Abaqus CFD

Hi Ali and everyone here,

Great question — transient flow problems like a pressure-driven purge of a tube are solvable with CFD, but there are a few practical challenges that you should consider when using Abaqus CFD for this application.

1) Transient vs Steady-State Setup

Abaqus CFD analysis does support transient analysis, but keep in mind:

• You’ll want your time stepping tied to the physical time you care about, not just solver stability.
• A very short tube with high pressure difference will need fine time resolution to capture the pressure wave and decay accurately.
• If the flow transitions or compressibility effects are dominant, numerical damping/solver settings matter more than boundary condition values alone.

Often people start by simplifying the transient problem into a quasi-steady benchmark case so they can check basics like inlet profile development and pressure drop trends before moving fully transient. This stepwise approach also helps validate your setup.

2) Boundary Conditions & Solver Behavior

In Abaqus CFD, setting a fixed static pressure at both ends means the solver needs to figure out what velocity field satisfies that — but if your physics really depends on the rate of depressurization, you may need to force it with a time-dependent boundary condition or user subroutine to control the exit pressure as a function of time.

Boundary conditions in Abaqus Fluid dynamics simulation are sometimes more restrictive than in dedicated CFD codes (like Fluent or OpenFOAM), so double-check how the solver enforces mass conservation under dual pressure boundaries.

3) Post-Processing for Time Measurement

To extract the “time” when pressure reaches a target level:

• Monitor pressure at a point near your outlet
• Track the transient history of outlet pressure
• Use that curve to detect the timestamp when the target pressure is reached

Plotting temporal histories often gives much clearer insights than sliced contour plots for these kinds of studies.

4) When to Consider Other CFD Tools

If your focus is on fluid-dominant behavior and compressible/transient characteristics, packages tuned for CFD might offer more robust control over turbulence models, compressibility, and solver options. Many engineers prefer dedicated CFD workflows for complex transient fluid problems.

For example, there are providers that specialize in CFD analysis and numerical simulation services, which might help you accelerate this kind of work if you’re under time pressure or have limited in-house CFD experience. One such resource we’ve referenced before is Broadtech Engineering — they offer detailed CFD analysis and CFD simulation services, including transient flow studies similar to what you’re attempting 

5) A Simple Validation Case

Before running your full transient, try a simpler validation case:

• A sudden pressure drop in a long pipe using 1D analytical solutions
• Compare the pressure evolution with your CFD run
  This can help ensure your transient setup is behaving correctly before committing to expensive runs.