1. Simulation of Air-Cooling for the Gear Unit in Pump and Turbine Generator Systems M. Fujino* and T. Sakamoto** *Information Technology Center, Nippon Institute of Technology **Industrial Machinery Division, Hitachi Industries Co. Ltd

2. Gear Unit Gear unit A set of gear wheels with different diameters High-speed shaft; connected with gas or steam turbine Low-speed shaft ; connected with power generator Dimension : 1.8m ×1.6m ×1.2m Weight : 8×10 3 kg Efficiency : 98.8% Gas turbine : 15,500 kW 6,429 rpm Generator : 1,500 rpm Gas turbine Generator Gear Unit

3. Inside view of the gear unit Large wheel : Φ 1 =1.0m Cr Mo steel Small wheel : Φ 2 =0.23m Cr Mo steel Bearing : White steel With forced lubrication Casing : Cast iron Gear ratio=N1/N2=6,429/1,500 =Φ 1 /Φ 2 =4.3 N1=RPM of high-speed shaft =6,429 rpm N2=RPM of low-speed shaft =1,500 rpm Double helical type gear unit Casing Large wheel Bearing Small wheel

4. Cooling during the operation Gear wheels ： Distribution of pressurized oil inside the gear unit. Casing: Under study of making use air-convection environment.

5. Purposes Purposes are to: 1.Confirm the cooling of the casing by forced air convection on the outside the gear unit. 2. Get information on heat transfer and fluid dynamics in the gear unit.

6. Model creation by use of CAD (I-DEAS) Importing CAD model into VR through STL format Scale : 1.73m×1.50m×1.03m Diameter of large wheel : 1.28m Diameter of small wheel : 1.12m Gear Ratio : 1.28/1.12=1.14 Large wheel Small wheel Bearing Casing Y Z X O Symmetric with respect to the central X-Y plane

7. Outline of calculation Inlet air at 20 ℃ Outlet Cartesian grid numbers; 200×200×80 ( 3.2×10 6 ) X Z U i =0.0, 2.0m/s Heat conduction-convection systems Flow : single-phase air flow without oil flow without rotation of the wheels Model : ½ model cut with the central X-Y plane ( Z=0.0m) Turbulence model : RNG k- ε Re=2.31×10 5 ( U i =2m/s, 20 ℃ ) Buoyancy force : Bossinesq approximation Y Domain; 2.0m×2.0m×0.8m Gravity

8. Temperature boundary conditions Inlet air at 20 ℃ (U i =0.0, 2.0 m/s) Outlet Base floor : 20 ℃ I nner base wall : 70 ℃ due to adhesion of hot oil Wheels : 80 ℃ From the experimental data during the operation Bearings : 70 ℃ Top part of inner wall : 70 ℃ due to adhesion of hot oil

9. Resolution test of Cartesian grids Total number of grids (N t )=1.2×10 6 N t =2.0×10 6 ‘PRPS’ contours in the central X-Y plane (z=0.0m) 30mm 1.73m 1.50m N t = 3.2×10 6 in the main analyses without the cut-cell technique

10. Velocity vectors in the X-Y plane near the outside surface (z=0.44m) U i =0.0m/s at 20 ℃ Free convection outside the gear unit Without air blow

11. Free convection inside the gear unit Velocity vectors in the central X-Y plane (z=0.0m) U i =0.0m/s at 20 ℃ Without air blow ( Gr ｙ ≈10 9 > Gr c =10 8 )

12. Fluctuations of free convection currents inside the gear unit Fluctuations of the fully developed flow with time Free convection in the gear unit without air blow 01200600 t(s) At probe Energy balance : Unstable equilibrium with Chaotic oscillations : Turbulence in the closed chamber

13. Temperature distributions at surface of the casing Inner surface Outer surface Without air blow Ui=0.0m/s at 20 ℃

14. Forced air flow outside the gear unit Velocity vectors in the X-Y plane near the outside surface (z=0.44m) U i =2.0m/s at 20 ℃ With air blow

15. Increase in fluctuations of free convection currents inside the gear unit Velocity vectors in the central X-Y plane (z=0.0m) Ui=2.0m/s Fluctuating monitoring screen at probe Active Chaotic oscillations without the stable state With air blow at 20 ℃

16. Fluctuations of the casing temperature T ( ℃ ) Y (m) P R Q P Q R Casing X=0.88m, Z=0.39m With air blow: U i =2.0m/s at 20 ℃ Wheel: 70 ℃ P R Q Cross section Fluctuations with chaotic oscillation S S

17. Cooling of the casing X=0.88m, Z=0.39m Without air blow With air blow of Ui=2.0 m/s at 20 ℃ Y (m) T ( ℃ ) P R P R Q Q Casing Air blow The average of fluctuating temperatures Wheel: 70 ℃ R P Q Cross section S S

18. Decrease in outer surface temperature of the casing U i = 2.0m/s at 20 ℃ With air blow Without air blow Ui=0.0 m/s at 20 ℃

19. Conclusions 1.Simulation was successfully carried out using more than 2.0×10 6 Cartesian grids. 2.The casing was cooled by forced air-convection even at low velocity such as 2.0m/s on the outside the gear unit. 3.Free convection was observed inside the closed gear unit in both cases with and without air blow. The free convection currents fluctuated with the chaotic oscillation in the gear unit.