Abstract
The WAll Turbulence Active COntrol (WATACO) project aims at achieving reduction of the drag exerted by a turbulent flow on the flow-exposed surfaces by means of active flow control (AFC) techniques. The flow types considered are both internal (pipe and channel flows) and external (boundary layer flows) with or without an external pressure field and explore a broad range of Reynolds numbers. The project considers both an experimental and a numerical research approach. The considered flow forcing will be provided by wall-mounted dielectric barrier discharge (DBD) plasma actuators (PAs) arranged into streamwise-aligned arrays and lain out such to induce a crossflow-oriented flow along the positive and negative direction alternatively. This configuration leads to an induced flow similar to the one caused by oscillating the flow-exposed wall. This forcing, when performed on turbulent flows, has shown huge values of net power saving, thus largely overtaking passive flow control approaches, due to the hindering of the turbulence-generation mechanisms and related friction drag reduction (Ghaemi, 2020, Physics of Fluids). WATACO deploys a research group, from two research institutions (Politecnico di Torino and Università di Bologna), with extended expertise on both the project's areas of research: flow control and, in the specific wall-turbulence control, and plasma actuators science. The group members feature younger and expert researchers which have already worked together in previous projects and showed a very good degree of cooperation. The project PI is Jacopo Serpieri, from PoliTO, who has considerable experience with PAs for AFC for both internal and external flows. The project co-PI is Artuto Popoli, from UniBO, expert in the fields of plasma-actuators science and electrical engineering. The project aims at developing the flow actuators to be then deployed in a channel flow and a boundary layer flow facility as well as in the world unique CICLoPE pipe flow facilities. The experiments will encompass a variety of flow diagnostics aimed at both global-effect and local-in detail investigations of the actuation outcomes. Furthermore, numerical simulations, for the channel-flow case, will also be carried out making use of a high-accuracy (DNS), computationally affordable (minimum box) code. These simulations will implement reliable body force fields generated by the PAs. These fields will be retrieved by the solution of the drift-diffusion problem describing the DBD discharge by means of accurate simulations eventually validated by ad hoc experiments. Finally, the experimental activities on the external flow, subject or not to an external pressure field, will shed light on the performance of the considered actuation when developing flows are operated. Pressure drag manipulation, along with the friction drag, is likely to occur and needs to be assessed towards a correct evaluation of the efficiency of the deployed AFC. Results The PRIN 2022 PNRR “WAll Turbulence Active COntrol” (WATACO) project investigated plasma-based active flow control for turbulent skin-friction drag reduction, focusing on arrays of wall-mounted plasma actuators designed to generate spanwise oscillating forcing at the wall. The project combined experimental characterization, numerical modelling and flow simulations, integrating expertise in fluid dynamics, flow control, electrical engineering and non-thermal plasma physics. A central activity was the systematic characterization of oscillating plasma actuators in conditions relevant to turbulent-flow control, including high-Reynolds-number conditions. The actuators were used as an experimental platform to study how plasma-induced forcing interacts with near-wall turbulent structures. This required the development of thin, durable and scalable actuator arrays, including PCB-based solutions and dedicated power-electronics strategies, suitable for operation over surfaces of increasing size. The actuator response was studied through optical, electrical and thermal diagnostics. High-speed Schlieren imaging, with acquisition rates up to 10,000 fields per second, provided time- and space-resolved measurements of the transient plasma-induced flow and of the vortical structures generated by the discharge. These measurements were complemented by induced jet velocity, absorbed electrical power, actuator capacitance in plasma-OFF and plasma-ON conditions, and discharge-induced temperature. This characterization provided quantitative information on actuator performance, operating limits, repeatability and scaling behaviour. On the computational side, WATACO developed a hierarchy of plasma-actuator models, from phenomenological and semi-empirical descriptions of the plasma-induced body force to unsteady two-dimensional drift-diffusion-reaction models with non-equilibrium plasma kinetics. The resulting forcing fields were used as input for direct numerical simulations of the induced flow in laminar and turbulent conditions, supporting the interpretation of the experiments and the analysis of the control mechanisms. Overall, WATACO contributed to the understanding of how oscillating plasma actuators modify near-wall turbulent flows and under which conditions they can promote drag reduction. The project produced experimental datasets, diagnostic methodologies and computational tools that can support future studies on actuator design, electrical actuation strategies and plasma-based flow-control technologies.
Project details
Unibo Team Leader: Arturo Popoli
Unibo involved Department/s:
Dipartimento di Ingegneria dell'Energia Elettrica e dell'Informazione "Guglielmo Marconi"
Coordinator:
Politecnico di TORINO(Italy)
Total Unibo Contribution: Euro (EUR) 117.000,00
Project Duration in months: 24
Start Date:
30/11/2023
End Date:
28/02/2026
