**Principal Investigator:**

Michael Breuer

**Affiliation:**

Department of Fluid Mechanics, Helmut-Schmidt-University, Hamburg (Germany)

**Local Project ID:**

pr47me

**HPC Platform used:**

SuperMUC of LRZ

**Date published:**

**Fluid-Structure Interaction is a topic of major interest in many engineering fields. The significant growth of the computational capabilities allows solving more complex coupled problems, whereby the physical models get closer to reality. In order to simulate practically relevant light-weight structural systems in turbulent flows, scientists of the Helmut-Schmidt-University in Hamburg developed and implemented an original computational methodology especially for thin flexible structures in turbulent flows.**

Fluid-Structure Interaction (FSI) is a topic of major interest in many engineering fields. The significant growth of the computational capabilities allows solving more complex coupled problems, whereby the physical models get closer to reality. The long-term objective of the present research project is to simulate practically relevant light-weight structural systems in turbulent flows (for example outdoor tents as shown in Figure 1). In order to do that an original computational methodology has been developed and implemented especially for thin flexible structures in turbulent flows [1].

In order to reach the final objective to tackle civil engineering FSI applications, highly advanced solvers for both subtasks (fluid and structure mechanics) are applied. A coupling program does the required exchange of data between both codes. Therefore, the resulting FSI scheme is partitioned and divided into three parts:

• The fluid solver FASTEST-3D is a highly parallelized finite-volume 3D CFD solver. To simulate turbulent flows, eddy-resolving schemes such as large-eddy simulations (LES) are chosen.

• The structure solver Carat++ [5] developed at TU Munich is a 3D finite-element solver specialized in the prediction of thin structure deformations based on shell or membrane elements.

• The coupling program, CoMA [6], developed at TU Munich is responsible for the mapping between the non-matching meshes and for the exchange of data between the solvers.

To get suitable and stable results in FSI a “strong” coupling procedure is highly recommended. For partitioned solution algorithms this means that a sub-iteration process is required at each time-step in order to guarantee dynamic equilibrium between the fluid and the structure. One of the big challenges of this research project are the CPU-time requirements. To reduce the CPU-time consumption a special procedure for eddy-resolving schemes was developed using an explicit time-marching scheme [1].

In order to assure reliable numerical simulations for complex configurations, the present methodology needs to be validated at first on simpler test cases. For laminar flows several reference test cases (such as FSI3 from Hron and Turek, 2006) are available in the literature and the present methodology was validated based on this test case using HLRB2 [1]. However, for the turbulent regime the test cases are rare and often too challenging. Therefore, the short-term goal of the current project is to provide reasonable benchmark cases for the FSI community. For this purpose, complementary experimental-numerical investigations involving thin flexible structures in turbulent flows were carried out.

Two test cases, denoted FSI-PfS-1a and FSI-PfS-2a were released [2,3,4]. A thin flexible rubber plate with or without a rigid weight is clamped behind a fixed cylinder. The structure exposed to a sub-critical flow (Re = 30,470) leads to the formation of alternating vortices shedding behind the cylinder. Oscillating forces are generated on the plate. Consequently, the flexible structure deforms in the first swiveling mode with moderate displacements for FSI-PfS-1a and in the second swiveling mode with larger displacements for FSI-PfS-2a (cf. Figure 2). All computations were done on SuperMUC of the LRZ. The experimental and numerical results are found to be in close agreement in both cases. Thus, the computational framework used is validated. Furthermore, reliable test cases are now available. Detailed experimental and numerical data can be found on the ERCOFTAC Knowledge Base Wiki under these links:

http://qnet-ercoftac.cfms.org.uk/w/index.php/UFR_2-13

http://qnet-ercoftac.cfms.org.uk/w/index.php/UFR_2-14

**References and Links**

[1] Breuer, M., De Nayer, G., Münsch, M., Gallinger, T., Wüchner, R.: Fluid-Structure Interaction Using a Partitioned Coupled Predictor-Corrector Scheme for the Application of Large-Eddy Simulation, J. of Fluids and Structures, 29, 107-130, (2012).

[2] De Nayer, G., Kalmbach, A., Breuer, M., Sicklinger, S., Wüchner, R.: Flow past a Cylinder with a Flexible Splitter Plate: A Complementary Experimental-Numerical Investigation and a New FSI Test Case (FSI-PfS-1a), Int. Journal of Computers and Fluids, 99, 18-43, (2014).

[3] Kalmbach, A. and Breuer, M.: Experimental PIV/V3V Measurements of Vortex-Induced Fluid-Structure Interaction in Turbulent Flow - A New Benchmark FSI-PfS-2a, J. of Fluids and Structures, 42, 369-387, (2013).

[4] De Nayer, G. and Breuer, M.: Numerical FSI investigation based on LES: Flow past a cylinder with a flexible splitter plate involving large deformations (FSI-PfS-2a), Int. J. of Heat and Fluid Flow, 50, 300-315, (2014).

[5] Fischer, M., Firl, M., Masching, H., Bletzinger, K.-U.: Optimization of Nonlinear Structures based on Object-Oriented Parallel Programming, ECT2010: 7th Int. Conf. Eng. Computational Techn., Valencia, Spain, (2010).

[6] Gallinger, T., Kupzok, A., Israel, U., Bletzinger, K.-U., Wüchner, R.: A Computational Environment for Membrane-Wind Interaction, Int. Workshop on Fluid-Structure Interaction. Kassel Univ. Press, 283-294, (2009).

**Research Team & Scientific Contact:**

Univ.-Prof. Dr.-Ing. habil. Michael Breuer (PI), Dr.-Ing. Guillaume De Nayer

Univ.-Prof. Dr.-Ing. habil. Michael Breuer

Professur fuer Stroemungsmechanik (PFS)

Institut fuer Mechanik, Helmut-Schmidt-Universitaet Hamburg

Holstenhofweg 85, D-22043 Hamburg (Germany)

e-mail: breuer@hsu-hh.de

www.hsu-hh.de/pfs