Advanced Exhaust Performance Modelling of Mixed Turbofan Engines: Less is More

Forced mixing devices are commonly used to augment exhaust performance for turbofan engines with low and intermediate bypass ratios as emerging effects like noise and fuel burn reduction associated with the mixing of core and bypass gas streams outbalance the detrimental impacts like additional drag and weight for this engine size. However, the highly three-dimensional flow characteristics cause major challenges for a proper accounting in a simplified one-dimensional thermodynamic performance model of the mixer and nozzle component, which impact the overall engine cycle significantly. It is especially crucial for the determination of fan working lines as well as the generated gross thrust to feed the model with accurate input values. The present paper introduces the usage of stringent flow separated exhaust system models and its impact on rig-test execution and engine analysis. Benefits concerning off-design modeling as well as challenges arising with the outlined methodology are discussed in detail. Furthermore its capability as analysis pretest model is demonstrated by means of sea level testing of a midsized turbofan engine.