Hot Streak Characterization in Serpentine Exhaust Nozzles

Abstract

Abstract : Modern aircraft of the United States Air Force face increasingly demanding cost, weight, and survivability requirements. Serpentine exhaust nozzles within an embedded engine allow a weapon system to ful ll mission survivability requirements by providing denial of direct line-of-sight into the high-temperature components of the engine. Recently, aircraft have experienced material degradation and failure along the aft deck due to extreme thermal loading. Failure has occurred in speci c regions along the aft deck where concentrations of hot gas have come in contact with the surface causing hot streaks. The prevention of these failures will be aided by the accurate prediction of hot streaks. Additionally, hot streak prediction will improve future designs by identifying areas of the nozzle and aft deck surfaces that require thermal management. To this end, the goal of this research is to observe and characterize the underlying ow physics of hot streak phenomena. The goal is accomplished by applying computational uid dynamics to determine how hot streak phenomena is a ected by changes in nozzle geometry. The present research rst validates the computational methods using serpentine inlet experimental and computational studies. A design methodology is then established for creating six serpentine exhaust nozzles investigated in this research. A grid independent solution is obtained on a nozzle using several gures of merit and the grid-convergence index method. An investigation into the application of a second-order closure turbulence model is accomplished. Simulations are performed for all serpentine nozzles at two ow conditions.The research introduces a set of characterization and performance parameters based on the temperature distribution and now conditions at the nozzle throat and exit. Examination of the temperature distribution on the upper and lower nozzle surfaces reveals critical information concerning changes in hot streak phenomena due to changes