Experimental study of a turbulent pipe flow through a fractal plate

Abstract

We study flows forced through plates in a circular wind-tunnel. The plates are based on different iterations of a pattern which would correspond to the generation of a fractal object. Two types of patterns are considered: one leading to an orifice with a fractal perimeter, the other to a fractal equivalent of a perforated plate. We propose this approach as a systematic way to introduce scales forcing and construct a scale by scale multiscale flow. For the sake of comparison we also consider simple orifice plates having a different number of sharp edges but which are based on a single scale geometry (monoscale orifices). In terms of analysis we focus on the pressure drop across the plate as in terms of engineering application this is the most salient effect of the plate multiscale generation. We measure the pressure recovery as a function of the distance from the plate. We also use hotwire anemometry to understand the action of the fractal-based plate on the flow and measure velocity statistics on the pipe's axis. We found that as far as pressure drop recovery is concerned, it is not always necessary to choose large numbers of iteration for the fractal pattern. However, the velicity statistics can remember the order of the fractal generation over a long distance. In certain cases it would require a very long pipe to quantify the full recovery from the fractal-generated turbulent flow.