NuSiF CFD Solver

The NuSiF-Solver implements a 3D structured incompressible Navier-Stokes solver. This solver uses finite difference discretization on a staggered grid as described in this book by Michael Griebel. The program supports sequential and MPI IO output of the results in VTK file format, which can be visualized using the ParaView application.

Overview

The solver uses Chorin's projection method, which is explicit in the velocities and implicit in the pressure. Physical quantities are stored on a staggered grid: pressure at cell centers and velocities at cell faces. The time derivative is discretized with Euler's method. Spatial derivatives use central differences; the Donor cell differencing scheme is used for convective terms.

Supported Tool Chains

• GCC
• CLANG
• ICX

Parallelism

• Sequential
• MPI (derived datatypes, Cartesian topology, neighborhood collectives, MPI IO)
• OpenMP

Pressure Solvers

• Red-Black SOR
• Compressed Red-Black SOR
• Geometric Multigrid

Build

1. Configure

Copy or edit config.mk to select the tool chain and options:

# Supported: GCC, CLANG, ICX
TOOLCHAIN ?= GCC
# Supported: true, false
ENABLE_MPI ?= true
ENABLE_OPENMP ?= false
# Supported: rb, rbc, mg
SOLVER ?= rb
# Supported: seq, mpi
VTK_OUTPUT_FMT ?= seq

OPTIONS +=  -DARRAY_ALIGNMENT=64
#OPTIONS +=  -DVERBOSE
#OPTIONS +=  -DVERBOSE_AFFINITY
#OPTIONS +=  -DVERBOSE_DATASIZE
#OPTIONS +=  -DVERBOSE_TIMER

The verbosity options enable detailed output about the solver, affinity settings, allocation sizes, and timer resolution. For debugging, enable -DVERBOSE.

2. Build

make

Multiple tool chains can coexist in the same directory. Intermediate build results are stored in ./build/<TOOLCHAIN>/. The executable is named NusifSolver-<TOOLCHAIN>.

To see all executed commands:

make Q=

3. Clean

Remove intermediate build results for the active tool chain:

make clean

Remove all build results for all tool chains, including data and visualization output:

make distclean

4. (Optional) Generate Assembler

make asm

Assembler files are placed in ./build/<TOOLCHAIN>/.

CLANG Tooling Support

The Makefile generates a .clangd configuration with the correct compiler flags for the clang language server. This requires GNU Make 4.0 or newer. Note: the default Make version on macOS is 3.81 — install a newer version via Homebrew. Without GNU Make 4.0+, LSP support will be restricted to previously opened buffers.

Alternatively, use Bear to generate a compile_commands.json compilation database, which also enables jump-to-definition without a previously opened buffer:

bear -- make

The repository includes .clang-format and .clang-tidy files to enforce consistent formatting and naming conventions. To reformat all source files:

make format

This requires clang-format in your PATH.

Usage

Provide a parameter file describing the problem to solve:

./NusifSolver-CLANG dcavity.par

Two example test cases are included:

• dcavity.par — lid-driven cavity
• canal.par — empty canal flow

To plot the pressure solver residual as a function of iteration:

make plot