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A small-scale laboratory apparatus was built to study liquid friction modifier (LFM) behavior in a top-of-rail application. A field experiment was also carried out to complement the laboratory findings. KELTRACK® (a water-based LFM) was used as the test fluid. Laser-induced fluorescence served to measure the LFM thickness left on the track after the passage of the wheel. The lab experiments show that the LFM cannot withstand the high wheel-rail contact pressure in the nip present in cargo rail situations. As a result, the liquid is squeezed out laterally and attaches to the edges of the wheel contact band. This “edge liquid” is then carried down the track on the wheel. Gravimetric measurements of the wheel contact band confirm this observation, and show that only a minute amount of liquid is carried through the nip in the valleys between surface roughness features. In the field experiment, the LFM is applied from a trackside unit on a tangent section of the track. About 500 m downstream of the application point, the track has a curved section. LFM cannot be detected anywhere on the track a short distance (∼200 m) past the application unit. However, LFM is detectable on the curved sections of the track up to approximately 2 km from the application unit. This LFM on the curved track is believed to be due to transfer of the “edge liquid” from the wheel to the track, caused by the movement of the contact band as the train rounds a curve. The presence of LFM on the curved track far downstream is consistent with prior measurements of reduced lateral force on the curved track downstream of LFM application sites.

Train sanders are ubiquitous in remediating low wheel–rail adhesion. Sanders operate by taking sand stored in a hopper, pneumatically conveying it through a nozzle, then spraying it into the wheel–rail interface. In this research, the wheel–rail–sander system was simulated experimentally in a laboratory. The system was optically accessible, and Particle Tracking Velocimetry was used to observe the trajectory of sand particles approaching the nip. The percentage of sand conveyed through the nozzle that makes it to the wheel–rail nip – the deposition efficiency – was measured gravimetrically. The maximum efficiency was found to be 91% for 1.15 mm mean diameter silica sand with a proprietary coating, and the minimum efficiency was 59% for uncoated aluminum oxide with a 0.91 mm mean diameter, both at a simulated train speed of 18 km/h. Irregular particles were found to be less efficient when compared to spherical particles with a similar size and composition. Increasing the size of silica sand from 0.18 mm to 1.05 mm in diameter slightly decreased the sanding efficiency from 67% to 60%. There was no statistically significant dependence of the efficiency on the particle coefficient of restitution. The single parameter most closely correlated with the deposition efficiency is the expansion of the particle-laden jet downstream of the nozzle. Larger, round particles typically had the smallest jet expansion and the highest efficiency, whereas rough particles with large diameters were found to have a large jet expansion and lowest efficiency. Finally, the effect of train speed on deposition efficiency was studied. The deposition efficiency was found to be very low at low train speeds and asymptotically approaches a fixed value at higher speeds. A simple physical model is proposed that explains the low efficiency at low speeds.

Locomotive sanders are used to optimize the traction between the train wheels and the railhead by spraying sand into the interface. It has been previously shown that a large fraction of sand sprayed by the sanders does not make it through the wheel–rail nip, leading to sand wastage and thereby increasing the cost and refilling effort. In this study, pneumatic conveying of sand through the wheel–rail nip is numerically modeled through coupled computational fluid dynamics and discrete element method simulations. The gas phase, discrete phase, and coupled two-phase flows are separately validated against the literature, and the parameters affecting the deposition of sand into the nip are analyzed to determine their impact on sander efficiency. The aerodynamics associated with the particle-laden jet play a critical role in optimizing the amount of sand going through the wheel–rail interface, with the particle velocities being directly correlated with the sander efficiency. Particle–geometry interactions (e.g. particle bouncing) are found to have a negligible effect on the deposition. In the absence of crosswinds, it is recommended to employ particles with a smaller Stokes number to enhance the sander efficiency. A larger airflow rate through the nozzle is also recommended. Crosswinds strongly and adversely affect sander efficiency. The effects of crosswinds can be mitigated by reducing the nip–nozzle distance and using coarser particles.

A method for extracting solid boundary motion from dynamic CT images of a human oropharyngeal swallow is presented. The data-set has high spatial resolution () but low temporal resolution (10 Hz). The low temporal resolution results in motion artefacts (i.e. blurring, ghosting) due to the fast moving solid structures. Automated segmentation and registration methods were not successful, so a tool for manual 3D deformable registration was created as a plug-in for the open-source modelling software, Blender. The tool gives users a high level of control to sculpta mesh to match 3D volumetric image data. The resulting series of meshes, each corresponding to an instance in time, can be used in a fluid simulation using a technique such as smoothed-particle hydrodynamics.

ABSTRACTIn this article, measurements of full-scale freight train underbody aerodynamics relevant to top-of-rail spraying are presented. The velocity near the wheel was measured using hot wire anemometers mounted on the train. The pressure was measured using transducers mounted adjacent to the track. Velocity scaled linearly with locomotive speed and pressure scaled linearly with dynamic pressure, implying negligible Reynolds number effects. The mean velocity near the wheels was less than half of the locomotive speed when the vehicle moved at or greater than the ambient wind speed. The velocity upwind of the wheel was 30% greater than downwind of the wheel. These mean velocities are consistent with computational fluid dynamics simulations of the flow field in the vicinity of the wheel. Turbulence intensity levels were measured to be 0.08–0.16. The pressure at the track depends on the configuration of the leading car; the maximum pressure drop was 65% greater when the hopper car preceded the locomotive compared to when the locomotive preceded the hopper car.

A three-dimensional (3D) computer simulation of swallowing is presented. The soft structures (i.e. pharyngeal wall, soft palate and tongue) are simulated using finite element models. Bony structures (e.g. mandible, hard palate and hyoid) are simulated as rigid bodies. A fluid bolus is simulated using smoothed particle hydrodynamics (SPH). A Newtonian viscosity model is validated by comparing a 3D SPH simulation of Hagen–Poiseuille flow with theoretical results. A previously unreported source of error is reported and discussed. In the swallowing simulation, fluid boundaries are determined by the rigid and deformable surfaces, and the coupling is in one direction only. Movement of solid boundaries was determined in previous work for a deformable solid bolus. Two swallowing simulations are presented with different bolus viscosities in order to demonstrate that SPH can be used to simulate and track the liquid phase of a bolus during swallow. We find that SPH robustly handles moving boundary conditions as well as changes in viscosity. SPH simulations of the bolus are therefore potentially a useful visual aid to understand the effects of solid boundary motion on swallowing.

Application: This paper describes a new device for measuring the hydrodynamics of pulp fibers. The device may be used to predict the fiber separation that occurs in hydrocyclones, given a [...]

The three-dimensional velocity field in the single phase approach flow to a multiple layer woven forming fabric was measured using PIV. The measurements were conducted on a scaled-up model of a forming fabric in a water/glycerin flow loop. Each strand on the paper side of the model forming fabric had a filament diameter ( d) of 1 5 mm, and the flow loop test section was 3 1 0 mm squared, permitting the measurement of detailed velocity distributions over multiple strands of the fabric. The flow speed in the loop test section was varied to achieve screen Reynolds numbers between 12 and 6 5 . PIV measurements showed that when the distance t o the paper side of the fabric changes from 0.25d to 1 . 5d, the normalized ZD, CMD and MD velocity deviation decreases from 1 9 .7% to 4 .2%, 1 5 . 3 % to 1 .9% and 1 4 . 5 % t o 2 . 3 %, respectively; the ratio between maximum and minimum ZD velocity decreases from 3 .3 to 1 .2 . These findings indicate that the flow non-uniformity caused by the fabric weave is confined to a short distance above the fabric. CFD simulations of the same flow were consistent with the PIV measurements.

Abstract: In a companion article , we described computer simulations of the flow around 2 two-dimensional, tandem circular cylinders in a flow for . In this article we adopt a similar approach to characterize the flow around side-by-side cylinders with surface-to-surface separation/diameter in the range 0.1< s/D <30. The results revealed some distinct and interesting features of the flow, which are completely different than those observed at higher Reynolds numbers. At low Reynolds numbers, , for all gap spacings, the flow contains no regions of flow separation. At higher Re, four distinct flow behaviors were observed. For very small gap spacings, e.g. 0.1< s/D <0.6 at Re=20, two elongated “detached vortices” form downstream of the cylinders. The drag coefficient increases sharply with the gap spacing. For gap spacings 0.6< s/D <0.7 at Re=20, no vortices form anywhere in the flow. For gap spacings around s/D ≈1 separation regions form only on the inside portions of the cylinders. For larger gap spacings s/D >1 the flow reverts to something similar to that around an isolated cylinder in the flow, i.e. two attached vortices on the rear side of each cylinder. In general, the drag coefficient increases as the gap spacing increases. At higher Reynolds number it is known that the cylinder lift coefficients decrease monotonically with gap spacing. In contrast, at these lower Reynolds number the lift coefficient curves rise to a maximum for 0.3< s/D <3 and then decrease monotonically for larger s/D. [Copyright &y& Elsevier]

Abstract: The flow around two-dimensional cylinders at moderate Reynolds numbers has been much studied, both for cylinders perpendicular to the flow and for cylinders yawed to the flow. In contrast, yawed finite aspect ratio cylinders have received little attention. In this article we describe computer simulations of cylinders with aspect ratios 2⩽ L/D ⩽20 yawed at angles 0°⩽ α ⩽90° relative to a free stream. The simulations were carried out for Reynolds numbers in the range 1⩽Re⩽40. The simulations show that the Independence Principle [Zdravkovich MM. Flow around circular cylinders, vol. 2: applications. New York: Oxford University Press; 2003] is not accurate for α ⩽45°. We have also found that for all aspect ratios, the ratio of the lift to drag force reaches a maximum for 40°< α <50°. Finally, we present CL and CD relationships as best curve fits to computational data. [Copyright &y& Elsevier]

Abstract: Filament-level three-dimensional simulations of the flow through single layer woven fabrics were done using FLUENTTM. For screen Reynolds numbers, Re s, between 50 and 300, CFD simulations reproduce experimental measurements of wind tunnel screen pressure drops to within ±10%. Simulations of woven fabrics with geometric non-uniformities have also been undertaken. In these simulations one or more strands of the fabric is shifted laterally relative to its undisturbed location. If the filament displacement, normalized by the centre-to-centre separation between filaments, is ε, the enhancement in the flow rate through the enlarged opening in the fabric is given by approximately 2ε. A very simplified model of the geometry is consistent with this enhanced flow rate. The findings of this research are relevant to both wind tunnel and papermachine forming fabric design. [Copyright &y& Elsevier]

Student performance on mid‐term quizzes and final examinations was compared for several core undergraduate courses. A statistical comparison of the grades of students on these two tests showed only a modest correlation between grades. The modest correlation may be attributed to several factors: inaccurate grading of examinations, differences in the material tested on the mid‐terms and finals, and sampling error due to the small numbers of questions on examinations. Evidence is presented that sampling error is the primary source of the low correlations. In practice, the modest correlations of mid‐term quiz and final examination grades imply that the grades assigned to students are some aggregate of a true measure of the ability of students and randomness. The randomness arises because the instructor selects a particular subset of the course material for examination, not complete coverage of the course by question of all levels of difficulty.

The motion of flexible fibres suspended in an incompressible fluid is of interest to researchers in a wide variety of fields, including reinforced composite materials, biotechnology, and the pulp and paper industry. In this work, we concentrate on the application to pulp fibres and demonstrate how the complex hydrodynamic interaction between a flexible fibre and the surrounding fluid can be simulated using theimmersed boundary method. The computations involve a single fibre suspended in a two-dimensional shear flow at moderate Reynolds number. Previous experimental work differentiates the observed fibre motions into a well-defined set of “orbit classes,” which are reproduced in our simulations for fibres with varying flexibility. The computed fibre orientation angle distributions are compared to classical theoretical results and shown to exhibit a skewness which is not captured by either the linear theory or other recent numerical computations that ignore the fibre–fluid interaction. These simulations set the stage for further work in modeling flows with multiple fibres in three dimensions for the purpose of improving the papermaking process.

ABSTRACTPollutant measurements in traffic tunnels have been used to estimate motor-vehicle emissions for several decades. The objective in this type of study is to use the traffic tunnel as a tool for characterizing motor vehicles rather than seeking a tunnel design with acceptably low pollutant concentrations. In the past, very simple aerodynamic models have been used to relate measured concentrations to vehicle emissions. Typically, it is assumed that velocities and concentrations are uniform across the tunnel cross section. In the present work, a vehicle emitting a known amount of sulfur hexafluoride (SF6) was driven repeatedly through a 730-m-long traffic tunnel in Vancouver, Canada. Comparing the measured SF6concentrations to the known emission rates, it is possible to directly assess the accuracy of the simple tunnel aerodynamic models typically used to interpret tunnel data. Correction factors derived from this procedure were then applied to measurements of carbon monoxide and other pollutants to obtain gram-per-kilometer emission factors for vehicles. Although the specific correction factors measured here are valid only for the tunnel tested, the magnitude of the factors (up to two or more) suggests that the phenomena observed here should be considered when interpreting data from other tunnels.

The SAE Aero Design Competition is an annual model airplane competition sponsored by the SAE. The purpose of the competition is to design and build a model airplane, given certain constraints, that is capable of lifting the greatest possible payload. A team of students from the University of British Columbia entered, for the first time, the SAE Aero Design Competition in 1992. The UBC airplane lifted the most weight overall and won first place in the competition against a field of 60 competitors from the USA, Canada, and Europe. In 1993 a UBC team competed again, this time with a significantly improved entry. The team again lifted the most weight and again finished first. For the third year running, the UBC aircraft lifted the most weight at the competition held in 1994. This paper documents the team's experiences in these competitions, and emphasizes how the design of model airplanes for the competitions served the important didactic purpose of introducing aircraft design to the students.

Double-pulsed holograms form the basis of holographic particle image velocimetry. This technique is becoming widely used for measuring three-dimensional velocity fields. The major deficiency of holographic particle image velocimetry is that the double-pulsed holograms must be painstakingly surveyed by a human observer for determination of the location of objects within the holographic volume. A system that automatically and efficiently analyzes double-pulsed holograms of microbubbles in water is developed that eliminates the need for a human surveyor. The system employs a three-part algorithm: (1) Holograms of microbubbles are scanned in the holographic (x–y) plane. Microbubbles within the scanned region are detected by a CCD-based fast object-detection system. (2) Bubble images thus detected are focused (in the z-direction) by an autofocusing technique. (3) In-focus bubble images are analyzed by a simple set of image-analysis techniques, including edge detection and patch correlation. The output of this algorithm is the size, and the displacement between the two laser pulses, of microbubbles in the water.