Effect of Speed Ratio on the Performance and Flow Field of a Counter Rotating Turbine

Counter Rotating Turbine (CRT) is an axial turbine with nozzle followed by a rotor and another rotor that rotates in the opposite direction of the first one. Studies show that speed ratio is one of the parameters that affect the performance of a turbomachine. Present work involves computationally studying the performance and flow field of CRT with different speed ratios ranging from 0.85 to 1.17. Equivalent mass flow rates of 0.091 to 0.137 are considered. Turbine components nozzle, rotor 1 and rotor 2 are modeled. Total pressure, velocity, entropy and turbulent kinetic energy distributions across the blade rows are used to describe the flow through CRT. Enthalpy, turbulent and secondary losses are estimated at the exit of the rotors. Performance curves are plotted for rotor 1, rotor 2 and CRT in all the configurations. The performance of second rotor is improved in all the speed ratio cases. Overall efficiency of the CRT increased for speed ratios greater than 1. Results confirm that losses vary with speed ratio and the performance of CRT can be enhanced by changing the rotational speeds of the rotors.