Engine pre-entry thrust and standard net thrust evaluation based on the far-field method

Computation of engine pre-entry thrust is required to evaluate aircraft configuration drag. Numerical computation of this quantity requires knowledge of the captured streamtube, which depends on the stagnation line location. A new method that uses the far-field formulation is developed so that knowledge of the streamtube properties is no longer required. Using similar techniques, an alternative method to compute the standard net thrust, the basis of most thrust/drag bookkeeping systems, is introduced. The classical formulation to compute the standard net thrust needs interpolation of flow quantities in the nacelle's exit plane which leads to loss of accuracy. Theoretical development of the far-field method in power-on conditions is presented as well as an overview of the bookkeeping technique in CFD. Simulations are performed with ANSYS Fluent 13.0 on the isolated CFM56 nacelle in power-on conditions with varying boundary conditions. Results of the proposed approaches are in agreement with ESDU and classical formulations. Drag decomposition in terms of viscous, wave, spurious, induced, and through-flow drag is presented. Configuration drag is computed with two formulations which are in agreement.