TU CE GSC CE People at the Graduate School CE Alumni Nima Aghajari Research Project of Nima Aghajari

FSI-based optimization of profile structures

In many physical systems and engineering applications interactions between elastic structures and fluid flow can be obeserved. Typically mechanical systems that are exposed to high flow forces such as aircraft wings, rotor blades or buildings are affected most. This behaviour is known in literature as fluid-structure interaction (FSI) and has been investigated intensively in the past.

Due to its complexity the physical processes that occur during a FSI can usually not be solved analytically. In fact experimental setups are essential to provide reliable data. However, these are generally associated with enormous costs, which is why the demand for numerical simulations as development tool is increasing rapidly.

Based on validated computational results cost-saving parameter studies can be performed numerically to describe the influence of certain design parameters on the system behaviour. Furthermore, by utilizing appropiate optimization algorithms it would be possible to predict ideal configurations for a structure (e.g. geometry or stiffness) at a given operating condition.

Numerically, the interaction between fluid and elastic structure constitutes a coupled system, where the movement of the fluid and the structure is coupled bidirectionally via the structure's surface. In this work an implicit partitioned approach is applied to solve the coupled problem. This has the advantage of using arbitrary codes for the the corresponding structural and flow problem and furthermore yields the possibility of incorporating a flexible coupling scheme. The flow equations are solved by FASTEST, a parallel multigrid based finite volume solver for incompressible flows whereas structural calculations are carried out by the finite element solver FEAP. The communication between FASTEST and FEAP is realized with the coupling library MpCCI.

A particular challenge for the simulation of FSI in technical applications is the accurate calculation of turbulent flows. Direct numerical simulations (DNS) where the spatial and temporal scales of the turbulence are resolved completely ensure a high level of accuracy. However the computational cost of a DNS is also very high, even for simple problems, which makes its use for industrial applications currently not feasible. Reynolds-averaged Navier-Stokes (RANS) methods on the other hand, which model turbulent scales, are quite applicable for some industrial flow problems but yet lack the accuracy required for a FSI simulation. A compromise between accuracy and computing time can be found in the Large-Eddy-Simulation (LES). Here, large scaled eddys of the flow are simulated while the smaller universal scales are modeled, allowing it to be less time consuming than an ordinary DNS.

Multi-Physics: Fluid-Structure Interaction; Optimization

M. Schäfer, Numerical Methods

S. Ulbrich, Nonlinear Optimization and Optimal Control

Nima Aghajari

Dipl.-Ing.

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