Numerical study of the effects of confined airfoils usage in high bypass ratio turbofan engines

Turbofan engines are the main power plants used in the commercial airline industry. Increasing the bypass ratio (BPR) in turbofan engines enhances their propulsive efficiency and reduces both noise and harmful gas emissions. Over the years the aero engine industry has devoted huge efforts and enormous amounts of money to improve turbofans' propulsive efficiency through the increase of their BPR. Based on the current technology however, there is a practical limit to how much BPR can be increased before significant penalties associated with increased both engine weight and nacelle drag erode the benefits. This work numerically studies thus the benefits of using confined airfoils in the engine bypass flow region to counteract the turbofan engine weight and alleviate the efforts over the aircraft wing structure. Accordingly, a description of the proposed engine-airfoils arrangement, relative dimensions and airfoils adequate placement inside the engine bypass duct is initially presented. Two different flight conditions, take-off and cruise, are numerically assessed next using computational fluid dynamics (CFD) based approaches to characterize the particular bypass flow behavior. The numerical work includes the study of engine configurations similar to those used in long-range aircraft. A structured multi-domain mesh, in conjunction with both Reynolds-average Navier Stokes (RANS) and steady-state mixing planes approaches, are used in the numerical model utilized. The main results indicate that using confined airfoils produces substantial lift respect to the engine weight. Engine weight reductions of up to 23% are observed because of the use of confined airfoils in the engines bypass ducts.