Characterisation of turbulence in an open channel flow and in a fountain with tomographic PIV.

This work aims to improve the understanding of the fundamental characteristics of environmental flows by interpreting the turbulence in a 3D measurement domain. This thesis primarily describes the Tomographic PIV technique and the results of three experimental investigations of environmental flows. Two experiments were conducted in an open channel flow, divided into four sequential, identical pools, by a combination of regular grids. The first set of TPIV measurements were in the water column, while the second set of measurements were made along the channel bottom. The instantaneous structures in the flow were visualised and the turbulent kinetic energy k, energy dissipation ε and vorticity ω were analysed; their decay along the streamwise direction was revealed. Ejections (Q2) and sweeps (Q4) were identified along the channel bottom. A major contribution that resulted from the investigation pertains to the vibration correction of the cameras. TPIV measurements were taken of a regime of turbulent, forced fountain flows. The fountains were created by injecting a salt-water solution through a circular opening into the bottom of a reservoir of a water-ethanol solution, with their refractive indices carefully matched. The evolution of the fountain in its initial stages was captured and described in a series of chronological measurement volumes. Measurements of the fully developed fountains captured the large scale structures and their characteristics were analysed by considering the topology of the invariants of the velocity gradient tensor. The TPIV system was designed and built in-house at the University of Sydney. The experimental investigations described in this work revealed some interesting features of the environmental flows. The applicability and versatility of TPIV for these flows were demonstrated. The measurements allowed for the quantification and visualisation of the turbulence in the flows and hence shed light on the physics behind them

Characterisation of turbulence in an open channel flow and in a fountain with tomographic PIV.

This work aims to improve the understanding of the fundamental characteristics of environmental flows by interpreting the turbulence in a 3D measurement domain. This thesis primarily describes the Tomographic PIV technique and the results of three experimental investigations of environmental flows. Two experiments were conducted in an open channel flow, divided into four sequential, identical pools, by a combination of regular grids. The first set of TPIV measurements were in the water column, while the second set of measurements were made along the channel bottom. The instantaneous structures in the flow were visualised and the turbulent kinetic energy k, energy dissipation ε and vorticity ω were analysed; their decay along the streamwise direction was revealed. Ejections (Q2) and sweeps (Q4) were identified along the channel bottom. A major contribution that resulted from the investigation pertains to the vibration correction of the cameras. TPIV measurements were taken of a regime of turbulent, forced fountain flows. The fountains were created by injecting a salt-water solution through a circular opening into the bottom of a reservoir of a water-ethanol solution, with their refractive indices carefully matched. The evolution of the fountain in its initial stages was captured and described in a series of chronological measurement volumes. Measurements of the fully developed fountains captured the large scale structures and their characteristics were analysed by considering the topology of the invariants of the velocity gradient tensor. The TPIV system was designed and built in-house at the University of Sydney. The experimental investigations described in this work revealed some interesting features of the environmental flows. The applicability and versatility of TPIV for these flows were demonstrated. The measurements allowed for the quantification and visualisation of the turbulence in the flows and hence shed light on the physics behind them

Experimental Investigation of the Continual Jet

This thesis work primarily focusses on the study of the structure and development of the free jet generated though the round air jet nozzle. It also involves the study of the velocity fields generated by round jet at the nozzle exit velocity 5.67 m/s and with corresponding Reynolds number of 3070.The investigation was carried out in 2D (stereo PIV) and 3D (Tomo PIV). The scope of the study was further extended to understand the characteristics of all three velocity components in the developing shear layer and deriving the pressure fields over the space using the available velocity field data. Pulsed laser sheets were aligned such that it illuminates the centreline plane of the jet. The set-up was calibrated to translate the resulting pixel displacements into X, Y, and Z velocity components. The measurement was done with varying the laser power and varying the laser pulse time i.e. delay time. For measurement of the Tomo PIV the volume optics were used also volume self-calibration were carried out. The tracer particles used in the experiment were generated from the vegetable oil and compressed air was used for providing the necessary acceleratory movement to the particles. The result helped to study the different structures and development of the free jet along its centreline axis direction. The velocity range over entire field and pressure variations along the streamline axis are discussed. The maximum particle velocity was found to be 25 m/s in the jet core.This thesis work primarily focusses on the study of the structure and development of the free jet generated though the round air jet nozzle. It also involves the study of the velocity fields generated by round jet at the nozzle exit velocity 5.67 m/s and with corresponding Reynolds number of 3070.The investigation was carried out in 2D (stereo PIV) and 3D (Tomo PIV). The scope of the study was further extended to understand the characteristics of all three velocity components in the developing shear layer and deriving the pressure fields over the space using the available velocity field data. Pulsed laser sheets were aligned such that it illuminates the centreline plane of the jet. The set-up was calibrated to translate the resulting pixel displacements into X, Y, and Z velocity components. The measurement was done with varying the laser power and varying the laser pulse time i.e. delay time. For measurement of the Tomo PIV the volume optics were used also volume self-calibration were carried out. The tracer particles used in the experiment were generated from the vegetable oil and compressed air was used for providing the necessary acceleratory movement to the particles. The result helped to study the different structures and development of the free jet along its centreline axis direction. The velocity range over entire field and pressure variations along the streamline axis are discussed. The maximum particle velocity was found to be 25 m/s in the jet core

A stereoscopic PIV study on the behavior of near-field wingtip vortex structures

Wingtip vortex flow is of great importance because of its effect on practical problems such as landing separation distances for aircraft, blade/vortex interactions on helicopter blades, and propeller cavitations on ships. Extensive investigations have been conducted to improve the understanding of the tip vortex structure and its dissipation or persistence analytically, numerically, and experimentally. The universal feature of the water/wind tunnel generated wing tip vortex reported in the past is vortex wandering – the slow side-to-side movement of the wing-tip vortex core behind the wing. Thus, a primary result of wandering is that fixed probe measurements of velocity and pressure cannot be trusted at distances more than one chord downstream of the wing. For reliable data, the current study investigates the behavior and structure of the near-field wing-tip vortex generated by a square-tipped, rectangular NACA0012 wing by using the stereoscopic Particle Image Velocimetry (SPIV) technique. SPIV is a spatially resolved, instantaneous, three velocity component non-intrusive measurement technique used to conserve the three key feature of the wing-tip vortex during the measurement - small vortex core dimension, core structure, and strong unsteadiness of the core flow, which wasn\u27t possible with classical instrumentations. One of the great advantages of SPIV over the classical technique is that the vortex wandering can be removed by tracking the center of the vortex in every SPIV frame. By tracking the center of the vortex, the wandering and turbulence in the vortex can be separated. The results show that after re-centering the velocity field, the T.K.E. and Reynolds stress distributions become lower by more than twice at 4.0c downstream. This suggests that the vortex itself is laminar after the rollup and the higher turbulence intensity in the vortex core, reported in past studies, is mainly due to vortex wandering. This SPIV method is applied to investigate the angle of attack effect, downstream effect, and wind tunnel wall effect. Past studies suggest that the vortex rollup is completed about two chord lengths behind the wing trailing edge. The SPIV method confirmed that the vortex rollup is completed at 3.0c downstream for α= 5.0° and 4.0c for α= 10.0° by observing the re-centered Reynolds stress distributions. As for correcting the velocity profile, Devenport et al. (1996) found an analytical way to predict the wandering free velocity profile using the Reynolds stress at the vortex center. The velocity profile predicted by the Devenport et al. (1996) method is compared with the SPIV re-centered velocity profile. The results show that the two profiles agree with each other very well in the vicinity of core when the vortex wandering is large enough (about 20% of vortex core radius)

Aerothermal Analysis of Film Cooling Flows

Flow field and thermal film cooling parameters are analysed and compared for different blowing ratios for a 10°-10°-10° laidback fan-shaped film cooling hole geometry with an inclination angle of 35° and a wide spacing of P/D = 8 to ensure the absence of jet interaction. The influence of the coolant ejection on the aerodynamics of the hot gas is investigated and stationary as well as non-stationary vortex structures are identified. The present study uses an existing test rig at the Institute of Thermal Turbomachinery (ITS) at the Karlsruhe Institute of Technology (KIT) designed for generic film cooling studies with high spatial resolution applying stereoscopic particle image velocimetry (SPIV) as well as infrared thermography (IRT). Operating conditions of hot gas and cooling air inlet and exit are uniquely compliant with scaled engine-realistic conditions, including temperature ratio, turbulence intensity and coolant flow configuration

Experimental investigation of helicity in turbulent swirling jet using dual-plane dye laser PIV technique

This paper reports a new method of generating two light sheets using a dye laser system and the use of this dual-plane dye laser system to analyse average helicity and energy dissipation in a turbulent swirling flow. The dual-plane PIV system that was used in this study consisted of three cameras and a single frequency Nd:YAG laser, which was used to generate two parallel light sheet planes with differing wavelengths(colour). The method of generating two different light sheet wavelengths using a single laser source is an innovative and new technique. Stereoscopic PIV measurements were obtained in one plane with the use of two CCD cameras, and standard PIV measurements were obtained in the other plane with the use of one CCD camera. The light scattered by the particles on two different light sheets were separated using appropriate optical filters. The measurements obtained were used to estimate the components of the velocity gradient tensor. The tensor components were then used to determine the average vorticity components and helicity quantities of the fluid that was investigated. To determine the average turbulent kinetic energy dissipation, the continuity equation was used to infer the out-of-plane gradient of the out-of-plane velocity. From the analysis of the results, it was found that regions with high helicity were correlated with regions of high turbulent kinetic energy dissipation. © 2008 Springer-Verlag

Análise da qualidade de medidas F-PIV 2D-2C e 2D-3C da velocidade da fase líquida em uma coluna de bolhas

Orientadores: Sávio Souza Venâncio Vianna, Guilherme José de CastilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: A análise da fluidodinâmica em reatores de coluna de bolha é importante na compreensão dos mecanismos relacionados à transferência de calor, transferência de massa e taxa de reação química. A precisão das medições experimentais depende diretamente do domínio de medição. A Velocimetria por imagem de partículas (PIV) é uma técnica não intrusiva utilizada para determinar o campo de velocidade 2D ou 3D. Um campo 2D-3C (bidimensional, três componentes) pode ser determinado por duas câmaras com projeções diferentes numa disposição estereoscópica (PIV 2D-3C). A perda de correlação devido ao movimento fora do plano de pares de imagens de partículas, que é comum em aplicações PIV, pode ser reduzida usando o sistema PIV 2D-3C. Um problema encontrado nas aplicações 2D-3C PIV está relacionado com o acesso óptico em algumas instalações. Para determinar a velocidade da fase líquida, não é interessante registrar as bolhas no escoamento multifásico. Por conseguinte, as partículas traçadoras fluorescentes combinadas com um filtro passa-alta na câmara são utilizadas nos sistemas Fluorescent PIV (F-PIV). Este trabalho tem como objetivo avaliar a qualidade das medidas 2D-2C e 2D-3C F-PIV da velocidade da fase líquida no regime de escoamento homogêneo e de transição homogêneo-heterogêneo de uma seção de coluna de bolha. As imagens 2D-2C e 2D-3C F-PIV foram processadas utilizando standard cross-correlation (SCC), ensemble correlation (EC) e sliding-average correlation (SAC) para comparar a qualidade das medições. O coeficiente de correlação cruzada, a relação sinal-ruído (SNR) e a quantificação de incerteza PIV estimada por estatísticas de correlação foram utilizados como indicadores de qualidade. A baixa concentração de imagem de partícula (baixa ppp) e a baixa faixa dinâmica de velocidade (baixa DVR) foram identificadas como fontes de ruído dominante nas medidas PIV. O efeito do baixo ppp foi relacionado diretamente com o comportamento dos indicadores de qualidade baseados na conectividade de vizinhança espacial, erro de reconstrução 3C e no diâmetro do pico de correlação. Quanto às condições de qualidade da abordagem SCC, foram obtidos cinco limites que garantem que os outliers (falsos vetores) podem ser corrigidos sem que o campo vetorial perca a representatividade do escoamento. No regime de escoamento homogêneo, os ruídos randômicos causados pela baixa ppp foram consideravelmente reduzidos utilizando a abordagem SACAbstract: The fluid dynamics analysis in bubble column reactors is important in understanding the mechanisms related to heat transfer, mass transfer and chemical reaction rate. The accuracy of the experimental measurements depends directly on the measurement domain. Particle image velocimetry (PIV) is a non-intrusive technique used to determine the 2D or 3D velocity field. A 2D-3C (two dimensional, three-component) field can be determined by two cameras with different projections in a stereoscopic arrangement (2D-3C PIV). The loss of correlation due to the out-of-plane motion of pairs of particle images, which is common in PIV applications, can be reduced using the 2D-3C PIV system. A problem encountered in 2D-3C PIV applications is related to optical access in some facilities. In order to determine the liquid phase velocity, it is not interesting to record bubbles in the multiphase flow. Therefore, fluorescent tracer particles combined with a high-pass filter on the camera are used in the Fluorescent PIV (F-PIV) systems. This work aims to evaluate the quality of the 2D-2C and 2D-3C F-PIV measurements of the liquid phase velocity in the homogeneous and homogeneous-heterogeneous transition flow regime of a bubble column. The 2D-2C and 2D-3C F-PIV images were processed using standard cross-correlation (SCC), ensemble correlation (EC), and sliding-average correlation (SAC) to compare the measurements quality. The cross-correlation coefficient, signal-to-noise ratio (SNR) and PIV uncertainty estimated by correlation statistics were used as quality indicators. The low particle image concentration (low ppp) and low dynamic velocity range (low DVR) were identified as dominant noise sources in the PIV measurements. The effect of the low ppp was directly related to the behavior of the quality indicators based on the spatial neighborhood connectivity, 3C reconstruction error, and correlation peak diameter. Regarding the quality conditions for SCC approach, five limits were obtained that guarantee that the outliers can be corrected without the vector field losing the representativeness of the flow. In the homogeneous flow regime, the random noise caused by low ppp was considerably reduced using the SAC approachDoutoradoEngenharia QuímicaDoutor em Engenharia Química2296/2013CAPE

Comprehensive review and application of particle image velocimetry

For a fluid dynamics experimental flow measurement technique, particle image velocimetry (PIV) provides significant advantages over other measurement techniques in its field. In contrast to temperature and pressure based probe measurements or other laser diagnostic techniques including laser Doppler velocimetry (LDV) and phase Doppler particle analysis (PDPA), PIV is unique due to its whole field measurement capability, non-intrusive nature, and ability to collect a vast amount of experimental data in a short time frame providing both quantitative and qualitative insight. These properties make PIV a desirable measurement technique for studies encompassing a broad range of fluid dynamics applications. However, as an optical measurement technique, PIV also requires a substantial technical understanding and application experience to acquire consistent, reliable results. Both a technical understanding of particle image velocimetry and practical application experience are gained by applying a planar PIV system at Michigan Technological University’s Combustion Science Exploration Laboratory (CSEL) and Alternative Fuels Combustion Laboratory (AFCL). Here a PIV system was applied to non-reacting and reacting gaseous environments to make two component planar PIV as well as three component stereographic PIV flow field velocity measurements in conjunction with chemiluminescence imaging in the case of reacting flows. This thesis outlines near surface flow field characteristics in a tumble strip lined channel, three component velocity profiles of non-reacting and reacting swirled flow in a swirl stabilized lean condition premixed/prevaporized-fuel model gas turbine combustor operating on methane at 5-7 kW, and two component planar PIV measurements characterizing the AFCL’s 1.1 liter closed combustion chamber under dual fan driven turbulent mixing flow