Robust Optimization of an Aircraft Power Thermal Management System

The thermal management of modern aircraft has become more challenging as aircraft capabilities have increased. The use of thermally resistant composite skins and the desired for low observability, reduced ram inlet size and number, has reduced the ability to transfer heat generated by the aircraft to the environment. As the ability to remove heat from modern aircraft has decreased, the heat loads associated with the aircraft have increased. Early in the aircraft design cycle uncertainty exist in both aircraft requirements and simulation predictions. In order to mitigate the uncertainty it is advantageous to design thermal management systems that are insensitive to the design cycle uncertainty. The risk associated with design uncertainty can be reduced through robust optimization. In the robust optimization of the thermal management system three noise factors were selected: 1) engine fan air temperature, 2) avionics thermal load, and 3) engine thrust. The three controllable factors selected for the robust optimization were: 1) compressor pressure ratio, 2) return fuel heat exchanger (RFHX) area, and 3) recuperator heat exchanger (RHX) area. The robust optimization of the thermal management system identified the engine fan air temperature and the avionics thermal load as the dominate noise factors. The worst case noise factor combination resulted in a 258% increase in return fuel heat load. The robust optimization identified the compressor ratio as the dominate control factor followed by the RFHX area. The optimization of the controllable factors resulted in a 51% reduction in the mean return fuel heat load and a 63% reduction in return fuel heat load variance. The risk associated with design cycle uncertainty can be minimized through the employment of the robust optimization methodology.