Technical Note (For internal use by AWIATOR partners and Commission only) Three-dimensional instability mechanism in a four-vortex system; Benchmark computations. Prepared by: H.L.C. Moet (CERFACS) Work Package: WP1 Task: 1.1.1 Document No.: AW-CERFACS-111-001 Version: 1 (Draft) Issued by: CERFACS Date: July 17, 2003 Approved by: Task Manager: Issueing organisation: CERFACSThree-dimensional instability mechanism in a four-vortex system; Benchmark computations. Henri Moet CERFACS, Centre Europ¶een de Recherche et de Formation Avan»c¶ee en Calcul Scientiflque, 42, Av. G. Coriolis, 31057 Toulouse Cedex, France Abstract. To compare difierent numerical methods, a "benchmark" computation has been deflned within Subtask 1.1.1 "Design and Manufacture". The benchmark con- sists in simulating the unstable behaviour of a four-vortex system composed of two counter- rotating vortex pairs. An energy diagnostic is applied to analyse the evolution of the kinetic energy in the vortex o w governed by the instability mechanism with the purpose of esti- mating the artiflcial/numerical viscosity efiects. It is essential to demonstrate that numerical efiects are within acceptable limits which allows the use of the numerical methods for pre- dicting and selecting the desired vortex o w conflgurations. July 17, 2003Table of Contents 1 Introduction............................................. 6 2 The numerical model and initial condition ................... 7 2.1 The numerical code NTMIX3D ........ ...