Horizontal Flow Velocity Research Articles

Strong changes in englacial temperatures despite insignificant changes in ice thickness at Dôme du Goûter glacier (Mont Blanc area)

Abstract. The response of very-high-elevation glaciated areas on Mont Blanc to climate change has been analysed using observations and numerical modelling over the last 2 decades. Unlike the changes at low elevations, we observe very low glacier thickness changes, of about −2.6 m on average since 1993. The slight changes in horizontal ice flow velocities and submergence velocities suggest a decrease of about 10 % in ice flux and surface mass balance. This is due to less snow accumulation and is consistent with the precipitation decrease observed in meteorological data. Conversely, measurements performed in deep boreholes since 1994 reveal strong changes in englacial temperature reaching a 1.5 ∘C increase at a depth of 50 m. We conclude that at such very high elevations, current changes in climate do not lead to visible changes in glacier thickness but cause invisible changes within the glacier in terms of englacial temperatures. Our analysis from numerical modelling shows that glacier near-surface temperature warming is enhanced by increasing melt frequency at high elevations although the impact on surface mass balance is low. This results in a non-linear response of englacial temperature to currently rising air temperatures. In addition, borehole temperature inversion including a new dataset confirms previous findings of similar air temperature changes at high and low elevations in the Alps.

The evolution of flame length for the oil tank fire with different top cover widths and lip heights

This study presents a quantitative analysis and interpretation of the variation in oil tank fire flame lengths for different oil tank sizes, top cover widths, and horizontal air flow velocities. The experimental results show that, at first, the flame length rises slowly with an increase in air flow speed. Then, once over a critical speed (0.6 m/s), the flame length decreases significantly with a further increase in air flow speed. Based on the characteristic length, a new dimensionless heat release rate is obtained, allowing the correlation between flame length, air flow speed, and dimensionless heat release rate to be calculated, which can be used to predict the flame length of an oil tank fire under different air flow speeds, lip heights, and cover widths.

Efficient numerical representation of the impacts of flexible plant reconfiguration on canopy posture and hydrodynamic drag

This study considered a new approach for representing flexible canopies within large-eddy simulation that captures the impacts of reconfiguration on both the canopy posture and the canopy drag. The unsteady change in plant posture in response to the passage of turbulence structures (monami) was assessed using established steady-reconfiguration models responding to the unsteady velocity at the top of the canopy. The new drag and plant posture models improved the modelling of highly flexible canopies by more accurately capturing the observed vertical distribution of peak Reynolds stress. When compared to models that do not consider reconfiguration, or that represent it only through a velocity-dependent drag coefficient, the addition of a velocity-dependent canopy posture (unsteady reconfiguration) achieved up to a 56% reduction of the root mean square error for mean horizontal flow velocity and Reynolds stress profiles over the canopy. The RMSE for turbulence intensities and skewness were reduced up to 48% and 56%, respectively.

Impact of the Electromagnetic Brake Position on the Flow Structure in a Slab Continuous Casting Mold: An Experimental Parameter Study

Flow measurements are performed in a slab model for continuous casting of steel under the influence of a ruler type Electromagnetic Brake (EMBr). The Mini-LIMMCAST facility utilizes the low melting GaInSn alloy for flow modeling. Two-dimensional velocity distributions in the center plane of the rectangular mold with a cross section of $$300 \times 35\,\hbox {mm}^{2}$$ are determined by means of the ultrasound Doppler velocimetry. This study especially focuses on the influence of the vertical position of the EMBr and its magnetic flux density as well as the effect of different immersion depths of the submerged entry nozzle. The horizontal flow velocity just below the free surface can effectively be reduced by choosing an optimal position of the EMBr, while an improper positioning even increases the near-surface velocity compared to the case without activated brake. A general braking effect of the EMBr on the submerged jet is not observed. The decisive mechanism for controlling the near-surface flow results from a modification of the jet geometry and a reorganization of the flow field. In terms of an effective flow control an appropriate positioning of the EMBr has at least the same significance as the regulation of the magnetic field strength.

Verification of the Mathematical Model of Steam Film Condensation from a Flowing Steam-Air Mixture on a Bundle Made of Horizontal Tubes

A model of steam film condensation from a flowing steam-air mixture on a bundle made of horizontal tubes was described in previous publications. In the model, the bulk flow is simulated using single-phase flow equations, and the condensation is simulated by means of the boundary conditions on the tube surface considering the laminar flow of the condensate film. This model was supplemented with a simplified model to describe irrigation of the lower tubes in the bundle with condensate formed on the upper tubes. The results are presented of the model verification against the published experimental data on condensation on horizontal smooth tubes in a staggered tube bundle at a steam-air mixture pressure of 30 kPa, a forced horizontal flow velocity upstream of the tube bundle between 1.3 and 4 m/s, and an air volume fraction from 0 to 12%. Disagreement between the predicted and the experimental heat-transfer coefficients does not exceed 20% for all considered regimes. The calculations were performed using the ANES CFD-code being developed by the authors.

Design of a three-dimensional current sensor with measuring upwelling

A new three-dimensional flow velocity sensor which can measure upwelling was proposed. This sensor was composed of horizontal flow sensor and vertical flow sensor, and it can measured horizontal flow and tiny upwelling separately. The structure of horizontal flow and vertical flow velocity measuring device were analyzed and optimized based on static simulation, static calculation and an experiment. The results show that the sensor can measure both the small upwelling and the horizontal flow velocity in principle. Based on the root of energy loss, the amplifying structure was optimized. After optimization, the magnification factor was increased by 436.84%. According to experimental results, mechanical analysis of cross beams and static simulation, there was a good linear relationship between the flow resistance around the sphere and the output strain of the horizontal velocity measuring device, and it can be used to measure the horizontal flow velocity.

MRT-Lattice Boltzmann Model for Multilayer Shallow Water Flow

The objectives of this study are to introduce a multiple-relaxation-time (MRT) lattice Boltzmann model (LBM) to simulate multilayer shallow water flows and to introduce graphics processing unit (GPU) computing to accelerate the lattice Boltzmann model. Using multiple relaxation times in the lattice Boltzmann model has an advantage of handling very low kinematic viscosity without causing a stability problem in the shallow water equations. This study develops a multilayer MRT-LBM to solve the multilayer Saint-Venant equations to obtain horizontal flow velocities in various depths. In the multilayer MRT-LBM, vertical kinematic viscosity forcing is the key term to couple adjacent layers. We implemented the multilayer MRT-LBM to a GPU-based high-performance computing (HPC) architecture. The multilayer MRT-LBM was verified by analytical solutions for cases of wind-driven, density-driven, and combined circulations with non-uniform bathymetry. The results show good speedup and scalability for large problems. Numerical solutions compared well to the analytical solutions. The multilayer MRT-LBM is promising for simulating lateral and vertical distributions of the horizontal velocities in shallow water flow.

Determining the Relation between Groundwater Flow Velocities and Measured Temperature Differences Using Active Heating-Distributed Temperature Sensing

Active Heating-Distributed Temperature Sensing (AH-DTS) has the potential to allow for the measurement of groundwater flow velocities in situ. We placed DTS fiber-optic cables combined with a heating wire in direct contact with aquifer sediments in a laboratory scale groundwater flow simulator. Using this setup, we empirically determined the relationship between Δ T , the temperature difference by constant and uniform heating of the DTS cable and the background temperature of the groundwater system, and horizontal groundwater flow velocity. Second, we simulated the observed temperature response of the system using a plan-view heat transfer flow model to calibrate for the thermal properties of the sediment and to optimize cable setup for sensitivity to variation in groundwater flow velocities. Additionally, we derived an analytical solution based on the heat flow equation that can be used to explicitly calculate flow velocity from measured Δ T for this specific AH-DTS cable setup. We expect that this equation, after calibration for cable constitution, is valid for estimating groundwater flow velocity based on absolute temperature differences measured in field applications using this cable setup.

Horizontal oil-water two-phase dispersed flow velocity profile study by ultrasonic doppler method

Flow velocity is an important parameter in oil-water two-phase flow, which is closely related to the oil production estimation and production safety. In recent years, pulse-wave Doppler is widely studied because it can obtain the velocity profile along the ultrasound beam. In this paper, a new Pulse-wave Doppler system based on the industrial bus was designed to measure the velocity profile of oil-water two-phase flow. This system was used to study the velocity profile of a horizontal tube oil-water two-phase flow, the flow patterns include dispersion of oil in water and water (Do/w & w), oil in water emulsion (O/W), dual dispersions of water in oil and oil in water (Dw/o & Do/w) and water in oil emulsion (W/O). The velocity profile obtained was compared with the Laser Doppler Velocimetry (LDV) data under similar flow conditions. The results showed that, in water continuous flow patterns, the velocity profile of the two-phase flow can be described by a modified Nikuradse equation that describes the velocity profile of single phase pipe flow; in oil continuous flow patterns, the velocity profile also can be described by a modified Nikuradse equation with different parameters.

Morphological changes of ventilated supercavities in continuous and discrete incident gust flows

The behavior of ventilated supercavities under continuous and discrete gust flows was tested in a medium-sized high-speed cavitation tunnel at the Korea Research Institute of Ships and Ocean Engineering. To investigate the influences of experimental facilities on supercavitation observations, the experimental results were compared with experiments at the Saint Anthony Falls Laboratory under similar flow conditions. We suggested a new threshold criterion at which the total cavity length is shortened, which predicts that the total cavity length shrinks when the vertical velocity of an incident flow reaches approximately 4.5% of the horizontal flow velocity. Additionally, we found that discrete gust flows resulted in changes in the cavity shape that were smaller than those in continuous gust flows.

Hydrochemical behaviour of an underground dammed limestone aquifer in the subtropics

AbstractIn an island area with limited surface water resources, the conservation of fresh groundwater resources is important for the maintenance of the water supply and irrigation system to be used in agricultural activity. In a limestone aquifer used for irrigation on a subtropical island, the progress of the dissolution behaviour of the aquifer and the effects of CO2 storage and chemical weathering of the aquifer must be understood to ensure sustainable groundwater use. In this study, hydrochemical behaviour of the Ryukyu limestone aquifer was investigated using the residence time of slowly flowing groundwater, which is contained by a 2.3‐km‐long underground man‐made dam constructed in 2005 located at the southern edge of Okinawa Island, Japan. Groundwater dating and horizontal flow velocity measurements indicate that the groundwater horizontal flow is slow in the underground dam area, whereas the saturation index (SI) for calcite indicates that the majority of the limestone exists in a supersaturated condition. The range of SI for gypsum was indicative of subsaturation, and the SI increased with the groundwater residence time, suggesting that the dissolution of CaSO4 tends to proceed slowly through the common ion effect. The dissolution of CaCO3, however, tends to be in suspension within about a residence time of 20 years. The apparent dissolution rate of Ca in the Ryukyu limestone aquifer in this area was estimated to be approximately 2.70–4.06 nmol cm−2 year−1, a value much lower than that of the early stages of the limestone dissolution. The estimated groundwater CO2 (gas) concentrations are two order high (about 0.3–7%) relative to atmospheric CO2 (about 0.04%), and the groundwater pH shows a tendency to decrease from 7.4 to 6.9 over the last approximately 20 years, indicating that the hydration reaction of CO2 occurs in the Ryukyu limestone aquifer. These findings imply that high CO2 produced in the subtropical zone is consumed slower than CO2 production during limestone dissolution, with the exclusion of the early stage of the chemical weathering process, and causes groundwater acidification in the underground dammed limestone aquifer.

Effect of Water Head, Gradation of Clogging Agent, and Horizontal Flow Velocity on the Clogging Characteristics of Pervious Concrete

AbstractPermeability is an important index to estimate the working performance of pervious concrete. The previous studies show that pervious concrete clogs due to the ingress of the sediments and o...

Large-scale photospheric motions determined from granule tracking and helioseismology from SDO/HMI data

Context. Large-scale flows in the Sun play an important role in the dynamo process linked to the solar cycle. The important large-scale flows are the differential rotation and the meridional circulation with an amplitude of km s−1 and few m s−1, respectively. These flows also have a cycle-related components, namely the torsional oscillations.Aim. Our attempt is to determine large-scale plasma flows on the solar surface by deriving horizontal flow velocities using the techniques of solar granule tracking, dopplergrams, and time–distance helioseismology.Methods. Coherent structure tracking (CST) and time-distance helioseismology were used to investigate the solar differential rotation and meridional circulation at the solar surface on a 30-day HMI/SDO sequence. The influence of a large sunspot on these large-scale flows with a specific 7-day HMI/SDO sequence has been also studied.Results. The large-scale flows measured by the CST on the solar surface and the same flow determined from the same data with the helioseismology in the first 1 Mm below the surface are in good agreement in amplitude and direction. The torsional waves are also located at the same latitudes with amplitude of the same order. We are able to measure the meridional circulation correctly using the CST method with only 3 days of data and after averaging between ± 15° in longitude.Conclusions. We conclude that the combination of CST and Doppler velocities allows us to detect properly the differential solar rotation and also smaller amplitude flows such as the meridional circulation and torsional waves. The results of our methods are in good agreement with helioseismic measurements.

Counter-streaming flows in a giant quiet-Sun filament observed in the extreme ultraviolet

Aim. The giant solar filament was visible on the solar surface from 2011 November 8–23. Multiwavelength data from the Solar Dynamics Observatory (SDO) were used to examine counter-streaming flows within the spine of the filament.Methods. We use data from two SDO instruments, the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI), covering the whole filament, which stretched over more than half a solar diameter. Hα images from the Kanzelhöhe Solar Observatory (KSO) provide context information of where the spine of the filament is defined and the barbs are located. We apply local correlation tracking (LCT) to a two-hour time series on 2011 November 16 of the AIA images to derive horizontal flow velocities of the filament. To enhance the contrast of the AIA images, noise adaptive fuzzy equalization (NAFE) is employed, which allows us to identify and quantify counter-streaming flows in the filament. We observe the same cool filament plasma in absorption in both Hα and EUV images. Hence, the counter-streaming flows are directly related to this filament material in the spine. In addition, we use directional flow maps to highlight the counter-streaming flows.Results. We detect counter-streaming flows in the filament, which are visible in the time-lapse movies in all four examined AIA wavelength bands (λ171 Å, λ193 Å, λ304 Å, and λ211 Å). In the time-lapse movies we see that these persistent flows lasted for at least two hours, although they became less prominent towards the end of the time series. Furthermore, by applying LCT to the images we clearly determine counter-streaming flows in time series of λ171 Å and λ193 Å images. In the λ304 Å wavelength band, we only see minor indications for counter-streaming flows with LCT, while in the λ211 Å wavelength band the counter-streaming flows are not detectable with this method. The diverse morphology of the filament in Hα and EUV images is caused by different absorption processes, i.e., spectral line absorption and absorption by hydrogen and helium continua, respectively. The horizontal flows reach mean flow speeds of about 0.5 km s−1 for all wavelength bands. The highest horizontal flow speeds are identified in the λ171 Å band with flow speeds of up to 2.5 km s−1. The results are averaged over a time series of 90 minutes. Because the LCT sampling window has finite width, a spatial degradation cannot be avoided leading to lower estimates of the flow velocities as compared to feature tracking or Doppler measurements. The counter-streaming flows cover about 15–20% of the whole area of the EUV filament channel and are located in the central part of the spine.Conclusions. Compared to the ground-based observations, the absence of seeing effects in AIA observations reveal counter-streaming flows in the filament even with a moderate image scale of 0. ′′6 pixel−1. Using a contrast enhancement technique, these flows can be detected and quantified with LCT in different wavelengths. We confirm the omnipresence of counter-streaming flows also in giant quiet-Sun filaments.

Weather-Induced Transport through a Tidal Channel Calibrated by an Unmanned Boat

AbstractAn unmanned surface vehicle (USV) was designed and constructed to operate continuously for covering both flood and ebb and preferably a complete tidal cycle (e.g., ~24 h) to measure the vertical profiles of horizontal flow velocity. It was applied in a tidal channel at Port Fourchon, Louisiana. A bottom-mounted ADCP was deployed for 515 days. The first EOF mode of the velocity profiles showed a barotropic type of flow that explained more than 98.2% of the variability. The second mode showed a typical estuarine flow with two layers, which explained 0.47% of the variability. Using a linear regression of the total transport from the USV with the vertically averaged velocity from the bottom-mounted ADCP, with an R-squared value of 98%, the total along-channel transport throughout the deployment was calculated. A low-pass filtering of the transport allowed for examining the impact of 76 events with cold, warm, or combined cold–warm fronts passing the area. The top seven most severe events were discussed, as their associated transports obviously stood out in the time series, indicating the importance of weather. It is shown that large-scale weather systems with frontal lines of ~1500–3000-km horizontal length scale control the subtidal transport in the area. Cold (warm) fronts tend to generate outward (inward) transports, followed by a rebound. The maximum coherence between the atmospheric forcing and the ocean response reached ~71%–84%, which occurred at about a frequency f of ~0.29 cycle per day or T of ~3.4 days in the period, consistent with the atmospheric frontal return periods (~3–7 days).

Spatial variability of phosphorus adsorption in surface sediment at channel confluences: Field and laboratory experimental evidence

Field surveys and a laboratory experiment have been conducted to characterize the spatial variability of phosphorus (P) adsorption in surface sediment at channel confluences with a large tributary discharge. The results show that the grain size of surface sediment and the concentration of soluble reactive phosphorus in overlying water are the most important factors affecting the spatial variability of P in surface sediment. Their differences in the two combining flows can be reduced dramatically by the mixing layer, and the mixing distance can be largely decreased by the distortion of the shear layer and the complex bed morphology as they can increase the transverse mixing of the two combining flows. The influence of hydrodynamics is highlighted especially when other factors were comparable in the two tributaries. The downwelling flow shall improve the hyporheic exchange and induce more P to be absorbed onto the bed sediment at channel confluences. The horizontal flow velocity shall be a more appropriate indicator of the influence of hydrodynamics on P enrichment. Thus, the region of flow separation is beneficial to P adsorption, while the region of shear layer and maximum flow velocity are adverse to P enrichment. All these results help to better understand and predict the spatial variability of P adsorption in surface sediment at channel confluences.

Measuring solar active region inflows with local correlation tracking of granulation

Context. Local helioseismology has detected spatially extended converging surface flows into solar active regions. These play an important role in flux-transport models of the solar dynamo. Aims. We aim to validate the existence of the inflows by deriving horizontal flow velocities around active regions with local correlation tracking of granulation. Methods. We generate a six-year long-time series of full-disk maps of the horizontal velocity at the solar surface by tracking granules in continuum intensity images provided by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Results. On average, active regions are surrounded by inflows extending up to 10 deg from the center of the active region of magnitudes of 20-30 m/s, reaching locally up to 40 m/s, which is in agreement with results from local helioseismology. By computing an ensemble average consisting of 243 individual active regions, we show that the inflows are not azimuthally symmetric but converge predominantly towards the trailing polarity of the active region with respect to the longitudinally and temporally averaged flow field.

The stabilizing effect of collision‐induced velocity shear on the ionospheric feedback instability in Earth's magnetosphere

AbstractThe feedback instability in the ionospheric Alfvén resonator in Earth's magnetosphere is examined using a two‐dimensional multifluid numerical model of coupled ionosphere and magnetosphere. Two simulation configurations are used to demonstrate that the instability occurs under an assumption that is unrealistic for Earth's ionosphere. In the first configuration, a flat sheet height‐integrated conducting boundary replaces the ionospheric E layer. In the second configuration, plasma dynamics in a simplified E layer is resolved ignoring ion production, loss, and diffusion. For the same parameters (plasma and neutral density profiles and convection electric field), the instability develops only with the flat sheet boundary. When the E layer is resolved, the variation of ion‐neutral collision frequencies with altitude produces vertical shear in the horizontal ion flow velocity. The shear prevents density perturbations from remaining field aligned, causing them to decay rather than grow. It is suggested that the instability cannot occur in Earth's ionosphere because ion‐neutral collision frequencies always have a significant variation with altitude through the E layer.

Impact of intermittent aeration mode on enhancement of biological nutrient removal by the novel prototype IT/OD-MBR(Inclined Tube/Oxidation-Ditch Membrane Bioreactor) for high-rise building's wastewater recycling

A novel prototype IT/OD-MBR (Inclined Tube/Oxidation Ditch-Membrane Bioreactor) system has been developed for biological nutrient removal purpose. The intermittent aeration modes (aeration/non-aeration period) were varied to 60/60, 40/80, 30/90,80/40, 90/30 min. The prototype system was operated with horizontal flow velocity of 0.3 m/s, hydraulic retention time (HRT) of 24 h and fed with the raw wastewater from Julajakrapong building, which is a high-rise building inside Chulalongkorn University at a constant flowrate of 2 m3/day. From the long-term system operation, the most efficient energy-saving system with high performance of nutrient removal could be achieved with the aeration on/off mode of 30/90 min. Moreover, investigation of biofoulant characteristics on membrane surface was performed by SEM-EDX and FT-IR analyses. It was found that protein and carbohydrate were predominant compositions of the biofoulant substances. Main protein composition in the biofoulant was carbonyl group. The reclaimed water can be used for gardening and landscape purposes. Therefore, the novel IT/OD-MBR system can be considered as an alternative for high-rise building's wastewater recycling.

Tritium Tracers of Rapid Surface Water Ingression into Arsenic-bearing Aquifers in the Lower Mekong Basin, Cambodia

Arsenic (As) contamination of groundwaters in South and Southeast Asia is a major threat to public health in these areas. Understanding the source and age of the groundwaters is critically important to understanding the controls on As mobilization in these aquifers. Using tritium (3H) and noble gas (He and Ne) signatures, model groundwater ages and dominant hydrological controls were identified in a transect oriented broadly parallel to inferred groundwater flowpaths in Kandal Province, Cambodia in the lower Mekong Basin. Apparent 3H-3He ages showed that most groundwaters are modern (< 55 years), indicating relatively fast recharge even in the absence of large-scale groundwater abstraction. The age-depth relationship indicates a strong vertical component of groundwater flow and allows for recharge rates to be estimated. Vertical and horizontal flow velocities are heterogeneous and site-specific. The conceptual framework will be used to better understand As mobilization and subsequent transport with these and similar aquifers.