[{"data":1,"prerenderedAt":188},["ShallowReactive",2],{"$f1ydh9cjdotj4l":3},{"slug":4,"publishedAt":5,"category":6,"title":7,"summary":8,"image":9,"imageAlt":14,"readingMinutes":15,"serviceId":16,"keywords":17,"imageCaption":23,"sections":24,"sources":166},"free-cfd-software","2026-10-25","guides","Free CFD Software in 2026: What Each One Can and Cannot Do","Free CFD software in 2026 compared: OpenFOAM, SU2, code_saturne, FluidX3D, Ansys Student, SimScale. Licences, size limits, and how to check the answers.",{"src":10,"thumbnail":11,"width":12,"height":13},"\u002Fassets\u002Fcfd-cases\u002Fnozzle\u002Fimages\u002F01.webp","\u002Fbrand\u002Fstudies\u002Fnozzle.svg",1448,1086,"DEEB-FLOW illustration of a spray-drying chamber geometry",10,"review",[18,19,20,21,22],"free CFD software","open source CFD software","CFD software for students","OpenFOAM","Ansys Student","Concept illustration from the DEEB-FLOW case library. It is not a result from this article.",[25,32,78,89,106,113,125,138,148,160],{"id":26,"title":27,"paragraphs":28},"four-meanings","Four meanings of free",[29,30,31],"“Free” means four different things in CFD, and the difference decides whether you can use the result.","It can mean free to download and modify, under an open-source licence. Free for students, for educational use only. Free until your eleventh simulation. Or free for anything except commercial work. All four are on the list below, and all four are worth having, as long as you know which one you are holding.","The short answer: for most people the best free CFD software in 2026 is OpenFOAM for general work and source access, SU2 for compressible aerodynamics and shape optimisation, Ansys Student for learning a commercial workflow if you are a student, and FluidX3D for fast GPU simulation outside commercial use. This article gives the limits of each as their own pages state them, shows how large a problem each can hold, and ends with the afternoon test that tells you whether any of them, free or paid, is giving you the right answer.",{"id":33,"title":34,"paragraphs":35},"at-a-glance","The options at a glance",[36,77],{"table":37},{"head":38,"rows":43},[39,40,41,42],"Software","What “free” means","Method and strengths","Practical limits",[44,48,53,58,63,68,72],[21,45,46,47],"Open source under the GNU GPL","Finite volume; general incompressible, compressible, multiphase and heat transfer flows; a very large solver library","Command line; Linux, or Windows through WSL; you supply the judgement and the support",[49,50,51,52],"SU2","Open source under the LGPL 2.1","Unstructured finite volume; non-ideal compressible flow, incompressible flow with heat transfer, discrete adjoints for design","Strongest in aerodynamics; a smaller ecosystem than OpenFOAM",[54,55,56,57],"code_saturne","Free and open source, developed mainly by EDF R&D (version 9.0)","General-purpose finite-volume CFD with a long industrial record","A smaller user community outside the energy sector",[59,60,61,62],"FluidX3D","Free for non-commercial use","Lattice Boltzmann on GPUs and CPUs via OpenCL; very memory-efficient","Non-commercial licence; uniform Cartesian lattices; a weakly compressible, low-Mach method",[64,65,66,67],"CfdOF (FreeCAD)","Open source under the LGPL-3.0","A graphical front end for OpenFOAM inside FreeCAD, with cfMesh, snappyHexMesh and Gmsh meshing; RANS, LES, DES, free surface, buoyancy","As capable as the OpenFOAM it drives; macOS not widely tested",[22,69,70,71],"Free for verified students and educators, for educational use only","The commercial Fluent workflow","1 million cells or nodes for fluids, 128,000 for structures, up to 4 cores, Windows 10 and 11, licence valid to 31 March 2027",[73,74,75,76],"SimScale Community","A free plan for testing and learning","Browser-based, no installation","2,000 core hours, instances up to 16 cores, 10 simulations with quantitative output, after which results become qualitative only","The table holds three kinds of free. OpenFOAM, SU2, code_saturne and CfdOF are open source: you can read the code, change it and use it for any purpose. FluidX3D is free to use, but its licence excludes commercial work. Ansys Student and SimScale Community are commercial products with a free tier, and the tier exists to teach you the product; your projects are expected to move to a paid licence.",{"id":79,"title":80,"paragraphs":81},"licences","What does each licence actually let you do?",[82,83],"This is the question most comparison pages skip, and it is the one that gets a small consultancy into trouble.",{"list":84},[85,86,87,88],"**GPL and LGPL (OpenFOAM, SU2, CfdOF).** These licences govern distribution. The OpenFOAM Foundation states that the GPL does not force users to make their modifications public, and that OpenFOAM can be the basis of in-house software. The obligation arrives when you distribute compiled binaries: then the source must be available to those who receive them. Running OpenFOAM to deliver a study to a client is use, and distribution is something else. This is the usual reading of the GPL and not legal advice.","**Non-commercial (FluidX3D).** Free for research, teaching and personal projects. A paid study for a client is commercial use. Read the licence file before you put its pictures in a proposal.","**Educational use only (Ansys Student).** The download terms say free student downloads are for educational use only. A thesis, a course project, a competition entry: yes. A side job for a company: no.","**Free tier (SimScale Community).** The plan is described as free for testing and learning, and after ten simulations the output becomes qualitative only. Check whether projects on the free plan are visible to others before you upload anything confidential; the current plans page lists private projects as a paid feature.",{"id":90,"title":91,"paragraphs":92},"how-big","How big a problem can you run for free?",[93,94,95,96,99,100,101,104,105],"Each option has a different ceiling, and it pays to know it before you build the geometry.","**Ansys Student: 1 million cells.** That holds every classic benchmark comfortably: the lid-driven cavity, laminar pipe flow, the backward-facing step, a cylinder in a channel, a 2D airfoil. It holds a 3D pipe bend at modest resolution. As a rough worked example, a pipe cross-section meshed with 5,000 cells, including a boundary layer, allows about 200 cells along the axis. It does not hold an industrial 3D external aerodynamics case, which is usually far larger.","**SimScale Community: 2,000 core hours.** On the largest 16-core instance that gives, in hours of wall-clock time:",{"formula":97},[98],"2000 \u002F 16 = 125 h","That is plenty of computing for a semester. The binding limit is the ten quantitative simulations, so plan them. A mesh study alone uses three.","**FluidX3D: memory per cell.** Its documentation gives 55 bytes per cell for the D3Q19 lattice with its compressed storage, against about 344 bytes per cell for a conventional double-precision implementation, and states about 19 million cells per gigabyte of video memory. On an 8 GB card that gives, in cells:",{"formula":102},[103],"8 GB × 19 × 10⁶ \u002F GB ≈ 1.5 × 10⁸","That is a remarkable number for a consumer GPU. Remember what kind of cells they are: a uniform Cartesian lattice, refined everywhere or nowhere, with walls represented on that lattice. A boundary layer that a body-fitted finite-volume mesh resolves with 20 thin prism layers needs the whole lattice to be fine, or it is not resolved at all. For bluff-body wakes and visual transient flows this is a superb trade; for wall heat transfer it is a poor one.","**OpenFOAM, SU2, code_saturne: your hardware.** No artificial limit. The ceiling is your memory and your patience. Measure it: build the mesh, start the case, read the memory used per million cells on your own machine, and plan from that number rather than from anyone’s rule of thumb.",{"id":107,"title":108,"paragraphs":109},"accuracy","Is free CFD software less accurate?",[110,111,112],"No, and it is not automatically right either.","The equations, the discretisation and the turbulence models are the same families in free and commercial codes. When the setup is matched (same mesh, same schemes, same turbulence model, same boundary conditions) the results should agree closely; the OpenFOAM against Fluent article on this blog explains where they usually differ, which is in defaults and in the effort needed to reach a good setup.","What differs is who carries the risk of a bad setup. A commercial code has tested defaults, a support contract and a large user base that has met most errors before you. An open-source code gives you every switch and expects you to know which one matters. The accuracy is in the engineer either way.",{"id":114,"title":115,"paragraphs":116},"adjoint","The quiet strength of SU2: the adjoint",[117,118,119,120,124],"One feature deserves its own section, because few free codes have it and few comparison pages explain it.","Suppose you want to reduce the drag of a shape described by N design parameters. The obvious way to find which direction improves it is finite differences: change each parameter in turn and rerun. That costs N + 1 solutions for one gradient. The adjoint method computes the gradient of one objective with respect to all N parameters at the cost of roughly one extra solution, whatever N is.","**Worked example.** A wing section described by 50 shape parameters needs this many solutions per gradient, by finite differences and by the adjoint:",{"formula":121},[122,123],"N_FD = N + 1 = 51","N_adj ≈ 1 + 1 = 2","Over an optimisation of 20 design iterations that is the difference between about 1,000 solutions and about 40. The discrete adjoint is why SU2 is widely used in aerodynamic shape optimisation research. In practice an adjoint solution costs the same order as a flow solution without being identical, so read the ratio as an order of magnitude.",{"id":126,"title":127,"paragraphs":128},"which-one","Which one should you use?",[129],{"list":130},[131,132,133,134,135,136,137],"**A student who wants to learn the commercial workflow:** Ansys Student, if you qualify, alongside OpenFOAM through CfdOF so you also see what the defaults hide. One million cells will not hold you back while you learn.","**A student or engineer who wants to learn CFD itself:** OpenFOAM, and a small solver of your own. The article on how to learn CFD on this blog describes the order.","**Windows, and you want a graphical interface for OpenFOAM:** CfdOF in FreeCAD. It supports Windows 7 to 11 and drives both the OpenFOAM Foundation and the OpenCFD releases.","**A Mac:** SimScale in the browser is the least friction. CfdOF reports success on macOS without wide testing, and FluidX3D lists limited macOS support.","**Aerodynamic shape optimisation:** SU2, for the adjoint.","**A GPU and a non-commercial project with transient, visual flows:** FluidX3D.","**A small company doing paid work:** OpenFOAM, SU2 or code_saturne, after checking each licence for your use. Budget the real cost, which is time: time to learn, time to verify, time to find the setting that a commercial default would have chosen for you.",{"id":139,"title":140,"paragraphs":141},"afternoon-test","The afternoon test for any CFD software",[142,143,147],"Whatever you choose, free or paid, run one case with a published answer before you trust it with anything that matters. Two are ideal.",{"list":144},[145,146],"**The lid-driven cavity at Re = 100 and 1,000.** Compare the centreline velocity profiles with the tabulated values of Ghia, Ghia and Shin (1982). If your profiles sit on their points on a fine mesh, the pressure-velocity coupling and the basic discretisation work.","**The DFG cylinder in a channel, case 2D-2 at Re = 100.** The FeatFlow reference gives a maximum drag coefficient of 3.2200 and a Strouhal number of 0.30188. If your run sheds vortices at that frequency and reaches that peak drag, the unsteady solver and the time stepping work.","Do the comparison on two or three meshes, so you also see how the answer moves with resolution; the mesh independence article on this blog shows how to put a number on it. An afternoon of this tells you more about a code than a week of reading its feature list, and it is the habit that separates using software from using CFD.",{"id":149,"title":150,"paragraphs":151},"common-mistakes","Common mistakes, as they look on screen",[152],{"list":153},[154,155,156,157,158,159],"**A beautiful result you cannot use.** The work was done on an educational or non-commercial licence, and now a client wants it.","**A mesh built to 1.3 million cells on Ansys Student.** The limit is 1 million. Check before you mesh.","**Simulation eleven on SimScale Community shows colours and no numbers.** The ten quantitative runs were spent on trial and error.","**A heat transfer coefficient from FluidX3D.** The uniform lattice did not resolve the thermal boundary layer. Use the code for what it is good at.","**An OpenFOAM case with the tutorial defaults left in place.** It runs, and the answer belongs to the flow of the tutorial.","**“Free means inaccurate”, or “open source means trustworthy”.** Neither. Run the afternoon test.",{"id":161,"title":162,"paragraphs":163},"what-i-would-do","What I would do",[164,165],"If I were starting today with no budget, I would install OpenFOAM through WSL on Windows, add CfdOF for a graphical start, run the cavity and the DFG cylinder against their references, and keep a small solver of my own for experiments. If I were a student, I would add Ansys Student to learn the commercial workflow alongside it, because most employers use one. If I needed to optimise an aerodynamic shape, SU2.","The software is free. The verification is not, and it is the part that makes the answer worth anything. If you have a result from any of these tools and want a second opinion on whether it holds up, that is what a model review is for, and our CFD course teaches the verification habits from the first session.",[167,170,173,176,179,182,185],{"href":168,"label":169},"https:\u002F\u002Fopenfoam.org\u002Flicence\u002F","OpenFOAM Foundation: licence",{"href":171,"label":172},"https:\u002F\u002Fsu2code.github.io\u002F","SU2: the open-source CFD code",{"href":174,"label":175},"https:\u002F\u002Fwww.code-saturne.org\u002F","code_saturne, EDF R&D",{"href":177,"label":178},"https:\u002F\u002Fgithub.com\u002FProjectPhysX\u002FFluidX3D","FluidX3D: lattice Boltzmann CFD on GPUs",{"href":180,"label":181},"https:\u002F\u002Fgithub.com\u002Fjaheyns\u002FCfdOF","CfdOF: CFD workbench for FreeCAD",{"href":183,"label":184},"https:\u002F\u002Fansys.synopsys.com\u002Facademic\u002Fstudents\u002Fansys-student","Ansys Student: free student software and its limits",{"href":186,"label":187},"https:\u002F\u002Fwww.simscale.com\u002Fpricing\u002F","SimScale: plans and pricing",1792989860078]