Integration of the Cell Perturbation Method (CPM) for inflow turbulence boundary condition in PALM v6.0

In Large Eddy Simulation (LES), inflow turbulence boundary conditions are crucial in accuracy of predicting atmospheric turbulent flows in urban environments. The cell perturbation method (CPM; Muñoz-Esparza and Kosovic, 2018) assigns thermal perturbations near inflow boundary regions to enhance rapid turbulence development. In this study, we implement the CPM module for use in the PALM v6.0 (Parallelized Large-Eddy Simulation Model, version 6.0) LES model, expanding the model’s capability to simulate time-varying inflow turbulence boundary conditions. The module was coded using the Message Passing Interface (MPI) parallel programming standard based on the Synthetic Turbulent Generator (STG) method in the PALM model. The performance of the CPM module was evaluated against a series of idealized simulations under neutral, unstable, and stable stability conditions. The developed CPM method showed clear development into turbulent flow compared to simulations with no inflow turbulence and the STG turbulence method. The two turbulence inflow methods performed differently in turbulence patch distance and energy spectrum under different atmospheric stability conditions. The CPM developed turbulent fields in a shorter distance under unstable and neutral conditions, while the STG showed earlier development of turbulent fields in stable condition. This study demonstrated that the CPM can be used in time-varying inflow turbulent simulations in urban environments.