Numerical studies of nozzle thrust characteristics of supersonic civil aircraft by computational gas dynamics method
Modern gas turbine engines control is performed by the parameters accessible for measuring, which for the most part characterize indirectly the engine critical parameters such as thrust value R, specific fuel consumption C<sub>R</sub>, as well as parameters, affecting directly operational safety and reliability, such as gas temperature T<sub>G</sub>* in the combustion chamber (CC), stall margin (∆S<sub>m</sub>) etc. Employing the all-modes self-identified thermo­gas-dynamic model of the above said engine in modern digital automatic control systems (ACS) offer scopes for new opportunities of substantial control quality enhancing. This model allows computing with high precision the engine critical parameters in real-time scale, and realize the engine control directly by these parameters. The article presents the results of studying such methods for controlling the fuel consumption G<sub>FE</sub> into extra combustion chamber, and nozzle throat area F<sub>T </sub>of the multi-mode engine. The scheme of structural and algorithmic construction of such system is introduced. Implementation of the three control programs, such as thrust changing R<sub>Σ</sub> depending on throttle position, and minimum α <sub>ECC</sub><sup>min</sup> and maximum α <sub>ECC</sub><sup>min</sup> values limiting of the air-to-fuel ratio α<sub>ECC</sub> in the extra combustion chamber is being accomplished by affecting the fuel consumption ( G<sub>FE</sub> ). Ensuring the minimum possible value of the specific total fuel consumption C <sub>RΣ</sub> = (G<sub>FM</sub> + G<sub>FA</sub> )/ R<sub>Σ</sub> ) , as well as restriction of fan stall margin, are implemented by affecting nozzle throat area by the extremal controller. The effectiveness evaluation of the control methods under consideration was brought about by the integrated mathematical models “Engine - ACS - Onboard Mathematical Model” employed in CIAM. It was shown, that direct engine thrust control by the impact on fuel consumption into the extra combustion chamber allowed ensuring the thrust value invariance to the engine components degradation while in operation. The impact on the nozzle throat area herewith minimizes specific fuel consumption and limits the fan stall margin.