Mechanism of ionic wind enhancement by micro-/nanoprotrusion-induced local electric field modulation in a needle–ring electrode system

Ionic wind devices are promising for electronic cooling, active flow control, air purification, and microfluidic actuation, but conventional electrodes have limited discharge sites and relatively large dimensions, restricting further performance improvement. Although introducing micro/nano protrusions on the electrode surface can enhance the local electric field and extend the ionization region, their effects on electric field distribution, space charge transport, and ionic wind enhancement remain poorly understood. To address this, a two-dimensional axisymmetric ionic wind model coupling the drift-diffusion-Poisson equations with the incompressible Navier–Stokes equations was established and validated against experimental data from a bare needle-ring electrode. On this basis, the influences of protrusion size, position, discharge gap, spacing, and number on the ionic wind were systematically investigated, and an enhancement factor was introduced to quantify the reinforcing effect of the protrusions. The results indicate that small protrusions strengthen the ionic wind by reshaping the local electric field and increasing the space charge density near the needle tip. A 15 μm protrusion yields an enhancement factor of about 1.06, whereas oversized protrusions disturb or shield the primary discharge region and weaken the ionic wind. The optimal enhancement is achieved when the protrusion is located at approximately 100 μm away from the needle tip, while the effect becomes negligible at 1500 μm. As the discharge gap increases from 0 to 15 mm, the enhancement factor decreases from about 1.06 to 0.90. For double protrusions, the optimal spacing is 500 μm, and increasing the number of protrusions further raises the ionic wind velocity. These findings offer theoretical guidance for the design of micro/nano-structured electrodes in high-performance ionic wind generators.