CaLES: DIT Case Instructions

This README provides step-by-step guidance for running the Decaying Isotropic Turbulence (DIT) case using the CaLES solver.

Here, we present results computed using LES with the Smagorinsky model as the subgrid-scale model. Simulations are performed with a grid resolution of N = 32, using Smagorinsky model constant Cs = 0.18. The figure below shows the result :

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Step 1: Generate Initial Flow Field

Use TurboGenPY to generate the initial turbulence field.

Command:

python example.py -n 64 -m 5000 --output

• -n: grid resolution (e.g., 64³)
• -m: number of modes (e.g., 5000)
• --output: flag to write the result

This will generate initial velocity components (u_cbc.txt, v_cbc.txt, w_cbc.txt).

Step 2: Create Restart File

Use the initial field files to generate a restart binary file (fld.bin) for CaLES.

Command:

python write_restart_dit.py

Ensure that u_cbc.txt, v_cbc.txt, and w_cbc.txt are present in the working directory.

Step 3: Run the Simulation

Run the CaLES solver using the provided input.nml and generated fld.bin.

Monitor and compare the results at the nondimensional time steps:

• t = 0.284
• t = 0.665

Step 4: Compute Energy Spectrum

Post-process the velocity field to compute the turbulent kinetic energy (TKE) spectrum.

1. Extract velocity components from the binary field:

python read_restart_dit.py

This will generate:

• u.txt, v.txt, w.txt: velocity distributions

2. Compute the energy spectrum:

python example_tkespec.py

This script will use tkespec.py to compute the TKE spectrum from the velocity fields and save it to:

• tkespec.txt

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Note:

The DNS and LES calculations follow the same workflow. The only differences lie in the configuration of the SGS (subgrid-scale) model and wall modeling.

Additionally, DNS simulations require at least a 512-point grid to avoid energy pile-up and ensure numerical stability.