RBF Morph FSI features

RBF Morph – FSI CapabilitiesProf. Marco Evangelos Biancolini – University of Rome “Tor Vergata”

Outline

RBF Morph – FSI September 2016

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FSI capabilities overview Mode-superposition background Proposed workflow Test cases for steady and

unsteady studies Conclusions

FSI capabilities overview


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RBF Morph mesh morphing technology allows to carry out FSI studies through Fluent according to the following strategies: umorph feature to control wall surfaces movements; mode-superposition consisting of the ability of importing

modes and computing modal forces directly on the CFD mesh.

Moreover, enjoying the mesh consistency, modes can be used for the implementation of Reduced Order Models (ROM) prescribing a time history to individual modes and benefiting from the computation of modal forces.

Mode-superposition background4

The static and dynamic behavior of a discrete system (structures) can be determined using the equation of motion in modal coordinates q:

Starting from this framework and if nonlinearities are absent, according to mode-superposition method the deformation of deformable structures can be expressed as a linear combination of the retained natural modes (eigenvectors) multiplied by modal coordinates.Parameterizing the CFD case with natural modes, the mesh becomes “elastic”.

𝑀 𝑖𝑖 �̈�𝑖+𝐶𝑖𝑖 �̇�𝑖+𝐾 𝑖𝑖𝑞𝑖=𝐹 𝑖 (𝑡 )


Proposed workflow5


Modal basis is computed using a FEM solver

Modes are imported into CFD model using RBF Morph

CFD Model + Modal Basis = Flexible CFD Model Flexible CFD model allows to do steady

and transient aeroelastic runs at the same cost of a rigid one

Actual modal coordinates can be linked to FEM for stress recovery

Test cases (steady FSI)6

HIRENASD: static aero-elastic benchmark of the 1st AePW

Mode 1 - 25.5 Hz Mode 2 - 80.2 Hz Mode 3 - 106.1 Hz

Mode 4 - 160.3 Hz Mode 5 – 241.9 Hz Mode 6 - 252.2 Hz

NASTRAN FEM case

Source nodes Morphing preview (Mode 1)


Test cases (steady FSI)7


Test cases (unsteady FSI)8


Release of underwing bodies during the flight in military aircrafts. The loads acting on the elastic wing deflect the

structure Store separation causes a sudden change of

the total load and then a variation of the wing shape

The prediction of the transient behavior is of capital importance to prepare the pilot to get the right reaction



Mode 1 – 13.16 Hz Mode 2 – 76.90 Hz Mode 3 – 82.97 Hz

Mode 4 – 98.72 Hz Mode 5 – 213.45 Hz Mode 6 - 243047 HzSource nodes

CAD model



Large Fluctuation (steady state after 0.6 s)

FSI overhead computation time compared to CFD Unsteady Analysis (with no FSI) is +9%

Fast Fourier Transformation of the two

signals Forcing and wing response frequency

almost the same





Unsteady FSI Analysis of a Square Array of Tubes in Water Crossflow.Test case: A Flow Visualization Study of a Square Array of Tubes in Water Crossflow, D. S. Weaver & A. Abd-Rabbo, 1985

unsteady-FSI-12-cylindershttps://youtu.be/A0WPDyhlr8Q

https://youtu.be/A0WPDyhlr8Q

Conclusions13


The add-on version of RBF Morph provides a well-established feature to reliably end efficiently handle both steady and unsteady FSI studies in Fluent, adopting the mode-superposition approach.Using the same method, the stand-alone version of RBF Morph enables the accomplishment of steady state FSI studies providing that mesh nodes position is reachable and modifiable (such process is already in place for many solvers including OpenFOAM, CFD++ and SU2).Unsteady FSI studies can be carried out through OpenFOAM and SU2 by embedding the feature in the CFD solver environment.

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Engineering

RBF Morph FSI features