Increase In Turbulent Kinetic Energy Research Articles

Experimental Parametric Study on Flow Separation Control Mechanisms around NACA0015 Airfoil Using a Plasma Actuator with Burst Actuation over Reynolds Numbers of 105–106

Dielectric barrier discharge plasma actuators (DBD-PAs) have the potential to improve the performance of fluid machineries such as aircrafts and wind turbines by preventing flow separation. In this study, to identify the multiple flow control mechanisms in high Reynolds number flow, parametric experiments for an actuation parameter F+ with a wide range of Re values (105–106) for NACA0015 airfoil was conducted. We conducted wind tunnel tests by applying a DBD-PA to the flow field around a wing model at the leading edge. Lift characteristics, turbulent kinetic energy in the flow field, shear layer height, and the separation point of the boundary layer were evaluated based on pressure distributions on the wing surface and velocity of the flow field, with the effect of DBD-PA on the post-stall flow around the wing and the mechanism behind the increase in the lift coefficient CL analyzed based on these evaluation results. The following phenomena contributed to the increase in CL: (1) increase in turbulent kinetic energy; (2) increase in circulation; and (3) acceleration of the flow near the leading edge. Thus, this study effectively investigated the dependence of the increase in lift on F+ and the lift-increasing mechanism for a wide range of Re values.

The effect of the compound slope spillway on air entrainment and total kinetic energy using computational fluid dynamics

Abstract The spillway is a hydraulic structure used for managing discharge, dissipating energy, and aeration purposes. The objective of this CFD analysis was to compare the ways in which water moved over various slanted spillways. Both the turbulence and the air–water interface were located using the volume of fluid (VOF) technique and a realizable k-model. Five different spillway models with varying slopes (normal = 30°, compound1 = 20° and 39°, and compound2 = 39° and 20°) were modelled and simulated in ANSYS Fluent. Computational data have been compared to the experimental results, and the findings were astonishing – the CFD model precisely captured the all-important flow facets. The numerical model pinpointed the inception point that occurred due to changes in slope and structure. In comparison to the normal slopes of (30°) and the compound slopes of (39°/20°), the surge in the location of the inception point was around 58%. The results of the research indicate a significant increase in turbulent kinetic energy as a result of the introduction of the compound slope. The study conducted has effectively achieved a crucial objective of the project, which is to enhance the operational efficiency and reliability of the spillway under diverse flow conditions.

Research on the enhanced heat transfer performance of SCO2 caused by vortex generators with different geometric dimensions in novel airfoil channels

The performance of printed circuit heat exchangers (PCHEs) has a significant impact on the heat transfer efficiency and compactness of the supercritical carbon dioxide (SCO2) Brayton cycle system suitable for the fourth-generation nuclear energy system. Compared to PCHEs with other types of channels, the airfoil fin PCHEs have superior flow heat transfer performance. The installation of vortex generators (VGs) in the heat transfer channels can enhance heat transfer efficiently, but the application of them to PCHEs is very limited. In order to improve the performance of PCHE with airfoil fin channels, a novel channel structure combining airfoil fin channels with rectangular VGs is proposed, and the effect of geometric parameters of VGs on the thermal-hydraulic performance of the channels is also investigated. The results show that the VG improves the synergistic effect of velocity field and temperature gradient field, leading to the increase of turbulent kinetic energy and decrease of heat transfer entropy production in the channel, which finally promotes the enhancement of heat transfer. The comprehensive performance of the airfoil fin channel with VGs is 5.95%–19.47% higher than that of the conventional airfoil fin channel. The increase in the height and length of the VGs improves the heat transfer performance of the channel, and the increase in the width of the VGs weakens the heat transfer performance of the channel, and both increase the flow resistance of the channel. By comparing the comprehensive performance, it is found that the VGs have the best height of 0.2 mm, the best length of 0.8 mm and the best width of 0.04 mm. In addition, according to the noise performance statistics (NPS), the height of the VG contributes more to the Nu and Fanning friction coefficients of the airfoil fin channels.

Numerical investigation on the combustion performance of ammonia-hydrogen spark-ignition engine under various high compression ratios and different spark-ignition timings

This paper aims to numerically investigate the effects of high compression ratio (CR) on the performance of ammonia-hydrogen engines. In this work, four CRs from 10.7 to 13.7 with scanning spark timing (ST) from 28°CA to 0°CA BTDC were analyzed. The main results are as follows: As the CR increases, there is a trade-off relationship between the dissipation rate of turbulence and the turbulent kinetic energy (TKE). Initially, the TKE rises as the CR increases. As the CR continues to rise, the tendency for an increase in TKE diminishes, while the turbulent dissipation rate consistently rises. Additionally, there is an escalation in heat transfer loss. Therefore, there is a trend of rising and then falling in the flow velocity and turbulence intensity with the increase of the CR. Ammonia-hydrogen flame propagation is susceptible to temperature and flow field, and a high CR can improve ignition stability, shorten combustion duration, minimize cooling loss, and enhance output power. Unfortunately, the emission of NOx gradually rises as the CR increases. At high CR, the combustion performance is optimized by adjusting ST, and the maximum IMEP and ITE are 4 bar and 38.3 %, respectively. The ST for maximum braking torque (MBT) should be gradually delayed toward TDC as the CR increases.

Investigation of heat transfer characteristics in air-to-air heat exchanger with steady flow, oscillating flow and sound waves

A steady flow with a high flow rate, oscillating flow, and audible sound waves can enhance the heat transfer performance in air-to-air heat exchangers, while the comparison of influence mechanisms and degrees of different methods is ignored. This study investigates flow instability and heat transfer characteristics in an air-to-air heat exchanger under steady flow, oscillating flow and sound waves. The results show that steady flow and oscillating flow with different amplitudes have little effect on the distribution characteristics of velocity and vortices. However, the vortices disappear and generate periodically under 140 dB. Moreover, oscillating flow and sound waves exert distinct influences on flow instability. The cold side experiences the highest increase in turbulence kinetic energy when subjected to high-amplitude oscillating flow, while the greatest increase on the hot side occurs under high-amplitude sound waves, and the influence of steady flow on turbulence kinetic energy is relatively low. Additionally, the steady flow enhances the heat transfer performance by increasing flow rate, while the oscillating flow and sound waves promote the heat transfer between the fluid and surface. Under the effect of steady flow, oscillating flow, and sound waves, the values of heat flux are 1.22, 1.24, and 1.31 times that of the initial condition with the amplitude increasing to 0.683 m/s (140 dB). The results demonstrate that with the increase in amplitude acting on the inlet, the sound waves have the greatest impact on heat transfer performance, followed by oscillating flow, and the effect of steady flow is relatively slight. The research can provide guidelines for the development of heat transfer enhancement in air-to-air heat exchangers.

Effects of Patch Density and Incoming Sediment on Flow Characteristics and Bed Morphology

This study focuses on the effects of vegetation patch density, bed condition, and incoming sediment on flow structure and bed morphology within and around a patch. The variation in upstream adjustment velocity is not well defined for low-density vegetation patches but decreases with increasing patch density in high-density patches. The length of the upstream adjustment region is greater for high-density vegetation. Incoming sediment causes a reduction in both the steady wake velocity and the length of the steady wake at a low density. The length of the recovery region increases with density when vegetation is sparse, but remains constant in a dense patch. Additionally, the length of the recovery region decreases due to incoming sediment. Turbulent kinetic energy is not affected by the bedform and incoming sediment when reaching its first peak. However, the second maximum of the turbulent kinetic energy increases when the bed is movable. The evolution of bed morphology is closely related to the flow structure and the growth of the von Karman vortex street. Both the rising length and the adjusted length decrease with increasing patch density, while the incoming sediment causes an increase in the adjusted length. Behind the patch wake, the first minimum elevation, maximum elevation, and second minimum elevation decrease as the patch density increases. These values, in turn, increase with the sediment supply upstream of the flume.

Hydrodynamics intensification and interface control in the flotation conditioning process using fractal impellers

Flotation conditioning, an essential part affecting the function of flotation reagent and flotation performance, has gradually become a key field for the process enhancement of flotation. A fractal impeller device was proposed in this paper for use in pre-flotation pulp conditioning. The flow field characteristics and relevant effects on the liquid–solid mixing performance were investigated by the numerical simulation of computational fluid dynamics. The outcome of particle surface modification was assessed by studying changes in the contact angle and zeta potential of diaspore particles. These results showed that the increase of turbulent kinetic energy induced by the fractal impeller improved the dispersion of mineral particles. Meanwhile, the strong turbulence and high shear induced by the fractal impeller provided favorable conditions for collector adsorption and particle modification, leading to the increase in contact angle under relatively higher energy input. This work introduced a kind of novel fractal impellers used in the flotation conditioning to strengthen the flotation separation of minerals.

New scaling law for turbulent boundary layers with high surface mass transfer

A fundamental understanding of the phenomena occurring in the turbulent boundary layer in the presence of surface blowing is limited, and considerable disagreements persist even in describing primary quantities, such as the boundary layer profile. The theories based on the linear boundary layer equations show that the thickness of the sublayer increases in the presence of surface blowing; therefore, the viscous sublayer and law of the wall modify. In this study, direct numerical simulations (DNS) of turbulent boundary layers with uniform surface mass transfers are carried out in order to scale the velocity profile. Emphasis is placed on moderate to high mass transfer rates, which are relevant to the most common hybrid rockets configuration. DNS data are used to establish a functional law of the wall and a law of wake by means of the relation between the wall shear stress and surface mass transfer. Analysis of the mean kinetic energy budget shows that the magnitude of turbulent kinetic energy increases by surface mass transfer, and the production rate extends significantly in the inner layer as the injection rate increases. DNS data of various surface blowing are used to complete the closure of turbulence kinetic energy equation and develop an eddy viscosity model. The predicted turbulent kinetic energy and eddy viscosity agree with DNS data for moderate to high blowing rates.

Observational Estimates of Turbulence Parameters in the Atmospheric Surface Layer of Landfalling Tropical Cyclones

AbstractThis study analyzes observations collected by multilevel towers to estimate turbulence parameters in the atmospheric surface layer of two landfalling tropical cyclones (TCs). The momentum flux, turbulent kinetic energy (TKE) and dissipation rate increase with the wind speed independent of surface types. However, the momentum flux and TKE are much larger over land than over the coastal ocean at a given wind speed range. The vertical eddy diffusivity is directly estimated using the momentum flux and strain rate, which more quickly increases with the wind speed over a rougher surface. Comparisons of the eddy diffusivity estimated using the direct flux method and that using the friction velocity and height show good agreement. On the other hand, the traditional TKE method overestimates the eddy diffusivity compared to the direct flux method. The scaling coefficients in the TKE method are derived for the two different surface types to better match with the vertical eddy diffusivity based on the direct flux method. Some guidance to improve vertical diffusion parameterizations for TC landfall forecasts in weather simulations are also provided.

Analysis of multi-particulate flow through the horizontal eccentric annulus considering the borehole cleaning

Multi-particulate flow CFD modelling is carried out while taking eccentricity into account considering drilling horizontal oil wells. The present work focuses on the effect of different cuttings sizes and their concentration on borehole cleaning. The carrier phase is a CMC-Bentonite solution which is a non-Newtonian fluid and the secondary phase is sand cuttings with different sizes. The RNG-k-ε turbulence mixture model is implemented along with the Eulerian-Eulerian multiphase model. The present CFD work has been validated with different experimental work and analytical results. The cutting size distribution in terms of volume fraction has been plotted along the various planes. Contours for volume fraction for different cutting size and inlet cuttings concentrations are also obtained. The increase in turbulence kinetic energy through increase inlet axial slurry velocity and drillpipe rotation (from v = 1 m/s, N = 50 rpm to v = 3.5 m/s, N = 100 rpm) is very effective in reducing cuttings accumulation for slurry A. The migration of cuttings from stationary zone to suspension zone is high for larger cuttings as compared to smaller cuttings from plane P2. The equivalent two-phase simulation for considered five-phase flow of slurry A has the similar cuttings distribution.

Turbulent flow simulations in a simplified channel bend model of Dragon style rivers with constant curvature and different single-short-branch characteristics

This study investigates the turbulent flows in simplified Dragon style river channels with a constant critical curvature and different single-short-branch characteristics, using an effective numerical method based on real geometry statistics. First, when the branch outlet is closed, in the main channel, strong bed shear stresses are concentrated at the inner bend apex and downstream; as the branch widens, more flow enters the branch, reducing the downstream velocities, increasing the helical flow strength (I) and turbulent kinetic energy (TKE); however, when the branch radius is about 3.5 times the main channel width, the opposite occurs. Second, in this non-free-flowing branch, upstream of a critical section, the cross-sectional I and TKE increase with increasing width, but both decrease with increasing radius or decreasing orientation angle (relative to the direction tangent to the main channel). Third, when the branch outlet is open, in the main channel, the bifurcation location primarily affects the main channel flow, moving it upstream creates a more regular low-velocity zone and recirculation zone, and lower shear stresses downstream, and meanwhile, the cross-sectional I, TKE, and shear stresses decrease upstream but increase downstream of the bifurcation location, respectively. Finally, in this free-flowing branch, shear stresses occupy the inner branch; the recirculation zone grows with increasing branch width, reaches a maximum around a relative branch radius of 3.0 (scaled with main-channel width), and disappears at a branch orientation angle of about 67°; both the cross-sectional I and TKE become negative, and the graphical cross-sectional I (along the flow direction) curves downward with increasing width, upward with increasing radius, and straightens with decreasing orientation angle. Findings provide fundamental conditions for harmonious vegetative integration and gradual development of Dragon style river regulation patterns, especially to mitigate crises like the ‘suspended river’ issues in the lower Yellow River.

Inspiration of marine sponges to design a structure for managing the coastal hydrodynamics and protection: numerical study

Climate changes and sediment discharge within the oceans trigger many problems, such as coastline erosion and coral reef extinction hazards. Therefore, it is crucial to control wave hydrodynamics in the desired manner to protect marine environments. To prevent the promotion of sedimentation, nature has its response. The tubular sponge is a marvelous animal. It has a perforated body and sucks nutrition and water from these perforations; then, it pumps the undigested materials out from the top outlet. In the current study, an apparatus inspired by natural tubular sponges (synthetic sponges) was designed. The computational fluid dynamics derived from the Reynolds-averaged Navier-Stokes equations and image processing technique (surfaceLIC) was deployed to study how the synthetic sponge affects the wave hydrodynamics. The results revealed that the suction of the body and outflow shielding phenomenon of one sponge reduces the wave transmission by up to ≈7%. In addition, the swing motion of the jet by wave train and effluent cloud generation causes the shear on the sponge. Therefore, the momentum exchange enhances through the water column (≈46% increase of turbulent kinetic energy). It is similar to the swing behavior of flexible vegetation. Furthermore, the surfaceLIC result revealed that the effluent cloud shape changes to a pear shape, symmetric, stretched (transition), and asymmetric by increasing the pumping discharge to 600 L/h. Observing the chute–jet phenomenon by surfaceLIC also proved the diffraction and creation of a low-velocity zone in the shadow region, which is proof of a breaking wave due to the sponge’s suction/pumping and perforated body. Consequently, it can be concluded that a synthetic sponge can act as both rigid and flexible vegetation. The synthetic sponge is anticipated to mitigate sedimentation by creating unique vortices, circulating flow, and its body shape.

Theoretical analysis of a novel PCHE with enhanced rib structures for high-power supercritical CO2 Brayton cycle system based on solar energy

A printed circuit heat exchanger (PCHE) is one of the most significant components in the supercritical CO2 (SCO2) Brayton cycle system based on concentrated solar power, whose performance significantly affects the efficiency and compactness of the system. To improve the performance of PCHE with semicircular-straight channels, rib structures placed on the top flat wall of the semicircular channel are proposed, which are achieved by the double sides etched heat transfer plates, and the effects of the distributions of rib structures on the performance of channels are also investigated. The thermal-hydraulic performance of the conventional semicircular channel and the semicircular channel with different rib structures are compared. The results indicate that rib structures lead to an apparent increase of turbulence kinetic energy in channels, and improve the synergy between velocity and temperature gradient fields, leading to the heat transfer enhancement. Among the channels with different rib structures, the comprehensive performance of the semicircular channel with the spacing distribution of short rib structures (channel DR3) is the best, which is relatively 19.3–19.8% higher than that of the conventional semicircular channel. When the channel DR3 is adopted in PCHE, the effectiveness of PCHE could reach 98.4–98.7%, the efficiency of the SCO2 Brayton cycle system based on solar power could be increased by 15.3%, and the compactness of the system could be improved by 3.8%. This present work is of great significance for deepening the understanding of PCHE heat transfer mechanism and performance optimisation, as well as improving the overall performance and compactness of large-scale SCO2-based power systems.

The influence of turbulence on sediment phosphorus sorption

The effect of mean flow velocity on phosphorus (P) partitioning between water and sediment has received much attention in recent decades. However, the impact of turbulence on the efficiency and capability of sediment adsorbing and desorbing dissolved inorganic phosphorus (DIP) is still unclear. A series of contrasting experiments on the sediment sorption and desorption of DIP with the flow turbulence kinetic energy (TKE) ranging from 1.95 to 2.93 pa have been conducted. It was found that the adsorbed P onto unit mass of sediment increases with the increase in TKE. It is because an increase in TKE results in a rise in the effective adsorption capacity of sediment (bm) by 20–30% during the adsorption process. The bm shows the maximum rise from 0.18 to 0.25 mg/g when TKE increases from 1.95 to 2.93 pa with a fixed sediment concentration of 0.5 g/L. To account for the direct effect of TKE on P adsorption, the Langmuir model is modified by introducing a newly defined coefficient (fA−TKE). The fA−TKE shows a good linear relationship with TKE. Comparison between the modified model and the classic model shows that the amount of adsorbed P could be overestimated by over 50% if the direct effect of turbulence intensity is ignored. The experimental data show that the increase in TKE also enhances the desorption process, with the degree of P desorption (Ddes) increased by 44%. The relation between Ddes and TKE can be well represented using a logarithmic function to quantify the direct effect of turbulence intensity on desorption of P.

Experiments into the interaction of side dilution jets with bluff-body stabilised annular jets

Fundamental insights into the effects of side dilution jets on the flow behaviour and turbulence field in gas turbine combustors further advances the ability to use these jets to control (upstream) flame stability and (downstream) emissions. Despite this, the interaction of side dilution jets with typical flame anchoring mechanisms, such as bluff-bodies, and annular flows, both swirling and non-swirling, remains elusive due to the challenges of undertaking highly resolved laser diagnostics in such complex geometries. In this work, Particle Image Velocimetry (PIV) is used to investigate the interaction of turbulent side dilution jets (Red = 18,000 and 11,300) with bluff-body stabilised annular jets (Res = 35500 and 17800), under both swirling (S = 0.3) and non-swirling (S = 0) conditions. Boundary conditions for the cases studied are well-defined through Constant Temperature Anemometry, which in conjunction with the PIV resolved flow field means the results presented additionally serve as good benchmark cases for modelling (not undertaken here). The experiments are conducted in an optically accessible 700 mm long square-like (310 mm × 310 mm) enclosure equipped with four peripheral side dilution jets on the rounded corner supports.Results show that irrespective of the flow configuration used (swirling or non-swirling), side dilution jets considerably modify the overall flow field and lead to the development of characteristic recirculation zones on the periphery of the annular jet, named as Peripheral Recirculation Zones (PRZ). In the upstream region, PRZ significantly promote turbulence in the outer shear layer of the bluff-body stabilised annular jet, leading to a massive 176% (at x/D = 1.4) and 218% (x/D = 1.8) increase in peak turbulent kinetic energy. These high levels of turbulence further magnify closer to the location of the side jets. In the downstream (beyond x/D > 2) of the bluff-body stabilised annular jet, noticeable increases in centreline velocity decay (13%) and jet spreading (32%) are observed in the presence of a PRZ, which indicates better mixing and flow entrainment. The overall effects of side dilution jets vary directly and inversely with the Reynolds number of side dilution jets and annular jets, respectively. To resolve the flow dynamic behaviour independent of heat release, all tests are undertaken isothermally (non-reacting).

Large-Eddy Simulation of Wind Turbine Wakes in Forest Terrain

In this study, large-eddy simulation was employed to investigate the influence of the forest canopy on wind turbine wakes. Nine forest case studies were carried out with different vertical distributions of leaf area density (LAD) and values of leaf area index (LAI). It was found that the wake in forest canopies recovers at a faster rate when compared with the flat terrain. An interesting observation was the significant reduction in turbulence kinetic energy (TKE) in the lower part of the wake above the forest in comparison with the inflow TKE, which occurred for a wide range of turbine downstream positions. The increase of TKE, on the other hand, was mainly located in the region around the top tip. Analyses of the power spectral density showed that the increase in TKE happened at a certain range of frequencies for the forest canopy cases and at all the examined frequencies for the flat case. Wake meandering was also examined and was found to be of a higher amplitude and a lower dominant frequency for the forest cases compared with the flat case. In terms of the influence of forest canopy parameters, the LAI was found to have an impact greater than the vertical distribution of LAD. Specifically, the wake-added TKE and wake-added Reynolds shear stress were found to be approximately the same for cases with the same LAI, regardless of the vertical distribution of LAD.

Development and Validation of a CFD Combustion Model for Natural Gas Engines Operating with Different Piston Bowls

Nowadays, an accurate and precise description of the combustion phase is essential in spark-ignition (SI) engines to drastically reduce pollutant and greenhouse gas (GHG) emissions and increase thermal efficiency. To this end, computational fluid dynamics (CFD) can be used to study the different phenomena involved, such as the ignition of the charge, combustion development, and pollutant formation. In this work, a validation of a CFD methodology based on the flame area model (FAM) was carried out to model the combustion process in light-duty SI engines fueled with natural gas. A simplified spherical kernel approach was used to model the ignition phase, whereas turbulent flame propagation was described through two variables. A zero-dimensional evolution of the flame kernel radius was used in combination with the Herweg and Maly formulation to take the laminar-to-turbulent flame transition into account. To estimate the chemical composition of burnt gas, two different approaches were considered—one was based on tabulated kinetics, and the other was based on chemical equilibrium. Assessment of the combustion model was first performed by using different operating points of a light-duty SI engine fueled with natural gas and by using the original piston. The results were validated by using experimental data on the in-cylinder pressure, apparent heat release rate, and pollutant emissions. Afterward, two other different piston bowl geometries were investigated to study the main differences between one solution and the others. The results showed that no important improvements in terms of combustion efficiency were obtained by using the new piston bowl shapes, which was mainly due to the very low (+4%) or null increase in turbulent kinetic energy during the compression stroke and due to the higher heat losses (+20%) associated with the increased surface area of the new piston geometries.

Effect of coolant pulsation on film cooling performance on turbine vane

Combined with infrared thermography measurements, large eddy simulation was used to study the square-wave pulsating film cooling on turbine vane at the time-averaged blowing ratios of 0.5 and 1.5. On suction surface, the introduction of coolant pulsation results in the decrease of cooling effectiveness. On pressure surface, coolant pulsation at high blowing ratio can improve coolant coverage. Starting vortex is the typical structure in pulsating film cooling. However, on suction surface, due to fully-turbulent mainstream, plenty of small-scale vortices play a dominating role in flow fields, and the effect of starting vortex is unobvious. The statistic characteristics and power spectrum density (PSD) of velocity fluctuation were also analyzed in detail. The results show that the disturbance of coolant jet on suction-side mainstream boundary layer is very weak, However, on pressure side, coolant pulsation causes notable increase of PSD and turbulent kinetic energy.

Numerical Investigation of Flow Past Bio-Inspired Wavy Leading-Edge Cylinders

A numerical investigation is proposed to explore the flow past a novel wavy circular cylinder as a passive flow control, whose shape is determined by a sinusoidal function applied to its leading edge line, similar to studies with wavy leading-edge airfoils. The latter are motivated by the wavy-shaped tubercles found in the flippers of humpback whales, which are believed to improve their maneuverability. Our attempt is, therefore, to assess the effects of leading-edge waviness now on a simpler and canonical geometry: circular cylinders. The present work relies on iLES simulations conducted with Nektar++ at a Reynolds number of 3900. Besides the straight cylinder, two wavy geometries are assessed, which are determined by a single wavelength of 37.5% for two amplitudes, 3% and 11%, based on the mean diameter of the wavy cylinder. Our results showed that, contrary to what is usually the case with traditional wavy cylinders at similar Reynolds numbers, waviness caused a reduction in the near-wake recirculation length and an increase in the mean near-wake turbulent kinetic energy compared to the straight cylinder. This was followed by a reduction in base pressure (up to about 36%) leading to a rise in lift oscillations and also to a significant increase in the mean drag coefficient of up to about 28%. An attempt to detail the flow phenomena is provided, evidencing the emergence of counter-rotating pairs of streamwise vortices between peaks. It is argued that the differences observed in recirculation length, turbulent kinetic energy, and force coefficients start even prior to the formation of these coherent structures and end up with interactions with the near wake.

Flushing control strategies to improve the stability of a biogas slurry drip irrigation system: Behavioral characteristics and mechanisms

Biogas slurry drip irrigation can mitigate environmental pollution and reduce the use of chemical fertilizers to enable sustainable development. However, the stability of the biogas slurry drip irrigation system (BSDIS) is disrupted by emitter clogging; hence, it is essential to explore the flushing control strategy of BSDIS. By means of combining actual measurement and simulation, this study investigates the BSDIS stability based on the three technical parameters of the flushing control strategy. Appropriate flushing control strategies can improve system stability and cause spatial differences on the drip irrigation tape. Under various flushing control strategies, the system stability primarily undergoes delays, sensitivity, and ineffectiveness of flushing with time. Compared with the without flushing and emitter outlet downward-oriented treatment, the optimal flushing combination (the high frequency flushing + emitter outlet upward-oriented treatment) reduces the emitter clogging content by approximately 70.97% and increases system stability by 189.1%. In the internal hydrodynamics, the laying direction of emitters does not change the movement characteristics of water flow, although the clogging particles do not completely follow the water flow, with some particles settling owing to gravity, thereby clotting the emitters. When clogging occurs, the increase in flushing speed is conducive to the increase in turbulent kinetic energy on the inlet surface of the emitter, which facilitate the flushing of clogged substances. This study proposes optimal flushing strategy parameters along with a new management mode for the waste liquid represented by biogas slurry.