A Systematic Study on the Mechanical and Thermal Properties of Open Cell Metal Foams for Aerospace Applications

Abstract

Jet engine operating temperatures have been on the rise since the inception of the jet engine. High Operating temperatures mean increased efficiency, more power, and lesser emissions. However, operating temperatures of jet engines are limited by the operating temperatures of the turbine material. This temperature must not be exceeded or else it will damage the turbine components. To solve this problem, complex cooling schemes have been adopted. They employ the use of outside air to dilute the high combustion temperatures to make them suitable for turbine section exposure. This leads to a non-uniform temperature profile leaving the combustion area and therefore decreasing the overall engine performance by introducing thermal cycling and inconsistencies in operational temperatures. This research suggests placing an ultra-high temperature open cell metal foam ring in front of the combustion area and directly before the turbine section. Open cell foam with their 3-dimensional geometry help mix the hot and cool gasses entering the turbine area creating a more uniform temperature profile. This increases efficiency by raising the operational temperature of the jet engine. It also contributes to an increased lifetime since the mixing function of the metallic foam will reduce thermal cycling fatigue on turbine vanes and blades. This research presents a full investigation on the feasibility of this idea; it studies the potential of producing ultra-high temperature metallic foam from a list of currently available as well recently engineered materials. This work also investigates the pressure drop and heat transfer associated with the foam for a full assessment of the design. Infrared imaging for heat transfer measurements done on Al foam of 5 and 10 PPI (pores per inch) samples showed the mixing role of the metal foam as a function of thickness; it showed improvement of the temperature profile resulting from the averaging the hot and the cool gasses. Pressure drop testing provided data on pressure drop in Al foams in the compressibility region of air. Up to this point, similar data was not available. Pressure drop testing revealed that with careful design of pore size, ligament thickness and foam thickness, taking into consideration heat transfer capabilities of the foam, a feasible design of an ultra-high temperature open cell foam ring can be achieved with minimal pressure drop and increased heat transfer capabilities.