Jet suppression and parameter optimization in dual-throat Ludwieg tube wind tunnel using porous plate

Although the dual-throat Ludwieg tube wind tunnel can effectively suppress fast-opening valve disturbances, the high-speed jet induced by the sharp expansion of the first Laval nozzle severely damages the spatial uniformity of the downstream flow field. To mitigate this jet effect, an aerodynamic flow conditioning scheme involving the introduction of a porous plate at the inlet of the settling chamber is proposed. Based on unsteady numerical simulations, the effects of the damping coefficient, thickness, and configuration of the porous plate on the jet structures within the settling chamber flow field—both before and after stable wind tunnel operation—are investigated. Furthermore, the distribution patterns of the Mach number and turbulent kinetic energy (TKE) at the exit of the main Laval nozzle are quantitatively evaluated. The results indicate that the jet suppression efficacy of the porous plate is highly dependent on its aerodynamic and geometric parameters. An optimal damping coefficient exists (ζ = 2.11×10⁷); an excessively high damping coefficient can suppress the shock/expansion wave systems in the core flow region but incurs significant stagnation pressure losses and degrades the spatial uniformity of the Mach number distribution. Additionally, an optimal thickness is identified (h = 10 mm), beyond which internal micro-jet coalescence occurs within the porous plate, triggering large-scale jet structures that degrade the flow field quality. Addressing the dynamic instability induced by a single-stage thick porous plate, this paper verifies the superiority of a dual-stage flow conditioning configuration. Through the spatial truncation and multi-stage dissipation of the initial wakes, this layout successfully disrupts the low-frequency, large-scale jet structures, thereby effectively mitigating the global instability of the wind tunnel. This study clarifies the aerodynamic dissipation mechanisms of porous plates in dual-throat Ludwieg tube wind tunnels, providing valuable guidance for the design and optimization of low-disturbance flow fields in hypersonic wind tunnels.