Oil Sloshing Simulation for No Leaking Tank Design. Wenyan Ni NACCO Materials Handling Group October 31, 2012

Transcription

1 Oil Sloshing Simulation for No Leaking Tank Design Wenyan Ni NACCO Materials Handling Group October 31, 2012

2 Abstract In fork lift truck operations, hydraulic oil may leak from the air breather when hard braking and quick lowering actions are performed simultaneously on the truck. To avoid this leakage, Ansys/Fluent CFD is used routinely in the hydraulic tank design process at NMHG. CFD simulations are run for different design concepts to evaluate and compare each concept. CFD results also provide guidelines and direction for design changes to achieve the goal of no leakage. The CFD procedure and methodology for the tank sloshing simulations are introduced in this presentation. Typical CFD results for the tank sloshing simulations are shown. Challenges and limitations are addressed for discussion. Monday, October 08, Automotive Simulation World Congress 2

3 Contents NMHG and Counterbalanced Lift Trucks. Target and Challenge of No Leak Tank Design. Benefits of CFD Simulations. Simulation Details. Typical Simulation Results. Improvement and Validations of CFD Results. Conclusions. Monday, October 08, Automotive Simulation World Congress 3

4 NMHG and Its Products One of the world s largest lift truck manufacturers. Counterbalanced truck development center is based in Portland, Oregon. Main brands of our trucks: Hyster and Yale are registered trademarks of NACCO Materials Handling Group, Inc. Monday, October 08, Automotive Simulation World Congress 4

5 Counterbalanced Lift Truck Monday, October 08, Automotive Simulation World Congress 5

6 Target and Challenge of No Leak Tank Design Tank contains sufficient oil volume for lifting about 7 m in tight truck space (small air space). Variable truck operations from different drivers and for different applications (unpredictable sloshing pattern). Tanks need to be cleaned entirely before use (baffles not desirable). Monday, October 08, Automotive Simulation World Congress 6

7 Benefits of CFD Simulations Verify design at early design stage. Visualize oil sloshing pattern and check if leaks. Test options and provide direction for design improvements. Reduce costly physical tests and ensure no leak designs. Monday, October 08, Automotive Simulation World Congress 7

8 Procedure of CFD Simulations ProE: Hypermesh: Tgrid: Fluent: Obtain geometry. Cleanup geometry, generate surface mesh. Generate tetra volume mesh. Solve equations and process results. Monday, October 08, Automotive Simulation World Congress 8

9 Simulation Details Air and oil 2 phase transient laminar flows. Volume of Fluid explicit multiphase model. Patching the oil initial level. G loads measured from truck with accelerometers. Oil retuning flow rate with fork lowering action. Time steps based on mesh size, g loads and oil returning rate. Setup animations for oil volume fraction contours. Create a journal file for all the inputs of G loads, oil returning rate and time steps. About 4 hour simulation time on Lenovo D20 workstation with 2 CPU parallel for 2 seconds of physical actions. Monday, October 08, Automotive Simulation World Congress 9

10 Typical G Loads x-axis y-axis z-axis 4 Acceleration, m/s^ Time, sec. Monday, October 08, Automotive Simulation World Congress 10

11 Typical Results Oil Leaks Monday, October 08, Automotive Simulation World Congress 11

12 Typical Results No oil Leak Monday, October 08, Automotive Simulation World Congress 12

13 Improvement and Validation of CFD Results Pick the time span with the worst scenario from the G load data for potential oil leak. Learn truck capacity and drivers dramatic operation behaviors. Increase G loads by 15~30% to see the buffer before leak. Improvement and validation are continuous task. Monday, October 08, Automotive Simulation World Congress 13

14 Conclusions CFD simulation is an important part in our truck design process. CFD simulations provide design evaluation and guideline for design change to ensure designs meet the target. Fluent is a capable CFD code for the tank sloshing simulations in our no leak tank design. The CFD results have been verified from later truck tests. With the help from the CFD simulations, NMHG is reaching for no leak tank design. Monday, October 08, Automotive Simulation World Congress 14