Assessment of the Delayed Extra-LES model for the aerodynamics of simplified automotive models

Abstract

Aerodynamic Drag Reduction needs a high-fidelity simulation of the flow phenomena, but traditional high-fidelity numerical models, e.g., Direct Numerical Simulation or Large Eddy Simulation, are still too computational demanding for the automotive industry. This topic is of particular interest for researchers and manufacturers because of its potential impact on fuel consumption and global emissions for thermal vehicles, and/or energy savings for electric vehicles. The green economy, promoted by many governments around the world with an emphasis on the effects of climate change, has changed the automotive perspective in recent years, with global emissions and energy savings as a key policy. Between the different high-fidelity numerical models for turbulent flows, the hybrid RANS-LES formulations offer the best compromise between accuracy and computational cost. The use of the Delayed eXtra-LES hybrid model is here explored with simplified geometries of all the configurations of vehicles, e.g., the Ahmed body with $25°$ and $35°$ as rear slant angle and the SAE notchback reference model. The results are compared with steady and unsteady RANS simulations, suggesting that only DX-LES, even with a higher computational time, can describe correctly all the main flow phenomena occurring around vehicles.