This experimental study compares the effectiveness of steady and pulsed air jet vortex generators (AJVGs) with an acoustic synthetic jet. The results showed that: ⅰ) The flow physics associated with the formation of the boundary later embedded streamwise vortices by steady AJVG blowing is different to that occurring with corresponding pulsed air jet blowing, where a well defined vortex does not appear to be forming. This supports the view that the physical mechanism involved with pulsed air jets involves the formation of a "train" of discrete vortical structures which locally promotes significant levels of mixing and boundary layer re-energization, ⅱ) Acoustic synthetic jets, at least using the technology employed in this study, cannot cause the large scale distortions of turbulent boundary layers in moderate to high speed flows which are seen with AJVG blowing and are known to be effective in promoting the high levels of mixing necessary for the re-energization of turbulent boundary layers.
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