Unsteady turbulent flow with sudden pressure gradient changes

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 Re-tau = 180. 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 to the near-wall turbulence. Copyright (c) 2005 John Wiley D Sons, Ltd.