Sidewall Flow Research Articles

Effect of turbulence intensity on bubble-particle detachment mechanism in a confined vortex

Bubble-particle detachment induced by turbulence is the primary factor for the low recovery of coarse particles, which has attracted much attention in recent years. The prevailing centrifugal detachment theory has achieved broad consensus. However, due to the complexity of bubble-particle aggregate motion in the turbulent field, the influence of turbulence intensity on bubble-particle detachment mechanism remains unclear. In this study, a controlled rotating vortex was generated using a custom-made fluid channel to systematically investigate the effect of turbulence intensity on bubble-particle centrifugal detachment. Firstly, detachment behaviours of bubble-particle aggregates were captured using high-speed cameras, followed by flow field visualization of bubble-particle detachment processes using Computational Fluid Dynamics (CFD). Experimental results reveal three typical detachment modes of bubble-particle aggregates in the confined vortex: fluid shear, bubble oscillation, and particle centrifugal motion, with particle centrifugal detachment becoming dominant with increasing turbulence intensity. This shift is attributed to changes in turbulence intensity directly affecting the trajectories of bubble/aggregates and indirectly influencing the detachment mode of bubble-particle. Compared to low turbulence intensity, bubble-particle aggregates exhibit smaller rotational radii under high turbulence intensity, reducing the probability of fluid shear and bubble oscillation detachment by mitigating the influence of high-speed shear zones at the top of the cavity. Conversely, particles located at the edge of aggregates are more susceptible to acceleration by sidewall flow fields, favouring detachment through particle centrifugal motion. Moreover, unlike traditional centrifugal detachment theories, particles do not merely undergo independent circumferential motion on the bubble surface but participate as a whole with bubbles in centrifugal motion governed by vortices. These findings are expected to provide fundamental insights into the bubble-particle detachment mechanism in turbulent fields.

The influence of low-permeability geological inclusions on the seepage behavior of ionic rare earth leaching mining: A study using visual microfluidic technology

Ionic rare earth deposits often contain semi-weathered or slightly weathered low-permeability geological inclusions (LPGI), which significantly impact the permeation process and leaching efficiency of in-situ liquid leaching mining. To investigate the influence of LPGI with varying developmental degrees on the seepage process of ionic rare earth leaching mining, we developed six microfluidic chip models using Polydimethylsiloxane (PDMS). A visual experiment was conducted, employing water to drive gas at a rate of 0.5 μl/min, enabling observation of the seepage and displacement process. Using MATLAB image processing technology in conjunction with time-history diagrams, we analyzed the evolution patterns of the infiltration front position and saturation over time. Our findings revealed distinct capillary fingering and side wall flow phenomena during the process of liquid phase displacing gas phase infiltration, accompanied by horizontal and counter flows perpendicular to the solution's direction of advancement. Notably, when the solution traversed the LPGI, we observed significant flow-around phenomena and low saturation of the LPGI. These inclusions hindered solution infiltration, with wider LPGI resulting in greater inhibition. Additionally, the LPGI acted as a protective barrier, preventing solution intrusion into the underlying ore body. However, due to the air discharge is not timely, it was sealed by the outlet solution, forming a substantial leaching blind area near the outlet. This study unveils the seepage laws of ionic rare earth earth leaching mining involving LPGI of various developmental degrees, signifying its vital engineering significance in the efficient extraction of ionic rare earth.

Experimental Study of the Hydrodynamics of an Open Channel with Algae Attached to the Side Wall

The construction of large-scale water diversion projects has effectively alleviated the current situation of the uneven distribution of water resources in China. However, due to the siltation of very fine sediment and organic matter on the side wall of an open channel, and the slow velocity of the side wall flow field, it is easy for epipelic algae to be produced, which affects water quality. Because prototype observation cannot be used to predict the series of flow in real time, and the calculation of the mathematical model is affected by parameter limitations, these two methods often cannot truly reflect the hydrodynamic characteristics of an open channel with epipelic algae. Therefore, by referring to the design parameters of the water diversion project channel, this study took the epipelic algae growing on the side wall of an open channel as the research object and used the scale of 1:30 to carry out a generalized flume experiment. Through the analysis of the physical characteristics of the prototype sample, and the simulation of the cohesive force between the oblique side wall and the epipelic algae, multi-group and multi-series hydrodynamic tests were carried out. The velocity distribution law and flow field distribution law were analyzed. The research results show that the presence of epipelic algae has a certain hindering effect on the flow velocity and significantly reduces the range of the peak velocity of the channel along the water depth. The position of the maximum velocity on the vertical line of the channel flow appears at the relative water depth of 0.6. In the case of small flow, the epipelic algae group only reduces the average flow rate of the channel by 5~6%; in the case of large flow, the effect of epipelic algae on the channel flow rate is minimal. This paper includes important scientific guiding significance and practical value for the regulation of water quantity and water quality safety, as well as the protection of long-distance projects.

Study on the decelerating mechanism of the new control rod hydraulic decelerator for the CRHDS based on numerical simulation and experiment

Control rod hydraulic drive system is a new type of internal control rod drive technology for the nuclear heating reactor. Control rod hydraulic decelerator is one of the major components of the CRHDS. The CRHD performs the rod drop speed control function to reduce the rod drop impact force and prevent the control rod cruciform blade from being deformed or damaged. The composition and working principle of the new CRHD are analyzed. The theoretical model of the rod drop dynamic process was developed and the flow field analysis of the CRHD flow channels was carried out to close the model. The full scale rod scram tests have been conducted to get the rod drop dynamic data. The theoretical results agree well with the experimental results, which verify its correctness. The rod drop theoretical model was then used to analyze the influence of the reactor coolant operating temperature and the hydraulic deceleration cylinder sidewall flow area on the dynamic characteristics of the new CRHD. The research results lay the base for the design and further optimization of the CRHD.

Status and trend of hydrogeological experiments concerning the side-wall flow effect in porous media

Hydrogeological experiments provide an important means to understand groundwater seepage and solute transport problems. Basic hydrogeological parameters can be obtained for use in assessing groundwater resources. In current porous-media research, studies of side-wall flow are in a preliminary and qualitative phase, and lack systematic and comprehensive understanding. Side-wall flow refers to the non-uniform infiltration and solute transport that occurs near the seepage device boundary. Flow dynamics depends on the fluid under the specific hydraulic conditions, physical properties and chemical composition, medium permeability, the roughness of the side wall, geometric features, and physical chemistry. Such phenomena not only occur in indoor water flows and solute transport, but also under natural conditions in the field. Side-wall flow has features both in common as well as distinct from preferential flows. In porous-media experiments, once side-wall flow commences, it affects the groundwater flow field and chemistry field, resulting in parameter values deviating from actual values. Based on a comprehensive analysis of the influence of side-wall flow, a definition of the side-wall flow effect in porous media is given. Three directions of research are identified concerning side-wall flow: the mechanism of the side-wall flows effect, the study of its quantitative impact on seepage flow and solute transport, and the methods and measures that need to be taken in hydrogeological experiments to reduce (or prevent) side-wall flow development.

Monolithic lysimeters as tools to investigate processes in acid sulphate soil

The oxidation of sulphidic materials upon drainage of acid sulphate (AS) soils causes episodic hazards to aquatic ecosystems worldwide. Reintroducing a high groundwater level, in order to turn the soil reactions back to reduction, is an option to alleviate the environmental loading from these soils. In boreal conditions, with low soil temperatures and consequently slow chemical and microbial reactions, feasible tools are needed to effectively investigate the impacts of this practice on soil processes. With this aim, ten lysimeters containing AS soil monoliths (1m high, 0.5m wide) were set up in Finland to investigate the pore water quality and leaching of elements in response to an elevated water table. In this paper, the design of the lysimeters is described and results confirming their suitability for the purpose are presented. This paper focuses on the possible shortcomings of lysimeters in AS soils, such as unnaturally rapid oxidation of the sulphidic C horizon, side-wall flow of water in the ripening soil, and the impaired functioning of probes over time in the extremely acid soil and in the sulphidic materials. Dye and chloride tracing revealed that no significant sidewall flow occurred in the lysimeters. The continuous Eh measurements functioned unimpaired during the two-and-a-half-year experiment. Reduced conditions were preserved in the Cg horizon throughout the experiment. In drained horizons, Eh varied according to the water management practice and the growth of reed canary grass roots, but in the water-saturated horizons, Eh mainly responded to long-term changes in soil chemistry, such as the reduction of iron. Soil temperature in deep soil horizons closely corresponded to typical boreal conditions in winter, but it was a few degrees Celsius higher in summer. Our results demonstrate that it is feasible to simulate processes dependent on water management in AS soils with monolithic lysimeters.

Modeling Trench Sidewall and Bottom Flow in On-Site Wastewater Systems

Little is known about how much wastewater infiltrates the soil via the trench sidewall versus the trench bottom in onsite wastewater systems. Our objectives were to develop a method of simulating trench bottom and sidewall flow using a two-dimensional numerical computer model that would include the trench within the model space and determine how much sidewall flow would occur under steady-state conditions. We used HYDRUS-2D to simulate water flow in a two-dimensional cross section of a conventional gravel-filled trench and the surrounding drainfield. Hydraulic properties of the gravel were assumed (saturated hydraulic conductivity Ks =1,000 cm d−1 ) and simulations were run for drainfield soils consisting of a clay loam ( Ks =3.2 cm d−1 ) and a sand ( Ks =41 cm d−1 ) . Biomats were simulated at the bottom of the trench and part way up the trench sidewall ( Ks =0.2 to 2.8 cm d−1 depending on the simulation). Typical wastewater loading rates for Georgia of 2 and 4 cm d−1 for the clay loam and sand, respecti...

Overturning in a filling box

Overturning in a cylindrical filling box driven by a turbulent plume is examined theoretically and experimentally. We establish the initial penetration depth (h) of the buoyant flow that intrudes vertically up the sidewall as a function of the box radius (R) and height (H). Dimensional arguments reduce the problem to finding η = h/H as a function of the aspect ratio Φ = R/H. The flow is modelled in two parts, the radial outflow from the plume along the base of the box and the flow up the sidewall. The outflow is modelled as a forced radial gravity current with constant buoyancy flux while the sidewall flow is modelled as a line fountain. Two regimes were found: first, when the plume outflow is adjusting toward a pure gravity current on impact with the vertical wall and the rise height is given by η ∼ Φ−1/3; secondly, when the outflow is fully developed on, or before, impact and the rise height is given by η ∼ Const. Experimental results show good agreement with these scalings and allow the constants of proportionality to be established.

Design of a meso‐scale indoor lysimeter for undisturbed soil to investigate the behaviour of solutes in soil

SummaryIndoor cylindrical titanium lysimeters (80 cm internal diameter × 150 cm height) filled with undisturbed soil were constructed to study the behaviour of solutes in soil. They were equipped with thermometers, tensiometers, ceramic porous cups, percolate reservoirs, and an automatic irrigation system. Soil sampling was conducted using an original drilling technique. Examination of the wetting front and downward migration of Br− in an Andosol monolith showed no artificial sidewall flow.

Gravel Effect on Wastewater Infiltration from Septic System Trenches

Septic systems have been developed that use a chamber rather than gravel in drain line trenches. Gravel is thought to impede infiltration due to a masking effect, a reduction in biomat hydraulic conductivity when the gravel is embedded, or due to fine particles that wash off the gravel and form a low‐conductivity layer, but results from studies on the effect of gravel have varied. Our objective was to determine the effect of gravel masking and embedded gravel on water flow in septic system trenches. We used the finite‐element numerical model HYDRUS‐2D for our analysis. We simulated water movement from the trench bottom into the Bt1 and BC horizons of a Cecil soil. Gravel masking generally had little effect. In the BC horizon where the biomat hydraulic conductivity was one order of magnitude less than that of the soil, embedded gravel produced a chamber‐to‐gravel system infiltration ratio of 1.50. When sidewall flow was included in the BC horizon, the effect of embedded gravel was lessened and the infiltration ratio dropped to 1.33. In the Bt1 horizon where the biomat hydraulic conductivity was four orders of magnitude less than that of the soil, embedded gravel had more of an effect, producing an infiltration ratio of 1.93, close to the manufacturer's claim that chamber systems have twice the infiltration rate of gravel systems. When sidewall flow was included in the Bt1 horizon, the effect of gravel was diminished with an infiltration ratio of 1.70. Gravel had less of an effect than claimed by the manufacturer of the chamber system because lateral gradients pulling water into the areas beneath gravel particles compensated, in part, for the reduced cross‐sectional area available for infiltration in the gravel systems.

Construction and Performance of Large Soil Core Lysimeters

A method was developed to obtain large undisturbed soil cores and instrument those cores to collect vadose zone leachate data under agricultural field conditions. Twenty undisturbed soil core lysimeters were constructed at an irrigated‐field site in southeastern North Dakota. Construction of the undisturbed lysimeters consisted of utilizing a steel cutting bit to collect large (0.61‐m diam. by 1.68‐m deep) soil cores in sections of polyvinyl chloride (PVC) pipe, installing a leachate collection system, installing time domain reflectometry (TDR) soil moisture probes, and then finally placing them below grade so normal farming practices could continue. The described method of core collection is an improvement over other methods in that the cutting bit is reusable, the resulting core is larger and deeper than other methods, no heavy static weights are required, and it is not necessary to expose a free‐standing soil column. Leachate quality and quantity data is reported for 1990 through 1995 and compared favorably with larger, reconstructed profile lysimeters on the same site. Overall, the lysimeters functioned as intended for the first 6 yr of operation; however, two developed leaks and rodents damaged another. Possible sidewall flow was observed and may be avoidable in future designs.

Evaluation of a simple lysimeter-design modification to minimize sidewall flow

A common criticism of many soil lysimeter designs has been the existence of artificial flowpaths along the soil–wall interface. This artificial flow is referred to as sidewall flow. A simple lysimeter-design modification was evaluated that utilizes annular rings to divert sidewall flow near the soil surface into the soil column to minimize the occurrence of sidewall flow along the remainder of the column's length. A chloride-tracer experiment was used to evaluate the effectiveness of annular rings in minimizing sidewall flow in a mesoscale soil lysimeter (0.6 m in diameter and 1.83 m in height). The tracer-experiment data showed that even though sidewall flow may not have been completely eliminated it was reduced to an undetectable level based on chloride distributions and time domain reflectometry measurements. However, a delicate balance exists between minimizing sidewall flow and significantly altering the natural water-flow dynamics when using annular rings. The simple design modification provides a means of using a disturbed column of soil to evaluate models of solute transport, and to study preferential flow and contaminant mobility without concern for spurious data due to artificial flow along the soil–wall interface of the lysimeter.

Real-time observations of mesa shrinkage process in MBE of GaAs on (1 1 1)B patterned substrates and theoretical analysis

The faceting and shrinkage processes of mesa structures on GaAs (1 1 1)B substrates were monitored by microprobe reflection high-energy electron diffraction/scanning electron microscopy (microprobe-RHEED/SEM) installed in MBE chamber. To understand the experimental results, the calculation based on inter-surface diffusion model was conducted and the results are compared with the experiments. From the comparison we evaluated diffusion coefficient and incorporation lifetime of Ga adatoms. The lifetime and the diffusion coefficient of (1 1 1)B substrate were estimated, respectively, as 1/70 as small and 50 times as large as those of {1 1 0} side wall. The mesa shrinks faster when arsenic pressure is higher, because Ga adatoms on {1 1 0} side wall flow more towards (1 1 1)B top and less towards the bottom.

Comparison of Laboratory-Measured GCL Hydraulic Conductivity Based on Three Permeameter Types

Abstract Specimen preparation, installation, and testing procedures are presented for testing a needle-punched geosynthetic clay liner (GCL) in a consolidation-type, fixed-ring constant-flow-rate hydraulic conductivity apparatus. The proposed approach is illustrated by reporting the results obtained for a GCL statically confined to effective stresses of ∼3 and ∼35 kPa, hydrated and permeated with distilled water and concentrated aqueous salt solutions (0.6 and 2.0 N NaCl), and sequentially permeated with concentrated aqueous salt solutions (0.6 and 2.0 N NaCl) after initial permeation with distilled water. The issue of potential preferential sidewall flow in the fixed-ring permeameter tests was then addressed by comparing results with those conducted under otherwise similar testing conditions in a double-ring and flexible-wall permeameter. Reasonable reproducibility of the test results was obtained between the different types of permeameters, suggesting that, if present, preferential sidewall flow was negligibly small and was not significant on the calculated hydraulic conductivity values. This conclusion was found to be valid for the range of permeant types (distilled water and 0.6 and 2.0 N NaCl), static-confining stresses, and hydrating mediums considered. Premature arrival of the salt solution front in the effluent (i.e., solute breakthrough) during fixed-ring hydraulic conductivity testing was explained as a probable diffusion-dominated transport mechanism through the relatively thin GCL specimens.

Sidewall flow stability in the MHD channel flows

The velocity distribution between two sidewalls is M-shaped for the MHD channel, flows with rectangular cross section and thin conducting walls in a strong transverse magnetic field. Assume that the dimensionless numbersR m ≪1,M, N≫ 1, and σ* and that the distance between two perpendicular walls is very long in comparison with the distance between two sidewalls. First, the equation for steady flow is established, and the solution of M-shaped velocity distribution is given. Then, an equation for stability of small disturbances is derived based on the velocity distribution obtained. Finally, it is proved that the stability equation for sidewall flow can be transformed into the famous Orr-Sommerfeld equation, in addition, the following theorems are also proved, namely, the analogy theorem, the generalized Rayleigh's theorem, the generalized Fjørtoft's theorem and the generalized Joseph's theorems.

Interpreting non-steady state tracer breakthrough experiments in sand and clay soils using a dual-porosity model

The effects of preferential flow on 36Cl transport in undisturbed sand and clay soil monolith lysimeters were quantified using a dual-porosity model (MACRO). A double tracer test with 3H and 36Cl was performed simultaneously to check the possible occurrence of sidewall flow in the lysimeters. In the dual-porosity model MACRO, simulations can be performed in both one and two flow domains. Run in one flow domain, the model reduces to numerical solutions of Richards' equation and the convection-dispersion equation. In the sandy soil, the occurrence of preferential flow was tested by simulating in one domain, assuming that a certain pore fraction takes no part in water flow and solute transport. For the clay soil, the one domain case was compared with two domain simulations accounting for macropore flow. The double-tracer tests showed that sidewall flow did not occur in either soil type. Simulations of water flow showed good agreement with observed seepage until late autumn, but were less good during winter because the model does not account for soil freezing and snowpack/snowmelt. Simulated water flows were similar in one and two domain simulations, presumably because water contents in the lysimeters were maintained close to field capacity during the experiment. The simulations indicated that preferential flow occurred in the sandy soil, with the observed 36Cl breakthrough curves, assuming an unwetted volumetric pore fraction of 20%, reproduced reasonably well. The rate of 36Cl leaching was consequently increased by c. 25% compared with the simulation assuming no preferential flow. Macropore flow was clearly demonstrated in the clay soil. The two domain simulation matched the breakthough curve and accumulated 36Cl leaching accurately when the soil water pressure head defining the boundary between pore domains was set to −50 cm. This implies that preferential 36Cl transport was taking place in a wide range of pore sizes, including smaller mesopores. The one domain simulation failed to predict the pattern of breakthrough of 36Cl in the clay soil, in that it seriously underestimated leaching at early times and overestimated leaching towards the end of the experiment. Accounting for preferential flow with the dual porosity model resulted in significantly improved estimates of solute transport, compared to the classical convective-dispersive treatment, for both nonstructured sands and structured clay soils.

Effect of Trailing-Edge Ejection on Local Heat (Mass) Transfer in Pin Fin Cooling Channels in Turbine Blades

Experiments are conducted to study the local heat transfer distribution and pressure drop in a pin fin channel that models the cooling passages in modern gas turbine blades. The detailed heat/mass transfer distribution is determined via the naphthalene sublimation technique for flow through a channel with a 16-row, staggered 3 × 2 array of short pin fins (with a height-to-diameter ratio of 1.0, and streamwise and spanwise spacing-to-diameter ratios of 2.5) and with flow ejection through holes in one of the side walls and at the straight flow exit (to simulate ejection through holes along the trailing edges and through tip bleed holes of turbine blades). The pin fin heat/mass transfer and the channel wall heat/mass transfer are obtained for the straight-flow-only and the ejection-flow cases. The results show that the regional pin heat/mass transfer coefficients are generally higher than the corresponding regional wall heat/mass transfer coefficients in both cases. When there is side wall flow ejection, a portion of the flow turns to exit through the ejection holes and the rate of heat/mass transfer decreases in the straight flow direction as a result of the reducing mass flow rate along the channel. The rate of cooling air flow through a pin fin channel in a gas turbine blade must be increased to compensate for the “loss” of the cooling air through trailing edge ejection holes, so that the blade tip is cooled sufficiently.

Operating ranges of meteorological wind tunnels for the simulation of convective boundary layer (CBL) phenomena

The operating ranges of meteorological wind tunnels for convective boundary-layer (CBL) simulation are defined in this paper based on a review of the theoretical and practical limitations of the flow phenomena and the facilities available. Wind-tunnel operating ranges are limited by the dimensions of the simulated circulations and of the tunnel itself, the tunnel flow speed and turbulence processes, and the characteristics of the measurement instrumentation. When it is desired to simulate both the CBL and the behavior of other flows imbedded within the boundary layer, such as power-plant plume rise and dispersion, then additional constraints exist on the fluid modeling process. The capabilities of meteorological wind tunnels can also be extended through the judicious use of boundary and side wall flow controls.

Comparison of Test Results Obtained on Plane and Annular, Fixed or Rotating Supersonic Blade Cascades

Results of an experimental research on the comparison of flow patterns in linear and annular, fixed and rotating supersonic blade cascades are presented. The fixed plane cascade and the fixed annular cascade give very similar results at low back pressure and the flow configuration (Schlieren pictures) and the pressure distributions are those given by theoretical calculations. In the rotating cascade the fully started supersonic regime was not obtained. At high back pressure, sidewall flow separation perturbates the flow pattern in the plane cascade. In the annular setups, the flow configuration with suction side flow separation is correctly predicted by the theory.