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DIRECT NUMERICAL SIMULATION OF UNSTEADY DECELERATING FLOWS

Yongmann M. Chung
School of Engineering and Centre for Scientific Computing University of Warwick Coventry CV4 7AL, UK

Majid Malek Jafarian
Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL, United Kingdom

Abstrakt

Direct numerical simulations are performed for a turbulent flow subjected to a sudden change in pressure gradient. The calculations are started from a fully-developed turbulent channel flow at Reτ= 180 and 360. The pressure gradient of the channel flow is then changed abruptly. The responses of the turbulence quantities (e.g., turbulence intensities, Reynolds shear stress, and vorticity fluctuations) and the near-wall turbulence structure to the pressure gradient change are investigated. It is found that there are two different relaxations: a fast relaxation at the early stage and a slow one at the later stage. The early response of the velocity fluctuations shows an anisotropic response of the near-wall turbulence. Four turbulence models are tested in this study: the S-A model, the k − ε model, the k − ω model, the Baldwin-Lomax model.