Large-Eddy Simulation of Bypass Transition on a Zero-Pressure-Gradient Flat Plate Using the Spectral-Element Dynamic Model

The present paper deals with the large-eddy simulation (LES) of a zero-pressure-gradient smooth flat-plate boundary layer undergoing bypass transition due to the presence of freestream turbulence of intensity around 3.0 %. Transition has been achieved by the introduction of synthetic turbulence into the freestream in a manner designed to invoke a behaviour closely resembling that of the ERCOFTAC T3A experiment. We make use of the spectral-element dynamic model (SEDM), implemented within the framework of a high-order spectral-difference solver, to carry out LES upon several sets of computational grids. Furthermore, comparisons against several other well known models such as the WALE and SIGMA model, are performed and presented in addition to implicit-LES (ILES). Our results show that the SEDM inputs relatively minor levels of dissipation into the pre-transitional region. This allows the fluctuating stresses to grow unhindered, until the critical amplitude, required for transition to occur, is reached. Furthermore, within the transitional region, the eddy-viscosity is dominant near the wall and not at the interface between the freestream and boundary layer where the breakdown mechanism predominates. The rapid grid convergence properties of the SEDM, demonstrated in this work, make them well-suited for use in conjunction with other high-order schemes.