Engineering problems can be quite straight forward when confined to a single size scale. For example, designing an elephant-proof fence is simply an exercise welding together enough big steel bars. But what if it also has to confine mice? By mixing the very large and very small size scales, the mouse introduces a whole new set of problems that will greatly complicate the design and construction of the fence. Tiny gaps irrelevant to the elephant can be escape ways for the mouse!
Fuel Pumps Present Big Problems With Meshing Tiny Gaps Between Sliding Bodies
Automotive engineers are having similar problems as they try to reduce emissions by minimizing leakage of engine oil into fuel through fuel pumps. The high operating pressures in modern designs can deform materials to widen the gaps between the plunger and cylinder walls and allow unexpected oil leakages.
Until now, this type of fluid-structure interaction case, where a thin fluid film is separating two deforming solids sliding past each other, meshing tiny gaps has been a challenge to model. The sliding motion would tend to skew the fluid elements in the gap, requiring a fine tetrahedral mesh in the gap and frequent remeshing to prevent mesh folding. New technology in ANSYS Fluent automatically ensures that a high quality mesh is maintained in the deforming gaps as identified by coupling with ANSYS Mechanical. The resulting simulations provide highly accurate oil leakage flow rates that account for the structural deformations and can be used to optimize pump performance.
ANSYS 19.0 Ensures High Quality Mesh Dynamically Fills Tiny Gaps for Accurate Simulations
In ANSYS 19.0, we introduced an engineer-ready workflow that includes two new features that together address this need:
- System coupling loads can now be transferred at a sliding mesh interface and,
- Nodes on one side of an interface can be projected onto the other side of the interface.
In the case of a fuel injector, the motion/deformations of the plunger would be sent from Mechanical to a copy of the plunger in Fluent.
This copy of the plunger would be interfaced with the fluid, and the fluid nodes would be projected normally onto the plunger during the simulation, such that they only inherit the normal displacements and not the large axial displacements. As a result, the fluid elements would not be sheared while the interface connection maintained. The node projection feature is not restricted to system coupling simulations, and likely has many applications beyond what I've listed. I'm excited to see how our customers make use of it to tackle meshing tiny gaps in challenging FSI simulations and better their products.