University of Applied Sciences HTW Berlin, FB2 Wilhelminenhofstr. - - PowerPoint PPT Presentation

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University of Applied Sciences HTW Berlin, FB2 Wilhelminenhofstr. - - PowerPoint PPT Presentation

Aug 29, 2023 31 likes •237 views

University of Applied Sciences HTW Berlin, FB2 Wilhelminenhofstr. 75A, 12459 Berlin, Germany Thermo-& Fluid dynamics group Prof. Dr.-Ing. Stefan Frank e-mail : stefan.frank@htw-berlin.de Numerical Investigations on the Performance

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University of Applied Sciences HTW Berlin, FB2

  • Wilhelminenhofstr. 75A, 12459 Berlin, Germany

Thermo-& Fluid dynamics group

  • Prof. Dr.-Ing. Stefan Frank

e-mail : stefan.frank@htw-berlin.de

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Manoochehr Darvish , Stefan Frank

STAR European Conference 2011

March 22-23

Numerical Investigations on the Performance Characteristic of Radial Fans with Forward Curved Blades by means of CFD

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Agenda

  • Sirocco fan Introduction

◊ Applications ◊ Advantages/Disadvantages ◊ Characteristic curves

  • Model parameters / Modeling physics
  • CFD Simulations outline
  • Rotation modeling
  • Overview of the generated mesh configurations
  • Results

◊ Characteristic curves: CFD vs. Experiment ◊ Simulation time ◊ Steady vs. Unsteady simulations

  • Conclusions

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Commonly used blade shapes in Radial fans

(with their maximum attainable efficiencies)

Forward curved blades (65%) Radial-Tip blades (70%) Radial blades (60%) Backward inclined Airfoil blades (92%) Backward inclined blades (78%) Backward curved blades (85%) Key factors for fan type selection:

◊ Pressure ◊ Flow rate ◊ Efficiency ◊ Noise generation ◊ Space constraints ◊ Drive configuration ◊ Cost ◊ ...

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Sirocco fan specifications

◊ Large blade angles ◊ Small size relative to other fan types ◊ Operation at low speeds  low level of noise

  • Flow separation between the blades
  • Low efficiency
  • Scroll housing is required

Applications: − Automotive industry − HVAC applications

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Sirocco Fan Performance Curve

Region of Instability Best Efficiency Point (BEP) Throttle Range Overload Range

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Model Parameters

◊ Fan wheel outer diameter (D2) :200 mm ◊ Inner/Outer diameter (D1/D2) : 0.8 ◊ Number of blades : 38 ◊ Rotor width : 82 mm ◊ Scroll housing width: 87 mm ◊ Volute opening angle (α) :7° Modeling Physics  Ideal gas  Segregated flow  Mass Inlet / Pressure outlet  Rotational speed:1000 rpm  Steady-State Moving Reference Frame (MRF)  Rotor Positions: 0°,3°,6°

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CFD Simulations outline

Turbulence models Mesh Configuration

  • Realizable k-ε
  • SST k-ω
  • Spalart-Allmaras
  • Polyhedral
  • Trimmer
  • Polyhedral-Trimmer
  • Structured grid

CFD Simulations

Unsteady

(Rigid Body Motion )

Steady-state

(Moving Reference Frame )

  • Polyhedral
  • SST k-ω

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Rotation of computational domains

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  • Rigid Body Motion (RBM) :

Implicit unsteady Position of the cell vertices : Moving Instantaneous local flow behavior  Time accurate solution Time consuming Powerful computer is needed

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  • Moving Reference Frame (MRF) :

Rotation of computational domains

Frozen Rotor (in some literatures) Steady-state Position of the cell vertices: Fixed Constant grid flux generation 

conservation equations

Approximate analysis

  • f Motion (Time-

averaged solution) Time efficient

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Mesh configurations

Conformal Interface Non-Conformal Interface

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Polyhedral Trimmer Polyhedral- Trimmer Structured Mesh generator Star-CCM+ ANSYS ICEM Number of Cells (in millions) Total 4.2 6.1 4.0 3.7 Rotor 2.6 4.8 2.7 2.4 Stator 1.6 1.3 1.3 1.3 Interface Mesh Conformal Non-conformal Non-conformal Non-conformal Mesh generation time 2-4 hours 5-7 days

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Mesh configurations comparison

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Mesh configurations comparison

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Workstation : CPU : Intel Core i7 (2.8 GHz) RAM : 8 GB

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Turbulence models comparison

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Turbulence models comparison

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Workstation : CPU : Intel Core i7 (2.8 GHz) RAM : 8 GB

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Flow separation in the Nozzle at lower flow rates

Non-uniform inlet flow: » Dominant flow field generated by Rotor » Flow attachment to one side & separation from the other side

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Steady vs. unsteady simulation at 675 m³/h (Overload range)

Static Pressure in Pa Torque in Nm Efficiency in % Exp. 115.8 0.500 41.5 MRF 112.6 0.460 43.9 RBM 114.5 0.470 43.7 Steady (MRF) Unsteady (RBM)

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Steady vs. unsteady simulation at 145 m³/h (Throttle range)

Unsteady (RBM) Steady (MRF) Static Pressure in Pa Torque in Nm Efficiency in % Exp. 115 0.100 44 MRF 126 0.101 48 RBM 118 0.099 46

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Conclusions

  • Unstructured mesh configurations can be used effectively for simulating

sirocco fans.

  • The best results are achieved by using polyhedral cells.
  • The best balance between the simulation time and accuracy is achieved

by using Polyhedral cells as well.

  • Trimmer (as a single mesher) is not suitable for sirocco fan simulation.
  • SST k-ω turbulence model is the most suitable model for simulating

sirocco fans.

  • At intermediate and higher flow rates, steady-state MRF approach

provides the same level of accuracy as unsteady RBM approach.

  • At lower flow rates, flow becomes highly unsteady, and the flow condition

is not suited to steady-state MRF approach.

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Thank you for your attention!