暂冲式风洞大开角扩散段性能的实验研究

布置有多层孔板（丝网）的大开角扩散段通过参数的优化设计，可有效缩短暂冲式风洞启动时间，均匀进入稳定段的气流速度，并降低阀后噪声和气流脉动。针对某大型暂冲式风洞大开角扩散段设计关键技术开展专题研究，设计并进行了不同扩散段扩开角角度和中心体分流锥型式的组合实验，从压力损失、出口截面速度分布和降噪特性三个方面进行了对比分析。试验结果表明：试验件45°扩开角＋65°平底锥的压力损失相对最小，而增加导流尾锥的中心分流锥由于底部难以形成稳态的分离涡使得其压力损失明显偏大，其它试验件组合的压力损失值则相接近；各试验件出口截面的速压分布均呈现以中轴线对称分布的双驼峰趋势，且孔板的开孔率偏高时出口剖面速度分布相对更平滑；试验马赫数下的大开角段对气流噪声的消声量约为12～14dB，对频率在2kHz以上的气流噪声具有相对较强的消声能力，同时气流经过设置有多层孔板的大开角扩散段后，气流波动幅值明显降低，气流脉动得到有效地抑制。

Experimental research of wide-angle diffuser performance for the intermittent wind tunnel

The starting time for the intermittent wind tunnel can be effectively reduced by parametric optimization design of the wide-angle diffuser with multilayer perforated plates, which makes flow velocity into the settling chamber uniform and reduces noise and flow fluctuation behind the valve. The paper studies key design techniques for the wide-angle diffuser of a largescale intermittent wind tunnel. Various experiments combining with different diffusing angles and different centerbody cones are conducted . Comparative analysis from pressure loss, velocity distribution at exit of diffuser and noise reduction characteristics are performed. The experimental results show that minimum pressure loss can be obtained when 45°diffuser combining with 65°truncated cone is utilized. But the pressure loss will apparently increases due to no steady separation vortex evolution if the centerbody tail cone is added. For other combinations of diffusers and cones with different angles, similar pressure losses can be found. From the results, we can also see the axisymmetric hump trend of dynamic pressure distributions at the exit for various diffuers and smoother velocity distributions when the perforated plate has a higher perforation ratio. Additionally, we find that the flow noise suppression level can approximately reach 12 -14dB for some test Mach numbers if the wide-angle diffuser is used, especially for the frequency above 2kHz. Moreover, the flow fluctuation amplitude is obviously reduced after the air flows through the wide-angle angle with multilayer perforated plates.