Starting Issues and Forward-Facing Cavity Resonance in a Hypersonic Quiet Tunnel

Abstract

AFOSR/NA Unclassified and Approved for Public Release M.S. thesis by Rodrigo Segura with development of LDI for Mach-6 quiet tunnel and measurements in Mach-4 quiet tunnel Laminar-turbulent transition is a pivotal factor for the design of hypersonic vehicles but the mechanisms that induce transition are not well understood. A laser differential interferometer (LDI) is a non-intrusive optical device that measures the optical path length difference between two laser beams. The LDI is a reliable calibrated instrument to assist the study of boundary layer instability-wave growth in hypersonic flow and has high sensitivity and frequency response. An LDI with a commercial balanced photodetector capable of detecting optical path length differences of lambda/21,000 from DC to 80 MHz was assembled and tested in the Purdue Quiet-Flow Ludwieg tube. Fluctuations in the subsonic region of a forward-facing cavity were measured with the LDI and compared to those detected with a Kulite pressure transducer at the base of the cavity. Predictions of self-resonating deep cavities were confirmed. The LDI was then adapted and transferred to the Boeing/AFOSR Mach-6 Quiet Tunnel. hypersonic boundary layer transition optical instrument supersonic cavity flow oscillations experiment Unclassified Unclassified Unclassified Unlimited 151 ii Este trabajo va dedicado a mi papá, mi mamá, mi hermano, y mi Dios. A ustedes les debo todo lo que soy. iii ACKNOWLEDGMENTS I want to thank my advisor, Professor Steven P. Schneider for building and managing the hypersonic wind tunnels at Purdue University and giving me the opportunity to work on this project. Had it not been for his vote of confidence, the LDI would sit in a drawer for years to come. Furthermore, his expertise and frankness helped me get through the difficulties encountered in this experimental research. I would also like to thank my committee members, Professors Steven H. Collicott and Anastasios S. Lyrintzis, their guidance and suggestions are appreciated. The machinists and technicians at the Purdue Aerospace Sciences Laboratory were extremely helpful during the course of the project. I thank them for their excellent craftsmanship and valuable technical assistance. I would like to express my special gratitude to Madeline Chadwell, Robin Snodgrass, and John Phillips all of whom went out of their way to assist me with unexpected experimental breakdowns on multiple occasions. Jerry Hahn and Jim Younts were also included in that crew. The office and information systems staff at the Aeronautical and Astronautical Engineering department at Purdue University also played an important role. Linda Flack's timely reminders made the logistics of my academic life easy. I would like to give special thanks to Joan Jackson; she made me laugh and was patient and helpful even when I demanded her help on rather short notice. Joe Kline's technical assistance is appreciated. A great deal of contribution came from my fellow researchers.

Roughness-Induced Instability in a Hypersonic Laminar Boundary Layer

“…Several methods were used to control separation of the nozzle-wall boundary layer caused by the diffuser section and its various inserts [28]. This separation was visible as a large low-frequency oscillation that occurred simultaneously on the signals from the probe and the wall hot films.…”

Measurements of Resonance in a Forward-Facing Cavity at Mach Six

“…A decrease of the maximum quiet conditions of the Mach 4 quiet tunnel during the 2000s forced Juliano et al to test their cavity model at lower freestream pressures than Ladoon et al [13]. It is interesting to also note that Ladoon et al tested cavity depths ranging from L∕D 0.272 to 1.984 and could not find the critical depth [13,14]. It is unclear why Ladoon et al [13] was unable to determine the critical depth using the same method as Juliano et al [14].…”

“…In the late 2000s, Juliano et al [14] found the critical depth for a similar model in the same facility as used by Ladoon et al [13]. Juliano et al [14] adjusted the L∕D from 0.5 to 3.0, and pressure fluctuations were compared for each depth tested in the experiment.…”

“…Juliano et al [14] adjusted the L∕D from 0.5 to 3.0, and pressure fluctuations were compared for each depth tested in the experiment. The rms amplitude of the pressure fluctuations within the cavity increased by about two orders of magnitude near L∕D 1.2, which is the critical cavity depth [14].…”

“…Juliano et al [14] adjusted the L∕D from 0.5 to 3.0, and pressure fluctuations were compared for each depth tested in the experiment. The rms amplitude of the pressure fluctuations within the cavity increased by about two orders of magnitude near L∕D 1.2, which is the critical cavity depth [14]. A decrease of the maximum quiet conditions of the Mach 4 quiet tunnel during the 2000s forced Juliano et al to test their cavity model at lower freestream pressures than Ladoon et al [13].…”