INVESTIGATION OF THE EFFECT OF SPEED VARIATIONS ON THE CONTRA-ROTATING AXIAL COMPRESSOR STAGES

The present study investigates the speed effect of rotational rotors on the performance of contra-rotating axial compressor and flow behavior. In the present study, a two-stage contra-rotating axial flow compressor with rotor-stator-rotor configuration is considered. The results are presented based on numerical viscous flow simulation in three dimensions by solving Navier-Stokes, continuity, and energy equations using Ansys CFX commercial software. Initially, to validate the results, the absolute and relative flow angle curves for each rotor in the radial direction were extracted using the present simulation and compared with the other investigations. To investigate the effect of different rotor speeds, five different speeds of the second rotor are considered. In the first and second cases, the second rotor speed is reduced by 20 to percent compared to the reference case (in the third case, the speeds of the first and second rotors are equal) and in the fourth and fifth cases, the speed of the second rotor is increased by to percent. The results show that increasing the second rotor speed in the fourth and fifth cases decreases the vortex flows, the blockage in the blade passage and consequently, decreases the flow entropy. The compressor performance curve shows a higher mass flow rate and pressure ratio. In contrast, decreasing the second rotor speed results in undesirable behavior in the flow structure even under design and choke conditions, leading to enhanced tip leakage flow and increased flow entropy which in turn decreases pressure ratio and mass flow rate as well. Results show that by reducing the revolution of the second rotor (in Cases I,II), the tip leakage flow is stronger, resulting in the interface of the main flow and tip clearance flow to upstream which creates vertical flows in design and chock conditions as well as stall condition. This occurrence causes an increase in the original losses and entropy in the compressor.