Internal Drag Evaluation for a Through-Flow Nacelle Using a Far-Field Approach

Abstract

The main objective of this research is to propose a method for decomposing the total drag of a nacelle into external, internal, and wake drag. From a bookkeeping agreement, the internal drag (i.e., the drag generated inside a nacelle) is the engine manufacturer’s responsibility and is not to be included in the aircraft’s total drag. Consequently, computing the internal drag is mandatory for the airframe and engine constructors concerned and can be achieved either experimentally or by computational-fluid-dynamics analysis. Up to now, aerodynamic engineers have used a near-field approach to compute the internal drag using computational-fluid-dynamics analysis, but this method has serious drawbacks, including its dependency on the accurate location of the stagnation line. The new method proposed here has been applied to multiple two- and three-dimensional test cases, and results show that it is independent of the location of the stagnation line and yields accurate results that agree well with experimental and empirical data. Results also show that the wake drag of a through-flow nacelle is caused by the flow passing through the nacelle and so needs to be added to the internal drag.