The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Eric C. Marineau - One of the best experts on this subject based on the ideXlab platform.
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Particle image velocimetry measurements of Mach 3 turbulent boundary layers at low Reynolds numbers
Experiments in Fluids, 2018Co-Authors: Jonathan M. Brooks, Ashwani K. Gupta, Michael S. Smith, Eric C. MarineauAbstract:Particle image velocimetry (PIV) measurements of Mach 3 turbulent boundary layers (TBL) have been performed under low Reynolds number conditions, \(Re_\tau =200{-}1000\), typical of direct numerical simulations (DNS). Three reservoir pressures and three measurement locations create an overlap in parameter space at one research facility. This allows us to assess the effects of Reynolds number, particle response and boundary layer thickness separate from facility specific experimental apparatus or methods. The Morkovin-scaled streamwise Fluctuating Velocity profiles agree well with published experimental and numerical data and show a small standard deviation among the nine test conditions. The wall-normal Fluctuating Velocity profiles show larger variations which appears to be due to particle lag. Prior to the current study, no detailed experimental study characterizing the effect of Stokes number on attenuating wall-normal Fluctuating velocities has been performed. A linear variation is found between the Stokes number (St) and the relative error in wall-normal Fluctuating Velocity magnitude (compared to hot wire anemometry data from Klebanoff, Characteristics of Turbulence in a Boundary Layer with Zero Pressure Gradient. Tech. Rep. NACA-TR-1247, National Advisory Committee for Aeronautics, Springfield, Virginia, 1955). The relative error ranges from about 10% for \(St=0.26\) to over 50% for \(St=1.06\). Particle lag and spatial resolution are shown to act as low-pass filters on the Fluctuating Velocity power spectral densities which limit the measurable energy content. The wall-normal component appears more susceptible to these effects due to the flatter spectrum profile which indicates that there is additional energy at higher wave numbers not measured by PIV. The upstream inclination and spatial correlation extent of coherent turbulent structures agree well with published data including those using krypton tagging velocimetry (KTV) performed at the same facility.
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Particle image velocimetry measurements of Mach 3 turbulent boundary layers at low Reynolds numbers
Experiments in Fluids, 2018Co-Authors: Jonathan M. Brooks, Ashwani K. Gupta, Michael S. Smith, Eric C. MarineauAbstract:Particle image velocimetry (PIV) measurements of Mach 3 turbulent boundary layers (TBL) have been performed under low Reynolds number conditions, $$Re_\tau =200{-}1000$$ R e τ = 200 - 1000 , typical of direct numerical simulations (DNS). Three reservoir pressures and three measurement locations create an overlap in parameter space at one research facility. This allows us to assess the effects of Reynolds number, particle response and boundary layer thickness separate from facility specific experimental apparatus or methods. The Morkovin-scaled streamwise Fluctuating Velocity profiles agree well with published experimental and numerical data and show a small standard deviation among the nine test conditions. The wall-normal Fluctuating Velocity profiles show larger variations which appears to be due to particle lag. Prior to the current study, no detailed experimental study characterizing the effect of Stokes number on attenuating wall-normal Fluctuating velocities has been performed. A linear variation is found between the Stokes number ( St ) and the relative error in wall-normal Fluctuating Velocity magnitude (compared to hot wire anemometry data from Klebanoff, Characteristics of Turbulence in a Boundary Layer with Zero Pressure Gradient. Tech. Rep. NACA-TR-1247, National Advisory Committee for Aeronautics, Springfield, Virginia, 1955 ). The relative error ranges from about 10% for $$St=0.26$$ S t = 0.26 to over 50% for $$St=1.06$$ S t = 1.06 . Particle lag and spatial resolution are shown to act as low-pass filters on the Fluctuating Velocity power spectral densities which limit the measurable energy content. The wall-normal component appears more susceptible to these effects due to the flatter spectrum profile which indicates that there is additional energy at higher wave numbers not measured by PIV. The upstream inclination and spatial correlation extent of coherent turbulent structures agree well with published data including those using krypton tagging velocimetry (KTV) performed at the same facility.
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PIV Measurements of Mach 2.7 Turbulent Boundary Layer with Varying Reynolds Numbers
54th AIAA Aerospace Sciences Meeting, 2016Co-Authors: Jonathan M. Brooks, Ashwani K. Gupta, Michael S. Smith, Eric C. MarineauAbstract:A series of Particle image velocimetry (PIV) experiments have been performed in the AEDC White Oak Mach 3 Calibration Wind Tunnel to investigate the effect of the Reynolds number based on the momentum thickness, Reθ = 1673 − 7130, on mean streamwise and wall normal Fluctuating Velocity and Reynolds stress profiles in a turbulent boundary layer. High Reθ cases show the Morkovin transformed wall normal Fluctuating Velocity profile in good agreement with Klebanoff incompressible data as well as DNS above ~0. 4δ, and streamwise Fluctuating Velocity agreement above 0. 1δ. No conclusive Fluctuating Velocity magnitude dependence on Reθ is observed. The greater error at lower spatial resolution and higher Stokes number indicates that the spatial resolution and particle response have a greater influence on Fluctuating Velocity profiles. Estimates of the power spectra density from PIV measurements reveal truncation of energy at high wavenumbers due to particle lag and spatial filtering. The flatter spectra of the wall normal Velocity, compared to the streamwise direction, leads to increased energy at high wavenumbers which could explain why the wall normal Fluctuating Velocity profile is more susceptible to measurement error from particle lag and spatial filtering.
Jerome Morchain - One of the best experts on this subject based on the ideXlab platform.
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evaluation of local kinetic energy dissipation rate in the impeller stream of a rushton turbine by time resolved piv
Chemical Engineering Research & Design, 2009Co-Authors: Florian Huchet, Alain Line, Jerome MorchainAbstract:Abstract The present paper is dedicated to the direct measurement of the dissipation rate of kinetic energy, e ¯ , by means of time-resolved 2D-PIV, in the impeller region of a stirred vessel. Experimental estimation of e ¯ is carried out without simplifications, since all spatial gradients of the Fluctuating Velocity components are directly measured. At each point, measurements have thus been realized in three orthogonal planes. The present results have been compared with previous ones and discussed according to experimental techniques. A special attention is focused on the contribution of measurements in each plane and some new ideas have been suggested for the assessment of e ¯ . In addition, in each measurement plane, the time-variation of the instantaneous Fluctuating Velocity gradients have been also presented, exhibiting periodicity, with large values of instantaneous dissipation rate, linked to the trailing vortex induced by the blade rotation.
Michael Yianneskis - One of the best experts on this subject based on the ideXlab platform.
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on the quantification of energy dissipation in the impeller stream of a stirred vessel from Fluctuating Velocity gradient measurements
Chemical Engineering Science, 2004Co-Authors: S Baldi, Michael YianneskisAbstract:The turbulence energy dissipation rate (e) in the impeller stream of a vessel of diameter T=100mm stirred by a Rushton turbine of diameter D=T/3 was directly measured with particle image velocimetry (PIV). Both 2-D and 3-D PIV techniques were employed to measure the mean velocities, Reynolds stresses and e in the vessel for Reynolds numbers of 15 000–40 000. e was determined directly from measurements of the Fluctuating Velocity gradients by analysing the PIV images with a resolution of 100μm. The values of the normalised ensemble-averaged dissipation rate (e/N3D2) in the impeller stream were in the range 5–10. The measured Fluctuating Velocity gradients compared well with similar data obtained using a four-channel laser anemometer. The results are also compared with those of earlier works employing non-direct methods to estimate e and show that some of these methods yield comparable values, although the spread of the some of the data previously reported is significant. The present results show the feasibility of direct measurement of the e distribution with PIV and provide useful information for the design of mixing processes as well as for its more accurate estimation in future work.
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determination of dissipation rate in stirred vessels through direct measurement of Fluctuating Velocity gradients
Proc. 11th European Conference on Mixing, 2003Co-Authors: S Baldi, Andrea Ducci, Michael YianneskisAbstract:2-D and 3-D PIV and 4-channel LDA techniques were employed to measure the turbulence energy dissipation rate in vessels stirred by Rushton impellers. The measurements were made in vessels of diameter T = 100 mm and 294 mm and stirred by impellers of diameter D = T/3. The impellers were rotated at speeds corresponding to Reynolds number of 40,000 to ensure fully-turbulent flow in the vessels. e was determined directly from measurements of the Reynolds stress gradients by analyzing the PIV images over interrogation areas down to 0.1 mm. Similar LDA data were obtained in the larger 294 mm vessel, with a resolution of around 50 μm. The Fluctuating gradient results obtained with the two techniques compare well and show that direct measurement of the e distribution is feasible with both PIV and LDA methods. © 2004 WILEY-VCH Verlag GmbH and Co.
Karen A Flack - One of the best experts on this subject based on the ideXlab platform.
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turbulence structure in rough and smooth wall boundary layers
Journal of Fluid Mechanics, 2007Co-Authors: Ralph J Volino, Michael P Schultz, Karen A FlackAbstract:Turbulence measurements for rough-wall boundary layers are presented and compared to those for a smooth wall. The rough-wall experiments were made on a woven mesh surface at Reynolds numbers approximately equal to those for the smooth wall. Fully rough conditions were achieved. The present work focuses on turbulence structure, as documented through spectra of the Fluctuating Velocity components, swirl strength, and two-point auto- and cross-correlations of the Fluctuating Velocity and swirl. The present results are in good agreement, both qualitatively and quantitatively, with the turbulence structure for smooth-wall boundary layers documented in the literature. The boundary layer is characterized by packets of hairpin vortices which induce low-speed regions with regular spanwise spacing. The same types of structure are observed for the rough- and smooth-wall flows. When the measured quantities are normalized using outer variables, some differences are observed, but quantitative similarity, in large part, holds. The present results support and help to explain the previously documented outer-region similarity in turbulence statistics between smooth- and rough-wall boundary layers.
Jason Monty - One of the best experts on this subject based on the ideXlab platform.
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On the use of the Reynolds decomposition in the intermittent region of turbulent boundary layers
Journal of Fluid Mechanics, 2016Co-Authors: Y. S. Kwon, Nicholas Hutchins, Jason MontyAbstract:In the analysis of Velocity fields in turbulent boundary layers, the traditional Reynolds decomposition is universally employed to calculate the Fluctuating component of streamwise Velocity. Here, we demonstrate the perils of such a determination of the Fluctuating Velocity in the context of structural analysis of turbulence when applied in the outer region where the flow is intermittently turbulent at a given wall distance. A new decomposition is postulated that ensures non-turbulent regions in the flow do not contaminate the Fluctuating Velocity components in the turbulent regions. Through this new decomposition, some of the typical statistics concerning the scale and structure of turbulent boundary layers are revisited.