Delayed detached eddy simulation of pedestrian-level wind around a building array – The potential to save computing resources

The appropriate selection of a turbulence model directly affects the prediction of pedestrian-level wind (PLW) around buildings. Delayed detached eddy simulation (DDES) model, has been reported to be able to predict airflow around a building as good as large eddy simulation (LES) does, but with a lower mesh requirement and much less computing time. This study aims to see if DDES model can perform similarly when simulating the wind flow around a building array. This hypothesis is tested by comparing wind velocities of DDES, LES, and a benchmark wind tunnel experiment. Sensitivity assessments of DDES model are conducted, including the mesh resolution and the choice of an unsteady Reynolds Averaged Navier-Stokes (URANS) model used in conjunction. The normalized minimal grid sizes (0.005 for the building array's windward side and 0.0025 for the lateral and leeward sides) and the unsteady k−ω shear stress transport (SST) model are the most economical and effective. Simulated results are further quantified using four validation indices. Specifically, the correlation coefficient R between the predicted mean velocities using DDES and LES is 0.90, which basically proves our hypothesis in the mean flow field; but DDES only takes 80.3% of the computing time using LES. The time histories and spectrums of instantaneous velocities are also analyzed, indicating that DDES performs the similar predictions as LES of the unsteady flow fluctuations, while it has the potential to save computing time and mesh numbers.