1 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

CFD and FEA for aeroelasticityconsiderations

By Dr John Lin, Senior Engineer, ANSYS

2 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

A brief introduction

• Sydney University – Ph.D in Aeronautical; Topology optimization of aircraft wing structures

• CRC-ACS – Composite Research Engineer

• ANSYS (Australia + UK) – FEA & CFD Engineer

3 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Agenda

• Classical aeroealsticity and CFD aeroelasticity

• What we can do with FSI (Fluid structural interaction)

• AePW 2 participation− Forced oscillation case

− Flutter case

• Conclusion

4 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Classical Aeroelasticity vs CFD aeroelasticity

• Classical aeroelasticity typically implies the use of doublet lattice method (based on potential flow).

• CFD aeroelasticity means employing CFD methods to solve the aerodynamics, which will generally provide greater accuracy. Effects from the viscous drag, turbulence, dissipation, boundary layer, and energy are accounted for.

• The coupling between FEA and CFD is called FSI (Fluid structural interaction)

5 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Currently with 2 way FSI

• 2-way thermal-structural FSI solution of a bimetallic strip.There are two different metals with different coefficients of thermal expansion bonded together to form the cantilever beam

• Goal: Proof of concept case for modeling:Bimetallic thermostats, temperature meters and controllers use this technology.

• ANSYS products used • Fluent• Mechanical

(Coupled field elements)

6 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Currently with 2 way FSI

• Both steady/static and transient 2-way FSI performed on a realistic wind turbine

• Goal: Model the structural response of the wind turbine under normal and extreme conditions (sudden wind speed & direction change)

• ANSYS products used • CFX• Mechanical• Composite Prep/Post

• Other Industrial Applications• Turbomachinary

7 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

The Aeroelasticity Prediction Workshop 2

• Case 1− Unforced steady-state

− Forced oscillations

• Case 2− Unforced steady-state

− Flutter

8 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Spatial permutations

1.3 mil0.000188”

4.0 mil0.000126”

11.7 mil0.000084”

Cell countWall distance

9 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Steady-state validation

10 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Forced Oscillation Ө=1, f = 10Hz

• Temporal convergence was achieved (0.003125, 0.0015625, 0.00078125)• Spatial convergence prove to be difficult

11 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Forced Oscillation

12 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Flutter case

• Modelling challenge from flutter motion− Grid quality deterioration

− Mesh failure

• Moving deforming mesh approach− Supports non conformal interface

− Non conformal cylindrical interface to accommodate pitch motion

− Layering + non-conformal interface to accommodate plunge motion

13 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Flutter results

14 © 2015 ANSYS, Inc. March 15, 2016 ANSYS Confidential

Summary

• The industry currently uses the doublet lattice aerodynamics approach for evaluating flutter

• Unsteady CFD aeroelasticity increases computational cost

• Unsteady CFD provides higher fidelity in large, unsteady, turbulent scenarios

• Further investigation is required to study the temporal resolution required (∆t) for flutter case