UNDERSTANDING BROWNOUT USING DUAL-PHASE PARTICLE IMAGE VELOCIMETRY MEASUREMENTS

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dc.contributor.advisorLeishman, John Gen_US
dc.contributor.authorSydney, Anish Joshuaen_US
dc.contributor.departmentAerospace Engineeringen_US
dc.contributor.publisherDigital Repository at the University of Marylanden_US
dc.contributor.publisherUniversity of Maryland (College Park, Md.)en_US
dc.date.accessioned2012-07-06T11:17:33Z
dc.date.available2012-07-06T11:17:33Z
dc.date.issued2011en_US
dc.description.abstractTo better understand the development of brownout dust clouds generated by rotor- craft, the dual-phase flow environment produced by one- and two-bladed laboratory-scale rotors operating over a mobile sediment bed were studied. Three size ranges of character- ized glass microspheres were used to represent the sediment particles. Time-resolved flow visualization, particle image velocimetry, and particle tracking velocimetry were used to make the flow measurements. The high imaging rate of these systems allowed the time- history of the rotor wake interactions with the sediment bed to be documented, providing a better understanding of the transient processes and mechanisms that lead to the uplift of sediment and the formation of dust clouds near a rotor in ground effect operation. In particular, the fluid dynamics of the blade tip vortices near the bed were examined in detail, which were shown to have a primary influence on the mobilization of sediment. In general, the near-wall measurements documented at least five fundamental uplift and sediment transport mechanisms below the rotor: 1. Creep, 2. Modified saltation and saltation bombardment, 3. Vortex induced trapping, 4. Reingestion bombardment (local and global), and 5. Secondary suspension. In addition, a further mechanism related to the local unsteady pressure field induced by the convecting wake vortices was hypothesized to contribute to the uplift of sediment. The highest sediment entrainment levels occurred within the wake impingement zone, mainly from the erosion aspects of the tip vortices on the bed. Once entrained, significant quantities of sediment were intermittently trapped in the vortex-induced upwash field. Secondary sediment suspension was found to be more prevalent with the two-bladed rotor because of the propensity for merging of adjacent blade tip vortices and the resulting higher upwash velocities. The trapping of suspended sediment particles into the vortex flow was shown to cause recirculation of the particles back onto the sediment bed, thereby ejecting more sediment through bombardment mech- anisms.en_US
dc.identifier.urihttp://hdl.handle.net/1903/12535
dc.subject.pqcontrolledAerospace engineeringen_US
dc.subject.pquncontrolledAerodynamicsen_US
dc.subject.pquncontrolledBrownouten_US
dc.subject.pquncontrolledRotorcraften_US
dc.titleUNDERSTANDING BROWNOUT USING DUAL-PHASE PARTICLE IMAGE VELOCIMETRY MEASUREMENTSen_US
dc.typeThesisen_US

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