Like it or not, fluids and solids interact

In a simple world, you could simulate fluid flow and pretend that the walls of the container were inert. In reality, however, there may be significant interaction between the fluid and its container, and thus your CFD software must be able to account for these fluid-solid interactions.

CONVERGE CFD software allows you to easily model rigid body fluid-structure interaction (FSI). In addition, we support extensions to rigid body structures, including beam deformation and impulse-based contact models. CONVERGE automatically generates the mesh and then adapts that mesh to the object’s motion, which can be prescribed or calculated. This feature can be useful, for example, when simulating the blades of a windmill, wings of a bird, or deformation of a reed valve.

Complex interactions within the flow field

CONVERGE can simulate any number of FSI objects, and the density of the objects does not need to be constant. When each object interacts with the flow field, CONVERGE calculates the impact on all the other objects in the field.

Simulating heat transfer

The internal combustion engine industry is moving toward simulating the entire system rather than independent components. Conjugate heat transfer (CHT)—the simultaneous prediction of heat transfer in both the fluid and solid portions of the domain—is of critical importance in a full-engine simulation. The accuracy of the predicted combustion in the cylinder is dependent on the temperature boundary conditions in the cylinder. By including heat transfer in the cylinder head, liner, and piston in the simulation, the walls in the cylinder no longer have user-specified temperatures, but instead have their temperatures predicted as part of the system simulation. This makes the overall simulation results more predictive by reducing the dependence on boundary conditions.

There are several challenges when solving the fluid and solid domains together. The largest challenge to overcome is the difference in time-scales associated with the fluid and solid. In general, the heat transfer in the solid occurs more slowly than the convective and diffusive time-scales dictated by the fluid flow in the cylinder. CONVERGE overcomes this challenge by using a process called super-cycling. In super-cycling, periodically the fluid solver is frozen while the heat transfer in the solid is allowed to progress to steady-state. Super-cycling reduces the computational cost of the CHT simulation without compromising accuracy.

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