Hi @rommel_exe , Welcome to the forum! I took a look at the project link you provided and investigated the setup under the hood. The external flow volume operation is failing because of specific surface defects in your CAD model. The system log flags exactly where the Boolean subtraction is crashing: it is tripping over edge 8 , face 2 , and face 910 . When modeling complex aerodynamic assemblies like a Formula Student car, it is incredibly common to end up with microscopic gaps, self-intersecting surfaces, or tiny sliver faces (especially around the suspension or halo mounts). When the solver tries to mathematically subtract the car’s volume from the bounding box of air, these imperfections break the calculation. Here are three ways to get past this: 1. The Native CAD Fix (Highly Recommended) When prepping complex geometries in your parametric modeling software, it is best practice to run a “Geometry Check” or “Check Entity” tool before exporting. Zoom in on the areas causing the errors, look for short edges or unstitched surfaces, heal them, and re-export the model as a clean STEP file. 2. The SimScale Delete Face Tool In the CAD Edit mode, you can try searching for face 2 and face 910 and applying the Delete Face operation. SimScale will attempt to delete the broken polygons and mathematically patch the gap they leave behind, which often allows the flow volume to generate successfully. 3. The Surface Wrap Tool I noticed you have a “Wrap” operation sitting in your geometry tree! For incredibly complex or messy CAD assemblies where manual cleanup would take hours, the Wrap tool is a lifesaver. It essentially shrink-wraps your entire model to create a single, water-tight exterior surface. If cleaning the CAD is proving too difficult, try generating that Wrap surface first, and then apply the External Flow Volume operation to the wrapped model instead of the original CAD.