1. C.Hariharan and M.Govardhan
Chennai – 36
Indian Institute of Technology
Madras
Loss in Input Power due to Increase in
Clearance between Inlet Duct and Impeller in an
Industrial Centrifugal Blower
Thermal Turbomachines Laboratory
Department of Mechanical Engineering
Indian Institute of Technology Madras
1

2. Introduction
• Lee [3]
• C Hariharan et al [5]
Chennai – 36
Indian Institute of Technology
Madras
• Aayder et al. [1]
2

3. • In most of the time while design we omit the
clearance gap in between suction duct and
impeller.
Chennai – 36
Indian Institute of Technology
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Problem definition
• The area of clearance is only 0.5 to 2% of
inlet area.
3

4. Design
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Indian Institute of Technology
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Specification:
specific work
Design mass flow rate
operating range
Speed
- 24000 m2/s2
- 28.5 kg/s
- 20 kg/s to 31.5 kg/s
- 3000rpm
4

5. Dimension
Blades
Inlet Diameter
Inlet Blade angle
Exit Blade angle
- 15
- 0.7 m
- 32o
- 48o
Clearance gap
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Indian Institute of Technology
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Impeller:
- 1mm, 3mm and
5mm
- 0.6 %, 1.8% and
3%
clearance area
5

6. - constant angular momentum
- tongue clearance 5% of impeller
exit diameter
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Indian Institute of Technology
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Volute :
- Ratio between volute width and
impeller exit width 5.
6

7. Chennai – 36
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Fan Assembly with Ratio 5 volute
7

8. Numerical simulation
simplification
-Steady state
-Compressible (air ideal gas)
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- commercial CFD code CFX 14
- (3-D) Full fan
8

9. Chennai – 36
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- (3-D)
-Mass
-Momentum
-Energy
- turbulence model (K-Ɛ)
9

10. -Rotating domain
- impeller
Interface
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Indian Institute of Technology
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- Stationary domain
- suction duct
- volute
Frozen Rotor Technique
10

11. -Suction duct 0.8 million
-Impeller 4.5 million
-Volute 5.5 million
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Indian Institute of Technology
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Meshing
Y+ < 50
volume expansion factor < 25
Number of nodes in interfaces maintained almost
same
11

12. Chennai – 36
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Suction duct mesh
12

13. Chennai – 36
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Impeller mesh
13

14. Chennai – 36
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Impeller pasage
14

15. Chennai – 36
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Volute mesh
15

16. Chennai – 36
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Impeller inlet duct mesh
16

17. Chennai – 36
Indian Institute of Technology
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Clearance between impeller and
inlet duct
17

18. circumferential
radial
10
1100
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Indian Institute of Technology
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Number of nodes in clearance
18

19. -Stage performance
-Component performance
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Results
19

20. Chennai – 36
Indian Institute of Technology
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Stage Pressure raise
20

21. Chennai – 36
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Change in Stage Pressure raise
21

22. Chennai – 36
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Stage Efficiency
22

23. Chennai – 36
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Change in Stage Efficiency
23

24. Chennai – 36
Indian Institute of Technology
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Change in Total pressure at impeller
exit
24

25. Chennai – 36
Indian Institute of Technology
Madras
Change in static pressure at impeller
exit
25

26. Chennai – 36
Indian Institute of Technology
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Increase in input power
26

27. Chennai – 36
Indian Institute of Technology
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Return mass flow rate
27

28. Chennai – 36
Indian Institute of Technology
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Flow angle at inlet to impeller for
design mass flow rate
28

29. Chennai – 36
Indian Institute of Technology
Madras
Flow angle at inlet to impeller for
lowest mass flow rate
29

30. Chennai – 36
Indian Institute of Technology
Madras
Static pressure at impeller exit for
design mass flow rate
30

31. Chennai – 36
Indian Institute of Technology
Madras
Static pressure at impeller exit for
lowest mass flow rate
31

32. Chennai – 36
Indian Institute of Technology
Madras
Total pressure at impeller exit for
design mass flow rate
32

33. Chennai – 36
Indian Institute of Technology
Madras
Total pressure at impeller exit for
lowest mass flow rate
33

34. Chennai – 36
Indian Institute of Technology
Madras
Flow angle at Exit of impeller for
design mass flow rate
34

35. Chennai – 36
Indian Institute of Technology
Madras
Flow angle at Exit of impeller for
lowest mass flow rate
35

36. Chennai – 36
Indian Institute of Technology
Madras
Stream lines in impeller for
clearance of (a) 0mm
36

37. Chennai – 36
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Madras
Stream lines in impeller for
clearance of (a) 1mm
37

38. Chennai – 36
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Madras
Stream lines in impeller for
clearance of (a) 3mm
38

39. Chennai – 36
Indian Institute of Technology
Madras
Stream lines in impeller for
clearance of (a) 5mm
39

40. Chennai – 36
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Volute Pressure recovery coefficient
40

41. Chennai – 36
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Change in volute Pressure recovery
coefficient
41

42. Chennai – 36
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Volute loss coefficient
42

43. Chennai – 36
Indian Institute of Technology
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Volute loss coefficient
43

44. Chennai – 36
Indian Institute of Technology
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Change in Total pressure at volute
exit
44

45. Chennai – 36
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Change in static pressure at volute
exit
45

46. -The overall stage performance at design
and off design conditions, especially at
higher mass flow rate is not favorable
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Indian Institute of Technology
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conclusion
-Stage efficiency drops considerably as the
mass flow is increased and also there is an
increase in input power up to 32 kW
-There is a noticeable drop in total and
static pressure at exit of impeller
46

47. As the clearance increases, the flow is
found to be more uniform at the exit of the
impeller and also the possibility of flow
separation gets reduced at lower mass
flow rates especially near the trailing edge
of impeller.
Chennai – 36
Indian Institute of Technology
Madras
conclusion
The increased pressure recovery and
reduced loss at higher clearance has
positive effect on volute at all mass flow
rates.
47

48. Chennai – 36
Indian Institute of Technology
Madras
Thank you
48