# Fluid Modeling Techniques in Abaqus

Fluid Modeling Techniques in Abaqus

Many of our Abaqus customers don’t know that the Computational Fluid Dynamics approach (CFD) is not the only method of modeling fluids in Abaqus. There are many other possibilities and the right approach depends on the physics of the problem. This blog post discusses the multi physics methods of modeling fluids in Abaqus.

• CFD method: This is the well-known and traditional method for fluids modeling. It’s based on Eulerian formulation, in which material flows through the mesh and can be accessed through the Abaqus/CFD solver. Application example: Flow through exhaust systems.
• CEL method: This is a coupled Eulerian Lagrangian method primarily used in problems involving unbounded fluids where fluids free surface visualization is required. It’s also possible to simulate interaction between multiple materials, either fluids or solids. This method is accessible through Abaqus/explicit solver. Application example: Fluid motion in washing machine.
• SPH method: This is a smooth particle hydrodynamics approach primarily used to model unbounded fluids that undergo severe deformation or disintegrate into individual particles. This method uses a Lagrangain approach in which material moves with the nodes or particles and can be accessed through the Abaqus/explicit solver. This method can be used for fluids as well as for solids. Application example: bird strike on an aero structure.

We can compare these three methods against multiple parameters such as materials, contact, computation speed, etc. to understand their applications and limitations:

• Material considerations:

SPH method is most versatile in terms of material support. SPH supports fluids, isotropic solids as well as anisotropic solids.

CFD is the only technique that can model fluid turbulence

CFD is the only technique to model porous media

CFD and CEL allows material flow through the mesh: Eulerian

• Contact considerations:

CEL method allows non-conforming meshes at the interface. The other two methods do not.

CEL and SPH allow contact interface topology change due to penetration. Application example: projectile impact on fuel tank.

• Geometry and mesh considerations:

SPH method does not require mesh refinement near small objects with geometry details.

CEL and CFD do require minimum of several elements to model boundary layer accurately. However CEL can perform mesh refinement on its own as the analysis proceeds.

SPH allows for conversion of continuum elements into small particles. With other methods, types of elements do not change as simulation proceeds.

CEL allows clear visualization of fluid free surface. In SPH only particles are rendered and in CFD fluid surface is not visible.

• Analysis type considerations:

CFD and CEL can incorporate heat transfer in flow problems.

• Computational considerations:

CFD can simulate larger time increments in case of longer duration transient flows. In the other two methods, there is restriction on maximum time step due to the explicit nature of the solver.

SPH excels in terms of accuracy vs. mesh size because it does not require finer mesh near regions of geometry details.

SPH excels over CEL in models having very small “material to void” ratio.

For a given mesh size, CFD is less expensive compared to CEL.

### Ankur Kumar

Simulation Specialist at Tata Technologies
Ankur has 11 years of experience in Computer Aided Engineering and has obtained the SIMULIA Design Sight, EPP and Support certifications from Dassault Systemes.