Optimization and Model Validation of Transonic Compressors

Licentiate thesis, 2012

Economical aspects such as reduced specific fuel consumptions and ever growing environmental requirements on emissions and percieved noise levels, are the major drivers in the search for improvement of aircraft engines. For turbofan engines, the global trend is towards higher efficiency which is accomplished by increasing component efficiencies, the bypass ratio and overall pressure ratio while keeping the engine weight low. Concerning the low pressure system, the reduction in weight can be realized by decreasing the number of stages in the compressor. However by doing so, the aerodynamic load per stage must be increased in order to maintain the same pressure ratio. As the aerodynamic load increases, it becomes more difficult to maintain a high efficiency on the aerodynamic design point and keep a sufficiently high stability margin along the compressor working line. In this thesis a new design methodology, accounting for both efficiency and stability, is presented. In order to utilize the design process for industrial applications, the reduction in total design time and computational resources are also adressed. The validity of the presented analysis method is put to test by means of two validation cases. The first case is a transonic rotor in isolation and the second case is a three stage highly loaded transonic compressor.