Katasonov M.   Kozlov V.V.   Pavlenko A.M.  

Experimental investigations of disturbances generated by localized surface vibrations in a flat plate boundary layer

Reporter: Katasonov M.

In recent years, much attention has been paid to the study of laminar-turbulent transition at high or enhanced level of free-stream turbulence. Scenario of this transition was proposed by prof. Morkovin and called “bypass transition”. It is characterized by longitudinal localized disturbances, which is develops in boundary layer and create favorable conditions for the high-frequency wave disturbances (secondary instability, wave packets) that can subsequently transform into turbulent spots. The formation mechanism of secondary unstable oscillations is still far from complete understanding. At the present experiments the localized streaks are modeled in a Blasius boundary layer by means of membrane placed at flat plate surface. Membrane was driven by air pulse of 200 ms duration. Downstream development of artificial disturbances were investigated experimentally using hot-wire constant temperature anemometry. Investigations were carried out in the subsonic low-turbulent wind tunnels T-324 of ITAM SB RAS. Free stream velocity was in the range 3.5≤U≤18 m/s. The free stream turbulence level was 0.04%. As shown at previous experiments, the localized surface vibrations are produce two type of boundary layer disturbances: localized streaks and wave packets. At the adverse pressure gradient or separation area the amplitude of those wave packets grows. The present experiments with zero pressure gradient, are showed that wave packets, which appeared near the fronts of artificial streaks, were change their stability according linear stability theory. Wave packet amplitude grow, if his frequency belong to the unstable region (U=13–18 m/s), and decay if it is out of this range (U=3.5 and 11 m/s). At the same time, the streak magnitude decay downstream.
This work was supported by the project of the President of the Russian Federation for Leading Scientific Schools (NSH- НШ-8788.2016.1) and Russian Science Foundation 16-19-10330.

To reports list