Towards small scale sensors for turbulent flows and for rarefied gas damping

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dc.contributor.authorEbrahiminejad Rafsanjani, Amin
dc.contributor.supervisorBhiladvala, Rustom
dc.date.accessioned2018-01-02T21:41:47Z
dc.date.available2018-01-02T21:41:47Z
dc.date.copyright2017en_US
dc.date.issued2018-01-02
dc.degree.departmentDepartment of Mechanical Engineeringen_US
dc.degree.levelMaster of Applied Science M.A.Sc.en_US
dc.description.abstractThis thesis makes contributions towards the development of two different small-scale sensing systems which show promise for measurements in fluid mechanics. Well-resolved turbulent Wall Shear Stress (WSS) measurements could provide a basis for realistic computational models of near-wall turbulent flow in aerodynamic design. In aerodynamics field applications, they could provide indication of flow direction and regions of separation, enabling inputs for flight control or active control of wind-turbine blades to reduce shock and fatigue loading due to separated flow regions. Traditional thermal WSS sensors consist of a single microscale hot-film, flush-mounted with the surface and maintained at constant temperature. Their potential for fast response to small fluctuations may not be realized, as heat transfer through the substrate creates heat-exchange with fluid, leading to loss of spatial and temporal resolution. The guard-heated thermal WSS sensor is a design introduced to block this loss of resolution. A numerical flow-field with a range of length and time and scales was generated to study the response of both guard-heated and conventional single-element thermal WSS sensors. A conjugate heat transfer solution including substrate heat conduction and flow convection, provides spatiotemporal data on both the actual and the “measured” WSS fluctuations calculated from the heat transfer rates experienced due to the WSS field. For a single-element sensor in air, we found that the heat transfer through the substrate was up to six times larger than direct heat transfer from the hot-film to the fluid. The resulting loss of resolution in the single-element sensor can be largely recovered by using the guard-heated design. Spectra for calculated WSS from heat transfer response show that high frequencies are considerably better resolved in guard-heated sensors than in the single element sensor. Nanoresonators are nanowires (NWs) excited into mechanical vibration at a resonance frequency, with a change in spectral width created by gas damping from the environment, or a shift in the resonance peak frequency created by added mass. They enable a wide range of applications, from sensors to study rarefied gas flow friction to the detection of early-stage cancer. The extraordinary sensitivity of nanoresonators for disease molecule detection has been demonstrated with a few NWs, but the high cost of traditional electron-beam lithography patterning, have inhibited practical applications requiring large arrays of sensors. Field-directed assembly techniques under development in our laboratory enable a large number of devices at low cost. Electro-deposition of metals in templates yields high-quality single nanowires, but undesired clumps must be removed. This calls for separation (extraction) of single nanowires. In this work, single nanowires are extracted by using the sedimentation behavior of particles. Based on numerical and experimental analyses, the optimum time and region for extracting samples with the highest fraction of single nanowires ratio was found. We show that it is possible to take samples free of large clumps of nanowires and decrease the ratio of undesired particles to single nanowires by over one order of magnitude.en_US
dc.description.scholarlevelGraduateen_US
dc.identifier.urihttp://hdl.handle.net/1828/8929
dc.languageEnglisheng
dc.language.isoenen_US
dc.rightsAvailable to the World Wide Weben_US
dc.subjectturbulence fluctuationsen_US
dc.subjectWall shear stressen_US
dc.subjectThermal sensorsen_US
dc.subjectThermal anemometryen_US
dc.subjectLarge eddy simulationsen_US
dc.subjectWind turbine control systemsen_US
dc.subjectActive flow controlen_US
dc.subjectSeparation of nanoparticlesen_US
dc.subjectelectrodeposition in templatesen_US
dc.subjectRhodium nanowiresen_US
dc.subjectbidisperse suspensionen_US
dc.subjectNanowire fabricationen_US
dc.titleTowards small scale sensors for turbulent flows and for rarefied gas dampingen_US
dc.typeThesisen_US

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