Measurementimprovement of flow quality of slotted test section in transonic wind tunnel

跨声速风洞槽壁试验段流场品质提升措施研究

¹ State Key Laboratory of Aerodynamics, China Aerodynamics Research and Development Center, Mianyang 621000, China
² Facility Design and Instrumentation Institute, China Aerodynamics Research and Development Center, Mianyang 621000, China

Received: 24 September 2020

Abstract

Experimental studies were carried out in the 0.6 m×0.6 m continuous transonic wind tunnel of CARDC in order to investigate the flow characteristics of the slotted test section. Experimental results show that the root-mean-square deviation of axial Mach number in the model area is above 0.01 when the test section Mach number is above 1.0.Numerical simulation under the same conditions to investigate the flow characteristics of the slotted section, together with the experimental studies indicate tow phenomena may directly cause the Mach number fluctuation. Firstly, a straight section was installed to connect the nozzle and the test section in the wind tunnel. Weak shock waves due to the curvature discontinuity at the joint of the test section and the straight section contribute to Mach number fluctuation. Secondly, the open-area ratio of both the upper and lower wall of test section, each with 8 slots, is of 10%. The larger porosity leads to stronger expansion waves in the acceleration zone located at the inlet of the test section. The flow was over accelerated because of the stronger expansion wave and thus fluctuate the flow field severely. Two measures were taken to improve the flow quality of the slotted test section based on the above-mentioned analysis: ①Flexible plate instead of solid straight plate was installed to bridge nozzle and test section to eliminate the curvature discontinuity; ②Decreasing the open-area ratio of the upper and lower test section wall to 6% and the number of slots to 6. Numerical and experimental results show that the Mach number fluctuation in the model area was suppressed to a satisfactory degree.

摘要

以CARDC 0.6 m连续式跨声速风洞为研究平台，开展了改善槽壁试验段流场品质的研究工作。风洞建成后的第一期调试，发现当试验段Ma>1.0时，槽壁试验段模型区内轴向马赫数分布均匀性较差，均方根偏差σ_Ma>0.01。利用数值仿真计算辅助分析，确认低超声速时马赫数波动是由开槽数和开闭比选取不合适及喷管和试验段连接处曲率不连续引起。据此提出以下2种改进措施：①综合考虑洞壁干扰特性的影响，降低槽壁试验段开闭比，槽壁试验段改为开槽数为6、开闭比为6%的配置方案；②试验段入口设置弹性板，以实现喷管与试验段连接处型面曲线的曲率连续。对改进后的槽壁试验段数值仿真计算和试验验证，结果显示试验段模型区马赫数均匀性得到较好改善，均方根偏差指标达到了σ_Ma≤0.001（Ma < 1.0），σ_Ma≤0.006（Ma≥1.0）的国际先进水平。