Thermoacoustic Oscillations in Supercritical Fluid Flows

Pressure oscillations in supercritical Jet-A fuel flowing through four parallel, heated tubes connected to common manifolds have been observed in this study. Tests were performed with fuel inlet temperatures ranging from 70F to 700F, and fuel pressures ranging from 360-700 psi. Total fuel flow rate ranged from 5-55 lb/hr. Tubes were heated by blowing 800-950F nitrogen over them. Acoustic-mode oscillations, typically ranging from 100-500 Hz, occurred only when a large temperature gradient was created inside the heated fuel tubes. Pressure oscillation amplitudes ranged from 0.1-1.0 psi. Oscillations at the inlet and outlet manifolds that were caused by a mode with the characteristic length of a single fuel tube were separated by a phase lag that was a function of the manifold cross-passage diameter. A lower-frequency mode was also observed, which had a characteristic length based of the summed lengths of a single fuel tube and a single manifold passage. An acoustic simulation using the COMSOL Acoustics Module was performed to predict frequencies based on geometry and flow conditions of the experiment