Towards plasma-based swirling jets

Adding an azimuthal velocity component to a stream coming out from a circular orifice leads to a swirling jet. Swirling jets are among the most common jet topologies present in industrial applications mostly thanks to their ability to enhance heat transfer [Huang, L. and El-Genk, M.S., 1998, International Journal of Heat and Mass Transfer, 41.3, pp.583-600]. They are usually made by means of helicoidal insets installed in the nozzle outlet. Given their versatility of use and their low intrusiveness, plasma actuators (PAs) have been considered as flow control devices in jet flows; although, mainly for aeroacoustics purposes [Crawley, M., Kearney-Fischer, M. and Samimy, M., 2012, 18th AIAA/CEAS Aeroacoustics Conference, p. 2211]. This preliminary study aimed to explore the feasibility of inducing a swirling motion to a circular jet by exploiting the momentum injection of the Dielectric barrier discharge plasma actuators (DBD-PAs). Using high-resolution planar PIV, the wall jet produced by an array of DBD-PAs, in quiescent air, was investigated at various PAs input signal’s voltage. The mechanical power output of the PAs was estimated from the time-averaged velocity fields obtained with PIV. This, together with electrical measurements assessing the consumed electrical power allowed estimating the efficiency at the tested operative conditions and for the considered configurations. Results indicate that with the current design only low swirl numbers could be obtained. A comparison was made between actively and passively induced swirling jets. The latter were obtained by means of 3D-printed helical insets. Various swirl numbers were tested and the relative time-averaged velocity fields were retrieved using a five-hole probe. A plasma-based active swirler proof-of-concept was developed and tested. The obtained flow field was measured and compared against the unforced circular jet and the passively generated swirling jets. The results obtained highlight a small and localized swirling effect underlining a control authority limited by the implemented design conditions. Future developments should consider a measurement setup with an increased dynamic range and new PAs with greater authority.