abstract a method and an apparatus for simulating the operation of a pressured air source or sink such as a compressor or a turbine for a vehicle internal combustion engine calculates momentum sources at interfaces in the compressor or the turbine a model stores steady state values of mass flux and enthalpy change related to rotational speed inlet pressure and temperature and outlet pressure the simulation can be an input to an engine control module for controlling the operation of the vehicle engine connected with the compressor or turbine application_number US 34200406 A description typically devices such as compressors are used to increase combustion engine performance by compressing the inlet air devices such as turbines are typically used to extract energy from the exhaust gases the energy extracted by the turbine can be used to drive a compressor as in a turbocharger or to provide power for other purposes such as driving an auxiliary device or to add mechanical power to the engine output the present invention concerns a turbine or compressor simulation model that utilizes mass flows enthalpy rise or drop and junction compressor or turbocharger to calculate momentum source at the inlets and outlets the simulation model is intended to improve the prediction of turbine and compressor performance under conditions of pulsed flow to improve the modeling of compressor surge stability to compute mass flow when it is not uniquely defined by the inlet and outlet pressures and to improve the prediction of pressure wave transmission while using look up maps to represent the steady state performance in.