Further understanding the small scale coherent structures which occur in high Reynolds number turbulence would be of enormous benefit. Therefore, the aim of the current project was to make well resolved three-dimensional flow measurements of the mixing flow between counter rotating impellers, using Tomographic Particle Image Velocimetry (TPIV).TPIV software was developed, with a novel approach permitting a significant reduction in processing time, and a series of numerical accuracy studies contributing to the fundamental understanding of this new technique. Basic flow characterisation determined the local isotropy, homogeneity and expected Reynolds number scaling. A favourable comparison between planar PIV and TPIV increased confidence in the latter, which was used to assess the dynamics and topology of the dissipation scale structures. In support of previous investigations similar topology, strain rate alignment, scale-invariance, and clustering behaviours are demonstrated. Correlated high enstrophy and dissipation regions occur in the periphery of larger structures, resulting in intermittency. Geometry characterisation indicates a predominance of tube-like structures, which are observed to form from larger ribbon-like structures through unsteady breakdown and vortex roll-up. Significant correlation between intermittent fields of dissipation and enstrophy describe the fine scales effects. These relationships should pave the way for more accurate models, capable of relating small scales and large scales during the prediction of dynamically important quantities.

The objective of this research is to experimentally investigate the flow characteristics past a bileaflet mechanical heart valve (BMHV) in an anatomical model of the aorta. The measurements were made within a mock circulation loop that produced physiological pressure and flow conditions of the aorta. The velocity was measured upstream and downstream of the valve at single points using laser Doppler velocimetry and on planes using planar particle image velocimetry. Viscous and turbulent stresses were evaluated as indicators of potential blood damage. Measurements were first made with a BMHV mounted at the inlet of an axisymmetric channel, which was similar in geometry to channels previously used, and then with the BMHV mounted at the inlet of an anatomical model of the aorta. By comparing these results, the effects of the anatomical shape of the aorta on the flow past the valve were determined. It was found that the level of turbulence past the valve was significantly greater in the axisymmetric model and that the shape of the anatomical aortic sinus, in particular, was effective in reducing turbulence. Additionally, measurements with the valve mounted in three orientations at the inlet of the anatomical aorta showed that the turbulence and the viscous stresses past the valve were lower when the valve was positioned such that its line of symmetry was parallel with the plane of aorta curvature than when it was normal to it. It was further found that flow in the right coronary artery was highest when the valve was positioned with its central orifice aligned with the opening to this artery. The results of this research may be used to assist surgeons in choosing the best implantation orientation of a BMHV.

This work investigates flow measurement capabilities within meso- and micro-scaled medically relevant devices using particle image velocimetry (PIV). Medical devices can be particularly challenging to validate due to small length scales and complex geometries, which can reduce measurement accuracy by introducing noise and reducing available signal. Although the sources of such problems are often device specific, the effective outcome is a reduction in the signal-to-noise ratios (SNRs) of PIV images and correlations. This effort utilizes advanced PIV processing and post-processing techniques to establish protocols for achieving high accuracy PIV measurements in challenging flow environments. This investigation takes place within three wide-ranging medically related devices. First, channel flow in a microfluidic device is investigated to evaluate improvements in measurement accuracy gained using phase correlations in comparison to confocal microscopy. This work found substantial improvements in error with respect to the ensemble field for phase correlations while only moderate improvements were observed for confocal imaging with standard processing techniques. Secondly, an evaluation of stenting procedures was executed resulting in the first published PIV and computational fluid dynamics (CFD) joint study on bifurcating stents. This work analyzes steady flow in three bifurcation angles and four different single- and double-stenting procedures, which are clinically used in coronary bifurcations. Finally, a medical device analog was evaluated to develop a comprehensive CFD validation dataset, including a full uncertainty analysis for velocity and wall shear stress as well as estimates for pressure fields and relevant flow statistics including Reynolds stresses and dissipation. / Ph. D.

<p>For internal flows, the detachment of the boundary layer is a major contributor to pressure loss. To improve efficiency, it is essential to characterize these regions to understand the location and magnitude. Particle Image Velocimetry (PIV) is applied to provide time-resolved measurements to achieve accurate results without perturbing the flow. This thesis covers the methodology for creating an adaptable optical measurement technique in a high frequency study of separated regions in transonic internal flows. Focus on the optimization of the laser optical array and image acquisition system yield improved Dynamic Spatial Range (DSR) and Dynamic Velocity Range (DVR). Further analysis is provided on the flow dynamics of the seed particle, with local seeding solutions provided for improved seeding density in high-speed flows for various geometries. Light scattering efficiency of the particle is also analyzed to completely define the desired particle size. Two pulse-burst Nd:YAG lasers and two high speed cameras are used in this study to achieve a frame straddling technique necessary to resolve high frequency flows. Comparison of the recording media to the DSR highlights performance costs and benefits between the two cameras. Uncertainty measurements are determined from the calculated setup and compared to correlation statistics-based uncertainty quantifications. Image processing and cross-correlation software are used to provide analysis on the flow characteristics for two separate studies with comparison to Computational Fluid Dynamic predictions.</p>

Of the potential feedstocks for biofuels, microalgae is the most promising, and raceway ponds are the most cost-effective method for growing mircoalgal biomass. Nevertheless, biofuel production from algae must be more efficient to be competitive with traditional fuels. Previous studies using arrays of airfoils, triangles, and squares at high angles of attack show an increase in mixing in raceways and can improve productivity by up to a factor of 2.2. Some researchers say increasing mixing increases growth due to the flashing light effect while others claim it is the decrease in the fluid boundary layer of the cells that increases mass transfer. Whatever the reason, increasing growth by increasing mixing is a repeatable effect that is desirable to both reduce operation costs and increase production. An experimental raceway is constructed to test the effect of a delta wing (DW) on raceway hydraulics in the laboratory using fresh-water. The DW is an isosceles triangle made of plate material that is placed at a high angle of attack in the circulating raceway flow. Results from this investigation can be scaled to larger growth facilities use arrays of DWs. Two vortices are found downstream of the DW when used in this way and create significant vertical fluid circulation. Stereo particle image velocimetry (PIV) is used to quantify and optimize the use of delta wings as a means to increase fluid mixing. Stereo PIV gives three components of velocity in a measurement plane at an instant. Three studies are performed to determine the optimal paddle-wheel speed, angle of attack, and DW spacing in the raceway based on mixing. Two new mixing quantities are defined. The first is the Vertical Mixing Index (VMI) that is based on the vertical velocity magnitude, and the second is the Cycle Time required for an algal cell to complete a cycle from the bottom to the top and back again in the raceway. The power required to circulate the flow is considered in all results. The Paddle-wheel Speed Study shows that the VMI is not a function of streamwise velocity, which makes it very useful for comparison. The Cycle Time decreases quickly with streamwise velocity then levels out, revealing a practical speed for operation that is lower than typically used and consumes only half the power. The angle of 40° is optimal from the results of the Angle of Attack Study for both VMI and Cycle Time. The third study is the Vortex Dissipation Study and is used to measure the distance downstream before the vortices dissipate. This information is used to optimize the DW spacing for profit considering the additional costs of adding DWs.

A moving contact line is the idealized line of intersection between two immiscible fluids as one displaces the other along a solid boundary. The displacement process has been the subject of a large amount of theoretical and experimental research; however, the fundamental processes that govern contact line motion are still unknown. The challenge from an experimental perspective is to make measurements with high enough resolution to validate competing theories. An experimental method has been developed to simultaneously measure interface motion, dynamic contact angles, and local fluid velocity fields using micron-resolution Particle Image Velocimetry (µPIV). Capillary numbers range from 1.7 x 10^(⁻⁴) to 6.2 x 10^(⁻⁴). Interface velocities were measured between 1.7 µm/s and 33 µm/s. Dynamic contact angles were manually measured between 1.1 µm and 120 µm from the contact line, and calculated from µPIV data to within several hundred nanometers from the contact line. Fluid velocities were measured over two orders of magnitude closer to the contact line than published values with an increase in resolution of over 3400%. The appearance of a recirculation zone similar to controversial prediction below previously published limits demonstrates the power and significance of the method.

No description available.

The study of flow fields and heat transfer characteristics inside a gas turbine combustor provides one of the most serious challenges for gas turbine researchers because of the harsh environment at high temperatures. Design improvements of gas turbine combustors for higher efficiency, reduced pollutant emissions, safety and durability require better understanding of combustion in swirl flows and thermal energy transfer from the turbulent reacting flows to solid surfaces. Therefore, accurate measurement and prediction of the flows and heat loads are indispensable. This dissertation presents flow details and wall heat flux measurements for reacting flow conditions in a model gas turbine combustor. The objective is to experimentally investigate the effects of combustor operating conditions on the reacting swirl flows and heat transfer on the liner wall. The results shows the behavior of swirling flows inside a combustor generated by an industrial lean pre-mixed, axial swirl fuel nozzle and associated heat loads. Planar particle image velocimetry (PIV) data were analyzed to understand the characteristics of the flow field. Experiments were conducted with various air flow rates, equivalence ratios, pilot fuel split ratios, and inlet air temperatures. Methane and propane were used as fuel. Characterizing the impingement location on the liner, and the turbulent kinetic energy (TKE) distribution were a main part of the investigation. Proper orthogonal decomposition (POD) further analyzed the data to compare coherent structures in the reacting and non-reacting flows. Comparison between reacting and non-reacting flows yielded very striking differences. Self-similarity of the flow were observed at different operating conditions. Flow temperature measurements with a thermocouple scanning probe setup revealed the temperature distribution and flow structure. Features of premixed swirl flame were observed in the measurement. Non-uniformity of flow temperature near liner wall was observed ranging from 1000 K to 1400 K. The results provide insights on the driving mechanism of convection heat transfer. As a novel non-intrusive measurement technique for reacting flows, flame infrared radiation was measured with a thermographic camera. Features of the flame and swirl flow were observed from reconstructed map of measured IR radiation projection using Abel transformation. Flow structures in the infrared measurement agreed with observations of flame luminosity images and the temperature map. The effect of equivalence ratio on the IR radiation was observed. Liner wall temperature and heat transfer were measured with infrared thermographic camera. The combustor was operated under reacting condition to test realistic heat load inside the industrial combustors. Using quartz glass liner and KG2 filter glass, the IR camera could measure inner wall surface temperature through the glass at high temperature. Time resolved axial distributions of inner/outer wall temperature were obtained, and hot side heat flux distribution was also calculated from time accurate solution of finite difference method. The information about flows and wall heat transfer found in this work are beneficial for numerical simulations for optimized combustor cooling design. Measurement data of flow temperature, velocity field, infrared radiation, and heat transfer can be used as validation purpose or for direct inputs as boundary conditions. Time-independent location of peak location of liner wall temperature was found from time resolved wall temperature measurements and PIV flow measurements. This indicates the location where the cooling design should be able to compensate for the temperature increase in lean premixed swirl combustors. The characteristics on the swirl flows found in this study points out that the reacting changes the flow structure significantly, while the operating conditions has minor effect on the structure. The limitation of non-reacting testing must be well considered for experimental combustor studies. However, reacting testing can be performed cost-effectively for reduced number of conditions, utilizing self-similar characteristics of the flows found in this study. / Ph. D.

Energy conservation, efficiency, and environmental responsibility are priorities for modern energy technologies. The ever increasing demands for lower pollutants and higher performance have driven the development of low-emission gas turbine engines, operating at lean equivalence ratios and at increasingly higher turbine inlet temperatures. This has placed new constraints on gas turbine combustor design, particularly in regards to the cooling technologies available for the combustor liner walls. To optimize combustor thermal management, and in turn optimize overall engine performance, detailed measurements of the flame side heat transfer are required. However, given the challenging environment at which gas turbine combustors operate, there are currently only limited studies that quantify flame side combustor heat transfer; in particular at reacting conditions. The objective of the present work was to develop methodologies to measure heat transfer within a reacting gas turbine combustor. To accomplish this, an optically accessible research combustor system was designed and constructed at Virginia Tech, capable of operating at 650 K inlet temperature, maximum air mass flow rates of 1.3 kg/s, and flame temperatures over 1800 K. Flow and heat transfer measurements at non-reacting and reacting conditions were carried out for Reynolds numbers (Re) with respect to the combustor diameter ranging from ~11 500 to ~140 000 (depending on the condition). Particle Image Velocimetry (PIV) was used to measure the non-reacting flow field within the burner, leading to the identification of coherent structures in the flow that accounted for over 30% of the flow fluctuation kinetic energy along the swirling jet shear layers. The capability of infrared (IR) thermography to image surface temperatures through a fused silica (quartz) glass was demonstrated at non-reacting conditions. IR thermography was then used to measure the non-reacting steady state heat transfer along the combustor liner. A peak in heat transfer was identified at ~1 nozzle diameter downstream of the combustor dome plate. The peak Nusselt number along the liner was over 18 times higher than that predicted from fully developed turbulent pipe flow correlations, which have traditionally been used to estimate flame side combustor heat transfer. For the reacting measurements, a novel time-dependent heat transfer methodology was developed that allowed for the investigation of transient heat loads, including those occurring during engine ignition and shutdown. The methodology was validated at non-reacting conditions, by comparing results from an experiment with changing flow temperature, to the results obtained at steady state. The difference between the time-dependent and the steady state measurements were between 3% and 17.3% for different mass flow conditions. The time-dependent methodology was applied to reacting conditions for combustor Reynolds numbers of ~12 000 and ~24 000. At an equivalence ratio of ~0.5 and a combustor Reynolds number of ~12 000, the peak heat load location in reaction was shifted downstream by 0.2 nozzle diameters compared to the non-reacting cases. At higher equivalence ratios, and more visibly at a Reynolds number of ~24 000, the heat transfer distribution along the combustor liner exhibited two peaks, upstream and downstream of the impingement location (X/DN=0.8-1.0 and X/DN=2.5). Reacting PIV was performed at Re=12 000 showing the presence of a strong corner recirculation, which could potentially convect reactants upstream of the impingement point, leading to the double peak structure observed. The methodologies developed have provided insight into heat transfer within gas turbine combustors. The methods can be used to explore additional conditions and expand the dataset beyond what is presented, to fully characterize reacting combustor heat transfer. / Ph. D.

Laser flare can often be a major issue in particle image velocimetry (PIV) involving solid boundaries in a flow or a gas-liquid interface. The use of fluorescent light from dye-doped particles has been demonstrated in water applications, but reproducing the technique in an airflow is more difficult due to particle size constraints and safety concerns. The following thesis is formatted in a hybrid manuscript style, including a full paper presenting the applications of fluorescent Kiton Red 620 (KR620)-doped polystyrene latex microspheres in PIV. These particles used are small and monodisperse, with a mean diameter of 0.87 μm. The KR620 dye exhibits much lower toxicity than other common fluorescent dyes, and would be safe to use in large flow facilities. The first sections present a general introduction followed by a validation experiment using a standard PIV setup in a free jet. This work was the first to demonstrate PIV using fluorescent KR620-doped microspheres in an airflow, and results from the experiment were compared to similar data taken using standard PIV techniques. For the free jet results, Mie-scattered and fluorescent PIV were compared and showed average velocities within 3% of each other at the nozzle exit. Based on the PIV validation requirements used, this was deemed to be more of an indication of nozzle unsteadiness rather than an error or bias in the data. Furthermore, fluorescent PIV data obtained vector validation rates over 98%, well above the standard threshold of 95%. The journal article expands on the introductory work and analyzes testing scenarios where fluorescent PIV allows for velocity measurements much closer to a solid surface than standard, Mie-scattered PIV. The fluorescent signal from the particles is measured on average to be 320 ± 10 times weaker than the Mie scattering signal from the particles. This fluorescence-to-Mie ratio was found to be nonuniform, with the typical signal ratio for a single particle expected to fall between 120 and 870. This reduction in signal is counterbalanced by greatly enhanced contrast via optical rejection of the incident laser wavelength. Fluorescent PIV with these particles is shown to eliminate laser flare near surfaces, in one case leading to 63 times fewer spurious velocity vectors than an optimized Mie scattering implementation in a region more than 5 mm from an angled surface. In the appendix, a brief summary of an experiment to characterize the temperature sensitivity of the KR620 dye is included. This experiment concluded that the KR620 particles did not exhibit sufficient temperature sensitivity to warrant further investigation at the time. / Master of Science