CFD Modelling of Turbo-machinery

 CFD of Turbo-machinery

  by

Dr. Sharad N. Pachpute 

              Correct prediction  of rotating fluid flow  for better performance 

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Table of Content

1. Introduction to turbo-machinery
2. Classification of turbo-machinery
3. Major turbo-machinery in Thermal Power Plant
4. Governing equations for turbo-machinery
5. Modeling of turbo-machinery
6. ANSYS CFD Tools for turbo-machinery
7.Other CFD Tools for turbo-machinery
8. Resources and CFD Tools

 
  • CFD user must be familiar with basic understanding of turbo-machinery. Hence, classification and representation of turbine and pump have been elucidated well with diagrams.
  • The CFD model (like SRF, MRF, MIPI etc.) considered  for turbo-machinery depends on assumptions, boundary conditions and selection of computational domain.
  • CFD user must know advantage and disadvantage of each turbo-CFD model (refer user manual of  FLUENT ): click here: Best_practice_guidelines_for_turbomachinery_CFD
 

1. An Introduction to Turbo-machinery

• Turbo-machinery is defined as the machines which  transfer energy between a rotor (blades)  and a fluid fluid.  It can be  turbines and compressors.
• As turbine  rotates and transfers energy from a fluid to a rotor, a compressor transfers energy from a rotor to a fluid

 
 
Fig.1 Flow pattern around the fan for clockwise and anti-clockwise rotation.
Fig.2 Steam-turbine in power plant for power generation

2. Classification and Components of Turbo-machinery

2.1 Classification of Turbo-machinery

• Turbo-machines are classified into two types of power generation or power absorption 

 
 
 
Fig.3 Example of Turbo-machinery: steam turbine in  power generation
Fig.4 Example of Turbo-machinery for power absorption 

Turbo-machines are classified based on types of fluid flow 

 

2.2 Details of Axial Turbine Stage

Major components of axial flow turbine is given as below:
a) Stator comprises  a series of stationary blades acts as guide vane for incoming flows
b) Rotor comprises  a series of moving  blades and provide work/power to the shaft
   Application of Axial Flow Turbine: thermal  power plant and gas turbine of (aircraft engine)

(a)
                 
(b)
Fig.5 (a) Major parts of axial stage turbine, (b) blades for a single stage axial turbine.
 
 

2.3 Representation of  A Single stage Axial Turbine: 

(a)  Cascade view:
 
Fig.6 Cascade view of axial turbine.
 
(a) Meridinoal  view:
Fig.7 Meridional view of axial turbine.

2.4 Multistage Axial Turbine

• A series of stages forms a multistage turbine

• The energy (work) transfer in a single stage is limited by the blade speed
• If more energy transfer per unit mass is required , then number of stages are added one after other

(a) Schematic of multi-stage steam turbine
                                                      (b) turbine power house
 
(c) Multi-stage Steam turbine without casing
Fig.8 Multi-stage steam turbine for thermal power plant.

2.5 Radial  Turbine:

Application of radial turbine:Gas turbine, turbocharger and process industry   
 
 

                 

Components of radial turbine

 
 
                                      Fig.9 Components of radial turbine. 
 

2.6 Impulse Turbine vs Reaction Turbine:

 

2.7 Power Absorbing Turbo-machinery

2.7.1 Compressor Types

2.7.2 Axial Fans/blower 

 Fig.10 Different types of fans/blowers. 

2.7 Details of Pump

Fig.11 Components of pump.
 

Representation of Flow through the Pump:

 
Fig.11 Representation of pump.
 
Cascade view of Pump:
 
 
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Fig.12 Cascade view  of pump.
 

3. Governing Equations for Turbo-machinery

3.1 Single Rotating Frame (SRF):

• Governing Equation for Single Rotating Frame (SRF) model in a rotating frame:

 
 
 
 

3.2 Multiple Reference Frame (MRF):

 
           
where for each rotating zone: (1) the Coriolis force is added in the governing equations, (2) the flux is calculated from the relative velocity.


3.4 Euler’s Turbo-machine Equations

 
 

4. CFD Modeling of Turbo-machinery

4.1 Single Rotating Frame (SRF)

  • This model computes fluid flow in a rotating frame of reference that is adhere to a rotating machinery.
  • Flow is considered to be steady
           
        Refer for a detailed explanation: Rotating machinery training at OFW10_PDF
        Refer available OpenFOAM solver: OpenFOAM_SRF_Solvers

a)  Computational Domain

  1.                             
 
 b) Boundary conditions for SRF:
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4.2 Multiple Reference Frame (MRF):

  • The Multiple Reference Frame (SRF) model computes fluid flow using both the rotating and stationary reference frames.
  • Multiple frames to be modeled : i)  Rotating zone is solved in the rotating frame, ii)Stationary zone is solved in the stationary frame:
a)  Computational Domain for MRF:

b) Computational Mesh for MRF:

b) Velocity Contours for MRF:
 
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4.3 Mixing Plane Interface

  • This approach is used to model the axial flow turbines which comprises guide vanes, rotor and draft tubes


Periodic domain for CFD Analysis

 


Mixing Plane tutorial : Axial Turbine with Boundary conditions

                                       
 


Mixing Plane with a 3D view

 
 

4.3 Axial Turbine : Analysis of A single rotating blade:

• Create the blade model using ANSYS BladeGen
• Import it into ANSYS ICEM CFD and mesh the model

Rotor CFD Domain:
Stator CFD Domain:

5. CFD Tools for Turbo-machinery

 
ANSYS Tools : BladeGen,TurboGrid, CFX, FLUENTS
OpenFoam: SRFSimlpeFoam, MRFSimlpeFoam,
Star CCM

ØTurbo-machinery WIKI_Turbomachinery

  • ANSYS for Turbomachinery Solutions using ANSYS CFX, Mechanical abd  DesignXplorer: watch the following video:

ANSYS Fluent for Turbo-machinery modeling:

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