CFD analysis of open rotor engines using an actuator disk model

In the world of air transportation today, there is increasing emphasis on ‘Environmentally Responsible Aviation’ that addresses more energy efficient and environmentally sustainable aircraft with low emissions and noise. Due to its high propulsive efficiency, an Open Rotor gas turbine engine has the potential to significantly minimize the specific fuel consumption and reduce CO₂emissions in a new generation of transport aircraft. In mid-1980’s GE invested significant effort in advanced turbo-prop technology (ATP) and un-ducted fan technology (UDF). However, in spite of its potential for 30% savings in fuel consumption over existing turbofan engines with comparable performance, for a variety of technical and business reasons, the advanced turboprop concept never quite got-off the ground. However, with current emphasis on “Green Aviation” NASA and aircraft engine industry (GE, Pratt-Whiney and Rolls-Royce) are investing significant resources in Open Rotor research and development. The goal of this study is to develop a numerical model to study the performance of counter rotating open rotors (CROR). Advanced CFD studies using the unsteady Reynolds – Averaged Navier-Stokes (URANS) equations are quite complex and computationally intensive. Therefore as a first step, we have developed a simplified model based on Froude’s actuator disk method to replace the two spinning rotors with two actuator disks on an axisymmetric model. The URANS computations for this model were performed using the CFD solver ANSYS- FLUENT. The results of computations have been compared using the wind tunnel data on F31/A31 CROR from NASA Glenn’s Research Facility. It is shown that the simplified actuator disk model can predict results in excellent agreement with the test data for the hub pressure distribution, while maintaining computational simplicity.