Density cross sections and velocity profiles in high-speed air by UV Rayleigh scattering and by Raman excitation + laser induced electronic fluorescence (RELIEF)

1989 ◽  
Author(s):  
Richard B. Miles
Keyword(s):  
Cross Sections ◽  
High Speed ◽  
Rayleigh Scattering ◽  
Velocity Profiles ◽  
Excitation Laser

On the effect of surface roughness on velocity profiles and runout lengths of dry granular flows

2020 ◽  
Author(s):  
Lukas Reider ◽  
Roland Kaitna
Keyword(s):  
Surface Roughness ◽  
Cross Sections ◽  
High Speed ◽  
Maximum Flow ◽  
Velocity Profiles ◽  
Small Scale ◽  
Relative Roughness ◽  
Laser Sensors ◽  
Mass Flows ◽  
Set Up

<p>Gravitational mass flows like debris flows are often physically modelled as an assembly of particles flowing in simplified flume configurations. There is indication that natural flows exhibit a combined movement of sliding and internal deformation, which is not well understood and underrepresented in scaled laboratory experiments. In this study we investigate the effect of the surface roughness on the velocity profile and the runout of small-scale, dry granular avalanches. The experimental set-up is a 0.17 m wide flume with an inclination of 34° for the first 1.5 m, following an 0.8 m curved transition zone with a radius of 1.7 m, and ending in a runout zone with an angle of 4°. The tested material consisted of non-perfect spherical ceramic beads with a diameter of 2.8 to 4.3 mm. We tested four different types of surface roughness ranging from 0 to 6 mm height and additionally one macro roughness, which was higher than the maximum flow height. To also get information about the influence of the relative roughness experiments with three different starting volumes were undertaken. All fourteen experimental variations were repeated three times. Flow heights were measured with laser sensors at four different positions along the channel. Three of them were used to calculate the mean front velocity of the flowing mass in two cross sections. Furthermore, the experiments were recorded with a high-speed camera through one sidewall out of acrylic glass. The recordings were analysed using a PIV (Particle Image Velocimetry) software to derive velocity profiles in 1/1500 second time steps. Results show that the velocity profiles changed from the head to the tail of the flow and that the profiles of the two roughest surfaces are more alike than the smooth roughness configurations. The fraction of sliding on the total movement varied between 0 and close to unity. The runout length decreased the higher the roughness was and increased with higher starting volume. The shape of the velocity profiles at the deepest sections of the flows changed with surface roughness and with starting volumes. Only the velocity profiles for the two roughest surfaces show an inflection point. Our experiments highlight the importance of surface roughness as well as relative roughness for granular mass flows and provide data for model testing.</p>

Acoustic resonances and trapped modes in pipes and tunnels

2008 ◽  
Vol 605 ◽  
pp. 401-428 ◽  
Author(s):  
STEFAN HEIN ◽  
WERNER KOCH
Keyword(s):  
Cross Sections ◽  
High Speed ◽  
Hard Spheres ◽  
Cutoff Frequency ◽  
Three Dimensional ◽  
Absorbing Boundary Conditions ◽  
Trapped Modes ◽  
Absorbing Boundary ◽  
Complex Scaling Method ◽  
Acoustic Resonances

Acoustic resonances of simple three-dimensional finite-length structures in an infinitely long cylindrical pipe are investigated numerically by solving an eigenvalue problem. To avoid unphysical reflections at the finite grid boundaries placed in the uniform cross-sections of the pipe, perfectly matched layer absorbing boundary conditions are applied in the form of the complex scaling method of atomic and molecular physics. Examples of the structures investigated are sound-hard spheres, cylinders, cavities and closed side branches. Several truly trapped modes with zero radiation loss are identified for frequencies below the first cutoff frequency of the pipe. Such trapped modes can be excited aerodynamically by coherent vortices if the frequency of the shed vortices is close to a resonant frequency. Furthermore, numerical evidence is presented for the existence of isolated embedded trapped modes for annular cavities above the first cutoff frequency and for closed side branches below the first cutoff frequency. As applications of engineering interest, the acoustic resonances are computed for a ball-type valve and around a simple model of a high-speed train in an infinitely long tunnel.

scholarly journals Is ink heating a relevant concern in the High Speed Sintering process?

2021 ◽  
Author(s):  
Rhys J. Williams ◽  
Patrick J. Smith ◽  
Candice Majewski
Keyword(s):  
Cross Sections ◽  
Inkjet Printing ◽  
High Speed ◽  
Sintering Process ◽  
Significant Drop ◽  
Powder Bed ◽  
Consistent Manner ◽  
Fluid Properties ◽  
Different Temperatures ◽  
Accuracy And Repeatability

AbstractHigh Speed Sintering (HSS) is a novel polymer additive manufacturing process which utilises inkjet printing of an infrared-absorbing pigment onto a heated polymer powder bed to create 2D cross-sections which can be selectively sintered using an infrared lamp. Understanding and improving the accuracy and repeatability of part manufacture by HSS are important, ongoing areas of research. In particular, the role of the ink is poorly understood; the inks typically used in HSS have not been optimised for it, and it is unknown whether they perform in a consistent manner in the process. Notably, the ambient temperature inside a HSS machine increases as a side effect of the sintering process, and the unintentional heating to which the ink is exposed is expected to cause changes in its fluid properties. However, neither the extent of ink heating during the HSS process nor the subsequent changes in its fluid properties have ever been investigated. Such investigation is important, since significant changes in ink properties at different temperatures would be expected to lead to inconsistent printing and subsequently variations in part accuracy and even the degree of sintering during a single build. For the first time, we have quantified the ink temperature rise caused by unintentional, ambient heating during the HSS process, and subsequently measured several of the ink’s fluid properties across the ink temperature range which is expected to be encountered in normal machine operation (25 to 45 ∘C). We observed only small changes in the ink’s density and surface tension due to this heating, but a significant drop (36%) in its viscosity was seen. By inspection of the ink’s Z number throughout printing, it is concluded that these changes would not be expected to change the manner in which droplets are delivered to the powder bed surface. In contrast, the viscosity decrease during printing is such that it is expected that the printed droplet sizes do change in a single build, which may indeed be a cause for concern with regard to the accuracy and repeatability of the inkjet printing used in HSS, and subsequently to the properties of the polymer parts obtained from the process.

The Effect of Lewis Number on Instantaneous Flamelet Speed and Position Statistics in Counter-Flow Flames With Increasing Turbulence

2017 ◽  
Author(s):  
Sean D. Salusbury ◽  
Ehsan Abbasi-Atibeh ◽  
Jeffrey M. Bergthorson
Keyword(s):  
Flame Front ◽  
Turbulence Intensity ◽  
High Speed ◽  
Rayleigh Scattering ◽  
Turbulent Flame ◽  
Lewis Number ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Laminar Flames ◽  
Counter Flow

Differential diffusion effects in premixed combustion are studied in a counter-flow flame experiment for fuel-lean flames of three fuels with different Lewis numbers: methane, propane, and hydrogen. Previous studies of stretched laminar flames show that a maximum reference flame speed is observed for mixtures with Le ≳ 1 at lower flame-stretch values than at extinction, while the reference flame speed for Le ≪ 1 increases until extinction occurs when the flame is constrained by the stagnation point. In this work, counter-flow flame experiments are performed for these same mixtures, building upon the laminar results by using variable high-blockage turbulence-generating plates to generate turbulence intensities from the near-laminar u′/SLo=1 to the maximum u′/SLo achievable for each mixture, on the order of u′/SLo=10. Local, instantaneous reference flamelet speeds within the turbulent flame are extracted from high-speed PIV measurements. Instantaneous flame front positions are measured by Rayleigh scattering. The probability-density functions (PDFs) of instantaneous reference flamelet speeds for the Le ≳ 1 mixtures illustrate that the flamelet speeds are increasing with increasing turbulence intensity. However, at the highest turbulence intensities measured in these experiments, the probability seems to drop off at a velocity that matches experimentally-measured maximum reference flame speeds in previous work. In contrast, in the Le ≪ 1 turbulent flames, the most-probable instantaneous reference flamelet speed increases with increasing turbulence intensity and can, significantly, exceed the maximum reference flame speed measured in counter-flow laminar flames at extinction, with the PDF remaining near symmetric for the highest turbulence intensities. These results are reinforced by instantaneous flame position measurements. Flame-front location PDFs show the most probable flame location is linked both to the bulk flow velocity and to the instantaneous velocity PDFs. Furthermore, hydrogen flame-location PDFs are recognizably skewed upstream as u′/SLo increases, indicating a tendency for the Le ≪ 1 flame brush to propagate farther into the unburned reactants against a steepening average velocity gradient.

scholarly journals Scattering and Absorption Cross-sections of Atmospheric Gases in the Ultraviolet-Visible Wavelength Range (307–725 nm)

2020 ◽  
Author(s):  
Quanfu He ◽  
Zheng Fang ◽  
Ofir Shoshamin ◽  
Steven S. Brown ◽  
Yinon Rudich
Keyword(s):  
Refractive Index ◽  
Wavelength Range ◽  
Cross Sections ◽  
Rayleigh Scattering ◽  
Dispersion Relations ◽  
Optical Absorption Spectroscopy ◽  
Absorption Cross ◽  
Atmospheric Gases ◽  
Scattering Cross ◽  
Scattering Cross Sections

Abstract. Accurate Rayleigh scattering and absorption cross-sections of atmospheric gases are essential for understanding the propagation of electromagnetic radiation in planetary atmospheres. Accurate extinction cross-sections are also essential for calibrating high finesse optical cavities and differential optical absorption spectroscopy and for accurate remote sensing. In this study, we measured the scattering and absorption cross-sections of carbon dioxide, nitrous oxide, sulfur hexafluoride, oxygen, and methane in the continuous wavelength range of 307–725 nm using Broadband Cavity Enhanced Spectroscopy (BBCES). The experimentally derived Rayleigh scattering cross-sections for CO2, N2O, SF6, O2, and CH4 agree with refractive index-based calculations, with a difference of 1.5 % and 1.1 %, 1.5 %, 2.9 %, and 1.4 % on average, respectively. The O2-O2 collision-induced absorption and absorption by methane are obtained with high precision at the 0.8 nm resolution of our BBCES instrument in the 307–725 nm wavelength range. New dispersion relations for N2O, SF6, and CH4 were derived using data in the UV-vis wavelength range. This study provides improved refractive index dispersion relations, n-based Rayleigh scattering cross-sections, and absorption cross-sections for these gases.

scholarly journals On the Creation of a High-Speed Transport Highway in St. Petersburg

2019 ◽  
Vol 5 (4) ◽  
pp. 73-95
Author(s):  
Nikolai A. Senkin ◽  
Aleksandr S. Filimonov ◽  
Kirill E. Kharitonov ◽  
Vitaliy V. Yakovlev ◽  
Elizaveta O. Bondareva ◽  
...  
Keyword(s):  
Transport System ◽  
Cross Sections ◽  
High Speed ◽  
Tube Steel ◽  
Leningrad Region ◽  
Limit States ◽  
Passenger Traffic ◽  
Rod System ◽  
The Creation ◽  
Selection Of

As part of student research at the St. Petersburg University of architecture and construction, alternative proposals are being developed for the creation of a circumferential high-speed highway with a total length of 147.2 km. Тhe scheme is proposed in the form of a polygon with HUB in the nodes and consists of three main parts: 1 above-ground (62.6 km), 2 above-water (29.6 km) and 3 surface-underground (55.0 km). The main tracks are located in a four-tube steel beam, each tube of which is organized by the technology of vacuum tube transport with a pressure of 10% of the normal for high-speed passenger trains on a magnetic levitation cushion using a linear traction motor (Maglev system). The rail base of the 1520 mm gauge is located along the entire length of the track, both in parking lots, acceleration and braking zones, and on the main high-speed sections for movement with a maximum speed of 500 km per hour. The main direction of research was the development of load-bearing structures that provide the necessary functionality, reliability and safety of structures. In order to reduce the noise impact on the metropolis, overcome numerous artificial and natural obstacles, improve anti-terrorist protection, the main level of the rail track for the above-ground and above-water structures was adopted at +88.00 in the Baltic elevation system. Calculations of variants with determination of internal forces in elements and movements of nodes with use of the program complex SCAD Office 21.1are executed, when accounting for the full range of loads taking into account dynamic effects and non-linearity. The selection of cross-sections of elements according to the method of limit states according to the current norms is carried out. The advantage of the arch-cable-stayed variant with a span of 360 m in strength, stability, stiffness and vertical size (height of supports) is shown. The continuation of research and design work on this topic should lead to the emergence of a district high-speed transport system at the borders of communication between St. Petersburg and the Leningrad region with passenger traffic, quite comparable to the metro line. Aim: To develop a district high-speed transport system at the borders of St. Petersburg and Leningrad region with passenger traffic comparable to the metro line. Materials and Methods: Using the software package "SCAD Office 21.1", the trestle structures are calculated for the combination of operating loads, forces and influences, including the consideration of dynamic aspects and nonlinearity, as well as the selection of cross-sections of elements by the method of limit states. To determine the optimal trestle structures of high-speed highways, namely high-rise and long-length metal structures supporting the overpass beam, calculations with the selection of cross sections of four variants of cable-stayed systems (arch-cable-stayed; cable-stayed rod with inclined cables and steel lattice pylons; the same, steel pipe-concrete pylons; cable-stayed rod system with suspensions according to the patent US5950543 (A). Results: the results of the trial design adopted arch-cable option with a span of 360 m according to the criterion of metal consumption, the consumption of steel amounted to 20.9 tons per 1 m length of highway. Conclusion: the estimated volume of passenger traffic per day for the four-track high-speed line will be 280 thousand passengers, and 102 million passengers per year, which is quite comparable to this figure for the metro line.

scholarly journals Underway velocity measurements in the Alderney Race: towards a three-dimensional representation of tidal motions

2020 ◽  
Vol 378 (2178) ◽  
pp. 20190491 ◽  
Author(s):  
Alexei Sentchev ◽  
Thinh Duc Nguyen ◽  
Lucille Furgerot ◽  
Pascal Bailly du Bois
Keyword(s):  
Power Law ◽  
Cross Sections ◽  
Velocity Profiles ◽  
Significant Advance ◽  
Velocity Measurements ◽  
Energy Potential ◽  
Profile Shape ◽  
Power Law Exponent ◽  
The Cross ◽  
Flood Flow

The Alderney Race, located northwest of the Cotentin Peninsula (France), is a site with high tidal-stream energy potential. Circulation through the Alderney Race is complex, with current speed exceeding 3 m s −1 at neap tide. Towed acoustic Doppler current profiler (ADCP) measurements and static point velocity measurements were performed in July 2018 focusing on assessment of circulation and vertical structure of tidal currents. Transect surveys revealed peculiar features of local dynamics such as change in location of the tidal jet on ebb and flood flow. The spatial expanse of the tidal jet was quantified and regions with largely sheared or nearly homogeneous velocity distributions were identified on the cross-sections. Velocity profiles acquired along the cross-sections were accurately characterized using a power law. The spatial variability of the power-law exponent α was found to be large and correlated with the tidal conditions. The largest variation in profile shape was observed in the northern sector and assumed to be generated by the current interaction with a bathymetric constriction. The velocity profiles were found to vary from highly sheared on flood flow to nearly homogeneous on ebb flow, with corresponding range of power-law exponent α variation from 6 to 14. In the southern sector, over a relatively smooth bathymetry, the velocity profile shape was accurately approximated using the 1/7 power law with a range of variation of α from 6.5 to 8, with respect to the tidal conditions. To our knowledge, this is the largest field survey done using towed ADCP and the results could represent a significant advance in tidal site characterization and provide advanced information to turbine developers. This article is part of the theme issue ‘New insights on tidal dynamics and tidal energy harvesting in the Alderney Race'.

Air Bubble Injection Into a Liquid Stream in a Minichannel

2013 ◽  
Author(s):  
Randy Samaroo ◽  
Masahiro Kawaji
Keyword(s):  
High Speed ◽  
Liquid Velocity ◽  
Bubble Formation ◽  
Video Camera ◽  
Velocity Profiles ◽  
Bubble Behavior ◽  
Particle Image Velocimetry Technique ◽  
Air Bubble ◽  
Cfd Models ◽  
Laminar And Turbulent Flow

Air bubble injection experiments have been performed to obtain a better understanding and detailed data on bubble behavior and liquid velocity profiles to be used for validation of 3-D Interface Tracking Models and CFD models. Two test sections used were vertical rectangular minichannels with a width and gap of 20 mm × 5.1 mm and 20 mm × 1.9 mm, respectively. Subcooled water at near atmospheric pressure flowed upward under laminar and turbulent flow conditions accompanied by air bubbles injected from a small hole on one of the vertical walls. The experiments yielded data on bubble formation and departure, and interactions with laminar or turbulent water flow. Instantaneous and ensemble-average liquid velocity profiles have been obtained using a Particle Image Velocimetry technique and a high speed video camera.

scholarly journals Lagrangian velocity profiles in the wake of a high speed vessel

1994 ◽  
Vol 21 (2) ◽  
pp. 221-242 ◽  
Author(s):  
L. Meadows ◽  
G. Meadows ◽  
A. Troesch ◽  
S. Cohen ◽  
K.P. Beier ◽  
...  
Keyword(s):  
High Speed ◽  
Velocity Profiles ◽  
Lagrangian Velocity
Sign in / Sign up

Export Citation Format

Share Document