Identification of Flow Physics in a Counter Rotating Turbine

Flow in a Counter Rotating Turbine (CRT) stage is composite and three dimensional due to the blade geometry of nozzle, rotor 1 and rotor 2 that are twisted along the span, spacing between them, tip clearance provided on rotors and also because of oppositely rotating rotors. Present work analyzes the flow field through the nozzle and rotors at planes taken at various axial chord distances. Blade-to-blade contours and the hub-to-tip plots reveal the actual scenario of flow in the turbine stage. Nozzle and the two rotors are modeled in case of the CRT configuration. Boundary conditions are specified as pressure at inlet of the nozzle and flow rate at the outlet of rotor 2. Total pressure, velocity, entropy and TKE distribution through the blades are used to identify the flow over CRT. Flow through the blade rows is distinguished by effects of boundary layer, secondary flows near the hub, pressure gradient effects, presence of vortical flow structures in the passage and near the tip. Total pressure distribution near the midspan in case of nozzle and rotors show the presence of boundary layers and wake regions. Entropy and TKE contours show the loss regions in all the blade rows. Flow losses are more in rotor 2 than rotor 1. Secondary velocity vectors show the presence of vortex regions in the passage and tip clearance. Blade-to-blade contours of CRT reveal the actual flow scenario surrounding the blades. Hub-to-tip plots show the variations of flow parameters while moving from the bottom to top most position of blade. Thus, the present work identifies the exact flow structure in a counter rotating turbine and paves the way for researchers to negotiate flow losses and improve the CRT performance further.