Low Bypass Ratio Variable Cycle Engine Concepts for High Speed Aircraft

Abstract

There are many types of engines in aviation industry, among these turbofan engines are the most commonly used type. Low and medium bypass ratio engines are used predominantly in military aircraft and high bypass ratio ones are used in both civil and defence industries. Variable cycle engines (VCE) are advanced turbofan engines with multiple bypass ducts making them more efficient in a wider range of operat ing conditions. Adaptive cycle engines take it a step further by actively changing the fan pressure ratio (FPR) and making the engine performance even better. A new component recently patented called FLADE (Fan on bLADE) provides options such as having a third bypass duct hoping to further decrease SFC and improve efficiency. In this study, a FLADE’d engine will be studied to see if and how the addition of the FLADE affects the engine performance. An in-house built software called GESTPAN will be used for the analysis performed in this study. The fact that introducing new components to GESTPAN is relatively easy makes the adding of a FLADE component to models relatively easy. Although the initial intention was to study a triple by-pass ACE with FLADE, it was decided to concentrate the analysis on the comparison of a single bypass turbofan engine and a FLADE’d turbofan. Results show that the FLADE stream, when using a variable exhaust nozzle, is relatively resistant to choking. This means that it has the potential to alleviate spillage drag by increasing flow and decreasing specific thrust in low power conditions. This work indicates that the new FLADE’d engine has the potential to substantially increase propulsive efficiency of the FLADE stream. However, it is difficult to provide a substantial part of the thrust from this stream simple because of its lower specific thrust resulting in that the FLADE stream may not influence the overall engine performance to a great extent. This is because the kinetic energy contribution from the FLADE stream is almost negligible. Cruise analysis showed that adjusting the bypass ratio for the FLADE can result with considerable range benefits. Some of the other advantages of the FLADE could be that its stream can be used for cooling purposes such as a heat sink for cooling the turbine cooling air, which allows turbine inlet temperature (TIT) to be increased resulting with overall better engine performance.