Construction of a Hybrid PTV and its Application for the Flow Analyses of a Free-Horizontal-Axis Tidal Power Generation System

A new hybrid PTV algorithm in which a linear transformation was adopted, was constructed and its performances were validated. For the performance test, a set of numerical data on the Taylor-Green vortex flows was used. Using the data sets, artificial images were generated. In the test, the constructed hybrid PTV algorithm showed the best performance in the case where the particle number density was more than 4,000. In order to validate the applicabilities of the constructed hybrid PTV algorithm, it was used for the measurements of the rectangular wake flows. Further, the conventional PIV and PTV techniques were used for the measurements of the same flow fields for comparison. The vortical structures of the rectangular wake flows were compared with those obtained by the conventional PIV, a PTV technique (2-frame match probability), and by the constructed hybrid PTV algorithm. A numerical simulation (CFD) was carried out for the same rectangular wake flows in order to compare the results with those obtained by the PIV, the PTV, and the constructed hybrid PTV algorithmthrough which it was verified that the pressure distribution at the rear part of the S type blade was much more uniform than those of A and SE models. This implies that the S type loses much more kinetic energy in the blade wake. This result was affirmed by electric power[W] meter measurements. It was shown that the constructed hybrid PTV algorithm can be intensively used for the flow measurements of the free- horizontal-axis tidal power generation system. Following is the structure of this paper: In the first chapter, the research background and the purpose of the paper were mentioned. In the second chapter, the principles of the PIV and PTV techniques were mentioned, and the newly constructed hybrid PTV algorithm was explained in detail. The results of the performance test on the constructed hybrid PTV algorithm were mentioned. In the third chapter, an experiment on a rectangular wake was carried out in order to evaluate the performance of the constructed hybrid PTV algorithm. The results by the gray-level cross-correlation PIV and the 2-frame based PTV were also discussed for comparison with those obtained by the constructed hybrid PTV algorithm. In the fourth chapter, a practical application of the constructed hybrid PTV algorithm was made. The flow features around the blades of the free-horizontal-axis tidal power generation system were investigated. Lastly, summaries were made emphasizing the benefits of the constructed hybrid PTV algorithm for industrial applications.it was used for the measurements of the vortical structures of a free- horizontal-axis tidal power generation system. In the tests, three different models (A, S, SE) were used, and the measured velocity was used for constructing the velocity diagram based upon the momentum theory. The results attested that the SE model showed the highest output power at the same blade angles among A, S and SE models. Further, it showed that the SE model showed good performances of power generation under fast current speeds and the S model showed good performances under slow current speeds. Using the same shape model, higher blade angle showed higher power generation. The pressure fields were calculated using the velocity vector fieldsthrough which it was verified that the constructed hybrid PTV algorithm results showed better compatibility with those obtained by the CFD simulation. Validating the constructed hybrid PTV algorithm제1장 서 론 1 1.1 연구배경 1 1.2 연구목적 5 1.3 연구내용 6 제2장 하이브리드 입자추적유속계 9 2.1 PIV, PTV 방법의 원리 9 2.1.1 PIV 방법의 원리 9 2.1.2 PTV 방법의 원리 12 2.2 하이브리드 입자추적유속계의 원리 19 2.3 가상영상의 구축 30 2.4 하이브리드 입자추적유속계 알고리즘의 성능 비교 분석 32 제3장 사각주 후류 측정적용에 의한 실용성 성능 평가 44 3.1 실험장치 및 방법 44 3.2 결과 및 비교 46 3.2.1 속도장 비교 46 3.2.2 와도장 비교 53 제4장 자유수평축 조류발전시스템 56 4.1 조류발전의 개요 56 4.2 자유수평축 조류발전시스템의 모델의 개요 59 4.3 발전특성 분석 63 4.4 유동해석 결과 및 고찰 73 4.4.1 속도장 분석 73 4.4.2 운동량이론과 성능 분석 78 4.4.3 와도장 분석 98 4.4.4 압력장 분석 102 제5장 결론 107 참고문헌 10

Estimated Uncertainties in the Idaho National Laboratory Matched-Index-of-Refraction Lower Plenum Experiment

The purpose of the fluid dynamics experiments in the MIR (Matched-Index-of-Refraction) flow system at Idaho National Laboratory (INL) is to develop benchmark databases for the assessment of Computational Fluid Dynamics (CFD) solutions of the momentum equations, scalar mixing, and turbulence models for typical Very High Temperature Reactor (VHTR) plenum geometries in the limiting case of negligible buoyancy and constant fluid properties. The experiments use optical techniques, primarily particle image velocimetry (PIV) in the INL MIR flow system. The benefit of the MIR technique is that it permits optical measurements to determine flow characteristics in passages and around objects to be obtained without locating a disturbing transducer in the flow field and without distortion of the optical paths. The objective of the present report is to develop understanding of the magnitudes of experimental uncertainties in the results to be obtained in such experiments. Unheated MIR experiments are first steps when the geometry is complicated. One does not want to use a computational technique, which will not even handle constant properties properly. This report addresses the general background, requirements for benchmark databases, estimation of experimental uncertainties in mean velocities and turbulence quantities, the MIR experiment, PIV uncertainties, positioning uncertainties, and other contributing measurement uncertainties

A review of experiments on stationary bluff-body wakes

Experimental studies dealing with the wake of isolated stationary bluff-bodies are reviewed. After briefly recalling the pioneering works in this domain, the paper focuses on recent research conducted with the latest experimental methods and techniques. The review encompasses a range of topics, including, the effects of bluff-body geometry (non-circular cross sections and nonuniformity in spanwise direction), steady and unsteady (periodic and non-periodic) inflow conditions; surface proximity (rigid wall, confinement and water free surface) and non-Newtonian fluids. Focus is brought to the flow physics of the wakes, including especially the complex threedimensional and oscillatory behaviours induced by the periodic vortex shedding phenomenon. The paper aims to offer a critical and systematic review of new knowledge and findings on the subject area, as well as emerging? and the most frequently adopted experimental techniques. The review also helps identifying knowledge gaps in the literature that need to be addressed in future investigations

Experimental and computational study of turbulent mixing in a confined rectangular jet

Vortex behavior and characteristics in a confined rectangular jet with a co-flow were examined using vortex swirling strength as a defining characteristic. On the left side of the jet, the positively (counterclockwise) rotating vortices are dominant, while negatively rotating vortices are dominant on the right side of the jet. The characteristics of vortices, such as population density, average size and strength, and deviation velocity were calculated and analyzed in both the cross-stream direction and the streamwise direction. In the near-field of the jet, the population density, average size and strength of the dominant direction vortices show high values on both sides of the center stream with a small number of counter-rotating vortices produced in the small wake regions close to jet outlet. As the flow develops, the wake regions disappear, these count-rotating vortices also disappear, and the population of the dominant direction vortices increase and spread in the jet. The mean size and strength of the vortices decrease monotonically with streamwise coordinate. The signs of vortex deviation velocity indicate the vortices transfer low momentum to high velocity region and high momentum to the low velocity region. The developing trends of these characteristics were also identified by tracing vortices using time-resolved PIV data. Both the mean tracked vortex strength and size decrease with increasing downstream distance overall. At the locations of the left peak of turbulent kinetic energy, the two point spatial cross-correlation of swirling strength with velocity fluctuation and concentration fluctuation were calculated. All the correlation fields contain one positively correlated region and one negatively correlated region although the orientations of the correlation fields varied, due to the flow transitioning from wake, to jet, to channel flow. Finally, linear stochastic estimation was used to calculate conditional structures. The large-scale structures in the velocity field revealed by linear stochastic estimation are spindle-shaped with a titling stream-wise major axis. Vortex behavior and characteristics in a confined rectangular wake were also examined using swirling strength as a defining characteristic of a vortex. Instantaneous swirling strength field shows that positively (counterclockwise) rotating vortices are dominant on the right side of the wake and negatively (clockwise) rotating vortices are dominant on the left side. The population density, average size and strength of vortex cores all shows high peak values both sides of the wakes, while these peaks decrease quickly and the profiles broaden as the flow progresses downstream. The changing of vortex core maximum strength is seen relatively faster than the change of the core size. The results of mean cross-stream wise deviation velocity of vortex core shows the vortices in the wake spread from the neighborhood of wake to the centers of the free stream, and the mean streamwise deviation velocity indicates that vortices bringing high momentum fluid of the free stream into the the wake. Two point spatial cross-correlations of swirling strength with velocity fluctuations and concentration fluctuations were also calculated. All the cross correlation fields shown here exhibit a ``butterfly\u27\u27 like shape, with one ``wing\u27\u27 with positive correlation values and the other ``wing\u27\u27 with negative values. The axises of correlation fields are oriented in the streamwise direction in R λ u\u27 contours, and they tile towards the wake center on the both sides of the wake,while the axises in R λ v\u27 are oriented in the cross-stream direction, and they tile downstream on the both sides of the wake. The R λ phi\u27 results show some similarity to those of R λ v\u27, indicating the vortices play a similar role in mass transfer as in momentum transfer. Linear stochastic estimation was used to interpret the cross correlation result and visualize the underlining large scale coherent structures. The LSE results show a clear vortex street pattern in far fields of the wake, indicating the vortices, developed independently on both sides of the splitter plates, are reorganized and coherent as the flow develops downstream. Large-eddy simulations (LES) were performed for a confined rectangular liquid jet with a co-flow and compared in detail with particle image velocimetry (PIV) measurements. A finite-volume CFD library, OpenFOAM, was used to discretize and solve the filtered Navier-Stokes equation. The effects of grid resolution, numerical schemes and subgrid models on the LES results were investigated. Grid independence has been shown. The second and fourth order schemes showed the nearly same performance, while the fourth order scheme costs much more computationally. Subgrid model comparison showed that the locally dynamic procedure is necessary for complex flow simulation. Model validation was performed by comparing LES data for the one-point velocity statistics such as the mean and the root-mean-square velocity, shear stress, correlation coefficient, velocity skewness and flatness with the PIV data. In addition, LES data for the two-point spatial correlations of velocity fluctuations that provide structural information were computed and compared with PIV data. Very good agreement was obtained leading to the conclusion that the LES velocity field captures the large-scale structures present in the actual flow. Experimental data of combined particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) measurements are used to analyzed the flow between the two scalar interfaces of confined turbulent jet and wake flow. The fluid of center stream of both flow cases contains a fluorescent dye, and normalized PLIF images were used to discriminate the inner and outer boundaries of the center stream. The growth of the boundaries of both flow cases are plotted and analyzed. The mean and fluctuations of the passive scalar, velocity, stain rate, and vorticity are determined relative to the locations of the two boundaries. The results show some unique perspectives of this co-flowing confined rectangular jet flow. The fluctuations of the passive scalar shows high values close to the outer boundary of jet , and the most of the properties of the velocity fields show high values on the left side of inner boundaries of the jet. The results of wake case are very symmetrical about the center of the wake, indicating the presence of the vortex street

Advanced Computational Thermal Fluid Physics (CTFP) and Its Assessment for Light Water Reactors and Supercritical Reactors

Background: The ultimate goal of the study is the improvement of predictive methods for safety analyses and design of Generation IV reactor systems such as supercritical water reactors (SCWR) for higher efficiency, improved performance and operation, design simplification, enhanced safety and reduced waste and cost. The objective of this Korean / US / laboratory / university collaboration of coupled fundamental computational and experimental studies is to develop the supporting knowledge needed for improved predictive techniques for use in the technology development of Generation IV reactor concepts and their passive safety systems. The present study emphasizes SCWR concepts in the Generation IV program