An Experimental Study on Turbulent Boundary Layer Flow Control by Synthetic Jet through Spanwise Slot

Abstract

Active flow control for drag reduction in turbulent boundary layer is a hot research field nowadays. In order to explore the effect of the synthetic jet through a spanwise slot on the friction drag reduction of the turbulent boundary layer of a flat plate, the streamwise velocity are measured by a constant temperature hot-wire anemometer with and without synthetic jet. According to the measured experiment data, the mean velocity profiles, fluctuating velocity profiles, skewness and flatness are obtained respectively. Typical combinations of different frequencies and intensities of synthetic jet are selected to study the variation of the forcing effect in the streamwise direction. The experimental results show that the skin friction drag reduction in the turbulent boundary layer is related to the characteristics of the imposed synthetic jet and the distance between the local station and the slot. The synthetic jet leads to an increase of the skin friction drag in the station close to the slot, and as the flow moved downstream away from the slot, a reduction in the skin friction occurred with the tendency of firstly increasing and then decreasing. The reduction of skin friction caused by the synthetic jet of a higher frequency is more than that of a lower frequency. The power spectral density and autocorrelation of the fluctuating velocities indicate that the effect of the synthetic jet on the turbulent boundary layer decays in the streamwise direction.

Keywords

• synthetic jet
• turbulent boundary layer
• flow control
• hot-wire anemometer
• slot
• friction drag