Something that routinely comes up as a problem at work is when we size flow projects for piping systems. We calculate pressure drop across a length of fixed diameter for compressible gasses, but we do not calculate pressure changes through an expansion or contraction with gas (for example, pressure drop of air flowing at 3,500 scfm through 2" SCH 40 piping, expands to 4" SCH 40 piping). I can recall from my time in school that we would have used CFD to assist with a problem like this. Am I overlooking a way to be calculating this? I had envisioned something that could be incorporated into Excel, but it may be more difficult than that for compressible flow.