The presentation gives glances of the importance of CFD analysis of Turbomachines with an illustration/ case study. For more details, follow the webinar-02 "Application of CFD for Rotating Machinery Flow Analysis" For more such information follow: https://www.linkedin.com/in/ganeshvisavale/

1. Introduction Classification CFD Modeling Test Case Results
Application of CFD for Turbomachinery Flow Analysis
Dr. Ganesh Visavale
Cofounder & General Manager
LearnCAx (Centre for Computational Technologies Pvt. Ltd)
Pune: 411007. India
May 24, 2014
www.learncax.com Application of CFD for Turbomachinery Flow Analysis May 24, 2014 1 / 22

2. Introduction Classification CFD Modeling Test Case Results
Turbomachines
1 Compressors : transport of gas at increased
pressure
2 Turbines : rotary device which extracts work from
working fluid
3 Fans : transport gas at high volume flow rate and
low pressure
4 Pumps : transport fluid (liquids) at increased
pressure
5 Blowers : similar to pumps but deal with gases
6 Mixing tanks : impeller rotation causes stirring
action for chemical reaction processing
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3. Introduction Classification CFD Modeling Test Case Results
Flows with rotating systems
1 Turbomachinery or Rotating machinery add or
extract work from a fluid
2 Other use of rotating machinery is in mixing fluids
for chemical processing
3 The process consists of moving fluids and rotating
blades.
4 Devices which extract energy come under the
category of turbines
5 Devices which add energy come under categories
like pump, fans, compressors, blowers, fans etc.
6 All these devices come under a generalized term
called rotating machines or turbomachinery
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4. Introduction Classification CFD Modeling Test Case Results
Classification of Turbomachinery
Turbomachines
Fluid
Physics
Compress-
ible fluids
Aircraft
Gas
turbines
Steam
power
plants
Incompre-
ssible
fluids
Pumps
Hydraulic
turbines
Direction
of flow
Axial flow
devices
Centrifugal
flow
devices
Mixed flow
devices
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5. Introduction Classification CFD Modeling Test Case Results
How does CFD help ?
Conventional design process based on application of empirical design methods
Design of turbomachinery involves large number of variables & different design
configuration are possible which meet system requirement
CFD has been increasingly used to successfully design turbomachinery as well as
carry out analysis and validation requirements for existing design
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6. Introduction Classification CFD Modeling Test Case Results
CFD for Turbomachinery
Performance prediction
Internal flow visualization in the form of pressure
distribution, flow distribution, flow path through the
impeller, diffusor and other components
Qualitative and quantitative validation of performance
using simulations
Investigation of existing design
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7. Introduction Classification CFD Modeling Test Case Results
CFD Design Cycle
Initial design
Geometry
generation
Mesh gen-
eration
Inputs for
CFD problem
Solver
Post processing
Result ex-
traction
Optimum
design
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8. Introduction Classification CFD Modeling Test Case Results
CFD Design Cycle
Initial design
Geometry
generation
Mesh gen-
eration
Inputs for
CFD problem
Solver
Post processing
Result ex-
traction
Optimum
design
www.learncax.com Application of CFD for Turbomachinery Flow Analysis May 24, 2014 7 / 22

9. Introduction Classification CFD Modeling Test Case Results
CFD Design Cycle
Initial design
Geometry
generation
Mesh gen-
eration
Inputs for
CFD problem
Solver
Post processing
Result ex-
traction
Optimum
design
www.learncax.com Application of CFD for Turbomachinery Flow Analysis May 24, 2014 7 / 22

10. Introduction Classification CFD Modeling Test Case Results
CFD Design Cycle
Initial design
Geometry
generation
Mesh gen-
eration
Inputs for
CFD problem
Solver
Post processing
Result ex-
traction
Optimum
design
www.learncax.com Application of CFD for Turbomachinery Flow Analysis May 24, 2014 7 / 22

11. Introduction Classification CFD Modeling Test Case Results
CFD Design Cycle
Initial design
Geometry
generation
Mesh gen-
eration
Inputs for
CFD problem
Solver
Post processing
Result ex-
traction
Optimum
design
www.learncax.com Application of CFD for Turbomachinery Flow Analysis May 24, 2014 7 / 22

12. Introduction Classification CFD Modeling Test Case Results
CFD Design Cycle
Initial design
Geometry
generation
Mesh gen-
eration
Inputs for
CFD problem
Solver
Post processing
Result ex-
traction
Optimum
design
www.learncax.com Application of CFD for Turbomachinery Flow Analysis May 24, 2014 7 / 22

13. Introduction Classification CFD Modeling Test Case Results
CFD Design Cycle
Initial design
Geometry
generation
Mesh gen-
eration
Inputs for
CFD problem
Solver
Post processing
Result ex-
traction
Optimum
design
www.learncax.com Application of CFD for Turbomachinery Flow Analysis May 24, 2014 7 / 22

14. Introduction Classification CFD Modeling Test Case Results
CFD Design Cycle
Initial design
Geometry
generation
Mesh gen-
eration
Inputs for
CFD problem
Solver
Post processing
Result ex-
traction
Optimum
design
www.learncax.com Application of CFD for Turbomachinery Flow Analysis May 24, 2014 7 / 22

15. Introduction Classification CFD Modeling Test Case Results
CFD Design Cycle
Initial design
Geometry
generation
Mesh gen-
eration
Inputs for
CFD problem
Solver
Post processing
Result ex-
traction
Optimum
design
www.learncax.com Application of CFD for Turbomachinery Flow Analysis May 24, 2014 7 / 22

16. Introduction Classification CFD Modeling Test Case Results
CFD Modeling Approach
Concept called Moving Reference Frame is used
Reference frame has motion defined relative to stationary
coordinate system
This approach transforms an unsteady flow field with
respect to stationary frame into a steady flow field with
respect to the moving reference frame
This approach makes it easier to specify appropriate
boundary conditions, define a simpler CFD problem and
also takes less time and computational effort
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17. Introduction Classification CFD Modeling Test Case Results
CFD Modeling Approach
Mass, momentum, energy and other equations are solved in
stationary frame
Acceleration of fluid in moving frames is defined using relative
velocity of rotating frame and stationary frame
The convection terms and source terms in the momentum equations
are modified using the acceleration terms due to he moving reference
frame
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18. Introduction Classification CFD Modeling Test Case Results
CFD Modeling Approach
Single Reference Frame (SRF)
A moving reference frame is defined within
the model of a single fluid domain
This domain moves with the frame speed
around axis of rotation
Stationary boundaries form a surfaces of
revolution
This moving frame takes care of the rotation
effect of the blades
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19. Introduction Classification CFD Modeling Test Case Results
CFD Modeling Approach
Sliding mesh approach
Domain is divided in to rotating and non-rotating
zones
The interface is modeled as non-conformal surface
of revolutions
In this approach there is relative motion between
the zones and thus the approach becomes transient
in nature
The mesh is moved during each time step and
fluxes are modeled at sliding/moving interfaces
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20. Introduction Classification CFD Modeling Test Case Results
CFD Modeling Approach
Multiple Reference Frame (MRF) or Frozen
Rotor-Stator approach
Used when there is a stationary component that cannot
be modeled as surfaces of revolution
Two distinct domain are considered one in moving
frame and one stationary
An interface is defined between stationary and rotating
fluid zones
Velocity vector and velocity gradients are then
transformed at this interface
Flux, momentum, energy, and other scalars exchange at
interface
No relative motion between the domains
Interface is modeled as surface of revolution
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21. Introduction Classification CFD Modeling Test Case Results
Importance of Mesh Quality
Mesh generation is very critical and complex in case of
turbomachinery applications
Impeller and blades and diffusor/volute region are critical during
meshing
Casing, Impeller diffuser require separate meshing strategy and then
different meshes are merged to generate entire pump mesh
Hybrid mesh with tetrahedral and hex mesh elements and prism layer
to capture turbulent flow phenomenon
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22. Introduction Classification CFD Modeling Test Case Results
Finer mesh between the blades to capture the exact flow regions
Varied size mesh elements near the blades to capture flow details
Mesh orientation should be along the fluid flow direction
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23. Introduction Classification CFD Modeling Test Case Results
CFD Modeling Approach
Example: Centrifugal blower
2D model of a standard shaped centrifugal blower
36 blade impeller
Inlet total pressure : 180 Pa
Outlet: at ambient conditions.
Flow : turbulent in nature.
Blades rotation: angular velocity of 300rad/s in
clockwise direction.
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24. Introduction Classification CFD Modeling Test Case Results
CFD Modeling Approach: Centrifugal Blower
MRF approach
Need to define a moving reference
frame around the blades
Blades are not rotating
Mesh is not rotating
Motion is incorporated by using
Moving Reference Frame i.e. the
reference frame is moving w.r.t
stationary zone with the rotational
speed of blades (300rad/s)
SRF approach
The blades are rotating
Mesh is rotating at the
rotational speed of blades
Need to define a region around
the blades called as the moving
zone
Interface between the stationary
domain & rotating mesh is the
sliding interface
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25. Introduction Classification CFD Modeling Test Case Results
Grid: Centrifugal Blower
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26. Introduction Classification CFD Modeling Test Case Results
Pressure distribution
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27. Introduction Classification CFD Modeling Test Case Results
Velocity distribution
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28. Introduction Classification CFD Modeling Test Case Results
Summary
From the results of the pressure and velocity profiles we see that both
the approaches are almost identical.
SRF approach captures more details and gives better insights as
compared to MRF approach.
SRF is the unsteady simulation approach that is high on
computational time and cost.
MRF approach can be used as the quick first hand qualitative analysis
that incorporates the rotation effect using the steady state simulation.
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29. Introduction Classification CFD Modeling Test Case Results
References
FLUENT user guide- modeling flows with rotating reference frames.
esi CFD FAQ
Wikipedia, the free encyclopedia
adapco ONLINE
FLUENT tutorial: Using Sliding Mesh
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30. Introduction Classification CFD Modeling Test Case Results
Thanks...!
LearnCAx
Inspire | Educate | Mentor
CCTech - Pune
1 Akshay Residency, 50 Anand Park, Aundh, Pune-411007. India.
ganesh@learncax.com, www.learncax.com
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