Mechanical Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2795
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Item Near Threshold Sediment Transport by a Forced Jet Impinging on a Mobile Sediment Bed(2015) Corfman, Kyle; Kige, Kenneth; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although sediment transport has been extensively studied in the past, flows such as rotorcraft brownout with large-scale coherent structures call many of the simplifying assumptions into question. The objective of this study is to develop a model for the prediction of sediment removal, referred to as erosion, based on independent measurements of the single-phase flow and the evolution of bedforms on the surface of a mobile sediment bed. A series of phase-resolved particle image velocimetry (PIV) flow measurements have been conducted to quantify the stress induced by an acoustically forced impinging jet, analagous to tip-vortices within the rotor wake. The threshold conditions for incipient particle motion are quantified through a series of PIV measurements of the single-phase flow at conditions found to produce quantifiable erosion of the surface. A force balance approach is used to develop a model, following the theory presented by Bagnold (1966), to predict the transport of sediment due to the stress above the theshold. A series of surface elevation measurements are analyzed to quantify the removal of sediment, for the evaluation of the predicted model. An additional series of PIV measurements are performed on a prototype bedform, modeled after the observed bedforms, to quantify the changes in the flow field caused by their developement. The proposed model is shown to provide a better prediction of the observed erosion than classical sediment transport models, especially for cases close to the threshold conditions. For higher speed cases however, the model dramatically over predicts the observed erosion. Several physcially-based explanations are provided for this kink in the trend.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.