Particle Imaging Technique Research Articles

Pipe flow measurement by using a side-scattering holographic particle imaging technique

A side scattering holographic particle imaging technique has been developed and demonstrated to be a capable tool for obtaining good quality images of a particle field in a high Reynolds number pipe flow. Instantaneous three-dimensional velocity components can be measured. The streamwise velocity error is estimated to be about 5%. Limitations of this optical set-up are discussed. The methodology and results presented will be of use for designing a pulsed laser holographic technique for turbulent velocity measurement or particle diagnostics in a pipe flow.

The role of fuel-rich clusters in flame stabilization and NO x emission reduction with precessing jet pulverized fuel flames

Effects of controlling the local structure of turbulence in confined pulverized coal flames have been investigated using both reacting and nonreacting experiments. The reacting experiments, conducted in a 130-kW rotary kiln simulator, showed that flame ignition distance is reduced by more than a factor of 2 compared to a monochannel flame by use of a precessing jet of air to enlarge the scale of mixing in the emerging coal jet. NO x emissions are reduced from more than 200 ppm to 80 ppm (0% O 2 ) by using precessing jet burners. Qualitative cold-flow visualization studies demonstrated that precessing airflows break up the surrounding annular flow, simulating a coal transport flow, into much larger turbulent flow structures, causing increased residence times in the pre-ignition region. Particle-imaging techniques in a nonreacting flow show that, in the pre-ignition region, the motion of the smaller particles (<30 μ m) are affected by the large flow structures and form clusters with long residence times. Flame stability improvements are attributed to increased particle heating rates in the clusters by radiation due to increased absorptivity and increased residence time in the near burner zone. The NO x reduction can be explained by the generation of large-scale particle clusters that provide local instantaneous fuel-rich combustion environments. This work demonstrates that the production of large-scale clustering effects has the potential to provide an alternative means to simultaneously control NO x and improve flame stability relative to existing staging techniques, which control the mean stoichiometry of various flame zones.

Investigation of Flow Field around a Darrieus Rotor by Flow Visualization and Image Analysis.

Flow around a Darrieus wind turbine operating at low tip-speed ratios is studied by flow visualization using the dye injection technique and also by measuring the velocity field using a particle imaging and conditional sampling technique. The instantaneous flow patterns observed upon the visualization pictures correspond well to the measured velocity distributions, vorticity contours and velocity magnitude maps. It is found that two pairs of mushroom-type vortices are shed from the blade during a rotation of the rotor, which is due to the dynamic stall phenomenon. These stall vortices are produced by the flow separation over the suction side of the blade and the formation of roll-up vortices from the pressure side. The stall vortices at small incidence angles advance to the returning blade side, while those at large incidence angles grow along the moving blade and interact with flow near the blade. The effect of tip-speed ratios on the growth of stall vortices is also examined.

B204 ダリウス歯車における動的失速の可視化と速度場測定

Flow near and around a Darrieus wind turbine operating at low tip-speed ratios is studied by flow visualization with dye injection technique and also by measuring the velocity field with a particle imaging and conditional sampling technique. The instantaneous flow patterns observed in the visualization pictures are well reproduced in the measured velocity distributions, vorticity con-tours and maps of velocity magnitude. It is found that two pairs of mashroom-type vortices are shed from the blade during a rotation of the rotor, which is due to the dynamic stall phenomena. These stall vortices are produced by the flow separation over the suction side of the blade and the formation of roll-up vortices from the pressure side.

111 自動車空調用ユニット内流れの混合過程の可視化と画像計測

The flow in an air conditioning unit for automobile is studied experimentally at isothermal temperature conditions in a water tunnel to investigate the flow mixing mechanisms inside the unit at various angles of mixing plate. The mixing process of the flow is visualized by the laser induced fluorescence and the velocity field is studied quantitative by the particle imaging technique. The analized image of the two fluorescence dyes reproduces well the dispersion of heater flow in the full-scale unit, which indicates the usefulness of this visualization the technique of mixing flow.

Measurements and simulations of particle dispersion in a turbulent flow

A particle imaging technique has been used to collect droplet displacement statistics in a round turbulent jet of air. Droplets are injected on the jet axis, and a laser sheet and position-sensitive photomultiplier tube are used to track their radial displacement and time-of-flight. Dispersion statistics can be computed which are Lagrangian or Eulerian in nature. The experiments have been simulated numerically using a second-order closure scheme for the jet and a stochastic simulation for the particle trajectories. Results are presented for non-vaporizing droplets of sizes from 35 to 160 μm. The simulations have underscored the importance of initial conditions and early droplet displacement history on the droplet trajectory for droplets with large inertia relative to the turbulence. Estimates of initial conditions have been made and their effect on dispersion is quantified.

Unsteady crossflow on a delta wing using particle image velocimetry

5has shown that the vortex breakdown response is typically an order of magnitude slower than the convective time scale; in essence, this means that the location of breakdown substantially lags that expected from quasistatic considerations. In view of these observations of the phase lag of vortex breakdown location, one expects the cross-sectional development of the leading-edge vortices to exhibit an analogous phase lag. Such lag has been demonstrated using qualitative flow visualization.6 For this type of lag, the overall features of the velocity field during pitching maneuvers have been characterized separately.5 Therein, the velocity field at several instants during the wing motion is compared with its quasistatic counterpart to show the consequence of the movement of the location of vortex breakdown through the plane of interest. The unsteady loading in relation to the foregoing features of the flow structure has been reviewed independently7 and illustrates that corresponding phase lags and hysteresis of the unsteady forces are induced during a typical maneuver. The emergence of particle image velocimetry (PIV) provides the potential for detailed characterization of the unsteady velocity field past a moving delta wing with an accuracy comparable to laser-Doppler anemometry (LD A) but without the necessity of phase referencing. This high-resolution optical method allows detailed definition of the flow structure at a given instant, thereby providing a more accurate representation of the flowfield than can be accomplished with phasereferencing techniques. The objective of this note is to report on the first characterization of the unsteady flow structure past a pitching delta wing via particle imaging techniques and to reveal new features of the flow structure during pitch-up and pitch-down maneuvers. The major challenge of applying PIV to this class

Turbidity study of the process of film formation of polymer particles in drying thin films of acrylic latices: I. Intrastructure of acrylic latices studied with transmission spectrophotometry

The aim of this study is to determine the factors that define the process of film formation of binder particles in drying aqueous dispersion coatings, based on acrylic polymers. The film formation process is investigated with transmission spectrophotometry. In this paper static measurements are used to relate the turbidity behavior of thin latex films with the physical properties of the latex. This paper focuses on the intrastructure in films of concentrated acrylic dispersions. In concentrated latices the binder particles are arranged in closely packed structures, which cause colored light patterns, due to Bragg diffraction. Light waves traveling in the latex film are scattered at the internal structures of the spheres and the water voids. The pattern of the light transmission as a function of wavelength reveals the internal structure of the latex film. The influence of weight fraction, particle size, film thickness, and particle size distribution on the transmission pattern has been investigated. The results are verified with other particle size measurements and imaging techniques.