Boundary range sensitivity of nanosecond pulse diffuse discharges in atmospheric air: Simulation analysis based on axisymmetric fluid model

Diffuse discharges generated by fast rising edge of nanosecond pulses possess a larger discharge radius than classic streamer discharges. However, existing simulation studies often employ boundary ranges similar to those used for simulating streamer discharges, thus neglecting the influence of the boundary range on their characteristics. In this work, the characteristics of diffuse discharges in atmospheric-pressure air are investigated using a fluid model. The research focuses on the influences of plasma and Poisson equation boundary ranges, especially the top and right boundaries of the rectangular computational domain, on discharge evolution. The comparison between numerical simulations and experimental results reveals several key findings: When both plasma and Poisson equation boundaries are set to 5 cm×5 cm (exceeding six times the maximum discharge radius), the simulated discharge width and propagation velocity accord well with experimental measurements. However, consistent delays are observed in simulating the time required to reach the plate electrode, highlighting the inherent limitations of current fluid models in accurately simulating temporal scales. Reducing the plasma boundaries results in negligible fluctuations in electric field strength and electron density at the discharge head, indicating a minimal effect on macroscopic discharge characteristics. Narrowing the Poisson equation’s right boundary significantly reduces the discharge width while simultaneously increasing the discharge width relative to the domain size. Asymmetric propagation patterns occur between the upper and lower halves of the discharge gap. Nevertheless, appropriate reduction of the right boundary improves morphological consistency with experimental observations, thereby suggesting practical optimization strategies. Conversely, reducing the top boundary weakens the electric field “focusing effect” at the discharge head, homogenizes the spatial field distribution, and delays accelerating, thereby exacerbating deviations from experimental data. These results demonstrate that Poisson boundary conditions critically govern spatiotemporal discharge dynamics. Top boundary truncation significantly reduces the simulation accuracy, whereas adjusting the right boundary allows for a balanced optimization between computational efficiency and result reliability. This work provides theoretical guidance for selecting boundary conditions in the numerical modeling of diffuse discharges.