Large eddy simulation study of supercritical n-decane flow in jet-regenerative cooling channels: thermo-hydraulic behavior of circular vs. oval jet impingement configurations

Active regenerative cooling technology represents one of the effective approaches for reducing combustion chamber wall temperatures. Large Eddy Simulations (LES) have been conducted to investigate the flow and heat transfer behavior of supercritical n-decane within various regenerative cooling channels. The simulation findings demonstrate that in contrast to flat regenerative cooling channels, jet regenerative cooling channels substantially amplify turbulent disturbances and efficiently disrupt the growth of the fluid boundary layer. This is achieved through the combined mixing and perturbing actions of jet impingement and crossflow, ultimately yielding a notable 50.32 % enhancement in local maximum heat transfer efficiency. When the temperature draws near to the pseudo-critical point, the thermophysical properties of n-decane experience significant alterations, resulting in localized temperature fluctuations of the wall. Moreover, the smaller the hydraulic diameter, the faster the jet velocity, and the stronger the generated disturbances. When compared to circular jet orifices, oval ones prove more effective in facilitating lateral expansion of the fluid upon wall impingement, thereby minimizing kinetic energy losses. Specifically, at a hydraulic diameter of 0.3 mm, the average wall temperature of oval jets is 74.1 K lower than that of circular jets. The heat transfer process of supercritical n-decane within jet regenerative cooling channels comprises three distinct phases: a buoyancy-driven laminar acceleration phase, a shear-induced turbulent transition phase, and a fully developed turbulent stabilization phase.