展向离散抽吸法控制边界层转捩实验研究

通过实验成功发展了一种生成大振幅稳定条带的有效方法,即展向离散抽吸方法。在此基础上,开展条带控制边界层转捩的研究。实验在水洞中进行,以零压力梯度平板边界层为研究对象,利用氢气泡时间线法观测引入条带前后人工激发转捩边界层中扰动发展变化,分析条带对转捩的控制效果及参数影响。结果表明,展向离散抽吸方法生成的稳定条带最大振幅可达28.4%U（U为自由流速度）;实验中引入的宽度14和28mm的稳定条带都能起到抑制转捩的作用;条带振幅越大、宽度越窄,抑制效果越明显。研究结果为探索降低水/空气中航行器摩阻的新技术提供有价值的参考。

Experimental study on boundary-layer transition control by spanwise discrete suction

Delaying boundary layer transition is an important way to reduce friction drag of ve-hicles in air and water.Introducing steady streaks upstream is a new idea proposed recently to de-lay transition.Available studies demonstrated that the steady streaks of higher amplitude have higher ability to depress T-S wave propagation,and thus are more effective in delaying transi-tion.However,only relatively low amplitude steady streaks （12%U,whereU is the freestream velocity）can be obtained by the roughness elements method commonly used previously.This is because the generation of higher amplitude steady streaks needs higher roughness elements, which will lead to the bypass transition due to the stronger perturbation of vortex shedding caused by the elements.Moreover,recent theoretical studies show that there are some kinds of streaks wich do not suppress but instead promote the transition because of their acceleration of secondary instability.But this has not been verified by experiments yet.Thus,at least two prob-lems are valuable to be studied for the flow control technique.One is to develop an effective method to generate higher amplitude steady streaks;the other is to test the control effect of dif-ferent streaks on transition.In our studies,a new method,called spanwise discrete suction,has been developed to generate high amplitude steady streaks.Based on this,the streak control on the artificially excited transition in flat plate boundary layer has been studied using hydrogen bub-ble timeline method,by detecting the variation of perturbation evolution before and after the steady streaks introduced.The influences of streak spacing （corresponding to the suction hole spacing）and streak amplitude （depending on the suction intensity）are tested.The results show that spanwise discrete suction is an effective method to generate high amplitude streaks.The maximum amplitude of steady streaks generated by this method reaches as high as 28.4%U,even 〈br〉 higher than the upper amplitude threshold value of 26%U pred