极限条件下的大角度扩散段优化设计数值模拟

为提升某低速风洞大角度扩散段静压恢复性能,降低总压损失至分流隔板的水平,采用计算流体动力学(CFD)方法对该扩散段不同设计方案进行了模拟.采用阻尼网能有效抑制分离,阻尼网布置位置和开孔率对大角度扩散段内的流动状态和总压损失有很大影响.使用直线壁面扩散时,由于扩散角过大,第1层阻尼网对抑制大角度扩散段入口分离效果很弱,总压损失无法达到预期设定指标.采用三次曲线壁面扩散时,总压损失明显降低,小于预期指标,但存在小范围的分离.分级扩散能有效降低总压损失,按照最大静压恢复设计的分级扩散段,避免了入口的气流分离,能大幅度降低总压损失.对分级扩散的进一步研究表明,按照最大静压恢复设计的第1级扩散段扩散角已达到上限,为抑制第3级扩散段的分离,缩短第2级扩散段,减小第3级扩散段扩散角的方法是合理的.通过对不同方案流态的比较得出了最佳的参数匹配,总压损失指标达到了设计要求.因此采用数值模拟能够获得最佳的大角度扩散段设计结果. 

Numerical simulation for optimal design of wide angle diffuser in limited condition

In order to improve the static pressure recovery of specific low speed wind tunnel wide angle diffuser(WAD) and reduce the total pressure loss to the level of the splitter plates, different configurations of WAD were studied using computational fluid dynamics (CFD). The screens could restrain flow separation. The position and opening area ratio of the screens had an important effect on the flow regimes and total pressure loss. The total pressure loss using linear wall WAD was greater than the expected value. Due to the oversize diffuser angle, the first screen played a little role on separation control of WAD inlet. By use of cubic curve wall, the total pressure loss evidently decreased and was less than the expected value. But a little separation in WAD existed. Simple segment linear walls had profound function on the drop of total pressure loss. Based on the method of maximum static pressure recovery, WAD using three segment linear walls was designed. The separation of inlet disappeared. And the total pressure loss was reduced to a great extent. Further investigation on the diffuser of three segment linear walls indicated that the angle of the first level diffuser was upper limit to the edge of separation based on the method of maximum static pressure recovery. To restrain separation of the third level diffuser, the method was reasonable to shorten the second level diffuser length and reduce the third level diffuser angle. Combination of satisfactory parameters, which could significantly produce less total pressure loss to the expected level, was obtained based on flow regime analysis of different configurations. It is concluded that the optimal design of WAD can be obtained based on numerical simulation.