Investigation of the impact of a Variable Area Fan Nozzle on the overall performance of an UHBR-Highlift-Configuration

Abstract

It is well known that a high bypass-ratio (BPR) is necessary for efficiency enhancement of commercial aircraft engines. This can also be seen in the properties of the current re-engined midrange aircraft. Compared to their predecessors (BPR � 5 to 6), the new generation of mid-range aircraft with about 150 to 200 seats feature a take-o� BPR of �10 to 12. A frequently studied but as yet not adopted technology uniquely aimed at these types of engines is the variable area fan nozzle (VAFN). This concept allows an adjustment of the engine operating point and the nozzle flow via a variable nozzle geometry. Previous studies show that it can eliminate flutter problems and provide an additional degree of freedom in optimizing the thermodynamic e�ciency of an aircraft engine. But what is the effect of the employment of these concept on the external aerodynamics and hence on the e�ciency of the whole aircraft? This is discussed in the present paper for a VAFN-layout utilized for wind-tunnel testing that uses a mere translative adjustment of the nacelle aftbody for changing the nozzle area. The CFD-results for several VAFN-settings of two high-lift configurations with a close coupled UHBR-TPS engine (BPR � 15 to 20) show an impact on the overall airframe lift and drag due to the jet flow, differing from that of a fixed nozzle engine. The comparison with the fixed nozzle engine also shows different flow conditions at the engine intake. The discussion of the outcomes is done by including the estimation of the impact on fan aerodynamics and the produced thrust.