Abstract: Aiming at the active thermal protection problem of aerodynamic heating, ideal wet wall（IWW）for analyzing the heat transfer characteristics of transpiration cooling on the outer surface of aircraft was proposed. It assumes a thin layer of coolant exists on the surface, simplifying the complex multi-scale flow and heat/mass transfer processes in transpiration cooling into the ejection effect of the phase-change gas on the boundary layer. Focusing on a two-dimensional porous flat plate, the study establishes a partitioned model coupling the high-temperature mainstream boundary layer, the ideal wet wall, and the internal flow within the porous medium, which is then solved numerically. The simulation conditions are set with a mainstream total temperature of 5200 K, an inlet velocity of 3042 m/s, and an initial temperature of 300 K for both the coolant (water) and the solid wall. Numerical results indicate that the presence of the IWW significantly reduces the heat flux transferred to the porous medium. Furthermore, the vast majority of incoming heat is carried away by the liquid water, maintaining the porous wall surface temperature below the saturation temperature of liquid water phase change, resulting in a net heat flux approaching zero. Additionally, arc wind tunnel experiments were conducted to validate the numerical results. At a coolant mass flow rate of 37.5 g/(m²·s), the calculation error for the porous wall surface temperature was 12.5%; at a flow rate of 50 g/(m²·s), the error decreased to only 0.6%, confirming the IWW model's capability to accurately explain experimental phenomena. Under the investigated conditions, this model resolves the difficulties associated with phase interface tracking and high computational complexity in transpiration cooling simulations, while revealing the distribution laws of heat flux density and temperature across the porous wall under various coolant flow rates.