LES-based vortical flow characterization in a 90°-turned pipe bend

The present work is concerned with the characterization of the vortical flow topology within a 90°-pipe bend by means of a well-resolved, highly comprehensive Large-Eddy Simulation (LES). The considered flow configuration is closely related to the cooling channels encountered in the internal combustion (IC) engines of motor vehicles. Accordingly, its geometrical properties as well as the volume flow rates are in accordance with those conditions that occur in a practical engine environment. The relevant flow rates studied presently, expressed in terms of the flow Reynolds numbers, correspond to Reb=7200, 10500 and 14000. The dynamics of the residual turbulence is described by the Wall-Adapting Local Eddy-viscosity (WALE) model. A preliminary comparative assessment of this and some other Subgrid-Scale (SGS) models, including both the standard Smagorinsky model and its dynamic version, has been performed by means of computing fully-developed pipe flows at relevant Reynolds numbers. The resulting flow field has been subsequently prescribed at the inflow cross-section of the pipe elbow. The WALE formulation, applying a modified WALE constant Cw=0.325 as recommended within the OpenFOAM® Code, proved to be advantageous compared to Smagorinsky models. Furthermore, an intensive study on optimization of the cross-sectional ’O-grid’ arrangement toward improvement of the computational results has proven that the cell arrangement in the circumferential direction was of decisive importance. The effects of the longitudinal and transverse curvature on time-averaged flow behavior within the 90°-pipe bend is analyzed in detail revealing complex vortical events following the well-known Dean vortices. In addition, the dynamics of the Dean vortices, derived on the basis of the three-dimensional mapping of the vortex position and its circulation as well as their varying behavior along the 90°-pipe bend, has been described by applying the vortex identification methodology according to Graftieaux et al. (2001). •A well-resolved LES of a pipe bend flow over a Reynolds number range is performed.•Focus is on the vortical flow events with respect to their formation and development.•These include the mean Dean vortex and two associated secondary vortexes.•Three-dimensional tracking of the vortex center traces within flow field is extracted.•A relationship is established between vortical structures and turbulence generation.