A third unconventional option for 3D analysis is a free program called OpenVSP. I’ve been debating how to categorize this one and you’ll soon see why.
OpenVSP is primarily a parametric geometry design tool—this means it is able to create computer-generated models of air vehicles, which can then be saved off as standard CAD files. This makes it a great alternative to most CAD software, especially if you only need to use it to update CFD geometry.
Being “parametric” also means that it uses constraints and modeling dependencies to automatically update a model. One such dependency could be ensuring that a wing’s tip chord is always 3 inches shorter than the root chord. This results in much quicker turnarounds if a geometry needs to be adjusted since any related adjustments are done automatically.
On top of the modeling functionality, OpenVSP also comes with its own 3D inviscid aerodynamics tool: VSPAERO. What I find interesting is that this is firmly an inviscid (i.e., frictionless) solver, but it offers a mesh-based panel method which takes into account the volume and curvature of aircraft components. VLM can’t do that, at least not natively.
You can also include actuator disks to simulate propellers, letting you see the effects on aerodynamics as well as on the trailing wake of the full vehicle. And finally, the thing that made me save this software for this category is its parasitic drag calculation feature, which captures a pretty good chunk of the viscous effects on an aircraft. You’d still need CFD for more complex analysis cases, but this feature saves you the time and effort of a hand calculation.
So here we are. I wouldn’t call OpenVSP a “true” 3D viscous tool, but it goes far enough beyond the 3D inviscid options that I’m including it with the CFD software anyways. And did I mention it’s free?
You might notice that in this discussion I didn’t include the “bonus” analysis tools that come along with CAD software—the one I’ve heard mentioned most is SolidWorks Flow Simulation. That’s because these are fine, but not great, and definitely not of the same caliber as, say, STAR-CCM+.
There isn’t much info available about the actual calculation methods used, and the options for mesh and solver settings are substantially more limited than a dedicated CFD tool. The CAD-based tools could get you decent qualitative results, like seeing which wing design out of a few options generates the most lift. But they just can’t handle the complexity of 3D flow well enough for me to truly trust the quantitative results.
If you already have something like Flow Simulation available to you and really don’t have budget for anything else, I don’t think there’s much harm in at least trying it out. But take its results with a grain of salt, preferably more. And make sure you’re using other analysis tools to validate your numbers.