用声激发扰动控制边界层转捩

本文对声激发控制边界层转捩问题在低湍流度风洞中作了进一步实验研究，实验成功地证实边界层的人工转捩位置可以用声激发振动控制，通过比较声激发装置的传递函数，声压和固定转捩位置所需的最小输入功率优了性能较佳的声激发装置，用大功率扬声器驱动产的声扰经模型内管道及模型表面上展向一排小孔传入边界层是一种有效可行的人工转捩控制方法，测量结果表明，强迫边界层转捩所需的声扰动强度对湍流边界层的速度型及壁面剪应力影响

Boundary Layer Transition Controlled by Acoustic Excitation Disturbances

A further expcrimental investigation of a controllable arti-ficial transition by means of internal acoustic excitation was carriedout in flat-plate boundary layers. The experiments successfully demons-rated that the artificial transition position can be controlled to some ex-tent by adjusting the input power of the acoustic generators so long asTollmien-Schlichting wave mode is attainable.This control has beenfound difficult in the high frequency bypass mode which can causeimmediate transition just behind the acoustic disturbance holes.Fourdifferent types of acoustic gcnerators were used to influence the transitionof the boundary layers.A More effcctive acoustic excitation device witha horn drivcr was found by comparing their transfer functions,soundpressure levels and transition threshold values.Meeasur ements of the velocity profiles of the boundary layer and the wall shear stressec on theflat plate were wade a pitot tube and two hot films respectively. Itwas found that the effects of acoustic excitation on the velocity profileand wall shear stress were very small.A reduction of the wall shearstress of about 2% was also observed at the downstream region not farfrom the acoustic disturbance holes at high frequency in excess of l kHz.