A new formulation for delayed detached eddy simulation based on the Smagorinsky LES model

Abstract

This dissertation describes an alternate formulation for Delayed Detached Eddy Simulation or DDES. Detached Eddy Simulation (DES) falls under the category of hybrid RANS/LES models where a single turbulence model functions as either a RANS (Reynolds-Averaged NavierStokes) or an LES (Large Eddy Simulation) model. Certain fundamental issues were identified in the original DES formulation, which led to revised formulations such as the Delayed DES (DDES) and Improved DDES (IDDES) with increasing complexity, which negatively impacted the readability of the model. This is the motivation to explore an alternate formulation for DES which aims to correct the issues found in the original DES, while at the same time being simple and easy to understand. Towards this end, the eddy viscosity formulation in a given RANS model is modified such that it mimics the Smagorinsky LES subgrid viscosity expression when the model is in eddy simulation mode. The resemblance of the resulting DES formulation to the Smagorinsky model allows the implementation of a dynamic procedure to compute the model constant, similar to the dynamic Smagorinsky model. This was found to improve the model performance in several cases. The description of this alternate DES formulation and the implementation of a dynamic procedure in this model will be the major focus of this dissertation.