Effects of Flow Passage Expansion or Contraction on Jet-Fuel Surface Deposition

The vast majority of previous flow studies of jet-fuel autoxidative deposition have been performed using straight cylindrical tubing of a constant diameter despite the fact that real aircraft fuel systems and nozzles contain complex flow passageways. As a result, the role of this complex flow environment and the resulting changes in heat transfer and flow on fuel oxidation/deposition chemistry are poorly understood. In the current work, experiments and computational fluid dynamics (CFD) modeling were performed for jet fuel flowing through heated tubes that have either a sudden expansion or contraction to study the effect offlowpath changes on fuel oxidation anddeposition.The experiments were conducted under isothermal wall (205 C), laminar flow conditions with monitoring of the outlet dissolvedO2 and post-test measurement of the surface carbon profile. The fuel flow rate was varied to study the role of residence time and oxidation extent on deposition near the geometry change. The CFDmodel includes a chemical kinetic mechanism, which was used to simulate the autoxidative deposition chemistry. With an expansion, the peak deposit occurs in the wide secondary tube. TheCFD simulations show increased deposition caused by a recirculation zone after the flow expansion. For the contraction, increased deposition occurs at the beginning of the narrow secondary tube.