Fluid Mechanics

In fluid mechanics, the focus at Fraunhofer ISE is on fluid dynamics, consisting of aerodynamics, which deals with moving gases, and hydromechanics, which deals with moving fluids. At the center of fluid dynamics are the continuity and Navier-Stokes equations, which can be solved by numerical methods. The so-called computational fluid dynamics (CFD) enables the solution of these non-linear partial differential equations of second order, so that even turbulent flows can be calculated reliably.

For this purpose, Fraunhofer ISE uses the software Comsol and Openfoam based on the finite element method and Ansys Fluent CFX with the finite volume method. Powerful workstations as well as a wide range of compatibility with design programs (imports) complement our know-how in individual 2D and 3D geometry generation (meshing).

Application Examples

Simulation of a Cleaning Basin

In a batch process, key processes such as chemical cleaning and texturing are realized in different reaction baths to create advantageous surface structures for the subsequent solar cells. Several thousand wafers are processed in one process bath. In order to increase the process quality, it is important to understand the flow of the wafers, which is influenced in particular by the design of various installations. Numerical simulation is used to simulate, experimentally validate and optimize the flow. The fine structures prevailing in the process bath, as well as dimensions of the basin, result in a complicated geometry to be meshed. Since the computation time increases strongly nonlinearly with the number of mesh elements, it is an effort to simplify fine structures in order to reduce the number of degrees of freedom for a model. The installations as well as the whole basin could thus be investigated in detail and the most significant flow disturbances could be identified and eliminated.

Strömung SimulationStrömung PIV
© Fraunhofer ISE

Velocity field of a time-dependent flow simulation (left) and the experimentally determined PIV result (right).

Brief Description:

  • Goal
    • Increase of process quality based on the investigation of the flow around the wafers
    • Detailed simulation of an entire cleaning basin
    • Optimization of the basin geometry
  • Procedure
    • 3D simulation with transient flow in the process basin
    • Subdivision of the overall model into submodels
    • Transfer of data between the individual calculation steps of the previous simulation
    • Validation via dye visualization, laser Doppler velocimetry (LDV) and particle image velocimetry (PIV)
  • Result
    • Identification and elimination of the most significant flow disturbances

Simulation of Wind Load on 2-axis Tracker

The wind behavior of a PV system is usually checked in wind tunnels. However, such measurements are very time-consuming and expensive and also only represent individual states. Therefore, we investigate wind loads using computational fluid dynamics (CFD). This makes it possible to investigate a wide variety of conditions in a short time and thus to optimize the system with regard to high wind speeds. Real weather data can be used, for example, to investigate the impact of a specific storm event.

We couple the CFD simulation with further FEM models, e.g. with a mechanical simulation to investigate the deformation and mechanical stress in the module in detail from the determined wind load. Or with thermal simulations to map convection effects and thus the spatially resolved module temperature.

Storms with high wind speeds are one of the effects of climate change. Therefore, it becomes more and more relevant to design solar farms according to such aspects. In contrast to the homogeneous mechanical load prescribed in IEC 61215, wind loads, especially from severe storms, are highly inhomogeneous. In addition, numerous factors influence the wind current and thus the resulting load, e.g. the angle of attack of the PV modules, the substructure and the wind direction.

2-axis trackers provide a large area of attack for wind. This can lead to critical loads and even failure of PV modules, especially at high wind speeds. To investigate the effect of a real storm on a 2-axis tracker, the weather data of this storm was evaluated and served as input values for the CFD simulation. The resulting wind load was simulated for different angles of attack of the tracker.

Windlast auf 2-Achsen Tracker
© Fraunhofer ISE
Windlast auf 2-Achsen Tracker und resultierende Deformation der PV-Module.

Brief Description:

  • Goal
    • Determination of the deformation of a 2-axis tracker due to a real storm
  • Procedure
    • Evaluation of weather data and transfer to CFD simulation
    • Simulation of the wind load for different angles of attack of the tracker
    • Coupling with a mechanical FEM model to simulate deformation and mechanical stress
  • Results
    • Identification of critical angles of attack of the tracker
    • Identification of optimization potential to reduce wind load

Further Information on this Research Topic:

Research Topic

Heat and Cold Storage

Research Topic

Surfaces: Conditioning, Passivation and Light-Trapping

Research Topic

Efficient Heat Exchangers