Measured Flow Patterns Research Articles

Hydraulic investigation of flow and bed load transport in diverging compound channels with rigid and flexible vegetation

Floodplains are really important for the environment as they provide various functions for waterways, including ecological, hydrological, and geomorphic ones. During overbank flows, there are complex hydrodynamic conditions that occur as water interacts with the rough floodplain vegetation and drag forces due to the vegetation that changes the flow pattern. However, we still don't fully understand how floodplain vegetation influences channel-altering hydrodynamic forces and sediment transport. To address this, we conducted flume experiments and measured flow pattern and sediment transport under varied floodplain geometry and rigid and flexible conditions. For this purpose, a physical model was constructed in the laboratory, in which plastic rods with a diameter of 10 mm will be used as trees, and artificial grass will be grass vegetation. Thus, 36 experiments were conducted in which the sedimentation and hydraulic parameters of the flow were calculated by measuring the flow velocity, water surface, and sediment transport rate. The results show that in the floodplain with dense (rigid and flexible) vegetation, the friction coefficient (f) is even 1.5 times higher than in the floodplain without vegetation. The parameters such as flow velocity, bed shear stress and Darcy Weissbach friction coefficient increase in the vertical plane between the main channel and floodplains due to the difference in roughness between the main channel and floodplains. In addition, in the main channel, the flow resistance is almost constant and does not depend on the vegetation density. The Darcy-Weissbach friction coefficient is greatly increased in the presence of grass and tree vegetation on the floodplain, and the larger contribution of f is due to the grass vegetation. The results also showed the sediment transport rate has a direct relationship with the angle of divergence and density of vegetation and an inverse relationship with the relative depth of the flow. Therefore, as the sediment transport rate decreases in the diverging compound channel, the wavelength and height of the dunes increase. At smaller divergence angles, the dunes tend to the top of the zero line (the level of the sediments before the formation of the bed form). In the presence of vegetation, due to the increase in the roughness ratio of the floodplain to the main channel, the contribution of the main channel to the flow rate increases. As a result, the sediment transport rate increases.

Development of an in vitro setup for flow studies in a stented carotid artery bifurcation.

To investigate flow conditions in a double-layered carotid artery stent, a bench-top in vitro flow setup including a bifurcation phantom was designed and fabricated. The geometry of the tissue-mimicking phantom was based on healthy individuals. Two identical phantoms were created using 3D-printing techniques and molding with PVA-gel. In one of them, a clinically available CGuard double-layer stent was inserted. Measurements were performed using both continuous and pulsatile flow conditions. Blood flow studies were performed using echoPIV: a novel ultrasound-based technique combined with particle image velocimetry. A maximum deviation of 3% was visible between desired and measured flow patterns. The echoPIV measurements showed promising results on visualization and quantification of blood flow in and downstream the stent. Further research could demonstrate the effects of a double-layered stent on blood flow patterns in a carotid bifurcation in detail.

Wake flow patterns and turbulence around naturally deposited and installed trees in a gravel bed river

AbstractLarge wood structures, such as wood fragments, debris jams, or entire trees, create flow and habitat diversity in rivers. A key flow feature associated with such structures is the wake, characterised by a core zone of reduced velocity and shear layers at its margins. Wakes are largely controlled by geometric and structural properties of the wood. In the present study, the flow patterns and turbulence created by different wood structures were compared at two study sites: naturally eroded and fragmented oaks (Site A) and artificial poplar installations (Site B). Flow and turbulence were quantified using pointwise velocity measurements with acoustic Doppler velocimeters (ADVs) and surface particle tracking velocimetry (SPTV). The measured flow patterns exhibited similarities with shallow porous wakes that feature fluid advection through the structure into the wake core downstream. Two additional features of wood structures were identified in the present study: (i) the growth of the shear layers was hindered by bed friction like for shallow mixing layers and (ii) the presence of a tree stem and sediment deposit in the wake centre delayed or even suppressed the interaction of the shear layers and vortex street formation similar to a wake‐splitter plate. Methodologically, the combined ADV/SPTV measurement approach and the use of analytical models for shallow mixing layers proved to be highly valuable to decipher the complex flow patterns around wood structures in the field.

Intermediate fenestrations reduce flow reversal in a silicone model of Stanford Type B aortic dissection

Pulsatile, three-dimensional hemodynamic forces influence thrombosis, and may dictate progression of aortic dissection. Intimal flap fenestration and blood pressure are clinically relevant variables in this pathology, yet their effects on dissection hemodynamics are poorly understood. The goal of this study was to characterize these effects on flow in dissection models to better guide interventions to prevent aneurysm formation and false lumen flow. Silicone models of aortic dissection with mobile intimal flap were fabricated based on patient images and installed in a flow loop with pulsatile flow. Flow fields were acquired via 4-dimensional flow MRI, allowing for quantification and visualization of relevant fluid mechanics. Pulsatile vortices and jet-like structures were observed at fenestrations immediately past the proximal entry tear. False lumen flow reversal was significantly reduced with the addition of fenestrations, from 19.2 ± 3.3% in two-tear dissections to 4.67 ± 1.5% and 4.87 ± 1.7% with each subsequent fenestration. In contrast, increasing pressure did not cause appreciable differences in flow rates, flow reversal, and vortex formation. Increasing the number of intermediate tears decreased flow reversal as compared to two-tear dissection, which may prevent false lumen thrombosis, promoting persistent false lumen flow. Vortices were noted to result from transluminal fluid motion at distal tear sites, which may lead to degeneration of the opposing wall. Increasing pressure did not affect measured flow patterns, but may contribute to stress concentrations in the aortic wall. The functional and anatomic assessment of disease with 4D MRI may aid in stratifying patient risk in this population.

An Experimentally Derived Model to Predict the Water Film in a Compressor Cascade With Droplet Laden Flow

In recent years, overspray fogging has become a powerful means for power augmentation of industrial gas turbines. Despite the positive thermodynamic effect on the cycle, droplets entering the compressor increase the risk of water droplet erosion and deposition of water on the blades leading to an increase of required torque and profile loss. Due to this, detailed information about the structure and the amount of water on the surface is key for compressor performance. Experiments were conducted with a droplet laden flow in a transonic compressor cascade focusing on the film formed by the deposited water. Two approaches were taken. In the first approach, the film thickness on the blade was directly measured using white light interferometry. Due to significant distortion of the flow caused by the measurement system, a transfer of the measured film thickness to the undisturbed case is not possible. Therefore, a film model is adapted to describe the film flow in terms of height averaged film parameters. In the second approach, experiments were conducted in an undisturbed cascade setup and the water film pattern was measured using a nonintrusive quantitative image processing tool. Utilizing the measured flow pattern in combination with findings from the literature, the rivulet flow structure is resolved. From continuity of the water flow, a film thickness is derived showing good agreement with the previously calculated results. Using both approaches, a three-dimensional (3D) reconstruction of the water film pattern is created giving first experimental results of the film forming on stationary compressor blades under overspray fogging conditions.

Computational fluid dynamic investigations on effects of inserts in fast reactor fuel bundle hydraulics

Hydraulic characteristics of a 7 pin helical spacer fast reactor fuel bundle have been investigated with focus on flow non-uniformity in the central and peripheral sub-channels. It is seen that, there is large variation in the flow distribution among the sub-channels with significant flow bypass in the peripheral sub-channels. To improve the flow uniformity, the option of providing inserts in the peripheral sub-channels has been investigated. In this direction, three types of inserts, viz., semi-circular, triangular and circular inserts, have been studied. The improvement in the flow distribution among the central and peripheral sub-channels and the increase in friction factor as a result of inserts have been quantified. The investigation is based on 3 dimensional computational fluid dynamic simulations as well as experiments in water models. In the experiments the flow pattern at the exit of fuel pin bundle has been measured using Particle Imaging Velocimetry. The pressure drop has been measured using differential pressure transmitter. The measured flow pattern and pressure drop in the bundle are compared with predicted results. The detailed parametric studies indicate that, among the three inserts studied the triangular insert provides lowest friction factor and largest axial velocity fraction in the central sub-channels. The circular inserts offer the maximum friction factor.

Effect of Density and Total Weight on Flow Depth, Velocity, and Stresses in Loess Debris Flows

Debris flows that involve loess material produce important damage around the world. However, the kinematics of such processes are poorly understood. To better understand these kinematics, we used a flume to measure the kinematics of debris flows with different mixture densities and weights. We used sensors to measure pore fluid pressure and total normal stress. We measured flow patterns, velocities, and depths using a high-speed camera and laser range finder to identify the temporal evolution of the flow behavior and the corresponding peaks. We constructed fitting functions for the relationships between the maximum values of the experimental parameters. The hydrographs of the debris flows could be divided into four phases: increase to a first minor peak, a subsequent smooth increase to a second peak, fluctuation until a third major peak, and a final continuous decrease. The flow depth, velocity, total normal stress, and pore fluid pressure were strongly related to the mixture density and total mixture weight. We defined the corresponding relationships between the flow parameters and mixture kinematics. Linear and exponential relationships described the maximum flow depth and the mixture weight and density, respectively. The flow velocity was linearly related to the weight and density. The pore fluid pressure and total normal stress were linearly related to the weight, but logarithmically related to the density. The regression goodness of fit for all functions was >0.93. Therefore, these functions are accurate and could be used to predict the consequences of loess debris flows. Our results provide an improved understanding of the effects of mixture density and weight on the kinematics of debris flows in loess areas, and can help landscape managers prevent and design improved engineering solutions.

Effect of pipe rotation on flow pattern and pressure drop of horizontal two-phase flow

In this paper, the effect of pipe rotation on two-phase flow patterns and pressure drop of a horizontal pipe is experimentally investigated. To obtain two-phase flow patterns and related transition boundaries, a unique experimental set-up was constructed to measure flow patterns under different pipe rotational speeds. A Plexiglas pipe, with 4000 mm length and 25.4 mm ID was used in experiments to allow direct observation of flow pattern. For rotation of the pipe, an electromotor coupled with gearbox was used to allow different rotational speeds. The set-up also supports up to ±25° inclination. Air and water were used as the gas and liquid phase, respectively. Over 3800 experiments were conducted to draw flow pattern maps at six different rotational speeds of 0, 50, 100, 200, 300 and 400 rpm in both horizontal and 10° inclined pipe. To validate the results, experimental findings were compared with previous research for a horizontal fixed pipe case. Results show that pipe rotation has a significant effect on the flow pattern map and the transition boundaries. It was found that in horizontal pipe case, the stratified smooth flow regime decreases as the pipe rotation increases and disappears at high revolution speeds. Moreover, the annular regime enlarges with increasing pipe rotational speed. For a 10° inclined pipe, the stratified wavy region appears as the pipe rotation speeds up. It was observed that for both horizontal and inclined pipe, pressure drop considerably increases as the pipe rotational speed increases. Furthermore, the effect of pipe inclination on the pressure drop is reduced as the rotational speed increases.

Flow visualization of R32 in parallel-port microchannel tube

This paper presents visualization of two-phase flow of R32 in a parallel-flow microchannel tube with hydraulic diameter of 0.643 mm. Six visualization sections are installed in the facility, the same as in Li and Hrnjak (2017). Flow patterns are classified as: plug/slug, transitional, and annular flow. In plug/slug flow, a clear interface between liquid slug and vapor plug is observed. In transitional flow, the interface between slug and plug is broken and becomes a thick liquid ring and vapor bridge. In annular flow, only a liquid film is observed in the channel. The flow pattern map of R32 is reported. Mass flux changes from 50 to 300 kg-m−2s−1. The two-phase flow is generated by adding heat to subcooled refrigerant. The interface velocity and vapor plug length fraction (close to void fraction) are measured from high speed video. The velocity and vapor fraction agree to results based on a homogeneous assumption. When mass flux is 50 kg-m−2 s−1, the flow is always in plug/slug from vapor quality 0 to 1. Annular flow is observed at high quality when mass flux is higher than 100 kg-m−2 s−1. Transitional flow is observed when mass flux is higher than 150 kg-m−2 s−1, and it connects the plug/slug and annular flow patterns. Most flow pattern correlations fail to fit the measured flow pattern map. This is due to the difference in two-phase flow generation method and experimental conditions between this paper and the database used in correlations.

Relationship of aortic excess pressure obtained using pressure-only reservoir pressure analysis to directly measured aortic flow in humans

Objectives: A reservoir pressure model describing left ventricular-large artery interaction has been proposed as a useful heuristic model providing insight into the propagation of the central blood pressure as well as providing clinical prognostic information. A pressure-only approach to calculation of reservoir pressure waves has been proposed but this assumes that the resultant excess pressure is proportional to the volume flow rate out of the left ventricle; this has not been tested in humans.Approach: We use non-invasively acquired central pressure and flow data obtained in the 2nd Australian National Blood Pressure Study to test this assumption and to investigate the use of flow approximations based on excess pressure or an assumed triangular flow pattern in calculation of forward and backwards waves in the aortic root.Main results: Results from 821 subjects showed close association between the shape of measured flow patterns and calculated excess pressure, with mean coefficient of determination R2 = 0.931 ± 0.046(SD). For directly measured versus triangular flow approximation R2 was 0.918 ± 0.057. Comparison of the peak amplitudes of forwards (Pf) and backwards (Pb) going pressure waves resulted in significant correlation between Pfmax and Pbmax using both measured flow and the triangular flow approximation (0.83 and 0.79 respectively) and using excess pressure as a flow approximation (Pfmax 0.86 and Pbmax 0.77). All associations for peak pressures and integrals were high with R-values between 0.70 and 0.95.Significance: Pressure-only reservoir wave analysis appears to conform to the inherent assumptions underpinning the mathematical approach employed: this provides support for use of reservoir analysis as a non-invasive method to describe potentially important features and functions of ventriculo-vascular interaction without the requirement for flow measurement.

Internal flow measurements in pilot scale wet low-intensity magnetic separation

In the mining industry, ferromagnetic particles (e.g. magnetite) are concentrated using wet low-intensity magnetic separation (LIMS). The performance is to a large extent controlled by the internal flow conditions in the separator. In previous work, it was shown how an ultrasound pulse-echo setup can be used to simultaneously measure particle velocity profiles and local solids concentration variations in laboratory conditions.In this paper, a real-world case is demonstrated where the system is installed on one of the wet LIMS at the LKAB R&D facilities in Malmberget, Sweden. For the pilot scale experiments a setup with two ultrasound transducers, mounted at the bottom of the separator tank, is used. The design of experiments method is used to study the effects of the feed solids concentration, drum rotational speed, position of the concentrate weir, and the magnet assembly angle on the measured flow patterns. The results show that it is possible to detect changes in the flow velocity patterns and the local solids concentration, as the operational conditions of the separator are varied.Of the factors studied, the drum rotational speed has the strongest influence on the overall flow velocity in the dewatering zone. Also, the presence of a recirculating flow transporting gangue particles away from the concentrate is confirmed. The factor with the strongest influence on this recirculating flow is also the drum rotational speed, together with the magnet assembly angle. Using this method it is possible to make high quality measurements of internal flow velocity profiles. It is also possible to monitor material build-up on the separator drum, and e.g. detect overload of magnetic material. The insights gained, and the methods developed, have generated new possibilities to control, optimise, and develop the wet LIMS process.

Experimental Demonstration of a New Extension Plate Scour Countermeasure Downstream of Stilling Basins

AbstractLaboratory experiments were conducted in order to investigate the effectiveness of a new scour countermeasure consisting of a horizontal extension plate (EP) downstream of a gated spillway-stilling basin structure. These experiments were performed on a 1:30 scale model of one of the South Florida Water Management District (SFWMD) gated spillway structures, the S65E gated spillway, because it has experienced worrisome downstream scour. Currently, riprap is the only scour countermeasure documented for these structures. EPs of various lengths were installed downstream of the stilling basin, and the equilibrium scour was measured. It was found that a plate length of approximately 1.88 times the exiting flow depth was the shortest length that resulted in significant scour reduction and downstream scour translation. Measured flow patterns reveal that the EP altered the flow patterns by transferring the plunging flow downstream and eliminating the near-bed reattachment and surface recirculation, possibly...

A critical review of methods used to obtain flow patterns and volumes of individual domestic water using appliances

Determining the daily flow rates and water use patterns of specific household fixtures and appliances is important for water use monitoring, deriving effective strategies for water demand management, designing onsite water reuse systems, and efficient planning and investment in the urban water sector. Currently, there are a limited number of publications which address the need to measure flow patterns and volumes of individual household water-using appliances, or which analyze the alternatives to do so. This paper critically reviews and compares different methods of obtaining the specific flow patterns and volumes of water used by individual household water-using microcomponents (i.e. toilet, bath/shower, washbasin, washing machine, kitchen sink, dishwasher, etc.) in order to make recommendations about the appropriateness of these methodologies for various applications.

Comparison between experimentally measured flow patterns for straigth and helical type graft

The long-term success of arterial bypass surgery is often limited by the progression of intimal hyperplasia at the anastomosis between the graft and the native artery. The experimental models were manufactured from glass tubing with constant internal diameter of 8 mm, fashioned into a straight configuration and helical configuration. The aim of this study was to determine the three-dimensional flow structures that occur at the proximal anastomosis under pulsatile flow conditions, to investigate the changes that resulted from variations in the anastomosis angle and flow division, and to establishing the major differences between the straight and helical graft. In the anastomosis domain, a strong region of recirculation is observed near the occluded end of the artery, which forces the flow to move into the perfused host coronary artery. The proximal portion of the host tube shows weak counter-rotating vortices on the symmetry plane. The exact locations and strengths of the vortices in this region are only weakly dependent on Re. A detailed comparison of experimentally measured axial velocity patterns for straight and helical grafts confirm the very strong nature of the secondary flows in the helical geometry. The helical configuration promotes the mixing effect of vortex motion such that the flow particles are mixed into the blood stream disal to the anastomotic junction.

On the Characterization of a Non-Newtonian Blood Analog and Its Response to Pulsatile Flow Downstream of a Simplified Stenosis

Particle image velocimetry (PIV) was used to investigate the influence of a non-Newtonian blood analog of aqueous xanthan gum on flow separation in laminar and transitional environments and in both steady and pulsatile flow. Initial steady pressure drop measurements in laminar and transitional flow for a Newtonian analog showed an extension of laminar behavior to Reynolds number (Re) ~ 2900 for the non-Newtonian case. On a macroscale level, this showed good agreement with porcine blood. Subsequently, PIV was used to measure flow patterns and turbulent statistics downstream of an axisymmetric stenosis in the aqueous xanthan gum solution and for a Newtonian analog at Re ~ 520 and Re ~ 1250. The recirculation length for the non-Newtonian case was reduced at Re ~ 520 resultant from increased viscosity at low shear strain rates. At Re ~ 1250, peak turbulent intensities and turbulent shear stresses were dampened by the non-Newtonian fluid in close proximity to the blockage outlet. Although the non-Newtonian case's recirculation length was increased at peak pulsatile flow, turbulent shear stress was found to be elevated for the Newtonian case downstream from the blockage, suggesting shear layer fragmentation and radial transport. Our findings conclude that the xanthan gum elastic polymer prolongs flow stabilization, which in turn emphasizes the importance of non-Newtonian blood characteristics on the resulting flow patterns in such cardiovascular environments.

CO2 Leakage Prevention by Introducing Engineered Nanoparticles to the In-situ Brine

Introducing engineered nanoparticles into an aquifer or reservoir can potentially increase the storage efficiency and mitigate the risk of leakage of stored CO2. We have measured flow pattern and pressure drop during core floods in which high pressure liquid CO2 or a CO2 analogue fluid displaces an aqueous suspension of nanoparticles. The displacement front is more spatially uniform and travels more slowly compared to a control displacement with no in- situ nanoparticles. Pressure measurements are consistent with generation of a viscous phase such as an emulsion during the displacement. These observations suggest that a nanoparticle stabilized emulsion is formed during the displacement which acts to suppress the viscous instability.

A Test Bench for Validation of CFD Analysis for Air Flow in Thin Electronic Casing Model

This paper describes accuracy between experimental and calculated results of air flow pattern in thin electronic equipment. To measure flow patterns in the model of a thin electronic equipment, PIV measurement technique was employed. Dummy components (obstacles in the flow path in the thin electronic equipment) were set in the model and those configurations were altered for evaluating several flow patterns. For a CFD calculation, "OpenFOAM" was employed and the results of flow patterns from the CFD calculation were compared with the experimental results. A heat source was set in the model and temperature rise of the heat source was also measured. Then the relationship between flow patterns and the cooling performance were examined. As a result, the numerical results showed a good agreement with the experimental results when seeing in the over all velocity filed.

Comparison of Holographic and Tomographic Particle-Image Velocimetry Turbulent Channel Flow Measurements

Based on velocity measurements of a fully developed turbulent channel flow, the methods of holographic and tomographic particle-image velocimetry (PIV) are compared. The emphasis of this comparison is on the measurement of time-dependent three-dimensional small-scale flow structures, i.e., structures at a characteristic length on the order of the Taylor scale since such flow patterns can be hardly captured by any two-dimensional experimental technique. The findings show that the holographic PIV method is useful to measure flow patterns in larger volumes whereas the tomographic PIV should be used to resolve three-dimensional small-scale structures.

Swash zone boundary conditions derived from optical remote sensing of swash zone flow patterns

[1] Optical remote sensing is used to measure flow patterns in the swash zone. Timestack images are analyzed to measure the asymmetry and the relative duration of the inflow into the swash zone. This varies significantly between individual swashes, contrary to the classical analytical swash model for runup induced by bores, which predicts a similar flow pattern for all events. For swash forced by breaking bores, the gradient of the x-t locus of flow reversal varies over a wide range and flow reversal can occur simultaneously across the whole swash zone. This variation of the gradient of the locus of flow reversal in x-t space can be parameterized in terms of a single free variable in recent solutions to the nonlinear shallow water equations, which fully defines the swash boundary inflow condition. Consistent with the theory, the horizontal runup, the swash period, and the swash similarity parameter were observed to be independent of the swash inflow conditions but the flow asymmetry is not. Only a weak correlation was observed between the swash boundary condition and the Iribarren number and beach slope. Conversely, the analysis suggests that the degree of swash-swash interaction does influence the swash boundary condition and the resulting internal flow kinematics. The variation in inflow conditions is expected to influence the magnitudes of the velocity moments within the swash zone and therefore sediment transport rates.

Physical Modelling of an Aluminium Degassing Operation with Rotating Impellers—A Comparative Hydrodynamic Analysis

A hydrodynamic study of aluminum degassing by the rotating impeller technique was developed through experimental measurements obtained in a water physical model stirred with different impellers and air injection. The purpose of the work was to better understand degassing operation in molten aluminum through the analysis of the hydrodynamics of the system. Particle image velocimetry (PIV) was employed to measure flow patterns and turbulence characteristics of the ladle as a function of process and design variables, such as: a) impeller rotating speed (536 and 800 rpm), b) air flow rate (3 liters/min and 0 l/min), c) geometric design of the different impellers (impeller “A” made of a solid disc, impeller “B” with lateral nozzles and an impeller “C” with notches), where impellers “B” and “C” represent commercial designs. Impellers “B” and “C” presented similar flow behavior, with radial projection and pumping effect, while impeller “A” developed different flow patterns. By increasing the angular speed and the complexity of the impeller, stirring and turbulence increased through the entire ladle, while the vortex intensity grew. Gas injection modified the liquid flow patterns reducing the magnitude of the velocity in the liquid, and significantly increasing turbulence in the ladle.