Generalization of the Far-Field Drag Decomposition Method to Unsteady Flows

Far-field drag-prediction and decomposition methods are powerful tools that increase the accuracy of the drag coefficient computed from computational fluid dynamics results by removing the spurious drag caused by numerical procedures. Furthermore, these methods allow a physical decomposition of the drag in terms of viscous, wave, and induced drag. However, they are currently limited to steady flows. This paper presents a generalization of the commonly used drag-prediction and decomposition method to unsteady flows. This generalized method, designed for three-dimensional viscous, subsonic, and transonic flows, is defined for both inertial and noninertial coordinate systems and allows drag decomposition to be performed on either static or moving/rotating meshes. This generalization also allows the drag caused by the unsteady fluctuations of the flow to be identified.