The evolution from the initial sand accumulation to a mature barchan dune can be divided into five general stages. The first two stages are transient sand patches that disperse easily during downwind movement of the dune. In this study, we focused on the flow field changes around the dunes during the last three stages of dune evolution, namely the dome, protobarchan, and mature barchan stages. By means of particle image velocimetry, we measured the mean and turbulent flow fields around 3D-printed scale models of real dunes in a wind tunnel and discuss the significance of the airflow variation for dune evolution. We found that topographic forcing plays an important role in the changes of the mean and turbulent airflow structures. The airflow patterns on the windward slope were similar at all three stages, with deceleration at the windward toe and horizontal acceleration combined with vertical upward movement of the airflow along the windward slope. On the leeward sides of the dune during the three stages, the airflow structure evolved from airflow diffusion to airflow diffusion accompanied by transient flow separation, and then to complete airflow separation and reattachment. The turbulence intensity near the dune surface increased significantly as the dune matured and two zones with a high Reynolds shear stress appeared: in the middle of the windward slope and in the lee of the dune. Based on our results, we discuss the impact of changes in the airflow structure at different evolutionary stages on the evolution of dune morphology.

从最初的沙子积累到成熟的沙丘沙丘的演变可以分为五个大致阶段。前两个阶段是短暂的沙块，在沙丘顺风运动时很容易散开。在这项研究中，我们集中在沙丘演化的最后三个阶段，即穹顶，原始barchan和成熟barchan阶段，在沙丘周围的流场变化。通过粒子图像测速，我们测量了风洞中真实沙丘的3D打印比例模型周围的平均流场和湍流场，并讨论了气流变化对沙丘演化的重要性。我们发现地形强迫在均值和湍流气流结构的变化中起着重要作用。在所有三个阶段，迎风坡的气流模式都相似，迎风脚趾处的减速和水平加速度与气流沿迎风坡的垂直向上移动相结合。在三个阶段中，在沙丘的下风侧，气流结构从气流扩散演变为气流扩散，并伴随着短暂的气流分离，然后完成气流的分离和重新附着。随着沙丘的成熟，沙丘表面附近的湍流强度显着增加，并且出现了两个具有高雷诺剪切应力的区域：在迎风斜坡的中部和沙丘的背风处。根据我们的结果，我们讨论了不同演变阶段气流结构变化对沙丘形态演变的影响。在三个阶段中，在沙丘的下风侧，气流结构从气流扩散演变为气流扩散，并伴随着短暂的气流分离，然后完成气流的分离和重新附着。随着沙丘的成熟，沙丘表面附近的湍流强度显着增加，并且出现了两个具有高雷诺剪切应力的区域：在迎风斜坡的中部和沙丘的背风处。根据我们的结果，我们讨论了不同演变阶段气流结构变化对沙丘形态演变的影响。在三个阶段中，在沙丘的下风侧，气流结构从气流扩散演变为气流扩散，并伴随着短暂的气流分离，然后完成气流的分离和重新附着。随着沙丘的成熟，沙丘表面附近的湍流强度显着增加，并且出现了两个具有高雷诺剪切应力的区域：在迎风斜坡的中部和沙丘的背风处。根据我们的结果，我们讨论了不同演变阶段气流结构变化对沙丘形态演变的影响。随着沙丘的成熟，沙丘表面附近的湍流强度显着增加，并且出现了两个具有高雷诺剪切应力的区域：在迎风斜坡的中部和沙丘的背风处。根据我们的结果，我们讨论了不同演变阶段气流结构变化对沙丘形态演变的影响。随着沙丘的成熟，沙丘表面附近的湍流强度显着增加，并且出现了两个具有高雷诺剪切应力的区域：在迎风斜坡的中部和沙丘的背风处。根据我们的结果，我们讨论了不同演变阶段气流结构变化对沙丘形态演变的影响。