Way back in 2005, I co-authored a paper for the Fluent News magazine titled “FSI Makes Fluent More Flexible.” Now I’m here to talk about how RBF Morph makes ANSYS Fluent more flexible In RIBES Clean Sky Project and in ways that you can use to make your simulations more efficient.
In the 2005 paper my colleague and I wrote: “Fluid-structure interaction (FSI) is an important and interesting phenomenon, but it is a difficult challenge for numerical modeling. It even poses difficulties for numerical modelers. Structural behavior is a troublesome boundary condition for the CFD analyst, who prefers to assume that boundaries are rigid. The structural analyst, on the other hand, would like to assume that fluid inside or outside a structure merely generates a constant pressure on the walls.”
Thirteen years later, our computational tools have evolved; FSI is now a challenge that we can tackle. Multiphysics simulations, while still complex, are becoming more common in many fields. They are being made easier with enhancements like the advanced mesh morphing technology in RBF Morph, which can embed structural modes in Fluent to make the CFD model flexible. In this case, flexibility refers to the model’s ability to elastically deform under CFD-computed loads.
It’s well known that structural modes and related frequency signatures represent the dynamic behavior of a structure. RBF mesh morphing allows you to import a certain number of modes (the higher the number of modes introduced the lower the related truncation error will be). The modes, which are computed using ANSYS Mechanical, feed data straight into the Fluent solver. This operation makes the shape of the CFD model parametric with respect to modal shapes.
The flexible CFD model can be used for FSI steady-state analysis. Information exchange that is required for two-way FSI is not required anymore. Mesh updating (i.e., elastic deformation of the CFD model under the current computed loads) is performed in Fluent automatically. It is fast and effective, and it works on HPC as well.
FSI functionalities enabled by coupling RBF Morph and Fluent now make it easy to solve many calculation scenarios for industrial applications:
- Transient FSI with movement prescribed in advance. This includes flapping devices undergoing complex motion. The motion can be computed using FEA and multibody solvers, or it can be acquired experimentally. Structural mode acceleration in the CFD model can be used to set up reduced order models suitable for nonlinear flutter analysis.
- Steady-state FSI to model structural deformation on a CFD mesh. This can be used for aeronautical and motorsport applications (wing deformation), and lets you steer shape optimization to account for the coupled response. The deflection of the structure can strongly affect the surrounding flow field.
- Full coupled transient FSI. In this case, a time marching solution lets you capture the interaction between the flow vortices and the structural vibration.
You can get a better understanding of the workflow by watching the video that follows.
ANSYS A&D Industry Director, Paolo Colombo, was among the presenters at the workshop titled “Flexible Engineering Toward Green Aircraft” organized in December 2017 at Rome Tor Vergata University to share the great outcomes of the RIBES Clean Sky Project, where RBF morph and simulation were used to drive innovation. (RIBES is an acronym for “Radial basis functions at fluid Interface Boundaries to Envelope flow results for advanced Structural analysis.”) We discussed three examples to demonstrate the aforementioned approaches in aeronautical research.
The first example is summarized in the paper titled “Assessment and development of a ROM for linearized aeroelastic analyses of aerospace vehicles,” which was published in CEAS Aeronautical Journal by Castronovo et al. (2017). This work demonstrated how the transonic dip of the AGARD 445.6 wing can be captured by simulation.
The second example is taken from the paper titled “Static Aeroelastic Analysis of an Aircraft Wind-Tunnel Model by Means of Modal RBF Mesh Updating.” Published in the Journal of Aerospace Engineering by Biancolini et al. (2016), this paper compares the steady-state response as computed with traditional two-way multiphysics calculations and with modal superposition for the wind tunnel model of the P1XX wing by Piaggio Aerospace.
The third example comes from the paper titled “Fluid structure interaction analysis: vortex shedding induced vibrations” which was published in Structural Integrity Procedia by Di Domenico et al. (2017). This work demonstrates how a full-coupled transient FSI analysis can capture lock-in and lock-off of a hydrofoil.
Full presentations of all three examples are available on the RIBES Clean Sky project page. A book with the full proceedings will be available in late 2018, published by Springer. Keep an eye out for it!