Journal of Visualization - Volume 3, issue 1

Authors: Kobayashi, Toshio | Maeda, Masanobu

Article Type: Other

Citation: Journal of Visualization, vol. 3, no. 1, pp. 1-1, 2000

Article Type: Other

Citation: Journal of Visualization, vol. 3, no. 1, pp. 3-8, 2000

Authors: Coutanceau, M. | Migeon, C. | Ehrmann, P.

Article Type: Research Article

Abstract: Within the fundamental context of quasi-2D bluff-body near-wake investigation, we analyse the way the initial wake vortices (primary and secondary vortices) form and develop with time behind a short (5.2:1) cylindrical semicircular shell (hollow at the back), after an impulsive start in translation. The study includes the transition regime and non-usual cross-sectional shapes. The structure of the vortices is examined by means of precise visualizations both in the mid-cross and mid-span planes. The …particulars induced by the hollow face are deduced from a comparison with the cases of analogous solid cylinders and more particularly with the full semicircular cylinder (Boisaubert et al., 1996; Coutanceau et al., 1998). The crosswise analysis shows that, except some fundamental difference at the separation initiation and some differences in details, a similar development of the Bénard-Kàrmàn-vortices is observed, thus : - the regime of the occurring structures changes beyond the first phase of development (i.e. t* ≥ 6) when Reynolds number is passing through a critical value Re_c (here 120 ≤ Re_c ≤ 140) - Kelvin-Helmholtz instabilities are detected for Re = 600 in the rolled-up separated shear layers originating from the sharp body-edges. On the contrary, the spanwise analysis reveals that the hollow face plays an important role in the time-development of the induced body-end three-dimensionalities (end-vortices and opposite spanwise currents) and intrinsic three-dimensionalities respectively. Thus, as opposed to solid bodies similarly limited in span, the emergence of clear patterns of secondary Taylor-Görtler-like vortices in the near wake have been experimentally proved for the first time when Re passes beyond the transition value of Re_t ≈ 200. The consequence on the global structure of the flow is deduced. Show more

Keywords: three-dimensional formation, cylindrical shell, cross and spanwise visualization, primary and secondary instabilities

Citation: Journal of Visualization, vol. 3, no. 1, pp. 9-26, 2000

Authors: Murai, Y. | Matsumoto, Y. | Yamamoto, F.

Article Type: Research Article

Abstract: Overall, as well as individual, bubble behavior of a plane bubble plume which is confined by two parallel plates is investigated by means of several qualitative and quantitative flow visualization methods. These include observation, measurement of time-averaged void distribution, surface tufts and particle imaging velocimetry. Several kinds of unstable motion of the bubble convection, which depend on the free surface initial height and on the gas flow rate, are observed. The bubble motion along the bubble …plume is precisely measured by an image-processing method which also delivers velocity vectors, number density and size of the bubbles. Show more

Keywords: multiphase flow, bubble plume, particle imaging velocimetry (PIV),

Citation: Journal of Visualization, vol. 3, no. 1, pp. 27-35, 2000

Authors: Stella, A. | Guj, G. | Mataloni, A.

Article Type: Research Article

Abstract: This paper presents visualizations of reacting, round jets of the premixed and nonpremixed type realized by using interferometry and, complementarily, direct photography. The available interferometer, proposed by Carlomagno (1986), employs low-cost components and is flexible and robust to geometrical misalignments, allowing the drawbacks limiting the application of traditional interferometric systems to be overcome. Several flames are produced by varying the non-dimensional, governing parameters (Reynolds number, equivalence ratio, Grashof number). The results discussion …is organized considering laminar, transitional and turbulent flows. In the steady, laminar case, in view of the radial symmetry of the fringes pattern, the temperature field is reconstructed by the interferograms. The structure of the transitional and turbulent combusting jets, primarily determined by shear layer destabilization mechanisms and large-scale vortices formation due to buoyancy, is analyzed and differences with isothermal flows are pointed out. In turbulent regime, studied only for premixed combustion case, qualitative insights into the structure of the reaction zone as a function of the equivalence ratio and turbulence properties in the incoming fresh mixture are also deduced. Show more

Keywords: interferometry, jet flames, combustion, destabilization, coherent structures

Citation: Journal of Visualization, vol. 3, no. 1, pp. 37-50, 2000

Authors: Morioka, T. | Sakurai, N. | Maeno, K. | Honma, H.

Article Type: Research Article

Abstract: Nonequilibrium radiation phenomena behind strong shock waves in low-density air are observed by using a couple of CCD camera systems in a shock tube experiment. The simultaneous observation for total radiation and its spectral radiation is carried out in order to elucidate space-dependent contribution of an individual radiation spectrum to the total radiation intensity. The results are shown for the shock velocity range from 9.0 km/s to 12.1 km/s at the initial pressure 13.3 Pa. Wavelength …range is selected from 300 nm to 445 nm to investigate mainly the contributions from UV radiation. It is found that the band spectra due to the molecular species N_2^+ and CN mainly contribute to the first-peak, while the spectra due to the atomic species O^+ and N mainly contribute to the formation of the second-peak. It is also found that the Balmer series in H spectra strongly contributes to the second-peak. The radiation along the tube wall surfaces is composed of the same constituents as those around the tube axis as well as the spectra coming from the impurities. Show more

Keywords: strong shock wave, radiation, spectroscopy

Citation: Journal of Visualization, vol. 3, no. 1, pp. 51-61, 2000

Authors: Protopopov, V.V. | Danilov, V.V.

Article Type: Research Article

Abstract: In the x-ray region the reflectivity of a superpolished surface strongly depends on its roughness. This effect may be used to obtain a two-dimensional map of the roughness spatial distribution for flat surfaces with an average roughness height of the order of one nanometer or less. The method described in the paper lies in the illumination of the sample by a highly collimated x-ray beam, and a linear one-dimensional scanning of the sample with simultaneous registration …of the specular component of the reflected beam by multielement linear detector. This method may be used to monitor the surface quality of silicon semiconductor wafers, computer hard disks, x-ray and laser mirror substrates etc. Show more

Keywords: roughness, x-ray, reflection, scanning, linear detector

Citation: Journal of Visualization, vol. 3, no. 1, pp. 63-70, 2000

Authors: Kinoshita, K. | Togoshi, H.

Article Type: Research Article

Abstract: Typical patterns of volcanic clouds from Mt. Sakurajima are discussed with photographs and satellite images. Volcanic clouds are classified into three types, i.e., eruption cloud, steady flow as a plume, and sequential puffs, according to the variation of the ejection activity with time. While the rise of eruption clouds depends on the strength of the eruption, the vertical shapes of the plumes are sensitive to the velocity of the cross winds around and above the summit …of the volcanic mountain. Very strong winds cause blowing down and bouncing up of the plume along the mountain lee wave. Various patterns of horizontal dispersion are observed from the ground and from satellites; typical ones are linear advection, fan- and belt-type spreads, and flat stagnation. These patterns are essentially determined by the wind shear within the vertical thickness of the volcanic cloud. Show more

Keywords: volcanic eruption, plume dispersion, satellite imagery, mountain lee wave

Citation: Journal of Visualization, vol. 3, no. 1, pp. 71-78, 2000

Authors: Asztalos, B. | Yamane, T. | Nishida, M. | Masuzawa, T. | Konishi, Y.

Article Type: Research Article

Abstract: A centrifugal blood pump for artificial heart has to have low hemolysis and no thrombus formation. For finding and removing the fluid dynamic causes of the above mentioned phenomena, flow visualization was utilized, as flow visualization can identify the high shear and stagnation locations which relate to hemolysis and thrombus formation respectively. In the present paper, general fluid dynamic characteristics of centrifugal blood pumps will be extracted, through analyzing four typical centrifugal pumps with flow …visualization technique. Finding shear in the volute and diffuser regions, confirming vortex formation at washout holes, and quantitative analysis of the flow in the inlet regions are the shown examples. The obtained results correspond well to hemolysis tests, which proves that flow visualization is a useful tool in developing and analyzing blood pumps for artificial hearts. Show more

Keywords: flow visualization, particle tracking velocimetry, centrifugal blood pump, shear evaluation, artificial heart

Citation: Journal of Visualization, vol. 3, no. 1, pp. 79-92, 2000