Turbulent characterization generated by an active grid in a circular geometry.

Experimentally inducing turbulence is of importance in understanding many practical flows.Recently active grids have been used to control the turbulence intensity and the integral length scale. However, these studies are almost exclusively based on diamond grids inserted in a square section. The aim of the current study is to design and test an active grid suitable for small diameter circular sections, with the ultimate goal of controlling inlet conditionsfor reacting flows. The characterization of the turbulence created by the circular sector paddles includevarious parameters such aspaddle rotationspeeds, number and shapes of paddles andnumber of active gridstages. These parameterswere tested and compared in order to find the most efficient way to obtain a high level of turbulence intensity whileretaininghomogeneity. High turbulent intensities in the range of 10 to 20{\%} were achieved using the circular geometry, which was comparable to that of previous square geometry studies. These experiments and results will enable the study of high intensity turbulence in circular geometry.