Abstract
Instability characteristics observed in a micro-cavity swept by a visco-elastic fluid has been investigated. Surfactant solution used as a viscoelastic fluid was inserted in a micro-cavity whose length, depth and wide low path were set constant at 1, 0.2 and 0.4 mm, respectively. The time variation of the tonguing motion of the separation bubble formed in the downstream region in the cavity was measured when the Reynolds number defined with water viscosity, cavity depth and the mean velocity in a narrow flow path was change in three steps: 1, 5 and 20. From the results, it was found that the fluctuation time scale is from 1.9 to 4.5 s, which is located between the middle and longest relaxation times. It was also found that the time scale does not depend on the Reynolds number.
