This study focuses on the mechanism of flow-acoustic coupling in a T-junction, which has a transitional section entailing an expansion of pipe diameter. Six cases with varying length of the transitional section have been tested. It is shown that T-junctions with transitional sections can be a strong source of acoustic excitation and therefore can cause powerful acoustic resonance in the associated piping systems. Elimination of the transitional section reduces the excitation level drastically. The length of the transitional section with enlarged diameter is found to be the fundamental length scale determining the Strouhal number of flow excitation in the T-junction. To investigate the mechanism further, a series of experiments were conducted in a rectangular pipe system, which was considered as the 2D case of the T-junction. The results showed that the vortices formed in the outer and inner sides of the T-junction are both acoustic sources. They appear to form independently without interaction with each other, but are synchronized by the acoustic field. Flow visualization was carried out to gain images of the flow pattern when the resonance occurs. The images from flow visualization provided support to the measurements of the rectangular pipe system. Numerical simulations of the mean flow and acoustic field in the rectangular T-junction were performed. A simplied analysis of acoustic energy generation was also carried out. / Thesis / Master of Applied Science (MASc)

Call number: LD2668 .T4 1934 V41

No description available.

No description available.

Manipulation of high-speed duct flow by streamwise vorticity concentration that are engendered by interactions of surface-mounted passive and active flow control actuators with the cross flow is investigated experimentally in a small-scale wind tunnel. The controlled formation of these streamwise vortices can be a key element in the mitigation of the adverse flow effects in a number of applications including aero-optical aberrations owing to unsteady local transonic shocks, pressure recovery and distortion due to secondary flows in embedded propulsion system, thrusts reversal and augmentation for aerodynamic control. The effects of the actuation are investigated using various converging-diverging inserts along one of the test section walls. Passive actuation includes micro-vanes and active actuation is effected using high-frequency, surface-mounted fluidic oscillators. Hybrid actuation is demonstrated by combining the passive and active actuation approaches to yield a “fail-safe” device with significant degree of controllability. The investigations consider the effects of the surface actuation in three application areas namely, stabilization of transonic shocks, suppression of total-pressure distortion in offset ducts, and mitigation of separation in internal flow turning.

Self-assembly of nanoscale materials to form intriguing structures has garnered considerable attention due to their potential applications in optical, electronic, magnetic and information storage devices. Among all the efforts to pattern functional polymers and nano materials, flow-enabled self-assembly (FESA) stands out as a lithography-free evaporation-induced self-assembly technique to construct large-scale 0D, 1D and 2D periodic structures in a simple, robust and cost effective manner. In the first part of the thesis, flow-enabled self-assembly of polystyrene is chosen as the model system, and systematic experiments have been conducted to reveal intrinsic and external variables that lead to 3 possible FESA patterns (i.e., coffee ring induced spoke pattern, fingering instability induced strip pattern, and their intermediate network-like structures). In the second part of the thesis, applications of FESA in patterning electrochromic polymers and fabricating PS-PMMA strips as etching mask of Si microchannels are demonstrated. Both applications convincingly illustrate the advantages of cost effective, large yield and flexible control of flow-enabled self-assembly.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Computer Science / Master / Master of Philosophy