Free CFD Software — Real Alternatives to ANSYS Fluent and STAR-CCM+
An ANSYS Fluent or STAR-CCM+ licence is one of the heaviest line items in an engineering office, so the question of what to do without one keeps coming back. The short answer: the physics is available for free, the convenience is not. Free solvers reach the same result quality — provided you are willing to invest in meshing, boundary conditions and convergence checking yourself.
The general-purpose solvers
1. OpenFOAM
The open-source standard in CFD. A library of solvers for compressible and incompressible flow, multiphase, heat transfer, combustion and turbulence, with the familiar models (k-epsilon, k-omega SST, LES). It runs in parallel on a cluster with no core limit and no extra cost.
What is missing: there is no real graphical interface. Everything happens through text files in the case directory and the command line, and the learning curve — not the licence — is the expensive part here.
2. SU2
From Stanford, aimed at aerodynamics and optimisation. Its strength is the adjoint solver, which makes efficient shape optimisation possible — a capability that in the commercial world sits only in flagship products.
What is missing: it covers ordinary industrial internal-flow and multiphase problems less well than OpenFOAM.
3. Code_Saturne
Developed by EDF in France and actually used by them for power plant calculations. It covers incompressible and weakly compressible flow, heat transfer, radiation and combustion, and it has a graphical setup interface — rare in this world.
OpenFOAM
OpenFOAM Foundation
Comprehensive CFD solvers — flow, turbulence, heat transfer and multiphase. Text-file driven, no GUI.
Get it from the vendor
SU2
SU2 Foundation
Multiphysics CFD with adjoint-based design optimisation — systematic shape improvement.
Get it from the vendor
Code_Saturne
EDF
General-purpose CFD from EDF — turbulence, heat transfer, combustion and multiphase, with a GUI.
Get it from the vendorSpecial methods: lattice Boltzmann and awkward geometry
When the geometry is too complex for a classical mesh — porous media, rock, packed beds, blood vessels — the lattice Boltzmann method removes the meshing headache.
4. Palabos
From the University of Geneva, parallel, built precisely for flows through complex geometry. Cases are set up in C++ or Python.
5. OpenLB
A C++ library for the same family of methods, with parallelism built in. It is a library rather than a finished application — expect to write code around it.
Palabos
University of Geneva
An open lattice Boltzmann solver for fluid flow, from the University of Geneva.
Get it from the vendor
OpenLB
Karlsruhe Institute of Technology
A lattice Boltzmann framework in C++ for complex flow simulation.
Get it from the vendorResearch and high-resolution turbulence
6. Xcompact3d
High-order compact finite-difference schemes on Cartesian meshes, with very low numerical dissipation. Built for DNS and LES and scaling towards thousands of cores.
7. Nektar++
The spectral/hp element method — very high accuracy for a relatively small number of degrees of freedom. It also covers multi-physics problems.
8. Fluidity
From Imperial College, with an unstructured mesh that adapts itself as the run proceeds. Strong in multiphase flow and in ocean and atmosphere modelling.
9. MFiX
From the US Department of Energy, for gas-solid multiphase flow: fluidised beds, reactors, gasifiers. Validated against a large body of published experiments.
Xcompact3d
Xcompact3d Project
A high-order CFD solver for turbulence research on large parallel machines.
Get it from the vendorNektar++
Imperial College London / University of Utah
A spectral/hp element framework for high-accuracy simulation.
Get it from the vendorFluidity
Imperial College London
A CFD solver with adaptive unstructured meshes, from Imperial College London.
Get it from the vendorMFiX
US Department of Energy — NETL
Multiphase flow simulation for fluidised beds and reactors, from the US DOE.
Get it from the vendorWhat you actually need around the solver
Most of the time in CFD goes not into solving but into meshing and post-processing. These two are free and appear in almost every open-source workflow:
10. Gmsh
Generates 2D and 3D meshes, with a scripting language that lets you produce families of geometries and meshes repeatably.
11. ParaView
The standard result viewer: slices, streamlines, isosurfaces and animations, even on very large datasets.
Gmsh
Gmsh Project
FEA mesh generator with built-in geometry and scripting — standard infrastructure for open numerical work.
Get it from the vendor
ParaView
Kitware / Sandia / Los Alamos
Large-scale simulation post-processing — slices, streamlines and animation.
Get it from the vendorAnd if you have no time to learn OpenFOAM
12. SimScale — Community plan
CFD and FEA in the browser on a cloud engine, with nothing to install. The free plan gives limited compute hours and makes projects public — so it is not suitable for client work.
SimScale (community plan)
SimScale GmbH
CFD and FEA simulation in the cloud from the browser. Community plan limited in compute hours and public.
Get it from the vendorBottom line
For research, for students and for an office willing to spend a month learning, OpenFOAM with Gmsh and ParaView is a complete workflow that lacks nothing on the physics side. What money buys at Ansys or Siemens is time: one interface, automatic meshing, material libraries, and support you can call when a project is on fire.
All free CFD tools on the site: the CFD category.