A method for computation and breakdown of the aerodynamic drag into viscous and wave components is proposed. The proposed method is based on a far-field approach in which the drag is determined from the momentum integral balance by considering fluxes evaluated on a surface far from the body. A general far-field expression of drag is derived by Taylor's series expansion with respect to entropy, pressure, and total enthalpy variations. Given a numerical solution of the Reynolds averaged Navier-Stokes equations, the method, allows for the determination of the drag related to entropy variations in the flow. However, the breakdown of entropy drag relies on a proper definition of the boundary-layer and shock wave region. For this purpose, a zone detection algorithm has been developed, which is based on nondimensional expressions from which the compression/expansion regions and the regions with dominant eddy viscosity can be determined. The identification of a spurious contribution, due to the numerical dissipation and discretization error of the flow solver algorithm, allows for drag computations weakly dependent on mesh size. Therefore, accurate drag evaluations are possible even on moderately sized grids. Polar curves (lift vs. drag) are presented for transonic flows around an airfoil and a wing-body configuration. It has been shown that Oswatitsch's classical formula for the entropy drag of a two-dimensional airfoil is not accurate in viscous flows, but a second-order correction term, here proposed, is required. The study of the transonic flow around a wing-body configuration demonstrates the capability to analyze realistic aircraft configurations, although the computation of the total drag requires the calculation of the vortex drag by a different method. The three-dimensional simulations also revealed that, in the case of a multiblock structured grid with skewness and stretching at block interfaces, the contribution of the spurious drag is even more important.
Computational fluid dynamics-based drag prediction and decomposition
Bestimmung des Reibungs- und Wellenanteils am Strömungswiderstand von Tragflügen aus der numerischen Strömungssimulation
AIAA Journal ; 41 , 9 ; 1647-1657
2003
11 Seiten, 19 Bilder, 1 Tabelle, 22 Quellen
Article (Journal)
English
dreidimensionale Strömung , Entropie , Grenzschichtströmung , mechanischer Wellenwiderstand , Navier-Stokes-Gleichung , numerische Strömungsberechnung , Rechengenauigkeit , Reibungswiderstand , Reihenentwicklung , Stoßwelle , Strömungswiderstand , Tragflügelumströmung , transsonische Strömung , zweidimensionale Strömung
PROSPECTS FOR DRAG PREDICTION USING COMPUTATIONAL FLUID DYNAMICS
SAE Technical Papers | 1990
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