Christian Dittert , Hannah Böhrk and Stefan Löhle

DOI Number XXX-YYY-ZZZ

Conference Number HiSST 2018-2280892

A re-entry body with sharp leading edges has advantages in aerodynamic performance, but the expected thermal loads exceed the limits of known materials. Active cooling methods are one possibility reducing surface temperatures to below the operating temperature of the used materials. The cooling effect of transpiration cooling is achieved through two basic mechanisms. When flowing through a porous, permeable material, the heat load is convectively transferred from the material to the fluid. As soon as the fluid flows out on the outside, it additionally forms a cooling film on the outside of the material, which reduces the heat flow acting on the material. However, pressure and temperature gradients along the leading edge geometry are redirecting the cooling flow in the direction of less loaded areas. This paper presents that transpiration cooling can be effectively used for cooling sharp leading edges as demonstrated during a plasma wind tunnel campaign at the Institute of Space Systems. During this campaign a wedge geometry comparable to a re-entry leading edge with adaptable permeability, was successfully tested at re-entry heat flux conditions with different cooling mass flows rates. In addition to the plasma wind tunnel tests, the structural design and the manufacturing of the wedge are presented as well. Reference measurements without cooling indicated surface temperatures up to 1600K near the stagnation point. First results with cooling showed that even for small cooling mass flows (0.85g/s) a cooling efficiency of over 50% can be achieved for the tip area. Towards the rear region the cooling efficiency is even increasing up to 70%. Additional measurements with different angles of attack indicate that oblique shocks have an effect on the outflow distribution. Finally, the wedge geometry is assessed with regards to its applicability as leading edge on the basis of the material temperatures determined during cooling.

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In Categories: HiSST 2018, Materials and Structures, Supersonic and Hypersonic Aircraft Design, Thermal and Energy Management Systems, Thermal Protection Systems
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