Internal flow analysis of Custom V-twin engine exhaust pipe. The analysis assumed direct exhaust gases from a well-tuned petrol engine; small undesirable substances, carbon monoxide (CO) etc. being neglected. Assumed substance concentrations by mass fraction were carbon dioxide (CO2) 15%, water vapor (H2O) 14%, and nitrogen (N2) 71%. The inlet velocity was set at 100 m/s (ca. 328 ft/s), and inlet temperature at 640 °C (1184 °F), at the outlet, the SOLIDWORKS Flow Simulation fixed environment pressure boundary condition was set. Surface goals on total pressure, average temperature (fluid), and average velocity were also set. When run, the analysis solver reported the following error "vortex crosses the pressure opening", stating that there was flow coming into the outlet due to a vortex at or near the opening (which can be seen). While the reported total pressure and average velocity at the outlet were plausible, the reported (ca. 52% reduced) average temperature (fluid) at the outlet was not; the numerical average temperature being falsely reduced by the vortex induced inflow at the fixed (20 °C (68 °F) environment pressure) boundary condition temperature. In the interests of learning, a subsequent analysis using extended (ca. 5 diameters) outlet geometry (allowing the vortex to fully develop and dissipate, see below) reported a ca. 1% reduced average temperature (fluid); indorsing the above evaluation.