Simulation of Air-Cooling for the Gear Unit in Pump and Turbine Generator Systems

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
Gas turbine

• 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 8103 kg
• Efficiency 98.8
• Gas turbine 15,500 kW
• 6,429 rpm
• Generator 1,500 rpm

Generator
Gear Unit
3
Inside view of the gear unit
Large wheel

• Large wheel F11.0m
• Cr Mo steel
• Small wheel F20.23m
• Cr Mo steel
• Bearing
• White steel
• With forced lubrication
• Casing
• Cast iron
• Gear ratioN1/N26,429/1,500
• F1/F24.3
• N1RPM of high-speed shaft
• 6,429 rpm
• N2RPM of low-speed shaft
• 1,500 rpm

Small wheel
Bearing
Casing
Double helical type gear unit
4
Cooling during the operation

• Gear wheels Distribution of pressurized
• oil inside the gear
  unit.
• Casing Under study of making use
• air-convection
  environment.

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Purposes

• Purposes are to
• 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.

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Model creation by use ofCAD (I-DEAS)
Scale 1.73m1.50m1.03m Diameter of large
wheel 1.28m Diameter of small wheel
1.12m Gear Ratio 1.28/1.121.14
Large wheel
Bearing
Small wheel
Casing
Y
X
Z
O
Symmetric with respect to the central X-Y plane
Importing CAD model into VR through STL format
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Outline of calculation
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
(Z0.0m) Turbulence model RNG k- e
Re2.31105 (Ui2m/s, 20?) Buoyancy
force Bossinesq approximation
Y
Gravity
Inlet air at 20?
Outlet
Ui0.0, 2.0m/s
Z
X
Domain 2.0m2.0m0.8m
Cartesian grid numbers 20020080 ( 3.2106 )
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Temperature boundary conditions
Top part of inner wall 70? due to adhesion of
hot oil
Inlet air at 20? (Ui0.0, 2.0 m/s)
Outlet
Wheels 80?
Bearings 70?
Base floor 20?
Inner base wall 70? due to adhesion of hot
oil
From the experimental data during the
operation
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Resolution test of Cartesian grids
Total number of grids (Nt)1.2106
30mm
1.50m
Nt2.0106
Nt3.2106 in the main analyses without the
cut-cell technique
1.73m
PRPS contours in the central X-Y plane
(z0.0m)
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Free convection outside the gear unit
Without air blow
Ui0.0m/s at 20?
Velocity vectors in the X-Y plane near the
outside surface (z0.44m)
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Free convection inside the gear unit
Without air blow
Ui0.0m/s at 20 ?
(Gry109gt Grc108)
Velocity vectors in the central X-Y plane
(z0.0m)
12
Fluctuations of free convection currents inside
the gear unit
At probe
Free convection in the gear unit without air blow

Energy balance Unstable equilibrium
with Chaotic oscillations Turbulence in the
closed chamber
0
1200
600
t(s)
Fluctuations of the fully developed flow with
time
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Temperature distributions at surface of the
casing

Ui0.0m/s at 20?
Ui0.0m/s at 20?
Inner surface
Outer surface
Without air blow
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Forced air flow outside the gear unit
With air blow
Ui2.0m/s at 20?
Velocity vectors in the X-Y plane near the
outside surface (z0.44m)
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Increase in fluctuations of free convection
currents inside the gear unit
With air blow
Ui2.0m/s
at 20?
Fluctuating monitoring screen at probe Active
Chaotic oscillations without the stable state
Velocity vectors in the central X-Y plane (z0.0m)
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Fluctuations of the casing temperature
With air blow Ui2.0m/s at 20?
R
Wheel 70?
R
X0.88m, Z0.39m
Y (m)
Q
Q
P
Fluctuations with chaotic oscillation
S
Casing
R
Q
P
Wheel70?
S
T (?)
Cross section
P
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Cooling of the casing
The average of fluctuating temperatures
Air blow
Wheel 70?
R
R
X0.88m, Z0.39m
Y (m)
Q
Without air blow
Q
With air blow of Ui2.0 m/s at 20?
P
Casing
S
R
Q
P
Wheel70?
S
T (?)
Cross section
P
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Decrease in outer surface temperature of the
casing
Ui0.0 m/s at 20?

Ui2.0m/s at 20?
Without air blow
With air blow
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Conclusions

• Simulation was successfully carried out using
• more than 2.0106 Cartesian grids.
• The casing was cooled by forced air-convection
• even at low velocity such as 2.0m/s on
  the
• outside the gear unit.
• 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.