Short nozzles design for real gas supersonic flow using the method of characteristics

Finding a supersonic nozzle minimum length is a classical application of the method of characteristics (MOC) for aerospace propulsion technology among many other applications, such as air and vapor handling processes. That methodology allows design contoured nozzle free of oblique shock waves created at sharp area changes in short nozzles. While the designing technique is well established in textbooks for ideal gas flow, the use of the MOC technique for real gas is problematic due to the highly complex fluid behavior, captured by modern real gas equations-of-state (EOS). This work presents the MOC devised for real gases using multi-parameter equations-of-state (MPEOS) for different substances and compositions. This paper also compares the MPEOS solution obtained from other classical EOS, such as Peng-Robinson, and the ideal gas equation to establish the optimal application range for each EOS and their effect on the nozzle wall construction. The study was carried out for a commercial fluid refrigerant, pure carbon dioxide, and a CO2 - CH4 mixture. The methodology can be used for designing industrial pieces of equipment, such as turbo-machineries and supersonic gas separators or supersonic ejectors, to evaluate the isentropic flow expansion within those devices.

Automated summary

This paper presents a method of using multi-parameter equations-of-state to design supersonic nozzles for real gases, and compares the results with other classical equations-of-state to evaluate their optimal application range.