横向沙丘背风侧气流重附风洞模拟

 二次流在沙丘形成和形态维持过程中扮演着重要角色。沙丘迎风坡气流加速和背风侧气流分离是最常见的二次流形式。沙丘背风侧的二次流,尤其是气流分离形成的分离涡和气流重附对沙丘背风坡的塑造、沙丘间距和排列模式都具有重要的控制作用。因此，设计了一系列具有不同迎风坡坡度的横向沙丘模型，采用粒子图像测速技术，通过风洞实验模拟了沙丘背风侧的气流分离和重新附着。实验结果表明，当来流风速垂直于沙丘脊线时，沙丘背风侧的气流重附距离介于4\^8 H~10\^8 H之间(H为沙丘高度)，最大重附距离出现在迎风坡坡度为15°的沙丘背风侧；沙丘迎风坡坡度是控制背风侧气流重附距离的主要因素，而自由风速对气流重附距离的控制作用较小。根据实验结果,还讨论了气流分离与重附对沙粒运移和沙丘形态维持的沉积学意义。

Wind Tunnel Simulation on Flow Reattachment on Lee of Transverse Dunes

Secondary airflow plays an important role in dune initiation and form maintenance. Airflow speeding\|up over the stoss slope and separating at the crest were described and mentioned widely in the dune dynamic researches. Secondary airflow in the lee side of dune, especially the flow separation (i.e. reversal vortex) and the reattachment, has an important significance in shaping the lee slope and in controlling the dune spacing and alignment. In this paper, a series experiments were conducted in a wind tunnel using Particle Image Velocimetry (PIV) to study the factors in controlling flow reattachment in the lee side of transverse dunes. The results showed that the flow reattachment distance in the lee side of various dune models are ranged from 4\^8H to 10\^8H (H is dune height) depending on different stoss slopes, the maximum of flow reattachment distance was found in the lee side of the transverse dune with a 15° stoss slope angle. The stoss slope angles have more influence in controlling the flow reattachment than free stream velocities. Finally, the sedimentary significance of the flow separation and the reattachment was discussed in detail.