A Zonal-LES Study of Steady and Reciprocating Engine-Like Flows Using a Modified Two-Equation DES Turbulence Model 2017-24-0030

A two-equation Zonal-DES (ZDES) approach has been recently proposed by the authors as a suitable hybrid URANS/LES turbulence modeling alternative for Internal Combustion Engine flows. This approach is conceptually simple, as it is all based on a single URANS-like framework and the user is only required to explicitly mark which parts of the domain will be simulated in URANS, DES or LES mode. The ZDES rationale was initially developed for external aerodynamics applications, where the flow is statistically steady and the transition between zones of different types usually happens in the URANS-to-DES or URANS-to-LES direction. The same “one-way” transition process has been found to be fairly efficient also in steady-state internal flows with engine-like characteristics, such as abrupt expansions or intake ports with fixed valve position. However, assuming that a pure LES treatment is applied on the in-cylinder region, the reciprocating nature of a real engine flow implies a “two-way” URANS-LES-URANS transition during the engine cycle. In the present work, we further validate the Zonal-LES mode (i. e. with only pure URANS and pure LES zones) of our simulation methodology on a fixed intake port case and, moreover, we study its behavior in a standard moving piston reference flow. Simulations are all carried out by means of the open source CFD toolbox OpenFOAM^® and results are compared against both experimental measurements and computational studies from other authors.