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Experimental Investigations of Airflow in the Human Upper Airways During Natural and Assisted BreathingSpence, Callum James Thomas January 2011 (has links)
Nasal high flow (NHF) cannulae are used to deliver heated and humidified air to patients at steady flows ranging from 5-50 l/min. Knowledge of the airflow characteristics within the nasal cavity with NHF and during natural breathing is essential to understand the treatment's efficacy. In this thesis, the distribution and velocity of the airflow in the human nasal cavity have been mapped during natural and NHF assisted breathing with planar- and stereo-PIV in both steady and oscillatory flow conditions. Anatomically accurate transparent silicone models of the human nasal cavity were constructed using CT scan data and rapid prototyping. Breathing flowrates and waveforms were measured in vivo and dimensionally scaled by Reynolds and Womersley number matching to reproduce physiological conditions in vitro. Velocities of 2.8 and 3.8 m/s occurred in the nasal valve during natural breathing at peak expiration and inspiration, respectively; however on expiration the maximum velocity of 4.2 m/s occurred in the nasopharynx. Velocity magnitudes differed appreciably between the left and right sides of the nasal cavity, which were asymmetric. NHF modifies nasal cavity flow patterns significantly, altering the proportion of inspiration and expiration through each passageway and producing jets with in vivo velocities up to 20.8 m/s for 40 l/min cannula flow. The main flow stream passed through the middle airway and along the septal wall during both natural inspiration and expiration, whereas NHF inspired and expired flows remained high through the nasal cavity. Strong recirculating features are created above and below the cannula jet. Results are presented that suggest the quasi-steady flow assumption is invalid in the nasal cavity during both natural and NHF assisted breathing. The importance of using a three-component measurement technique when investigating nasal flows has been highlighted. Cannula flow has been found to continuously flush the nasopharyngeal dead space, which may enhance carbon dioxide removal and increase oxygen fraction. Close agreement was found between numerical and experimental results performed in identical conditions and geometries.
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In Vitro Experimental Investigation Into the Effect of Compliance on Models of Arterial HemodynamicsGeoghegan, Patrick Henry January 2012 (has links)
Compliant (flexible) structures play an important role in several biofluid problems including flow in the lungs, heart and arteries. Atherosclerosis is a vascular disease which causes a remodelling of the arterial wall causing a restriction (stenosis) by thickening the intima and the formation of vascular plaque by the deposit of fatty materials. This remodelling alters the compliance of the artery stiffening the arterial wall locally. A common location for this to occur is in the carotid artery which supplies blood to both the brain and the face. It can lead to complete occlusion of the artery in the extreme case and is a major cause of stroke and ischemic infarction. Stroke is the third largest cause of death in the U.S.A., but even if not fatal it can cause coma, paralysis, speech problems and dementia. Atherosclerosis causes a change in the local hemodynamics. It can produce areas of flow separation and low wall shear stress, which can lead to endothelial dysfunction and to promotion of plaque growth.
In-vitro modelling with artificial flow phantoms allows the fluid mechanics of the circulatory system to be studied without the ethical and safety issues associated with animal and human experiments. Extensive work has been performed using both experimental and computational techniques to study rigid models representing the arterial system. Computational methods, in which the equations governing the flow and the elastic walls are coupled, are maturing. There is a lack of experimental data in compliant arterial systems to validate the numerical predictions. This thesis sets out to address the problems associated with the in vitro experimental analysis of compliant structures representing the human vasculature.
A novel construction technique that produced idealised compliant geometries representing both a healthy and stenosed carotid artery from transparent silicone material was developed. A complete analysis was performed of the circumferential and longitudinal response of the geometry, which allowed for dynamic similarity between in vitro and in vivo conditions to be achieved. Inherent difficulties associated with thin walled phantom construction were overcome, which included the design of a novel endplate that allowed for a smooth transition from the flow system to the flow phantom and a bottom up silicone injection system that ensured the phantom was free of bubbles. The final phantom evolution had a wall thickness that could be produced to within a tolerance of 5%. The constructed flow phantom was ported to a flow system producing a physiological inlet flow waveform scaled to in vitro conditions via Reynolds and Womersley number matching.
Experimental analysis was performed using a laser based optical technique, particle image velocimetry (PIV). A novel Light Emitting Diode (LED) illumination system was also implemented to obtain to obtain high speed planar PIV measurements. The combined set up of the LED light source, driver unit components and fibre optics for high speed imaging costs in the region of $US 650 which provides a far cheaper option in comparison to the pulse laser system (In the region of $US 50,000).
Results obtained in the healthy geometry were compared to a rigid geometry with the same dimensions. It was found that compliance reduced the peak velocity experienced. It also caused a reduction in wall shear stress (WSS) observed and acted to ameliorate the magnitude of the WSS. This is physiologically significant as high WSS can promote atherosclerosis. The introduction of a stenosis caused an increase in the peak velocity observed over the cardiac cycle. A large increase in WSS can be seen to occur in the stenosis throat in both a symmetric and asymmetric stenosed geometry. It is also evident that stenosis eccentricity is important, with asymmetry (where the centre of the stenosis does not coincide with the centre of the artery) producing a major change in WSS and flow field. The study of the flow field downstream of a symmetric stenosis exit showed a Kelvin-Helmholtz vortex ring system to occur between the jet exiting the stenosis throat and the low velocity reverse flow region that surrounded it. The strength of these vortices varied between the acceleration and deceleration phase, demonstrating the failings of a quasi-steady assumption. It was shown that varying the external pressure applied to the flow phantom, along with stenosis eccentricity, affected the inlet flow and pressure waveform and the failings of the common assumption to idealise the physiological flow wave with a sinusoidal input was presented.
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DYNAMIC MONITORING OF RAIL AND BRIDGE DISPLACEMENTS USING DIGITAL IMAGE CORRELATIONMurray, Christopher 26 September 2013 (has links)
Rail and bridge infrastructure assets are critical elements of Canada’s transportation network and their continued efficient and safe operation is necessary to ensure the nation’s economic livelihood. Monitoring technologies that can detect changes in performance as well as precursors to failure are an important element of ensuring this efficient and safe operation. Digital Image Correlation (DIC) is a monitoring technology that has the potential to provide critical data for infrastructure assessment and to replace various conventional sensors with one integrated monitoring solution.
In this research, the accuracy of DIC is evaluated using numerical, laboratory and field-based experiments. The sources of error of particular relevance to dynamic measurement using DIC are identified as (i) bias error in the sub-pixel interpolation scheme, (ii) the ratio of sample rate to the frequency of the signal being monitoring and (iii) the signal to noise ratio. It is also shown that the chosen sub-pixel interpolation scheme can greatly affect the accuracy of dynamic measurements.
The use of DIC was investigated for field monitoring of both horizontal and vertical railway displacements at sites with good and poor subgrade conditions under dynamic train loading. It is shown that there is a significant benefit to using an absolute displacement measurement system rather than a relative displacement measurement system as the former can capture irrecoverable rail displacements in both the vertical and horizontal directions.
Finally, DIC was also used for field monitoring of a very stiff reinforced concrete bridge during static and dynamic load tests. It is shown that when using DIC for deflection monitoring, corrections may have to be made to compensate for errors such as camera jitter and drift to acquire the most accurate results. Two potential correction methods were the use of a fixed reference point and generating composite images using average pixel intensity values from multiple images. It was found that using a fixed reference point was the optimal choice in this bridge test. It is concluded that DIC can be used as an effective displacement measurement tool for bridge assessment because it shows excellent correlation with linear potentiometer results and it can allow measurements to be taken without having to close the bridge. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-26 15:40:16.744
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Time-Resolved Particle Image Velocimetry Measurements of the 3D Single-Mode Richtmyer-Meshkov InstabilityXu, Qian, Xu, Qian January 2016 (has links)
The Richtmyer-Meshkov Instability (RMI) (Commun. Pure Appl. Math 23, 297-319, 1960; Izv. Akad. Nauk. SSSR Maekh. Zhidk. Gaza. 4, 151-157, 1969) occurs due to an impulsive acceleration acting on a perturbed interface between two fluids of different densities. In the experiments presented in this thesis, single mode 3D RMI experiments are performed. An oscillating speaker generates a single mode sinusoidal initial perturbation at an interface of two gases, air and SF6. A Mach 1.19 shock wave accelerates the interface and generates the Richtmyer-Meshkov Instability. Both gases are seeded with propylene glycol particles which are illuminated by an Nd: YLF pulsed laser. Three high-speed video cameras record image sequences of the experiment. Particle Image Velocimetry (PIV) is applied to measure the velocity field. Measurements of the amplitude for both spike and bubble are obtained, from which the growth rate is measured. For both spike and bubble experiments, amplitude and growth rate match the linear stability theory at early time, but fall into a non-linear region with amplitude measurements lying between the modified 3D Sadot et al. model (Phys. Rev. Lett. 80, 1654-1657, 1998) and the Zhang & Sohn model (Phys. Fluids 9. 1106-1124, 1997; Z. Angew. Math Phys 50. 1-46, 1990) at late time. Amplitude and growth rate curves are found to lie above the modified 3D Sadot et al. model and below Zhang & Sohn model for the spike experiments. Conversely, for the bubble experiments, both amplitude and growth rate curves lie above the Zhang & Sohn model, and below the modified 3D Sadot et al. model. Circulation is also calculated using the vorticity and velocity fields from the PIV measurements. The calculated circulation are approximately equal and found to grow with time, a result that differs from the modified Jacobs and Sheeley's circulation model (Phys. Fluids 8, 405-415, 1996).
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Particle Image Velocimetry (PIV) measurements in the wake of a cascade of compressor blades at stallQuesenbury, Robert C. 03 1900 (has links)
Approved for public release, distribution unlimited / The flow around second generation controlled-diffusion compressor blades in cascade at stall was examined through the use of a Particle Image Velocimeter (PIV). This examination was conducted from the trailing edge of the blade well into the wake region. Flow visualization techniques were used to observe and record the behavior of the region of flow separation. The PIV data showed that the separated regions continued to grow up to approximately 10% of blade chord length past the trailing edge. Past this point, these areas began to show signs of becoming entrained in the free stream. The flow visualization highlighted the extent of the backflow. The PIV measurements documented the velocity profiles within the wake region.
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Bases hidrodinâmicas para processos de transferência de gases em colunas com difusores / Hidrodynamics basis to gases transfer process in columns with diffusersSalla, Marcio Ricardo 27 May 2002 (has links)
Neste trabalho apresenta-se o estudo da transferência de massa (oxigênio) de bolhas de ar para a água, geradas por um difusor de ar, confeccionado com plástico microporoso e de fabricação nacional, em uma coluna de aeração. O processo de aeração conduziu à determinação do coeficiente volumétrico de transferência de massa, coeficiente volumétrico de transferência de massa global, e foi executado na coluna mencionada, construída em material transparente. Utilizou-se água de fonte, existente no abastecimento do Laboratório de Hidráulica Ambiental (SHS/CRHEA). Variou-se a vazão do ar no processo de aeração de 400 l/h a 2.000 l/h e o nível de água dentro da coluna de 0,50 m a 1,80 m. Optou-se pelo método químico para deaerar a água, utilizando sulfito de sódio anidro antes do início de cada ensaio. O aparelho WTW-323, um medidor de oxigênio do tipo membrana permeável, foi usado para determinar a evolução da concentração de oxigênio dissolvido na água durante todo o processo de aeração. Características hidrodinâmicas foram quantificadas, como os campos de velocidade ascensional das bolhas de ar, o diâmetro equivalente das bolhas e sua freqüência de ocorrência. Para essas quantificações utilizou-se equipamento Laser para velocimetria não-intrusiva. As características mencionadas são fundamentais para verificar as previsões para o coeficiente de transferência de massa encontradas na literatura. A coluna usada tem seção transversal quadrada de 0,19 m x 0,19 m, constante em toda sua extensão, e altura de 2,00 m. Através da determinação da eficiência de transferência de massa de oxigênio na água, variando a vazão de aeração e o nível de água na coluna, concluiu-se que a vazão entre 600 l/h e 800 l/h e nível de água de 1.80 m é que apresentou maior eficiência de transferência de massa. / The present work is a study of the oxygen mass transfer from air bubbles into water, generated by a diffuser of air, in a column of aeration. This diffuser was made of microporous plastic and produced in Brazil. The process of aeration in the column built with transparent material determined the volumetric coeficient of the mass transfer Kla. Water from the well located in the Environmental Hydraulic Laboratory (SHS/CRHEA) was used. The air flow in the process of aeration was changed from 400 l/h to 2000 l/h and the level of water, from 0,50 m to 1,80 m. The chemical method was chosen to deoxygenate water and sulfite of anhydrous sodium was used before starting each experiment. The equipment WTW-323, an oxygen gauge with permeable membrane, was used to determine the development of the oxygen concentration dissolved in water during the process of aeration. Several hydrodinamic characteristics were measured, such as the velocity range of the air bubbles, their diameter and their frequency, by using a laser equipment for non-intrusive velocimetry. These characteristics are fundamental to check the mass transfer coeficient that are in literature. The column used for the experiment had a square cross section of 0,19 m x 0,19 m in alI extension and height of 2 meters. After determination of the efficiency of the mass transfer of oxygen into water, changing the air flow rate and the level of water in the column, it was concluded that the air flow between 600 l/h and 800 l/h and the level of water of 1,80 m were the most efficient.
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An investigation into the use of Cross Correlation VelocimetryRockwell, Scott R 12 January 2010 (has links)
This study analyses the applicability of cross correlating the signal between two thermocouples to obtain simultaneous measurement of velocity, integral turbulent length scales, and temperature in fire induced turbulent flows. This sensor is based on the classical Taylor's hypothesis which states that turbulent structures should retain their shape and identity over a small period of time. If sampling rate is fast enough such that the signal from two thermocouples is sampled within this time duration, the turbulent eddy can be used as a tracer to measure flow velocity and fluctuation. Experiments performed in two laboratory scale devices: a heated turbulent jet and a variable diameter natural gas burner show that sampling rate, sampling time, and angular orientation with respect to the bulk flow are the most sensitive parameters in velocity measurements. Flows with Reynolds numbers between 300 (u=0.1m/s) and 6000 (u=2.0 m/s) were tested.
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The development of turbulent slender open-core annular jetsPadhani, Shahid Anwar January 2019 (has links)
The very first study of the development of the turbulent isothermal and incompressible air jet which issues at a constant velocity from a slender annular slot, circumnavigating an open core, into an otherwise quiescent and unbounded environment of the same density, is presented. The geometry of this source is defined by three diameters: the outer diameter of the slot $D_o$; the inner diameter of the slot $D_i$; and the diameter of the (circular) open core $D_v$. `Slender' refers to a slot for which the inner and outer diameters are approximately equal, i.e. $D_i/D_o\approx 1$. Our focus lies in understanding the development of the time-averaged flow with distance downstream and the influence of the source geometry on the development of the jet. Given the absence of information on jets issuing from the sources of interest, the investigation follows an approach reminiscent of the classic investigations into round jets. That is, it begins with the development of a nozzle and experimental set-up which are suitable for studying the slender open-core annular jet. In addition to the experimental measurements, a complementary mathematical model was developed to describe the unique near-field behaviour of the open-core jet. Measurements were acquired using flow visualisation and Particle Image Velocimetry. On examining the streamwise development of the flow, the slender almost fully open-core jet was delineated into four key regions and the characteristic scalings identified. The regions were as follows: a bounded induced-flow region; a near-source planar-jet region; a transitional region; and a far-field round-jet region. Fluid induced through the open core of the nozzle and subsequently entrained into the jet significantly enhanced the near-field dilution of the jet. Following on from this, the influence of the diameter ratio $D_i/D_o$ and ventilation ratio $D_v/D_i$ on jet coalescence was examined. Over the range of diameter ratios examined ($0.845 \leq D_i/D_o\leq 0.981$), experimental measurements and the predictions from mathematical modelling indicated that $D_i/D_o$ significantly influenced the volume flux induced through the core while the coalescing behaviour of the jet and the far-field region remained largely unchanged. Over the range of ventilation ratios examined ($0 \leq D_v/D_i\leq 0.90$), experimental measurements demonstrated that $D_v/D_i$ controlled the restriction experienced by fluid induced through the open core and significantly influenced the far-field behaviour of the jet. Our findings suggest that jet of interest is then uniquely characterised by the momentum flux $M_0$, the diameter ratio $D_i/D_o$, and the ventilation ratio $D_v/D_i$.
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WING-TIP VORTEX EVOLUTION IN TURBULENCEGhimire, Hari Charan 01 January 2018 (has links)
Planar and stereo particle image velocimetry measurements were conducted of a wing-tip vortex decaying in free-stream turbulence in order to understand the evolution of a vortex and its decay mechanism. The vortex decayed faster in the presence of turbulence. The decay of the circulation was found to be almost entirely due to a decrease in circulation of the vortex core, caused by the relative decrease in peak tangential velocity without a corresponding increase in core radius. These events were found to be connected with the stripping of core fluid from the vortex core. The increased rate of decay of the vortex in turbulence coincided with the formation of secondary vortical structures which wrapped azimuthally around the primary vortex. It was also found that regardless of the free-stream condition, the core scaled by peak tangential velocity and core radius.
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The MicroPIVOT : an Integrated Particle Image Velocimeter and Optical Tweezers Instrument for Microscale InvestigationsNeve de Mevergnies, Nathalie 01 January 2010 (has links)
This dissertation describes the development of a device capable of suspending a microscale object in a controlled flow. The uPIVOT is a system integrating two laser-based techniques: micron particle image velocimetry (uPIV) and optical tweezers (OT). The OT allows the suspension and manipulation of micron-sized objects such as microspheres or biological cells. uPIV provides imaging of the suspended object and velocity measurements from which fluid induced stresses can be determined. Using this device, we measured fluid velocities around an optically suspended polystyrene microsphere (an experimental first) and studied the interaction between two particles suspended in a uniform flow. The results were consistent with theoretical low Reynolds number, Newtonian flow predictions. Additionally, we analyzed a single cell's mechanical response to a controlled and measurable multiaxial external force (fluid flow) without the cell being physically attached to a surface. The cell's mechanical response was monitored by observing its morphology and measuring its deformation. The results show significant deformations of optically suspended cells at substantially smaller stresses than previously reported and demonstrate the opportunity to optically distinguish a cell by its trapping efficiency. These initial applications of the uPIVOT demonstrate the potential of this unique device as a research tool for novel studies in the fields of fluid/particle(s) interactions, non-Newtonian fluid mechanics, and single cell biomechanics.
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