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Backward-Facing Step

⚠️ NOTE: These are advanced workflow examples showing direct solver access and specialized workflows. They do NOT use the standard RL interface.

Looking for standard RL examples? See Getting Started for env.reset() / env.step() interface.

Flow over a backward-facing step demonstrates separated flow and reattachment.

Physical Description​

Configuration:

  • Channel with sudden expansion (backward-facing step)
  • Step height creates separation zone
  • Uniform inflow from left
  • Reynolds number Re = 600 (default)

Observations:

  • Kinetic energy (KE)
  • Turbulent kinetic energy (TKE)
  • Reattachment point location

Quick Start​

1. Basic Simulation​

Run transient step flow at Re=600:

python run-transient.py

What it does: Simulates separated flow from perturbed base state Outputs:

  • output/stats.dat - Time series of CFL, KE, TKE
  • Console shows KE, TKE evolution
  • Long time integration (1000 time units) Prerequisites: Requires steady state checkpoint from solve-steady.py

2. Find Steady State​

Solve for steady flow using Newton iteration with Reynolds ramping:

python solve-steady.py

What it does: Computes steady base flow for separated step flow Uses ramping: 100 → 200 → 300 → 400 → 500 → 600 for convergence Outputs:

  • output/600_steady.h5 - Steady checkpoint for restart
  • output/600_steady.pvd - Paraview visualization of recirculation zone Prerequisites: None

3. Observe Instability​

Two-stage simulation: steady solve + perturbed transient:

python unsteady.py

What it does: Demonstrates transition from steady to unsteady separated flow Stage 1: Solve steady state with Reynolds ramping Stage 2: Add perturbation and run long transient (Tf=1000) Outputs: Time series, Paraview animations, TKE evolution Prerequisites: None (computes steady state internally)

4. Test Control Response​

Apply step input actuation:

python step-control.py

What it does: Applies step change in actuation to measure flow response Control: Off until t=50, then constant actuation Purpose: System identification - measure step response Outputs: Time series showing response to actuation Prerequisites: None (uses internal initial condition)

MPI Parallelization: All scripts support parallel execution:

mpirun -np 4 python <script-name>.py