The Experts below are selected from a list of 4299 Experts worldwide ranked by ideXlab platform
Elias Siores - One of the best experts on this subject based on the ideXlab platform.
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the effect of cutting jet variation on surface striation formation in abrasive water jet cutting
Journal of Materials Processing Technology, 2003Co-Authors: Frank L Chen, Elias SioresAbstract:Abstract Abrasive water jet machining is an emerging technology which can shape almost all engineering materials, but also produces a characteristic striated surface finish which limits its potential applications. In this study, the characterisation of different materials’ cut surfaces is investigated using a scanning electron microscope. The effect of abrasive particle distribution in the jet on striation formation is detailed. A non-invasive technique: Laser Doppler Anemometry is used to analyse the abrasive particle distribution in the jet. Furthermore, the mechanisms of striation formation are discussed in detail and an effective striation minimisation technique applied to the cutting process is outlined.
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the effect of cutting jet variation on striation formation in abrasive water jet cutting
International Journal of Machine Tools & Manufacture, 2001Co-Authors: Frank L Chen, Elias SioresAbstract:Abrasive water jet machining is an emerging technology which can shape almost all engineering materials, but it also produces a characteristic striated surface finish which limits its potential applications. In this study, the characterisation of different materials' cut surfaces is investigated using a scanning electron microscope. The effect of abrasive particle distribution in the jet on striation formation is detailed. A non-invasive technique, Laser Doppler Anemometry, is used to analyse the abrasive particle distribution in the jet. Furthermore, the mechanisms of striation formation are discussed in detail and an effective striation minimisation technique applied to the cutting process is outlined.
Frank L Chen - One of the best experts on this subject based on the ideXlab platform.
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the effect of cutting jet variation on surface striation formation in abrasive water jet cutting
Journal of Materials Processing Technology, 2003Co-Authors: Frank L Chen, Elias SioresAbstract:Abstract Abrasive water jet machining is an emerging technology which can shape almost all engineering materials, but also produces a characteristic striated surface finish which limits its potential applications. In this study, the characterisation of different materials’ cut surfaces is investigated using a scanning electron microscope. The effect of abrasive particle distribution in the jet on striation formation is detailed. A non-invasive technique: Laser Doppler Anemometry is used to analyse the abrasive particle distribution in the jet. Furthermore, the mechanisms of striation formation are discussed in detail and an effective striation minimisation technique applied to the cutting process is outlined.
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the effect of cutting jet variation on striation formation in abrasive water jet cutting
International Journal of Machine Tools & Manufacture, 2001Co-Authors: Frank L Chen, Elias SioresAbstract:Abrasive water jet machining is an emerging technology which can shape almost all engineering materials, but it also produces a characteristic striated surface finish which limits its potential applications. In this study, the characterisation of different materials' cut surfaces is investigated using a scanning electron microscope. The effect of abrasive particle distribution in the jet on striation formation is detailed. A non-invasive technique, Laser Doppler Anemometry, is used to analyse the abrasive particle distribution in the jet. Furthermore, the mechanisms of striation formation are discussed in detail and an effective striation minimisation technique applied to the cutting process is outlined.
H.e.a. Van Den Akker - One of the best experts on this subject based on the ideXlab platform.
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Subcritical flow past a circular cylinder surrounded by a porous layer
Physics of Fluids, 2006Co-Authors: M. P. Sobera, Chris R. Kleijn, H.e.a. Van Den AkkerAbstract:A study of the flow at subcritical Re = 3900 around a circular cylinder, surrounded at some fixed small distance by a porous layer with a hydraulic resistance typical for that of textile materials, has been performed by means of direct numerical simulations. The flow in the space between the porous layer and the solid cylinder was found to be laminar and periodic, with a frequency locked to that of the vortex shedding in the wake behind the cylinder. Time averaged flow velocities underneath the porous material were in good agreement with experimental data from Laser Doppler Anemometry.
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estimation of turbulence power spectra for bubbly flows from Laser Doppler Anemometry signals
Chemical Engineering Science, 2005Co-Authors: Wouter Koen Harteveld, R F Mudde, H.e.a. Van Den AkkerAbstract:Abstract The accuracy of the estimation of turbulence power spectra from Laser Doppler Anemometry (LDA) signals in bubbly flows is studied. Special attention is paid to the influence of the gaps in the signal created by the bubbles. The performance of reconstruction and slotting techniques for the estimation of the power spectrum is determined by application to synthetic bubbly flow LDA signals, and checked by application to real data. Estimation of spectra of bubbly flow signals with reconstruction techniques is found to give poor results. In general, the application of reconstruction techniques to LDA signals gives bias in the spectrum due to the addition of noise and low-pass filtering. The nature of the filtering and noise for bubbly flow signals differs from that for single phase flows. For bubbly flow signals, the spectrum is reliable up to a cut-off frequency which is lower than the cut-off frequency for single-phase flow signals with similar data rates. In addition, slopes close to - 5 3 may appear for signals which in reality have flat spectra. For single phase flow, it is possible to correct for these artefacts. The work shows that it is not possible to create similar correction techniques for bubbly flow signals. The application of the slotting technique for estimation of power spectra of bubbly flow signals leads to much better results. Estimation of the spectrum beyond the mean data rate is well possible. The performance of several improvements of the slotting technique is discussed.
Mukund V Karwe - One of the best experts on this subject based on the ideXlab platform.
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velocity distributions and mixing in the translational region of a kneading section in a co rotating twin screw extruder
Food and Bioproducts Processing, 2004Co-Authors: L Yerramilli, Mukund V KarweAbstract:Velocity distributions in the kneading section of a co-rotating, self-wiping, twin-screw extruder were determined using Laser Doppler Anemometry to understand flow field and elucidate the mixing effectiveness of kneading blocks. Velocity profiles in the translational region were measured at three screw speeds using a Newtonian fluid. Effects of pitch and thickness of individual kneading disks, on the flow field, were also investigated. From the measured flow field, the total shear rate distribution and flow number were calculated. It was found that kneading blocks have substantial leakage flow, which increased with its pitch and rotational speed. Also, the flow number values indicated that there was more dispersive mixing than distributive mixing in the translational region of a kneading section.
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velocity profiles in the nip region of a co rotating twin screw extruder transitions between forward and reverse elements
Journal of Reinforced Plastics and Composites, 1998Co-Authors: Murali Chandrasekaran, Mukund V KarweAbstract:Laser Doppler Anemometry (LDA) was used to map velocity distributions in the nip region of a co-rotating twin-screw extruder. Axial and normal components of velocity were measured at 90 rpm for heavy corn syrup in a section having a reverse element between forward conveying elements. Flow towards the hopper was seen only in the nip region of the reversing section. The flow was seen to adjust to the change in direction of pitch within 4-5 mm, axially.
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application of Laser Doppler Anemometry to measure velocity distribution inside the screw channel of a twin screw extruder
Journal of Food Process Engineering, 1996Co-Authors: Mukund V Karwe, Valentinas SernasAbstract:Velocity measurements inside the screw channels of a co-rotating, self-wiping twin-screw extruder (ZSK-30) have been carried out using the noninvasive technique of Laser Doppler Anemometry. A two-dimensional Argon-ion Laser Doppler system was used to measure tangential and axial velocity components in one of the screws, away from the intermeshing zone. Heavy corn syrup with naturally occurring particles was used in the extrusion experiments. the measured tangential velocity distribution agreed with the expected distribution for a Newtonian fluid. Measurements also indicated that near the screw root and away from the flights, shear rates were substantially lower as compared to the shear rates near the barrel. the results indicated that this technique is suitable for making velocity measurements in a twin-screw extruder using model fluids.
Sophie Herpin - One of the best experts on this subject based on the ideXlab platform.
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Application of Laser Doppler Anemometry to estimate turbulent power spectra inside an urban canopy
2018Co-Authors: Sophie Herpin, Laurent Perret, Christian Tanguy, Romain Mathis, Jeanjacques LasserreAbstract:In the present contribution, we propose to make use of Laser Doppler Anemometry to investigate the dynamics of the flow inside an urban canopy immersed into a thick turbulent boundary layer. Previous studies dedicated to such flows (Castro et al. 2006; Reynolds and Castro 2008) have focused the core of their analysis on the roughness sublayer region or on the inertial region. In contrast, the region below the canopy interface have received little attention so far, and only mean velocity or Reynolds stresses data can be found in the literature. Indeed, getting access to the dynamics of the flow inside the canopy represents a real experimental challenge: the flow is turbulent, 3-dimensionnal, and due to the tight clearance, only non-intrusive Laser-based techniques such as LDA or PIV can be used. In this contribution, for the first time, a spectral analysis of the flow is carried out inside the canopy region. This is made possible thanks to very thorough LDA measurements as well as the use of advanced post-processing algorithm to compute temporal power spectra. Indeed, LDA measurement yields non-equidistantly spaced data points, and standard FFT algorithms cannot be used. A detailed comparison of various algorithms is undertaken, and a slight improvement is proposed to reduce the impact of measurement noise. Finally, the power spectra inside the canopy are analyzed and the main implications on the flow dynamics are discussed.
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Investigation of the flow inside an urban canopy immersed into an atmospheric boundary layer using Laser Doppler Anemometry
Experiments in Fluids, 2018Co-Authors: Sophie Herpin, Laurent Perret, Christian Tanguy, Romain Mathis, Jeanjacques LasserreAbstract:Laser Doppler Anemometry (LDA) is used to investigate the flow inside an idealized urban canopy consisting of a staggered array of cubes with a 25% density immersed into an atmospheric boundary layer with a Reynolds number of δ+=32,300. The boundary layer thickness to cube height ratio (δ/h=22.7) is large enough to be representative of atmospheric surface layer in neutral conditions. The LDA measurements give access to pointwise time-resolved data at several positions inside the canopy (z=h/4, h/2, and h). Synchronized hot-wire measurements above the canopy (inertial region and roughness sublayer) are also realized to get access to interactions between the different flow regions. The wall-normal mean velocity profile and Reynolds stresses show a good agreement with available data in the literature, although some differences are observed on the standard deviation of the spanwise component. A detailed spectral and integral time scale analysis inside the canopy is then carried out. No clear footprint of a periodic vortex shedding on the sides of the cubes could be identified on the power spectra, owing to the multiple cube-to-cube interactions occuring within a canopy with a building density in the wake interference regime. Results also suggest that interactions between the most energetics scales of the boundary layer and those related to the cube canopy take place, leading to a broadening of the energy peak in the spectra within the canopy. This is confirmed by the analysis of coherence results between the flow inside and above the canopy. It is shown that linear interactions mechanisms are significant, but reduced compared to smooth-wall boundary-layer flow. To our knowledge, this is the first time such results are shown on the dynamics of the flow inside an urban canopy.
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investigation of the flow inside an urban canopy immersed into an atmospheric boundary layer using Laser Doppler Anemometry
Experiments in Fluids, 2018Co-Authors: Sophie Herpin, Laurent Perret, Christian Tanguy, Romain Mathis, Jeanjacques LasserreAbstract:Laser Doppler Anemometry (LDA) is used to investigate the flow inside an idealized urban canopy consisting of a staggered array of cubes with a 25% density immersed into an atmospheric boundary layer with a Reynolds number of \(\delta ^+=32{,}300\). The boundary layer thickness to cube height ratio (\(\delta /h=22.7\)) is large enough to be representative of atmospheric surface layer in neutral conditions. The LDA measurements give access to pointwise time-resolved data at several positions inside the canopy (\(z=h/4\), h/2, and h). Synchronized hot-wire measurements above the canopy (inertial region and roughness sublayer) are also realized to get access to interactions between the different flow regions. The wall-normal mean velocity profile and Reynolds stresses show a good agreement with available data in the literature, although some differences are observed on the standard deviation of the spanwise component. A detailed spectral and integral time scale analysis inside the canopy is then carried out. No clear footprint of a periodic vortex shedding on the sides of the cubes could be identified on the power spectra, owing to the multiple cube-to-cube interactions occuring within a canopy with a building density in the wake interference regime. Results also suggest that interactions between the most energetics scales of the boundary layer and those related to the cube canopy take place, leading to a broadening of the energy peak in the spectra within the canopy. This is confirmed by the analysis of coherence results between the flow inside and above the canopy. It is shown that linear interactions mechanisms are significant, but reduced compared to smooth-wall boundary-layer flow. To our knowledge, this is the first time such results are shown on the dynamics of the flow inside an urban canopy.
