Hello @Kremella  ;nFirstly thank you for the reply.nIn incompressible flows course , we have shown that total pressure = static pressure +dynamic pressure.nIn compressible flow course , please check file below. The hypothesis is isentropic flow ( ideal gas) nSO , to solve our problem ( i am trying to solve compressible flow in a nozzle , so trying to understand pressure BC in Fluent) , we must know Total pressure and static pressure at the inlet and the outlet. nMy problem remains : nWhat is total pressure and static pressure for Ansys Fluent ? ( like i have written in the file below) ? nAs you know Fluent proposes : n1/ Gauge pressuren2/ Total Gauge pressure n3/ Absolute pressure = Gauge pressure+operating pressure n4/ Supersonic initial gauge pressure n( there is no problem for oprerating pressure : it is a floating pressure , not considered by fluent )If you can answer me also this question please :nFluent proposes an option : Back flow pressure specification : a/ Total presssure b/ static pressure nWhat is the meaning please and what is the influence on results ? ( i have checked Fluent help , but still not clear )nnI hope i was clear and sorry for english mistakes.nKind regards n