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C.Hariharan and M.GovardhanC.Hariharan and M.Govardhan
Thermal Turbomachines Laboratory
Department of Mechanical EngineeringIndian Institute of Technology Madras
Loss in Input Power due to Increase in Clearance between Inlet Duct and Impeller in an
Industrial Centrifugal Blower
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6Introduction
• Aayder et al. [1]
• Lee [3]
• C Hariharan et al [5]
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6Problem definition
• In most of the time while design we omit the clearance gap in between suction duct and impeller.
• The area of clearance is only 0.5 to 2% of inlet area.
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6Design
Specification:
specific work - 24000 m2/s2 Design mass flow rate - 28.5 kg/soperating range - 20 kg/s to 31.5 kg/sSpeed - 3000rpm
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6Dimension
Impeller:Blades - 15Inlet Diameter - 0.7 mInlet Blade angle - 32o
Exit Blade angle - 48o
Clearance gap - 1mm, 3mm and 5mm
clearance area - 0.6 %, 1.8% and 3%
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Volute :- constant angular momentum
- tongue clearance 5% of impeller exit diameter
- Ratio between volute width and impeller exit width 5.
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6Fan Assembly with Ratio 5 volute
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6Numerical simulation
- commercial CFD code CFX 14
simplification-Steady state -Compressible (air ideal gas)
- (3-D) Full fan
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- (3-D)-Mass-Momentum -Energy
- turbulence model (K-Ɛ)
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6- Stationary domain
- suction duct- volute
-Rotating domain - impeller
Interface
Frozen Rotor Technique
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6Meshing
-Suction duct 0.8 million-Impeller 4.5 million-Volute 5.5 million
Y+ < 50 volume expansion factor < 25
Number of nodes in interfaces maintained almost same
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6Suction duct mesh
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6Impeller mesh
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Impeller pasage
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6Volute mesh
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6Impeller inlet duct mesh
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6Clearance between impeller and
inlet duct
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Number of nodes in clearance
circumferential 1100radial 10
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6Results
-Stage performance
-Component performance
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6Stage Pressure raise
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6Change in Stage Pressure raise
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6Stage Efficiency
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6Change in Stage Efficiency
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6Change in Total pressure at impeller
exit
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6Change in static pressure at impeller
exit
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6Increase in input power
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6Return mass flow rate
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6Flow angle at inlet to impeller for
design mass flow rate
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6Flow angle at inlet to impeller for
lowest mass flow rate
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6Static pressure at impeller exit for
design mass flow rate
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6Static pressure at impeller exit for
lowest mass flow rate
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6Total pressure at impeller exit for
design mass flow rate
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6Total pressure at impeller exit for
lowest mass flow rate
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6Flow angle at Exit of impeller for
design mass flow rate
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6Flow angle at Exit of impeller for
lowest mass flow rate
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6Stream lines in impeller for
clearance of (a) 0mm
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6Stream lines in impeller for
clearance of (a) 1mm
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6Stream lines in impeller for
clearance of (a) 3mm
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6Stream lines in impeller for
clearance of (a) 5mm
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6Volute Pressure recovery coefficient
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6Change in volute Pressure recovery
coefficient
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6Volute loss coefficient
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6Volute loss coefficient
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6Change in Total pressure at volute
exit
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6Change in static pressure at volute
exit
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6conclusion
-The overall stage performance at design and off design conditions, especially at higher mass flow rate is not favorable
-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
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6conclusion
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.
The increased pressure recovery and reduced loss at higher clearance has positive effect on volute at all mass flow rates.
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Thank you
