Effects of Rotational Speed of Rotors and Inlet Mach Number on Performance of a Contra-Rotating Axial Compressor - Numerical Study

In conventional turbojet engine the turbine power is being utilized to rotate the compressors whereas in the Hybrid air breathing propulsion system, an electric motor will be used to give power input to rotate the compressor. So, the space available without a turbine could be used to accommodate a contra-rotating compressor where alternative blade rows rotate in a counter direction. Previous studies show the contra-rotating compressors are superior to conventional ones. The objective of the present work is to design a contra-rotating compressor and to numerically analyse the effects of rotational speed of rotors and inlet Mach number on the performance of the same. Numerical simulations are performed for different rotational speed values of rotors ranging from 5000 RPM to 15000 RPM and with four inlet Mach numbers starting from 0.5 to 0.8. It is found that the pressure ratio of the compressor increases with the rotational speed of the rotors and the increment is more pronounced when the second rotor is greater than or equal to the first rotor speed. The power consumption is not linear for the increase in the speed of the rotor. This imposes a restriction to the performance of the engine with the power available. The power consumption is too high when the speeds of both the rotors are 15000 RPM. Operating the compressor with 10000 RPM and 15000 RPM speeds for the first and second rotors respectively yields a good trade-off between power consumption and pressure ratio.