The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Yasushi Takeda - One of the best experts on this subject based on the ideXlab platform.

  • development of a novel flow metering system using ultrasonic Velocity profile measurement
    Experiments in Fluids, 2002
    Co-Authors: Michitsugu Mori, Yasushi Takeda, T Taishi, Masanori Aritomi, N Furuichi, Hiroshige Kikura
    Abstract:

    A new flow metering system using an ultrasonic Doppler method has been developed. By this method, an Instantaneous Velocity profile is measured and its integral is evaluated to give flow rate. Instead of making multidimensional flow mapping to evaluate its performance, the method was assessed in laboratory experiments where single line measurements were used over the whole pipe diameter or radius to determine the flow rate. The system shows a good capability of tracking transient flows. Its accuracy was investigated using the National Institute of Standards and Technology (NIST) flow standards in Gaithersburg, MD, USA; averaged results show its deviation from NIST results to be 0.18% for Re=400 K and 0.58% for Re=2.6 M. Good repeatability and reproducibility were also confirmed.

  • spiral and circular waves in the flow between a rotating and a stationary disk
    Experiments in Fluids, 1999
    Co-Authors: Lionel Schouveiler, Mariepierre Chauve, Yasushi Takeda
    Abstract:

    Circular and spiral waves are observed in the flow between a rotating and a stationary disk. These waves are generated by instabilities of the stationary disk boundary layer. This experimental work is devoted to their study by means of flow visualization and measurements of the associated Velocity fields. In particular, Instantaneous Velocity profiles are measured by ultrasonic Doppler anemometry. The spatio-temporal characteristics of the waves are studied with the help of Fourier transforms of these Velocity signals.

  • Instantaneous Velocity profile measurement by ultrasonic doppler method
    Jsme International Journal Series B-fluids and Thermal Engineering, 1995
    Co-Authors: Yasushi Takeda
    Abstract:

    The Ultrasonic Velocity Profile (UVP) measuring method has been developed at PSI. It utilizes pulsed ultrasonic echography together with the detection of the Instantaneous Doppler shift frequency. This method mainly has the following advantages over the conventional techniques : 1) an efficient flow mapping process, 2) applicability to opaque liquids and 3) a record of the spatiotemporal Velocity field. After a brief introduction of its principle, the characteristics and specifications of the present system are given. Then examples such as for oscillating pipe flow, T-branching flow of mercury and circular free jet flow in fluid engineering are described, which confirm the above advantages. In a further in-depth study of fluid dynamics, results of an investigation of modulated wavy flows in a rotating Couette system are presented. The position-dependent power spectrum and time-dependent energy spectral density were used in order to study the dynamic characteristics of the flow, and subsequently the Velocity field was decomposed into intrinsic wave structure based on the two-dimensional Fourier analysis.

Philippe Coussot - One of the best experts on this subject based on the ideXlab platform.

  • new technique for reconstructing Instantaneous Velocity profiles from viscometric tests application to pasty materials
    Journal of Rheology, 2004
    Co-Authors: Jeanchristophe Baudez, Stephane Rodts, Xavier Chateau, Philippe Coussot
    Abstract:

    We present a new technique for reconstructing the Instantaneous Velocity profiles during creep, dynamic, or ramp tests under controlled stress in wide-gap Couette flows, from a series of similar tests under smaller stress amplitudes. This approach is based on a rigourous theory, and since it requires that the fluid does not flow close to the outer cylinder, it is particularly suitable for yield stress fluids. The interest of this reconstruction technique is that it is simpler than direct techniques (nuclear magnetic resonance, light scattering, particle imaging velocimetry, etc.) and has almost no limitations in time and space resolution. Thus, one can obtain the Velocity profiles under steady-state and transient flows. We show that for a commercial hair gel the Velocity profile obtained with this technique is in excellent agreement with that found from magnetic resonance imaging rheometry within the range of measurement (four decades of Velocity). From other tests with a mustard and a kaolin–water suspen...

F Scarano - One of the best experts on this subject based on the ideXlab platform.

  • three dimensional vortex organization in a high reynolds number supersonic turbulent boundary layer
    Journal of Fluid Mechanics, 2010
    Co-Authors: G E Elsinga, Ronald J Adrian, B W Van Oudheusden, F Scarano
    Abstract:

    Tomographic particle image velocimetry was used to quantitatively visualize the three-dimensional coherent structures in a supersonic (Mach 2) turbulent boundary layer in the region between y/? = 0.15 and 0.89. The Reynolds number based on momentum thickness Re? = 34000. The Instantaneous Velocity fields give evidence of hairpin vortices aligned in the streamwise direction forming very long zones of low-speed fluid, consistent with Tomkins & Adrian (J. Fluid Mech., vol. 490, 2003, p. 37). The observed hairpin structure is also a statistically relevant structure as is shown by the conditional average flow field associated to spanwise swirling motion. Spatial low-pass filtering of the Velocity field reveals streamwise vortices and signatures of large-scale hairpins (height > 0.5?), which are weaker than the smaller scale hairpins in the unfiltered Velocity field. The large-scale hairpin structures in the Instantaneous Velocity fields are observed to be aligned in the streamwise direction and spanwise organized along diagonal lines. Additionally the autocorrelation function of the wall-normal swirling motion representing the large-scale hairpin structure returns positive correlation peaks in the streamwise direction (at 1.5? distance from the DC peak) and along the 45° diagonals, which also suggest a periodic arrangement in those directions. This is evidence for the existence of a spanwise–streamwise organization of the coherent structures in a fully turbulent boundary layer.

Marc Rabaud - One of the best experts on this subject based on the ideXlab platform.

  • Instantaneous Velocity profiles during granular avalanches
    Physical Review Letters, 2005
    Co-Authors: Sylvain Courrech Du Pont, Raphael Fischer, Philippe Gondret, Bernard Perrin, Marc Rabaud
    Abstract:

    We perform experimental measurements of the Instantaneous Velocity profile of the flowing layer during granular avalanches. In the pile depth, the Velocity profile follows a pure exponential decrease in contrast with steady flows that are known to exhibit a well developed upper linear part. The Velocity profile in the pile width is a plug flow with two exponential boundary layers at the walls. Even though no steady state is observed during the avalanche, these Velocity profiles are self-similar and build up almost Instantaneously, with time independent characteristic lengths.

Ronald J Adrian - One of the best experts on this subject based on the ideXlab platform.

  • three dimensional vortex organization in a high reynolds number supersonic turbulent boundary layer
    Journal of Fluid Mechanics, 2010
    Co-Authors: G E Elsinga, Ronald J Adrian, B W Van Oudheusden, F Scarano
    Abstract:

    Tomographic particle image velocimetry was used to quantitatively visualize the three-dimensional coherent structures in a supersonic (Mach 2) turbulent boundary layer in the region between y/? = 0.15 and 0.89. The Reynolds number based on momentum thickness Re? = 34000. The Instantaneous Velocity fields give evidence of hairpin vortices aligned in the streamwise direction forming very long zones of low-speed fluid, consistent with Tomkins & Adrian (J. Fluid Mech., vol. 490, 2003, p. 37). The observed hairpin structure is also a statistically relevant structure as is shown by the conditional average flow field associated to spanwise swirling motion. Spatial low-pass filtering of the Velocity field reveals streamwise vortices and signatures of large-scale hairpins (height > 0.5?), which are weaker than the smaller scale hairpins in the unfiltered Velocity field. The large-scale hairpin structures in the Instantaneous Velocity fields are observed to be aligned in the streamwise direction and spanwise organized along diagonal lines. Additionally the autocorrelation function of the wall-normal swirling motion representing the large-scale hairpin structure returns positive correlation peaks in the streamwise direction (at 1.5? distance from the DC peak) and along the 45° diagonals, which also suggest a periodic arrangement in those directions. This is evidence for the existence of a spanwise–streamwise organization of the coherent structures in a fully turbulent boundary layer.

  • piv study of small scale flow structure around a rushton turbine
    Aiche Journal, 2001
    Co-Authors: Kendra V Sharp, Ronald J Adrian
    Abstract:

    The structure of turbulent motions was measured in a region surrounding the blade tips of a Rushton turbine mixer. The tip vortices responsible for micromixing were created in this region, as was the radial jet that drives the large-scale circulation responsible for macromixing. Measurements of Instantaneous Velocity fields in axial–radial planes showed large cycle-to-cycle variability relative to the mean. The average measurements of the azimuthal vorticity and the Reynolds stresses in the radial–axial plane showed the growth and motion of the tip vortices as they drift away from the blades. Radial and axial spatial derivatives were measured to assess various methods of computing the turbulent viscous dissipation. The small scales were significantly anisotropic at the Reynolds numbers studied.

  • theory of cross correlation analysis of piv images
    Flow Turbulence and Combustion, 1992
    Co-Authors: Richard D Keane, Ronald J Adrian
    Abstract:

    To improve the performance of particle image velocimetry in measuring Instantaneous Velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.