Obtaining an accurate reading of mass flow rate at the turbine inlet is the first step in correctly adapting a thermodynamic model to a GT unit. The amount of air coming into the engine will determine its real time compressor performance ratio, combustion characteristics, efficiencies, temperatures, and emissions throughout the unit. For combined cycles, the inlet air mass flow rate for each unit will also determine similar parameters throughout the steam cycle.
As opposed to gas and oil industries, where gases and fluids flow in round, symmetrical pipes, inlet air flows into the gas turbines through sometimes rather short, irregular inlet ducts. As a result, the flow does not become fully developed within the duct, and the flow distribution is irregular and does not show a pattern. Because of these complexities, a pitot tube approach is not a viable option for measuring inlet flow rate. Other approaches are ineffective, and would cause significant pressure drop that decrease the efficiency of the compressor.