Developing an Application for Refractory Open Cell Metal Foams in Jet Engines
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NN11.3.1
Developing an Application for Refractory Open Cell Metal Foams in Jet Engines
Wassim E. Azzi, William L. Roberts and Afsaneh Rabiei* Department of Mechanical and Aerospace Eng., North Carolina State University 3211 Broughton Hall, 2601 Stinson Dr. Raleigh, NC 27695-7910 ABSTRACT The thermodynamic efficiency of the Brayton cycle, upon which all gas turbines (aeropropulsion and power generation) are based on scales with the peak operating temperature. However, the peak temperature is limited by the turbine blades and the temperature they can withstand. The highest temperatures in the gas turbine occur in the combustor region but these temperatures are often too high for turbine blades. As a result, the combustion products must be diluted with relatively cooler air from the compressor to reduce the temperature to tolerable levels for the turbine blades. This research suggests placing a ring of high temperature open cell metal foam between the combustors and turbine sections of the jet engine to mix and average the difference in temperatures resulting from the cooling schemes in combustor cans. Temperature mixing effect was tested using a special setup with the application of an infrared camera and streams of hot and cold air passing through the foam. High speed flow pressure drop around Mach 1 (340 m/s) was done on the same foam samples to understand pressure drop in the compressible regime of air. Infrared imaging showed that open cell metal foams successfully mixed and averaged the difference in temperatures of the hot and cold gasses thus creating a more uniform temperature profile while pressure drop testing revealed that open cell metal foams result in minimal pressure drop at high flows especially when the increase in temperature in taken into consideration. INTRODUCTION Jet engine operating temperatures have been on the rise since the inception of the jet engine [1]. High Operating temperatures can cause increased efficiency, more power, and fewer 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 inconsistencies in operational temperatures [2]. This research suggests placing an ultra-high temperature open cell metal foam in front of the combustion area and directly before the turbine section. Infrared imaging and high velocity flow pressure drop testing were performed in this study to validate the idea and feasibility of the idea EXPERIMENTAL PROCEDURE *
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Pressure Drop Testing Pressure drop testing has been done on numerous kinds of foams[3,4]; however, all th
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