Mechanical Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2795
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Item Development and Application of Mach 10 PIV in a Large Scale Wind Tunnel(2018) Brooks, Jonathan; Gupta, Ashwani K; Marineau, Eric C; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation presents the development of particle image velocimetry (PIV) for use in a large-scale hypersonic wind tunnel to measure the turbulent boundary layer (TBL) and shock turbulent boundary layer interaction (STBLI) on a large hollow cylinder flare (HCF) test article. The main feature of this application of PIV is the novel local injector which injects seeding particles into the high-speed section of the flow. Development work began sub-scale in a Mach 3 wind tunnel where the seeding particle response was characterized and the local injectors were demonstrated. Once the measurement technique was refined, it was scaled up to hypersonic flow. The particle response was characterized through PIV measurements of Mach 3 TBLs under low Reynolds number conditions, $ Re_\tau=200{-}1,000 $. Effects of Reynolds number, particle response and boundary layer thickness were evaluated separately from facility specific experimental apparatus or methods. Prior to the current study, no detailed experimental study characterizing the effect of Stokes number on attenuating wall normal fluctuating velocities has been performed. Also, particle lag and spatial resolution are shown to act as low pass filters on the fluctuating velocity power spectral densities which limit the measurable energy content. High-speed local seeding particle injection has been demonstrated successfully for the first time. Prior to these measurements, PIV applications have employed global seeding or local seeding in the subsonic portion of the nozzle. The high-speed local seeding injectors accelerate the particle aerosol through a converging/diverging supersonic nozzle which exits tangentially to the wall. Two methods are used to measure the particle concentration which shows good agreement to the CFD particle tracking codes used to design the injector nozzle profiles. Based on the particle concentration distribution in the boundary layer a new phenomenon of particle biasing has been identified and characterized. PIV measurements of a Mach 10 TBL and STBLI have been performed on a large (2.4-m long, 0.23-m dia.) HCF at a freestream unit Reynolds number of 16 million per meter. These are the highest Mach number PIV measurements reported in the literature. Particles are locally injected from the leading edge of the test article and turbulent mixing dispersed the particles for a relatively uniform high concentration of particles at the measurement section 1.83-m downstream of the leading edge. The van Driest transformed mean velocity in the TBL agrees well with incompressible zero pressure gradient log law theory. Morkovin-scaled streamwise velocity fluctuations agree well with the literature for the majority of the boundary layer.Item PARTICLE-TURBULENCE INTERACTION OF SUSPENDED LOAD BY A FORCED JET IMPINGING ON A MOBILE SEDIMENT BED(2014) Mulinti, Rahul; Kiger, Ken; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Phase-resolved two-phase flow experiments have been conducted to predict particle suspension and sedimentation within coupled particle-laden flows relevant to rotorcraft brownout conditions. Single phase and dual-phase PIV experiments have been conducted to study the interaction of a mobile sediment bed with characteristic flow structures similar to those within a rotor wake. Even though sediment transport has been extensively studied in the past, the rapidly evolving transient nature of brownout calls many of the simplifying assumptions that have been made to understand sediment transport mechanisms into question. Image intensity based phase-separation and a hybrid PIV/PTV techniques have been implemented to identify the gas and solid phases as well as to the resolve multi-valued velocity displacements within a given interrogation region. A calibration technique to identify the measurement volume using size-brightness as well as PIV correlation based criteria has been outlined. Simultaneous velocity measurements of the fluid and dispersed phase in two vertical co-planar planes are analyzed to examine the role of vortex interaction and its subsequent breakdown on sediment transport process. The mobilization conditions and wall-normal flux of particulates by the vortex-wall interaction are reported and are correlated to the local vortex conditions such as proximity to the wall and subsequent decay. The effect of the changing sediment bed profile on sediment transport rates is also studied. Modulation of mean and stochastic fluid flow properties due to the presence of particles and the effect of turbulent coupling between the particle and fluid momentum, as based on a modified drag law with dependence on particle Reynolds number as well as local volume fraction has been examined. A mesoscopic Eulerian formalism has been implemented to study the effect of particle inertia on the suspension process.Item SEDIMENT SUSPENSION EVENTS FROM RIPPLE BEDS IN OSCILLATORY FLOW: EXPERIMENTS(2009) Knowles, Philip Leland; Kiger, Kenneth T; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An experimental sediment flume is used to investigate sediment transport mechanics within an oscillatory turbulent boundary layer over a mobile sediment bed in the ripple bed regime. Two-phase PIV is utilized to simultaneously capture data from each phase, allowing examination of suspension mechanisms, carrier phase stresses, and to obtain statistics to describe the momentum exchange between the phases. The technique employs median filtering, as well as size and brightness criteria to separate and accurately identify each phase. Independent well-conditioned tests have been conducted to improve the algorithm to account for the imaging conditions encountered in the vicinity of a mobile bed in order to minimize cross-talk between the phases and allow quantification of the dispersed phase concentration. Results show that large-scale vortical structures are responsible for the ejection of sediment from the bed into the outer flow. These structures are a significant source of turbulent transport, but their overall contribution to the bed stress is small compared to the mean flow. Triple decomposition of the equations of motion show that long time averaged sediment flux is of similar magnitude to cyclic fluctuations and the time averaged flow consists of two counter rotating cells. Turbulent kinetic energy created at flow reversal advects over the sediment bed and keeps particles suspended in the flow. Calculation of the vertical particle drag, body force, and convection terms revels that at flow reversal the body force terms are larger than the drag causing the particles on average to settle. The particle convection terms are small compared to particle drag and body force terms. Some of the terms most significant in the particle drag are the fluctuating components indicating that the turbulence is keeping the particles suspended in the outer flow.