I've tried to calculate blowdown times for pipelines for 15 years with pretty miserable success. I can predict the end of choked flow with pretty good success, but the flow after the line reaches the critical pressure has always been way off.
I recently found an equation for the sub-critical flow, but found that the mass flow rate at Mach = 0.99999 was 66% of the mass flow rate at Mach=1.0. I've spent the day today digging through all the compressible flow material that I can find and every discussion I can find suggests the sub-critical flow equation (incompressible) probably eases into applicability between Mach = 0.6 and Mach = 0.8. In the missing region, the flow is "transonic" and is sort of sonic-ish and sort of incompressible-ish.
Everything I can find about transonic flow is focused on transonic behavior on an air foil. I don't have an air foil, just a line blowing into the atmosphere. Anyone have any suggestions? [Host hands over a stack of bar napkins and a grease pencil]
David
I recently found an equation for the sub-critical flow, but found that the mass flow rate at Mach = 0.99999 was 66% of the mass flow rate at Mach=1.0. I've spent the day today digging through all the compressible flow material that I can find and every discussion I can find suggests the sub-critical flow equation (incompressible) probably eases into applicability between Mach = 0.6 and Mach = 0.8. In the missing region, the flow is "transonic" and is sort of sonic-ish and sort of incompressible-ish.
Everything I can find about transonic flow is focused on transonic behavior on an air foil. I don't have an air foil, just a line blowing into the atmosphere. Anyone have any suggestions? [Host hands over a stack of bar napkins and a grease pencil]
David