CFD-15. Scale-Adaptive Simulation Model

With this entry on Computational Fluid Dynamics (CFD) we finish the series of cases related to turbulence modelling. In this example we will deal with the SAS (Scale-Adaptive Simulation) method that solves turbulent structures by adapting the resolution scale to the mesh size and time step used.

In this way, a solution similar to that of a stationary RANS method can be obtained in areas of low interest and a better resolution solution such as IDDES in areas where higher accuracy is desired.

CFD Model

In this case we will study the vortex street that appears behind an obstacle in the fluid field. The mesh is imported from an Ansys Fluent file. This is shown below:

Meshing of the CFD domain for the simulation

As boundary conditions, symmetries are placed on the side walls, an outlet at atmospheric pressure and a uniform inlet with a velocity of 15 m/s and automatic external turbulence. A No-Slip Wall is placed on the body wall as a No-Slip Wall condition.

CFD Simulation and Results

Once more, a stationary solution with SST turbulence model is first calculated. These results are exported with Acutrans to be used as initial condition for the subsequent transient analysis. This process has already been described in previous posts and can also be found in our Downloads section.

The flow recirculation zone fits as expected as shown in the picture:

Recirculation zone of the stationary analysis

However, this result is a time average. In order to visualise the unsteady flow patterns, a transient analysis with a suitable turbulence model such as SAS is required. The following image shows the velocity results of the corresponding analysis:

Velocity field and its temporal fluctuations with the SAS turbulence model

The recirculation zone is also found to fluctuate around the average, as expected.

Finally, we show the results of the Q-Criterion isosurfaces, which allow in this case a very clear visualisation of the vortex patterns generated in the domain.

Vortices generated in the flow through the analysed body by CFD simulation

With these results we conclude the series of entries dedicated to the study of turbulence and its modelling using Computational Fluid Mechanics (CFD). The handling of these concepts and their application to industrial cases are part of the knowledge available to ICEMM as a company with extensive experience in the analysis and optimisation using this technology.

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