双下侧布局二元超声速进气道掺混气动特性

针对一种冲压发动机用设计飞行马赫数范围为2.5～3.5的双下侧布局二元超声速进气道掺混气动特性开展了高速风洞实验和一体化数值仿真研究。研究结果表明：（1）在混和段内气流是通过两股气流的撞击以及横截面上二次流形成的旋涡不断掺混的,这也是混和段气流损失的主要原因。采用二元进气道的双下侧布局在整个混和段内气流除了在射流区内不均匀外,在1.5D截面至掺混段出口截面4.5D处慢慢趋向均匀。（2）掺混段出口截面与进气道出口截面总压恢复系数变化规律一致。随着来流马赫数和侧滑角的增大,掺混段出口截面总压恢复系数均是逐渐下降,而随着迎角的增大其总压恢复系数是提高的。（3）导流段损失和混和段损失均随着来流马赫数和侧滑角的增大而增大,整个掺混段损失增大。而随着迎角的增大,由于导流段损失逐渐下降,混和段损失变化不大,所以整个掺混段损失是降低的。（4）随着导流角的增加,进气道的总压恢复系数几乎未受影响,而掺混段的总压损失呈线性提高。研究范围内随着导流角的增大,气流导流段的总压损失几乎不变的,而由于径向速度分量增大,混和段损失增加,同时掺混出口截面承受反压能力降低。

论“口风”在竹笛演奏中的作用

口风的合理调控对竹笛演奏效果的积极作用是显而易见的。由于旋律中的乐句长短不一,力度、音量的强弱大小不同,因而在处理音色、音高等方面,口风的变化则显得至关重要。

Suppression of fluctuation on the angle of arrival for freespace optical communication

In order to increase the coupling efficiency and suppress the random angular jitter induced by atmosphere turbulent, the fine tracking system with fast steering mirror （FSM） is demonstrated. The field experiment results of free-space optical communication link across 16 km show that when there is no tracking, the range of the x-axis coordinates＇ fluctuation achieves 46 pixels, corresponding to the incident angle of 73.6 μrad, and its mean square deviation is 6.5 pixels, corre- sponding to the incident angle of 10.4/.trad. When there is tracking, the range of fiuctuation is suppressed to 10 pixels and 16 ktrad, and the mean square deviation reduces to 1.5 pixels and 2.6 brad for the spot＇s centroid and the incident angle, respectively. Significantly, the coupling efficiency increases by 6 times, and the fluctuation of received light power decreases obviously.