Computational Aspects of Unsteady Flows,
DOUGLAS AIRCRAFT CO LONG BEACH CA
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This paper is concerned with the calculation of unsteady flows and particular with the development of numerical methods for solving unsteady boundary-layer equations and their application to the flows around practically important configurations such as oscillating airfoils. It provides a brief review of recent work and emphasizes the need for numerical methods which can overcome possible problems associated with flow reversal and separation. The ziz-zag and characteristics box schemes are described in this context and, when embodied in a method which permits interaction between solutions of inviscid and viscous equations, the characteristic box scheme is shown to avoid the singularly associated with boundary-layer equations and prescribed pressure gradient. Calculations have been performed for a cylinder started impulsively from rest and oscillating airfoils and the results are presented and discussed. It is concluded, for example, that turbulence methods based on an algebraic specification of eddy viscosity can be adequate, that location of transition is important to the calculation of the location of flow separation and, therefore, to the overall lift of an oscillating airfoil.