Separation Delay on an Airfoil: DBD Plasma Actuator

Description

This project simulates the use of Dielectric Barrier Discharge (DBD) plasma actuators to prevent boundary layer separation on a NACA 0012 airfoil using ANSYS Fluent. Flow separation on the suction side of an airfoil reduces lift, increases drag, and in severe cases causes stall, all driven by the boundary layer losing enough energy to detach from the surface. DBD actuators address this without moving parts: a high voltage difference between cathode and anode ionizes the surrounding air into plasma, generating an electrical current that in turn produces a magnetic field, which acts on the ions in the boundary layer and adds momentum back into the flow, suppressing separation. The airfoil has a chord length of 0.1 m and carries two DBD actuators, one near the point of maximum thickness and one near the trailing edge. Two flow cases are studied: 50 m/s at 15° angle of attack, and 20 m/s at 12° angle of attack. The geometry is built in SpaceClaim and meshed in ANSYS Meshing with a structured grid of 463,701 elements.

Methodology

Turbulence is resolved with the k-epsilon model, and the energy equation is active. The electromagnetic physics — voltage distribution, and the x and y components of the magnetic vector potential — are introduced through three User-Defined Scalars (UDS), with their steady-state transport equations solved alongside the flow equations. A source term in the magnetic field transport equations is added via a UDF, using an electrical diffusion coefficient of 0.5 for ionized air and a magnetic permeability of 1.2566×10⁻⁴. Current density components are computed from the potential field, and the resulting electromagnetic body forces are fed back into the flow through three additional source terms: one each in the energy equation, x-momentum equation, and y-momentum equation, all implemented via UDFs. User-Defined Memory (UDM) is used to store and expose the current density vector for post-processing. Air density follows the ideal gas law throughout.

Analysis

Velocity and pressure contours around the airfoil, along with velocity vectors, are obtained for both flow cases, confirming that the plasma-induced body force effectively suppresses boundary layer separation that would otherwise occur at these angles of attack. Lift coefficient results and surface pressure distributions along the airfoil are reported for each case, quantifying how much the DBD actuation improves aerodynamic performance relative to an uncontrolled baseline, and demonstrating that the UDF-based electromagnetic coupling is delivering the intended momentum addition to the boundary layer.