Numerical investigation of the blockage effect of trees on airflow distributions in a wind tunnel

Trees play a significant role in regulating microclimates and enhancing outdoor comfort. Their effects have been widely investigated through on-site tests, wind tunnel (WT) experiments, and numerical simulations. WT experiments, known for their controlled conditions, are increasingly used to investigate the blockage effect of trees. However, the impact of this effect on experimental data is often overlooked. Therefore, we conducted numerical simulations to analyze the blockage effect of trees on airflow distributions under different wind speeds, leaf area density (LAD), drag coefficient (DC), tree canopy morphologies, and blockage ratios (BRs). By comparing the results under various conditions with the case of LAD = 0, we aim to quantify the extent of this impact. The results indicate that LAD and DC are key parameters affecting the blockage effect of trees. The cuboid model exhibits a more significant blockage effect on airflow distributions compared to the cylinder, truncated cone, and ellipsoid models. For tree canopies with low LAD and DC, the impact on airflow distribution is minimal. For the cuboid model with an LAD of 3.0 m²/m³, a DC of 0.5, and a BR of 8 %, the average airflow deviation is approximately 4.28 % compared to the case of LAD = 0. However, when the BR is in the range of 8%–12 %, the WT experimental data need to be corrected. The BR in WT experiments can be appropriately increased for other tree canopy morphologies. This study provides guidance for investigating the blockage effect of trees in WT experiments.