Breakdown of a low-speed streak caused by turbulent fluctuations

Abstract

Streak instability and subsequent breakdown caused by disturbances whose frequency-spectrum was similar to that of wall turbulence were examined experimentally. A low-speed streak was generated by using a small piece of wiregauze-screen and disturbanceswere introduced to excite the streak instability through two small holes behind the screen. Two kinds of turbulent signals having different spanwise coherency were considered. Occurrence and growth of sinuous instability modewere compared with those for anti-symmetric forcingwith the same frequencyspectrum. The results showed that the occurrence of sinuous instability mode was dependent on the spanwise coherency of the forcing disturbance.