Effectiveness of thermionic emission for cooling hypersonic vehicle surfaces

Electron transpiration cooling (ETC) is a proposed thermal management approach for the leading edges of hypersonic vehicles that utilizes thermionic emission to emit electrons to carry heat away from the surface. This paper presents a modeling approach for implementing ETC in a computational fluid dynamics (CFD) framework and assesses the modeling approach using a set of previously completed experiments. The modeling approach includes coupling the fluid modeling to a material response code to model in-depth surface conduction and accounts for space-charge-limited emission. The effectiveness of ETC for multiple test cases are investigated including a case with a sharp leading edge, case with in-depth material conduction, and a blunt body (i.e. capsule). For each of these test cases, ETC affects the surface properties, most notably the surface temperature, suggesting that ETC occurs for bodies in thermally intense, ionized flows, no matter the shape of the leading edge. An equation is provided to estimate the heat transfer induced by ETC.