Quantitative schlieren imaging coupled with inverse Abel transformation for flow field studies in a cylindrical surface DBD

Abstract

The present work is devoted to the proper application of the schlieren imaging technique, combined with inverse Abel transformation, to record the flow field induced by atmospheric pressure cold plasmas, in a quantitative manner. Theoretical principles, along with meaningful diagrams, design of the schlieren setup, and involved calibration process, are given in detail. It is demonstrated that erroneous conclusions may be reached if Abel transformation is omitted. The concept is employed to study flow field parameters around a surface dielectric barrier discharge, operating in ambient air and having a cylindrical configuration, rather than a typical planar design. Maximum density and lowest temperature equal to 1.24 kg m -3 and 285.4 K, respectively, and lowest density and maximum temperature equal to 1.11 kg m -3 and 318.8 K, respectively, downstream of the driven electrode and close to the surface are identified with respect to the unperturbed air where density equals 1.21 kg m -3 and temperature equals 291.5 $K$. The temperature and density patterns unveil intense perturbations at shorter distances from the surface and lower amplitudes of the sinusoidal (10 kHz) voltage that sustains the discharge. Electrohydrodynamic effects seem to dominate over thermal mechanisms in governing the flow field. The importance of the quantitative schlieren technique, as a non-invasive one, in the study of dielectric barrier discharges is justified by the interest that they attract in numerous demanding cases of plasma-assisted flow field control (propulsion, actuators, etc.).