The design and qualification of a longitudinal gust generator in a low-speed, blow-down, open-return wind tunnel was conducted. Flow-impeding louvers were used to rapidly change the blockage ratio at the inlet, effectively reducing test section flow speeds up to $$60\%$$ and $$52\%$$ for the closed and open test section configurations of the wind tunnel, respectively. The wind tunnel responds more quickly for higher fan speeds, shorter tunnel lengths, and during louver closing motions (deceleration). A mathematical model developed to predict the wind tunnel’s response shows these same trends and agrees with the experimental data to within 0.03 in amplitude ratio and $$4.3^\circ$$ in phase lag, for all cases studied. Comparison of the closed to open test section configurations reveals that flow disturbances propagate nearly instantaneously, or in a globally unsteady manner, within the closed configuration, while they convect at speeds similar to that of the mean flow when testing in the open configuration.

中文翻译：

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上游百叶系统非定常低速风洞的设计与鉴定

在低速、排污、回风风洞中进行了纵向阵风发电机的设计和鉴定。阻流百叶用于快速改变入口处的堵塞比，有效降低风洞封闭和开放测试段配置的测试段流速高达$60\%$$和$52\%$$，分别。对于更高的风扇速度、更短的风道长度以及百叶窗关闭运动（减速），风洞的响应速度更快。为预测风洞响应而开发的数学模型显示了这些相同的趋势，并与实验数据一致，振幅比在 0.03 以内，相位滞后在 4.3 美元以内，对于所有研究案例。封闭和开放测试部分配置的比较表明，流动扰动几乎是瞬时传播的，