Local Flow Patterns Research Articles

Prediction of Regional Ground Water Flow to Streams

AbstractDatabase information on geology, hydrology, and hydrometeorology may form an excellent basis for studying ground water flow and seepage to surface water in a catchment. In a field case study of a 114 km2 catchment, geological database information was used to determine layer thicknesses and boundary conditions as well as to parameterize a ground water flow model. Hydraulic head and stream flow data were used to estimate the model parameters by nonlinear regression. The uncertainty of the estimated parameters and of the predicted stream flow gains was quantified by individual likelihood method confidence intervals. During four stages of calibration, ranging from using only head data to also using an extensive set of measured stream flow gains, no parameter estimates changed significantly, but the number of parameters was increased from 12 to 14 in order to fit local stream flow gains. This indicates that the geology‐based parameterization is firm.Adding stream flows to the calibration data reduced the uncertainty of the estimated parameters significantly. However, the uncertainty of some of the parameters was significant even when an extensive set of measured stream flow gains and hydraulic heads was used to calibrate the model. Parameter uncertainty is reflected in the uncertainty of the predicted stream flow gains. When an extensive set of stream flow data was used during calibration, the prediction uncertainty is up to ±25% in large streams, and up to ±60% in smaller streams. The confidence intervals in general are skewed, and they are very skewed in the case where no stream flow measurements were used to calibrate the model.The case study shows that even when relatively extensive geological information and calibration data are available, there may be significant uncertainty connected with the prediction of local discharge of ground water to streams. Reducing uncertainty in such cases will require extensive field investigations in order to improve the definition of recharge areas and to describe the local fluxes and flow patterns in the aquifers.

Flow Boiling in Horizontal Tubes: Part 3—Development of a New Heat Transfer Model Based on Flow Pattern

A new heat transfer model for intube flow boiling in horizontal plain tubes is proposed that incorporates the effects of local two-phase flow patterns, flow stratification, and partial dryout in annular flow. Significantly, the local peak in the heat transfer coefficient versus vapor quality can now be determined from the prediction of the location of onset of partial dryout in annular flow. The new method accurately predicts a large, new database of flow boiling data, and is particularly better than existing methods at high vapor qualities (x > 85 percent) and for stratified types of flows.

Climatology of Regional Flow Patterns around Basel

Recently a method has been developed to classify local-scale flow patterns from the wind measurements at a dense network of stations. It was found that in the area around Basel twelve characteristic near-surface flow patterns occur. However, as the dense network of stations was running for one year only during the MISTRAL field experiment, no reliable climatology of the flow patterns can be inferred from these data. Mainly the annual cycle is not well determined from a single year of observations. As there exist several routinely operated meteorological stations with longer data records in and near the area discussed, a method was searched to identify the local flow patterns from the wind observations at these few permanent stations. A linear discriminant analysis turned out to be the best method. Based on wind data from 11 stations which were simultaneously in operation during 1990-1995, a six-year climatology of the flow patterns could be obtained and compared to synoptic weather types. Although there are relations to existing synoptic classes there is no unique correspondence between them and the flow patterns.

Augmented heat transfer in a rectangular duct with angled ribs

Heat transfer augmentation in a rib-roughened duct is affected by the rib configurations, such as rib height, angle of attack, shape, rib to rib pitch, and aspect ratio of a duct. These have been the main subjects in studying the average heat transfer and the friction loss of the fully developed flow. Investigating distributions of local heat transfer coefficients and flow patterns in a duct with the rib turbulators is necessary to find the characteristics of heat transfer augmentation and to decide the optimal configurations of ribs. In the present study the numerical analyses and the mass transfer experiments are performed to understand the flow through a rib roughened duct and the heat transfer characteristics with various angles of attack of ribs. A pair of counter-rotating secondary flow in a duct has a main effect on the lateral distributions of local mass transfer coefficients. Downwash of the rotating secondary flow, reattachment of main flow between ribs and the vortices near ribs and wall enhanced the mass transfer locally up to 8 times of that in case of the duct without ribs.

Wind-driven rain distributions on two buildings

Wind-driven rain is an important consideration in the hygrothermal performance of building envelope parts. Wind-driven rain (in liquid form) can increase the amount of moisture present in the structure by more than 100 times that due to vapor diffusion. To date, very little work that provides field or laboratory wind driven rain data to moisture transport models is available. This information is a definite requirement as a boundary condition by the more sophisticated hygrothermal models such as LATENITE and WUFIZ which consider both vapor and liquid moisture flows. In this paper, the wind driven rain striking the exterior facade of two buildings (one twice the size of the other) is generated using a three-dimensional computational fluid dynamics (CFD) model that solves the air flow and particle tracking of the rain droplets around these two buildings. These simulations were carried out for a city center region. Four factors which govern wind-driven rain are investigated in this work: (a) upstream unobstructed wind conditions, (b) the rainfall intensity, (c) the probability distribution of raindrop sizes, and (d) the local flow patterns around the building. All four of these governing factors make wind-driven rain on a building facade very distinct. Simulations were carried out for three wind speeds of 5, 10 and 25 m/s, three rainfall intensities of 10, 25 and 50 mm/h and three wind directions 0°, 30° and 45° from the west face of the buildings. In this paper, only the results of the 0° wind direction are discussed. The results show distinct wetting patterns on the top of the building of both the two buildings which is most concentrated at the corners when the wind was normal to the facade surface. For the tallest building a distinct wetting pattern is displayed in the mid-height of the building. This information from wind engineering is directly employed for the design of building envelope moisture control. Results on a series of simulations are presented to demonstrate the effect of wind conditions, rain intensities, the interaction between the two buildings, and the droplet sizes on the wetting patterns on the faces of the short and tall building.

Nitrate removal in riparian wetland soils: Effects of flow rate, temperature, nitrate concentration and soil depth

Riparian zones, located adjacent to intensely managed agricultural fields, are thought to play an important role in removal of nutrient contaminants including NO − 3 from groundwater. We studied the effect of flow rate, NO − 3 concentration and temperature on NO − 3 removal in soil columns under saturated-flow conditions. Bibb (coarse-loamy, siliceous, acid thermic Typic Fluvaquent) sandy loam soil was collected from a riparian forest located in Nomini Creek Watershed, Virginia. Soils included in the study were a permanently inundated surface horizon, a seasonally saturated surface horizon, a shallow subsurface horizon and a deep subsurface horizon. Soil columns were infiltrated with NO − 3 amended groundwater at concentrations from 14 to 36 mg NO − 3-N L −1. Column operating temperatures varied between 8 and 20°C and flow rates between 0.01 and 0.09 mL min −1. Following a 48 h equilibrium period, effluent NO − 3 and N 2O concentrations were determined. Denitrification was the primary mechanism of NO − 3 removal, with higher denitrification capacities found in the surface horizons. Effluent NO − 3 concentrations could be described by a linear combination of temperature, flow rate and influent NO − 3 concentrations. Low temperatures and increased flow rates reduced the denitrification capacity in all soils. Our results showed that the NO − 3 removal capacity present in the Bibb soil should theoretically be sufficient to remove most, if not all, NO − 3 from the groundwater at the Nomini Creek study site. However, on-site measurements of NO − 3 concentration in receiving streams indicated that this capacity is not fully realized in the field, suggesting the importance of other factors such as local hydrology and groundwater flow patterns.

Reconstruction of Current Flow and Imaging of Current-Limiting Defects in Polycrystalline Superconducting Films

Magneto-optical imaging was used to visualize the inhomogeneous penetration of magnetic flux into polycrystalline TlBa2Ca2Cu3Ox films with high critical current densities, to reconstruct the local two-dimensional supercurrent flow patterns and to correlate inhomogeneities in this flow with the local crystallographic misorientation. The films have almost perfect c-axis alignment and considerable local a- and b-axis texture because the grains tend to form colonies with only slightly misaligned a and b axes. Current flows freely over these low-angle grain boundaries but is strongly reduced at intermittent colony boundaries of high misorientation. The local (<10-micrometer scale) critical current density Jc varies widely, being up to 10 times as great as the transport Jc (scale of approximately 1 millimeter), which itself varies by a factor of about 5 in different sections of the film. The combined experiments show that the magnitude of the transport Jc is largely determined by a few high-angle boundaries.

Drag and Flow Field around Elasto-Flexible Cylinder in Uniform Flow.

The purpose of this experiment is to clarify the mechanism of drag reduction in the natural swimming of fish, whales and dolphins. It is well known that the change in their shape and the local deformation of their skin contribute to drag reduction, especially in the case of dolphins. Therefore, in order to understand the interaction between a deformable surface and the local flow pattern, RFFRC (rigid front flexible rear cylinder) models of a simplified marine animal were studied in a water tunnel. The laser light sheet method was used to visualize the flow field around the models. The vortex pair shedding period from the models, the deformation of the models' cross-sectional form and models' drag were measured simultaneously. The following results were obtained. For some types of RFFRC which could be deformed easily in response to a change in the local flow pattern with vortex shedding, the increase in flow velocity in the wake was observed. In the case the St number was about 20% higher than that of a rigid cylinder. Although, the drag that some types of RFFRC had was higher than that of the rigid one. However, the other types of RFFRC which could not quickly deform show no difference in St number, whereas the mean drag of this type was about 20% lower and the time variation of the drag became smaller than that of the rigid cylinder.

Groundwater flow modelling to assist dryland salinity management of a coastal plain of southern Australia

Groundwater flow modelling has been undertaken for an area of 10 500 ha within the regional unconfined aquifer system of a coastal plain of southern Australia, in the vicinity of the town of Cooke Plains, to predict the impact of various land management options (including recharge reduction and discharge enhancement) on the extent of land salinisation caused by shallow saline watertables. The model was calibrated against field data collected over 6 years. Sensitivity analysis was performed to assess the influence of mesh size, boundary conditions, and aquifer parameters, and particularly rates of recharge and evaporative discharge, on groundwater levels. These were varied until the model was shown to be capable of simulating seasonal trends and regional and local flow patterns. The model was then used to predict the impact of the management options on groundwater levels. The results showed that continuing current annual crop–pasture rotations will result in watertable rises of approximately 0·2 m in 20 years (significant in this setting), with a further 50 ha of land salinised. A reduction in the rates of groundwater recharge through the establishment of high water-use perennial pastures (e.g. lucerne) showed the most promise for controlling groundwater levels. For example, a reduction in recharge by 90% would result in watertable declines of 0·6–1·0 m within 5–10 years, with the return to productivity of 180 ha of saline land. Small-scale (say &lt;100 ha) efforts to reduce recharge were found to have no significant impact on groundwater levels. Enhanced groundwater discharge such as pumping from a windmill was found to be non-viable due to the relatively high aquifer transmissivity and specific yield. The modelling approach has enabled a relatively small area within a regional aquifer system to be modelled for a finite time (20 years) and has shown that extension of the boundaries of the model would not have altered the predicted outcomes. Furthermore, the analysis of sensitivity to cell size in an undulating landscape where net recharge areas can become net discharge areas with only small increases in groundwater level is novel, and has helped to build confidence in the model. Modelling has demonstrated that dryland salinisation can be controlled by reducing groundwater recharge over substantial tracts of land, and is not dependent on recharge reduction over an extensive area upgradient, at least over the next 20 years.

Study of turbulent boundary layer structure using the invariants of the velocity gradient tensor

The geometry of the velocity field in a numerically simulated incompressible turbulent boundary layer over a flat plate at Re θ = 670 is studied with the use of the invariants of the velocity gradient tensor ( P, Q, and R). These invariants are computed at every grid point in the flow and used to form the discriminant ( D = 27 R 2/4 + Q 3). Of primary interest are those regions in the flow where the discriminant is positive—regions where, according to the characteristic equation, the eigenvalues of the velocity gradient tensor are complex. An observer moving with a frame of reference that is attached to a fluid particle lying within such a region would see a local flow pattern of the type stable-focus-stretching or unstable-focus-compressing. When the flow is visualized in this way, continuous, connected, large-scale structures are revealed that extend from just below the buffer layer (y + ≈ 1.0) out into the beginning of the wake region. These structures are aligned with the mean shear close to the wall and arch in the cross-stream direction away from the wall. In some cases, the structures observed are very similar to the hairpin eddy vision of boundary-layer structure proposed by Theodorsen [1]. Recently, this conceptual picture has been used by Perry et al. [2] to develop a successful model of the turbulent boundary layer based on an extension of the attached eddy hypothesis first proposed by Townsend [3]. That the structure of the flow is revealed more effectively by the discriminant rather than by the vorticity is important and adds support to the recent analysis of channel flow structure by Blackburn et al. [4]. Of particular importance (and also in contrast with the use of the vorticity) is the fact that the procedure does not require the use of an arbitrary threshold in the discriminant. Further analysis using computer flow visualization shows a high degree of spatial correlation between the regions of positive discriminant, extreme negative pressure fluctuations, and large instantaneous values of Reynolds shear stress ( u′ v′).

Bhopal Gas Leak: A Numerical Investigation of the Prevailing Meteorological Conditions

Abstract A three-dimensional mesoscale model was used to understand the meteorological conditions and the influence of the terrain on the local flow pattern during the Bhopal methyl isocyanate (MIC) gas leak. The study reveals that under the prevailing conditions of weak wind and strong stability the lakes in Bhopal influenced the local circulation significantly and caused northwesterly flow near the surface. The modified flow pattern resulted in the transport of MIC into the city area of Bhopal. However, with the increase in the ambient synoptic wind, the role of the lakes was found to diminish. Further, the other topographical features such as the hillocks in and around the city and the gently rolling terrain toward the southeastern sector of the city seem to have played a secondary role in influencing the meteorological conditions on the episodic night.

Study of Secondary Flow in Centrifugal Blood Pumps Using a Flow Visualization Method with a High-Speed Video Camera.

Four pump models with different vane configurations were evaluated with flow visualization techniques using a high-speed video camera. These models also were evaluated through in vivo hemolysis tests using bovine blood. The impeller having the greatest fluid velocity relative to the impeller, the largest velocity variance, and the most irregular local flow patterns in the flow passage caused the most hemolysis. Even if the pumps were operated at almost the same speed (rpm) at the same output, the impeller showing more irregular flow patterns had a statistically greater rate of hemolysis. This fact confirms that the existence of local irregular flow patterns in a centrifugal blood pump deteriorates its hemolytic performance. Thus, to optimize the design of the pump, it is very important to examine the secondary flow patterns in the centrifugal blood pump in detail using flow visualization with a high-speed video camera.

Deposition patterns of inhaled radon decay products in human bronchial airway bifurcations

Particle deposition patterns within three-dimensional models of human bronchial airway bifurcations are simulated by a numerical fluid dynamics and particle trajectory model. The three geometric models of a segmental bronchial airway bifurcation, employed in the present study, are: 1) a symmetric “idealized bifurcation model”; 2) a symmetric “physiologically realistic bifurcation model”; and, 3) an asymmetric “idealized bifurcation model”. Inspiratory deposition patterns for 1 nm (unattached radon progeny), 10 nm (ultrafine radon progeny), and 200 nm (attached radon progeny) particles reveal that particle deposition is enhanced at the carinal ridge, consistent with the action of local flow patterns. Carinal deposition enhancement is slightly higher for the symmetric physiologically realistic and the asymmetric idealized models relative to the commonly used symmetric idealized bifurcation model, thereby providing a reasonable range for local deposition enhancement factors. Together with reduced mucociliary clearance at carinal ridges, such localized accumulations of radon decay products may produce local cellular doses, which can significantly exceed dose estimates based on uniform nuclide distributions.

High sulfate concentrations in limestone springs: An important factor in conduit initiation?

Major ion concentrations in 404 springs in carbonate strata were found to exhibit a wide range in sulfate values. Sulfate concentrations are often much larger than would be expected from the analysis of samples from surface outcrops. Springs in the Sierra Madre Oriental (Mexico), the Rocky Mountains Front Range (Canada), and the Peak District (England) show similarities in sulfate concentration and in spatial distribution. Springs with high sulfate concentrations are found close to base level and are thermal. Springs with low sulfate concentration are found at higher elevations above base level and are not thermal. There is a direct relationship between sulfate concentration and spring temperature, and an inverse relationship with discharge. The results from the three areas described support a model of local and regional flow patterns, with deep regional flow providing the warm sulfate-rich water. The initial fracture porosity development in these aquifers may owe as much to the removal of sulfur minerals as to the removal of carbonate minerals. High sulfate values are frequently found in carbonate aquifers, so this model may be of widespread applicability.

Fluiddynamic characterization of airlift tower loop bioreactors with and without motionless mixtures

In a 60 l airlift tower reactor with outer loop fluiddynamical measurements were carried out in presence of three motionless mixer modules (Type SMV, Sulzer) in water, 0.6%, 0.9% and 1.2% CMC solutions. The global mixing properties were determined in the liquid and gas phases by tracers. Detailed local measurements revealed differences of local flow patterns and mixing properties in the unhindered riser and in the immediate wake of the mixer module. The local liquid velocities were measured by the pseudorandom heat pulse technique. The local bubble velocities were determined by the ultrasound Doppler technique. The dependence of liquid velocity, gas velocity and gas holdup on the superficial gas velocity were determined. The radial profiles of the mean liquid velocities and their standard deviations were evaluated in water and CMC solutions upstream and downstream of the motionless mixer modules. The radial profiles of the mean large-bubble velocities and mean small-bubble velocities and their standard deviations were determined as well. The influence of the presence of the motionless mixers in the riser on these properties was evaluated.

Impact of microsensor-caused changes in diffusive boundary layer thickness on O2 profiles and photosynthetic rates in benthic communities of microorganisms

Although O2 microsensors used for study of benthic photosynthesis have tip diameters of less than 10 pm and stem diameters of about 150 pm at a distance of 0.5 cm from the tip, they do change the local flow pattern in the overlying water and thereby reduce the thickness of the diffusive boundary layer (DBL). The reduced DBL resulted in a lower diffusional resistance towards export of 0, from communities with a net production of Oa, and insertion of a microsensor in such a community therefore resulted in lowered O2 concentrations. The total diffusion flux out of the photosynthetic layer was not significantly dffected by the presence of the microsensor. The higher upward flux into the water phase was counterbalanced by a reduced downward flux into the sediment. The O2 profiles and diffusion fluxes were only affected when the surface was smooth, while the effect of microsensor insertion was undetectable when the surface was made irregular by small tufts, bubbles, etc. In the investigated cyanobacteria-dominated mats, the gross photosynthetic rates as measured by the light/dark shift technique were unaffected by the presence of a microsensor.

132 柔軟な弾性表面を持つ円筒周りの流れ場の可視化

The purpose of this study is to clarify the mechanism of decreasing the drag in natural swimming of fish, whale and dolphin. A cylinder which has Elasto-flexible surface simplified marine creature was placed in a water tunnel, and using Laser Light Sheet method to visualize flow field around the model, vortex pair shedding period from the model, deformation of its cross-sectional form and hydrodynamical drag of the model were simultaneously measured. As a result, the following were found: the rigid front flexible rear cylinder model has showed about 20% higher St number than rigid cylinder model. The local deformation of the surface changed local flow pattern and wake due to some interaction between flexible surface and vortex. Time variation of the drag of the Rigid Front Flexible Rear Cylinder (RFFRC) became smaller than rigid one.

Large strain deformation of a copper—tungsten composite system. II. Applications

Abstract A model composite system comprised of tungsten fibres in a polycrystalline copper matrix has been used to examine the processes which control (i) matrix texture development, (ii) recrystallization behaviour in the matrix and (iii) the damage accumulation process. The composite was deformed in plane strain compression with the fibres parallel to the direction of zero strain (i.e. perpendicular to the loading axis). Experimental measurements were made of local and global texture development as well as metallographic observations of the pattern of recrystallization events and metallographic observations of damage events in the tungsten fibres or at the copper—tungsten interface. Physically based explanations are used to describe the results in terms of the local flow pattern in the matrix and the local distribution of stresses.

Hemodynamic stress and experimental aortoiliac atherosclerosis.

Human aortic atherosclerosis is predominantly localized to the infrarenal aorta where flow is bidirectional and wall shear stress oscillates. Similar flow patterns have been related to carotid atherosclerosis. The thoracic aorta is usually spared, where flow and shear stress are unidirectional. We hypothesized that because heart rate and systemic blood pressure modulate flow velocity and shear stress oscillation, both these hemodynamic forces may enhance aortoiliac atherogenesis. Eighteen male cynomolgus monkeys were fed an atherogenic diet for 6 months (mean serum cholesterol = 535 +/- 35 mg/dl). Heart rate was determined with 24-hour electrocardiographic telemetry at monthly intervals and blood pressure was measured by direct arterial cannulation. The product of mean heart rate and mean blood pressure was used to define hemodynamic stress for each animal. Atherosclerotic lesion formation at three standard thoracic aortic sites was quantitatively compared with lesion formation at five standard infrarenal aortoiliac locations with computer-assisted morphometry. There was significantly more plaque in the aortoiliac segment than in the thoracic aorta (12.4% +/- 9.0% vs. 6.4% +/- 4.5% area stenosis, p = 0.02). No correlation was found between the degree of serum lipid elevations and lesion formation in either aortic location. Mean heart rate was 113 +/- 18 beats/min (87 to 163 beats/min) and mean blood pressure was 85 +/- 19 mm/Hg (62 to 130 mm Hg). Heart rate and blood pressure alone were not significantly related to lesion formation. A significant correlation was, however, found between hemodynamic stress and maximum lesion thickness (r = 0.47, p < 0.05) in the aortoiliac region but not in the thoracic aorta (r = 0.19, p > 0.10). This study demonstrates that heart rate and blood pressure exert a mutually potentiating effect on aortoiliac atherosclerosis but not on thoracic aortic atherosclerosis. Regional differences in aortic atherosclerosis may therefore be attributable to the interaction between these hemodynamic forces and the local flow patterns specific to each aortic location. Additional investigation of these hemodynamic factors in relation to human aortic atherosclerosis is warranted.

Anisotropic Chemical Etching of Copper Foil: II . Experimental Studies on Shape Evolution

Wet chemical etching of copper foil. (35 μm thick) at the base of the photoresist cavity (100 μm deep) was investigated experimentally in two geometries (width:depth of 1:1 and 5:1), two acidic cupric chloride solutions, and various flow rates in the range of Péclet number between 107 and 2930. Anisotropic etch profiles were obtained for all conditions investigated. In a etching solution, results indicated that a salt film precipitated on the entire surface and the etch rate was controlled by the rate of convective mass transfer of product removal. The etch rate was highly nonuniform (anisotropic) owing to the presence of local microhydrodynamic flow patterns within the cavity which influenced the local mass‐transfer rate. In a etching solution it was concluded, based on the observations of surface roughness, that the film precipitated only in the corners of a 5:1 (width:depth) cavity, whereas the rest of the surface dissolved film‐free. Moreover, the dependence of etch rate on fluid velocity was weak. For the same solution and 1:1 cavities, dissolution proceeded under conditions of film precipitation on the entire surface.