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Design of Blood-Lubricated Bearings Using Fluent Presentation to the 2003 Fluent User Group Meeting Cambridge Technology Development, Inc. CTD Edward Bullister,

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Presentation on theme: "Design of Blood-Lubricated Bearings Using Fluent Presentation to the 2003 Fluent User Group Meeting Cambridge Technology Development, Inc. CTD Edward Bullister,"— Presentation transcript:

1 Design of Blood-Lubricated Bearings Using Fluent Presentation to the 2003 Fluent User Group Meeting Cambridge Technology Development, Inc. CTD Edward Bullister, Ph.D.

2 Overview  Physics of Thin-Film Lubrication  Governing Equations of the Lubrication Approximation  Numerical Implementation in Nekton Fluent  Example Problems  Steady  Unsteady

3 Physics of Lubrication Outflow < Inflow Couette Flow Becomes Unbalanced when Plates are not Paralllel UU

4 Approximation to N-S Equations  Assumptions:  Laminar Flow, Re Small (no inertia)  L/B - Large (reasonable; typically ~1000)  No Slip  Incompressible Case Presented Here

5 Lubrication Analogues Physical VariableComputational Analogue PressureTemperature Gap 3 /  Thermal Conductivity K RHSHeat Source Q Fluid FluxHeat Flux Note:  μ

6 Implementation in Fluent  UDFs for:  Material Properties  Heat Source  In Nonplanar Bearings, Integration of Pressure x- and y- Components

7 Computational Work Comparison Direct SolutionLubrication Approximation Dimensions:32 Equations:Full (Navier)-StokesEnergy

8 Force Predictions Comparison With Long–Bearing (L/D >> 1) Theory L/D Fluent Force Prediction (Newtons) Exact Solution(Newtons) Infinitely Long Difference76%10%0.6%  Conditions:  No cavitation (continuous film)  D = 40 mm; 3500 RPM; Gap = 2 mils; ε = 0.1; μ = 5 cp  Close Agreement where exact Solution is valid

9 Details of Journal Bearing at L/D = 1 Pressure (Pascal)

10 Cavitating Journal Bearing at L/D = 1 Pressure (Pascal)

11 Thrust Bearing  D = 40mm  ω = 3500 RPM  h = mils  4 Contoured Quadrants

12 Thrust Bearing – Steep Contours Pressure Footprint Beneath Rotating Thrust Bearing (Plotted via its Temperature Analogue) Computational Grid

13 Stiffened Thrust Bearing

14 Example: Unsteady Bearing

15 Bearing Stability Continuous vs. Cavitating  

16 Trajectories in Stable and Unstable Bearings

17 Stability Problem  Eigenvalue Analysis  Predicts continuous film bearing neutrally stable:  = 0 + i  /2  Simulations  Use unsteady time stepping procedure  Simulate with initial bearing eccentricity not at equilibrium with steady applied load  Track motion of piston in response to net forces

18 Unsteady Simulation Results  Bearing takes Circular Orbit around equilibrium position  Period of Orbit about ½ that of cylinder rotation consistent with: Eigenvalue Analysis Experimentally Observed “whirl” instability Trajectory of Simulated Bearing

19 Recommendations  Design for sufficient load capacity to maintain allowable gaps at operating speeds  For continuous film bearings, avoid symmetry  For unstable bearings, avoid symmetry

20  Design of Fluidic Devices  Design Support and Analysis  CFD Analysis Brought to you by… attbi.com


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