benefits (0.6%) and medical insurance ($185/month)$ 2,368Travel to (US) technical conference$ 1,200Tuition & fees three semesters ($362/credit hour)$ 8,686Other (Mathcad® and portable data storage HD)$Total Cost:$ 37,073XLTPJB® 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.23