Variation Of Flow Characteristics Research Articles

RPAS operations in urban airflow: Efficient modelling of representative wind speed variations along a flight path through a flow field with changing turbulence characteristics

For remotely piloted aircraft systems (RPAS) operating in the urban environment, the flight path will most likely pass through the turbulent airflow of building wakes. To attenuate or reject instabilities caused by the turbulent airflow, control systems strategies are being developed in preparation for increased demand on the smaller urban air mobility vehicles. In this paper, results from urban airflow measurements of four 1:300 scaled Canadian city model flow fields are examined to provide detailed understanding of flow characteristics that can be found in typical Canadian cities. The results show common patterns for the range of inner city wind speed and turbulence intensity but that within the urban boundary layer (UBL) the variation of flow characteristics does not have a gradient with respect to altitude and that flow characteristics are highly variable along representative flight paths. For the purpose of simulation of RPAS response to the complex urban airflow, methods for using real urban flows data as inputs to simulations is presented. Demonstration of an Advancing Fourier Series (AFS) method, using the measured city data, shows successful preservation of the spatial- and temporal-correlations for reconstruction of a flow time series offering a novel, efficient and flexible approach for implementation of a time-based simulation of RPAS response in complex flow environments such as the urban environment.

A Numerical Study on Cross Flow Heat Exchanger with Different Reynolds (Re) Numbers

Heat exchangers are highly popular in engineering and industrial applications. Numerical studies on heat exchangers to investigate the performance of heat transfer have been carried out widely by Computational Fluid Dynamics (CFD) in recent years. In this study, a circular pipe with hot water in cross flow is investigated in different Reynolds (Re) numbers. Flow is turbulent flow and the Re number varies from 3165 to 4643 in the circular pipe. The air is at a temperature of 303 K and the water is at 333 K. Variation of flow characteristics and thermal performance is observed according to an increase in Re numbers such as Wall Shear Stress (WSS), Skin Friction Coefficient (Cf), Nusselt Number (Nu), heat transfer coefficient (h) and surface temperature of the circular pipe. Results show that there are no significant changes for the WSS and Cf values in the specified range of the Re number. However, when the thermal performance is evaluated, the temperature of the surface of the circular pipe, heat transfer coefficient, and Nu number values are increased by an increase in the Re number. Here, the increase is approximately 2% for the specified range of Re number, and it is shown that it can be increased by the flow conditions. The maximum Nu number is 4482.37 at the Re number of 4643. As a result, the Re number is highly effective in controlling the heat transfer performance of a heat exchanger

"Development And Assessment of Immediate Release Nitrofurantoin Tablet and Sustained Release Trimethoprim Tablet: Formulation, Characterization and Comparative Evaluation"

The research includes an examination of material properties, an investigation into the compatibility of the drug and excipients, the development of analytical techniques, and the determination of tablet production methods for immediate and sustained release layers. The methodology for material characterization encompassed the analysis of the pharmaceuticals' solubility in various aqueous solutions and buffers. The evaluation of the compatibility between excipients and medications was conducted utilizing FT-IR spectroscopy. Furthermore, calibration curves were devised by the research team for Nitrofurantoin and Trimethoprim, enabling the quantification of these pharmaceutical substances via UV spectrophotometry. The preparation of the tablets involved the utilization of direct compression and moist granulation methods, respectively, for the immediate and sustained release layers. This required the application of a variety of excipients and polymers. The tablets underwent a thorough evaluation in a controlled laboratory environment, which encompassed assessments of their dimensions, resistance to deformation, mass variability, and susceptibility to fracturing, concentration of active component, breakdown time, and solubility. The findings demonstrated that the regression coefficients in the calibration curves were substantial, thereby validating the accuracy of the drug concentration estimations. The results of the solubility studies indicate that Nitrofurantoin becomes more soluble in acidic environments. However, it should be noted that the solubility of both Trimethoprim and Nitrofurantoin is influenced by various solvents and buffers. An investigation into the compatibility of pharmaceuticals and the excipients was conducted through the utilization of FT-IR spectroscopy to ascertain such compatibility or interaction. A micromeritics analysis of granule flow parameters unveiled batch-specific variations in flow characteristics which will impact the manufacturing procedure. Upon scrutinizing the tablets, discrepancies in multiple measurements were discovered among various samples, suggesting the possibility of atypical tablet characteristics. Nitrofurantoin and Trimethoprim exhibited a progressive release from their tablets over time in various samples, as indicated by the drug release profiles observed in vitro; this suggests that the tablets have distinct release kinetics. Nevertheless, the medication release data exhibited irregularities in its presentation, such as sporadic inputs, absent values, and potentially erroneous statistics. The presence of these inconsistencies has the potential to compromise the dependability and comprehension of the results. In brief, the research provides extensive knowledge regarding the development, examination, and assessment of Nitrofurantoin rapid release tablets and Trimethoprim sustained release tablets.

Detailed numerical investigations of the in operando adjustable flow field in a diamond unit cell-based interpenetrating periodic open cellular structure (interPOCS)

In the field of heterogeneous catalysis, additively manufactured so-called Periodic Open Cellular Structures (POCS) applied as catalyst supports have demonstrated their advantages over conventional randomly packed bed reactors in terms of heat management and pressure drop (Busse et al., 2018; Inayat et al., 2016). Since the internal flow field and the pressure drop are mainly influenced by the geometrical properties of the unit cell (unit cell type, strut diameter and cell size), the resulting transport characteristics of the structure is already determined during the design phase of the unit cell (Horneber, 2015). By inserting one POCS based on a diamond unit cell (offset structure) into the cavities of a second diamond cell structure (fix structure), a completely new type of so-called interpenetrating Periodic Open Cellular Structures (interPOCS) is formed which allows for an in operando adjustment of the global and local morphological properties of the structure (Do et al., 2017; Do et al., 2020). With detailed, spatially resolved computational fluid dynamics (CFD) simulations using the open source toolbox OpenFOAM® (Weller et al., 1998) and an additional in-house random-walk particle tracking implementation called disTrackFoam (Trunk et al., 2021), we systematically investigated the local and global flow characteristics within the interPOCS in dependency of the relative positioning of the fixed and offset structure. The obtained results show that this highly adjustable structure allows for a broad variation of flow characteristics in a chemical reactor without changing the system’s periphery. This study demonstrates that interPOCS represent a completely new application of additively manufactured catalyst support structures enabling highly flexible in operando tuning of the flow field and mass transport in a heterogeneously catalyzed reactor system.

Does the performance enhancement through multi-model averaging at the catchment outlet gets translated to the interior ungauged points?

Accurate prediction of streamflow is essential at both the outlet and interior points for effective water resource management. This study aimed to investigate whether improved simulation results at the catchment outlet through Multi-Model Averaging (MMA) can be translated to interior ungauged points in a catchment. To achieve this, the study considered ensemble combinations of 81 conceptual hydrologic models and calibrated each model using four objective functions for two study areas (Jagdalpur and Wardha subbasins of Godavari basin). Six MMA methods were applied to evaluate their performance at interior points in the catchment. The findings revealed that, when compared to the best performing hydrologic model, the best MMA method showed an improvement in terms of Nash-Sutcliffe efficiency, ranging from 2.2% to 3.8% at the interior point of Jagdalpur and 2% to 12% at the interior points of Wardha. MMA methods with KGE-calibrated models as input exhibited better performance in terms of NSE, while those using LogarithmicNSE-calibrated and parent models as input ensembles showed better performance in terms of Percentage bias and Skill Score. Bayesian model averaging and Genetic Algorithm based averaging methods were identified as the most appropriate MMA methods, and the study findings suggest that the performance of these techniques varies at different interior points based on their spatial and temporal variation of flow characteristics. Overall, this study would be beneficial for better flow prediction at internal ungauged points, which is crucial for effective water resource management in areas where there is limited data or where new developments have occurred.

Influence of uniform magnetic field on hydrothermal characteristics and entropy production in a nanofluid filled rectangular grooved channel

The implementation of a uniform magnetic field can be beneficial for controlling thermal convective processes in magneto-thermal devices and systems. In research of productive energy employment and superior thermal efficiency, the present numerical research study aimed to investigate the flow structure, thermal behaviors, and entropy production of nanofluids with a mixture of CuO and water in a rectangular grooved channel subjected to the uniform magnetic field in the transverse direction. Convective dynamics in such rectangular grooved channels subjected to a uniform magnetic field have not been comprehensively investigated considering flow structures, thermal performances and entropy characteristics. The impact of different variables namely nanoparticle volume concentrations, Φ Hartmann numbers, Ha and Reynolds numbers, Re on the hydrothermal characteristics is numerically explored. According to acquired outcomes, the uniformly implemented magnetic field in the rectangular grooved channel causes significant variations of flow characteristics demonstrated by the streamline patterns and reduces the extent of the recirculation flow zone in rectangular grooves at Re = 250 and 1250. During the application of the uniform magnetic field, the thermal boundary layer formed in the rectangular grooves becomes thinner, while the temperature gradient in the near regions of the heated walls increases. Numerical simulations show that the average Nusselt number, Nuavg increases by approximately 9.08% for Ha = 8 and 30.42% for Ha = 24 at Re = 250, and by 0.087% for Ha = 8 and 21.13% for Ha = 24 at Re = 1250, compared to the case where no uniform magnetic field is applied, Ha = 0. It can be observed that for a given value of Re, the total entropy reduces sharply for Ha>8, due to the significant effect of high magnetic field intensity over both thermal and flow distributions. The outputs of this study could be very beneficial for designers modeling any device or system including thermal energy transportation in various industrial applications such as cooling circuits of electronic components and fast fission reactors, materials science and metallurgical processes.

Visualization study on the flow characteristics of a nitrogen pulsating heat pipe

An experimental setup for visualization study of a nitrogen pulsating heat pipe (PHP) is developed. The PHP is a flat-plate PHP fabricated using MEMS technology with silicon base plate and BF33 glass cover plate. The hydraulic diameter of the channel is 667 μm and the overall dimension of the PHP is 70 × 25 × 2 mm3. The filling ratios (FRs) in this study are measured with visualization images. Six filling ratios are adopted ranging from 15% ∼ 94% and the PHP only fails to start-up with 15% FR. Flow images of nitrogen PHPs are obtained for the first time. Four types of flow patterns are observed. The variations of flow characteristics and fluid motion with heat loads and FRs are analyzed. The fluid motion diagram and flow pattern proportion are extracted from the visualization results as well. Large amplitude oscillating motion is rarely observed in the nitrogen PHP. And annular flow is found to be dominant in low and medium FR working conditions, which indicates the one-dimensional slug flow model may have a narrow application range for the flat-plate nitrogen PHP.

Abstract WP258: Post-stroke Microvascular No-reflow Demonstrates Spatiotemporal Heterogeneity Using Visible-Light Optical Coherence Tomography

Introduction: The spatiotemporal pattern of microvascular reperfusion in vivo after large vessel recanalization is poorly understood. Combining chronic cranial window with embedded microprism (CCW-MP) and visible-light optical coherence tomography angiography (Vis-OCTA) enables the study of mouse cortical cerebrovasculature up to 60 days post-stroke. Vis-OCTA/CCW-MP can identify the presence or absence of microvascular flow, without labelling, up to 1 mm in cortical depth of the mouse brain at 1.3 micron resolution. We sought to build on these findings to understand the pattern of microvascular no-reflow in a mouse model of stroke that simulates large vessel occlusion and reperfusion. Hypothesis: Different regions of the cortex have striking variation in flow characteristics after macrovascular reperfusion. Methods: All mice studied were 3-4 mo old, C57/Bl6 background, and subject to IMPROVE guideline. Control mice (n=3) were studied to confirm absence of cortical or vascular changes induced by CCW-MP surgery. Test mice (n =6) underwent CCW-MP as previously published. After 2 weeks to allow for healing post-surgery, mice were subject to transient middle cerebral artery occlusion (tMCAO) to model large vessel occlusion and reperfusion. Vis-OCTA measured cortical flow at baseline, 24 hours post-stroke, and 72 hours post-stroke. Cortical mouse vascular regions were divided into layers 1-3: layer 4 : layer 5-6 from top to bottom. Results: Control mice showed no neuronal death, astrogliosis, microgliosis, or neutrophil recruitment induced by CCW-MP implantation. There was no significant difference between vascular density for prism-adjacent cortex and prism-remote cortex. We also determined that the CCW-MP images cortical vascular territory supplied by the middle cerebral artery. For the test mice, all six mice survived combined surgery. Vis-OCTA showed four of six mice had reduction of microvascular flow > 20% from baseline by 72h post-stroke at layer 5-6. Conclusions: Microvascular reperfusion post large vessel recanalization can be incomplete up to 72 hours post-stroke, especially at deeper cortical levels. Further studies should define associated changes in inflammatory cells as well as oxygenation of vessels.

Characteristics of discharge frequency and their effects on flood channel formation in the middle and lower reaches of the Yangtze River before/after the impoundment of the Three Gorges Reservoir

三峡水库蓄水前后长江中下游流量特征变化及其对造床作用的影响一直受到学者的关注.采用枝城等6个水文站日均流量资料，分别统计了各站流量的经验频率分布，检验了8种概率密度函数的适用性，并讨论了三峡水库蓄水前后流量频率分布特征与造床流量的关系.研究表明：长江中下游干流洪中枯各级流量的频率分布具有分段特性，无法用皮尔逊Ш型或对数正态等常见函数来整体描述，但中洪流量区段符合分段幂函数；拟合得到的分段幂函数转折点可近似反映造床流量，包括临界值在内的函数特征参数受洞庭湖等调蓄作用影响，在螺山站上下游差异较大；三峡水库蓄水后，洪水削减使得各站的流量频率分段特性增强，分段幂函数仍然适用；由于三峡水库蓄水后流量过程变化和频率调整的影响，枝城、沙市、监利站造床流量将变为蓄水前的0.79、0.73、0.74倍，螺山、汉口、大通站造床流量将变为蓄水前的0.89、0.90、0.93倍.本文的方法和认识对于长江中下游径流特征分析和造床流量计算具有参考价值.;The variations of flow characteristics and their effects on channel formation in the middle and lower reaches of the Yangtze River before and after the impoundment of the Three Gorges Reservoir (TGR) have drawn much concern. Based on the data of the average daily discharge at six hydrological stations including Zhicheng Station, the empirical flow frequency distributions were calculated, and the applicabilities of eight probability density functions were tested. Furthermore, the relationships between the flow frequency distribution characteristics and the channel-forming discharges before and after the impoundment of the TGR were discussed. The results show that the flow frequency distributions in the study reach are segmented, which cannot be described as a whole by common functions such as Pearson Ш or Lognormal distribution. However, the frequency distributions of the medium-high flow conform to the broken power-law (BPL). The turning point of the BPL obtained by fitting approximately reflects the channel-forming discharge. Moreover, affected by the regulation and storage of Lake Dongting, the characteristic parameters including the critical values quite differently in the upper and lower reaches of Luoshan Station. After the TGR is impounded, the subsection characteristics of the flow frequency distributions are enhanced by the flood reduction, and the applicability of BPL are still considerable. Due to the influence of the flow process change and frequency adjustment by the impoundment of the TGR, the channel-forming discharge at Zhicheng, Shashi, Jianli, Luoshan, Hankou and Datong stations will be 0.79, 0.73, 0.74, 0.89, 0.90 and 0.93 times of that before the impoundment, respectively. The method presented in this paper are of reference value for the analysis of runoff characteristics and the calculation of channel-forming discharge in the middle and lower reaches of the Yangtze River.

Effect of feed solid concentration on tailings slurry flocculation in a thickener by a coupled CFD-PBM modelling approach

The flocculation technique has been proven fruitful for separating beneficiation wastewater from tailings slurry in the thickening process. The tailings flocculation is significantly affected by the feed solid concentration and flow characteristics, however, it is difficult to capture the local solid concentration and the resulting variation in flow characteristics by a conventional experimental approach. This paper thus employed a coupled Computational Fluid Dynamics-Population Balance Model (CFD-PBM) modelling approach to explore the effect of feed solid concentration on the flocculation performance in and around the thickener feedwell. The flocculation kinetics induced by polymer-bridging was incorporated into the PBM framework by aggregation and breakage kernels. The proposed model was validated against the experimental results in terms of liquid velocity and floc size distribution. The designed inner feedwell with deflectors has been demonstrated to have better flocculation performance. The effects of the feed solid concentration on the flow characteristics (e.g. effective viscosity of the slurry, and turbulence dissipation rate) and floc size distribution have been investigated. Results mainly show that the local solid concentration and effective viscosity of the slurry increase with feed solid concentration, while the mean floc size first increases and then decreases. A moderate feed solid concentration facilitates the flocculation performance. This study helps to understand the essential effect of feed solid concentration on the flow characteristics and flocculation performance, thereby guiding the flocculation-thickening process to achieve the sustainable use of beneficiation wastewater and mineral resources.

Simulation of Turbulent Flow with High Reynolds Number over an Elliptical Cylinder

A complex turbulent flow with high Reynolds number (Re= 5 × 105, 1 × 106, 2 × 106 and 3.6 × 106) over an elliptical cylinder, is investigated using 2D URANS equations with a standard k-ε turbulence model. The present study compares the effect of various upstream velocity profiles on the variations in flow characteristics along the surface of an elliptical cylinder having variable axis ratios. The comparison of results with the published data for a circular cylinder in cross flow shows the importance of axis ratio and other velocity profiles to reduce the drag force and variation in pressure distribution. Drag force over an elliptical cylinder is found to be lower than that of a circular cylinder. The drag force is seen to increase with increasing slenderness ratio. The drag coefficient of an elliptical cylinder with an axis ratio 0.6 is found to reduce by half as compared to that of a circular cylinder. The influence of slenderness ratio and velocity profile over back pressure recovery, flow separation and shear stress distribution is observed for an elliptical cylinder.

Numerical predictions of the flow characteristics of subsonic jet emanating from corrugated lobed nozzle

PurposeThe purpose of this study is to investigate the aerodynamic characteristics of subsonic jet emanating from corrugated lobed nozzle.Design/methodology/approachNumerical simulations of subsonic turbulent jets from corrugated lobed nozzles using shear stress transport k-ω turbulence model have been carried out. The analysis was carried out by varying parameters such as lobe length, lobe penetration and lobe count at a Mach number of 0.75. The numerical predictions of axial and radial variation of the mean axial velocity, u′u′ ¯ and v′v′ ¯ have been compared with experimental results of conventional round and chevron nozzles reported in the literature.FindingsThe centreline velocity at the exit of the corrugated lobed nozzle was found to be lower than the velocity at the outer edges of the nozzle. The predicted potential core length is lesser than the experimental results of the conventional round nozzle and hence the decay in centreline velocity is faster. The centreline velocity increases with the increase in lobe length and becomes more uniform at the exit. The potential core length increases with the increase in lobe count and decreases with the increase in lobe penetration. The turbulent kinetic energy region is narrower with early appearance of a stronger peak for higher lobe penetration. The centreline velocity degrades much faster in the corrugated nozzle than the chevron nozzle and the peak value of Reynolds stress appears in the vicinity of the nozzle exit.Practical implicationsThe corrugated lobed nozzles are used for enhancing mixing without the thrust penalty inducing better acoustic benefits.Originality/valueThe prominent features of the corrugated lobed nozzle were obtained from the extensive study of variation of flow characteristics for different lobe parameters after making comparison with round and chevron nozzle, which paved the way to the utilization of these nozzles for various applications.

Numerical analysis of wind velocity effects on fire-wind enhancement

Variation in flow characteristics triggered through the fire-wind interface can potentially damage the buildings during bushfires. Fire-wind enhancement which is referred to as the increase of wind velocity, caused by the fire-wind interaction, is one of the destructive phenomena in this regard. In spite of the significance, the underlying mechanism contributing to this phenomenon is still not well understood. This study employs computational fluid dynamic (CFD) simulation to fundamentally investigate the effects of free-stream wind velocity on fire-wind enhancement through analyzing the momentum and buoyancy of fluid. Fire-wind interaction is shown to cause the generation of fire-induced longitudinal negative pressure gradient which results in fire-induced pressure and viscous forces in longitudinal direction. These forces are further found as the prime reason for the distortion of the wind velocity profile. A module is implemented to the FireFOAM solver to calculate and extract these forces quantitatively. The results reveal that under a constant fire intensity, the level of distortion and/or enhancement in the wind velocity profile comparatively reduces with the increase of free-stream wind velocity. A new non-dimensional group (modified Euler number) is introduced to take into account dominant fire-induced forces causing fire-wind enhancement. Richardson number and the modified Euler number are employed to determine the influence of free-stream wind velocity and longitudinal distance from the fire source on wind velocity enhancement. Large-eddy simulation (LES) results indicate that while the level of enhancement generally depends on both Richardson and the modified Euler number, the location of the maximum level of enhancement along the plume centreline coincides with the maximum value of modified Euler number under a constant free-stream wind velocity scenario.

Spatial variation of flow characteristics in a subarctic meandering river in ice‐covered and open‐channel conditions: A 2D hydrodynamic modelling approach

AbstractTo be able to understand year‐round river channel evolution both at present and in the future, the spatial variation of the flow characteristics and their sediment transport capabilities under ice cover need to be detected. As the measurements done through cross‐sectional drill holes cover only a small portion of the river channel area, the numerical simulations give insight into the wider spatial horizontal variation of the flow characteristics. Therefore, we simulate the ice‐covered flow with a hydrodynamic two‐dimensional (2D) model in a meandering subarctic river (Pulmanki River, Finland) in mid‐winter conditions and compare them to the pre‐winter open‐channel low flow situation. Based on the simulations, which are calibrated with reference measurements, we aim to detect (1) how ice‐covered mid‐winter flow characteristics vary spatially and (2) the erosion and sedimentation potential of the ice‐covered flow compared to open‐channel conditions.The 2D hydrodynamic model replicated the observed flow characteristics in both open‐channel and ice‐covered conditions. During both seasons, the greatest erosional forces locate in the shallow sections. The narrow, freely flowing channel area found in mid‐winter cause the main differences in the spatial flow variation between seasons. Despite the causes of the horizontal recirculating flow structures being similar in both seasons, the structures formed in different locations depended on whether the river was open or ice covered. The critical thresholds for particle entrainment are exceeded more often in open‐channel conditions than during ice‐covered flow. The results indicate spatially extensive sediment transport in open‐channel conditions, but that the spatial variability and differences in depositional and erosional locations increase in ice‐covered conditions. Asymmetrical bends and straight reaches erode throughout the year, whereas symmetrical, smaller bends mainly erode in open‐channel conditions and are prone to deposition in winter. The long ice‐covered season can greatly affect the annual morphology of the submerged channel. © 2019 John Wiley & Sons, Ltd.

Degradation of Aerodynamic Performance of an Intermediate-Pressure Steam Turbine Due to Erosion of Nozzle Guide Vanes and Rotor Blades

Deteriorations of nozzle guide vanes (NGVs) and rotor blades of a steam turbine through a long-time operation usually decrease a thermal efficiency and a power output of the turbine. In this study, influences of blade deformations due to erosion are discussed. Experiments were carried out in order to validate numerical simulations using a commercial software ANSYS-cfx. The numerical results showed acceptable agreements with experimental results. Variation of flow characteristics in the first stage of the intermediate pressure steam turbine is examined using numerical simulations. Geometries of the NGVs and the rotor blades are measured using a 3D scanner during an overhaul. The old NGVs and the rotor blades, which were used in operation, were eroded through the operation. The erosion of the NGVs leaded to increase of the throat area of the nozzle. The numerical results showed that rotor inlet velocity through the old NGVs became smaller and the flow angle of attack to the rotor blade leading edge became smaller. Consequently, the rotor power decreased significantly. Influences of the flow angle of at the rotor inlet were examined by parametric calculations and results showed that the angle of attack was an important parameter to determine the rotor performance. In addition, the influence of the deformation of the rotor blade was examined. The results showed that the degradation of the rotor performance decreased in accordance with the decrease of blade surface area.

하천 만곡도에 따른 흐름특성 변화

하천 만곡도에 따른 흐름특성 변화

Analysis of transient flow of MHD nanofluid past a non-linear stretching sheet considering Navier’s slip boundary condition

Induced boundary layer flow in the nanofluid caused by impulsively started nonlinear stretching sheet is analyzed in the presence of thermal radiation and magnetic field considering Navier’s velocity sip boundary condition. The similarity solution is achieved numerically using Galerkin finite element technique. The variation of flow characteristics viz. nanofluid velocity, temperature and nanoparticle concentration is examined corresponding to different flow parameters considered in the problem. The findings of the investigation reveal that nonlinearity in the stretching sheet leads to a deceleration in the nanofluid velocity, temperature and nanoparticle concentration while the unsteadiness in the stretching tends to decelerate the velocity whereas temperature and nanoparticle concentration are found to be increasing with increase in unsteadiness. The problem investigated in this article is basically an extension for unsteady case of the previously done works on nanofluid flow over a sheet stretching with a power-law velocity.

Runoff and subsurface drain response from mole and gravel mole drainage across episodic rainfall events

Shallow drainage techniques such as mole and gravel mole drainage are used in low permeability soils to siphon off infiltrating rainwater and mitigate the associated rise in watertable. Their purpose is to improve trafficability and agricultural production. In Ireland, long-term climate predictions envisage an increased level of short-term extreme rainfall events. Therefore, a key question is how these drainage techniques perform during episodic, high intensity rainfall events, specifically in terms of discharge hydrographs and associated parameters (principally flow start time, flow peak time, lag time, peak flow rate and flashiness index). We examined 12 rainfall events over a 1year period on a clay-loam dominated grassland site of 1.4% slope in the south of Ireland. Four drainage treatments, namely; (A) an un-drained control, (B) Mole drainage installed in January 2011 (sub-optimal installation conditions), (C) Mole drainage installed in July 2011 (optimal installation conditions) and (D) Gravel mole drainage installed in July 2011 were examined. Results showed that gravel mole drainage exhibited shorter response times to rainfall events and ultimately drained greater volumes. Drain flow from mole drainage treatments B and C produced longer start, peak and lag times and lower peak and total flows relative to the other flow discharges. Variations in discharges from all treatments were closely correlated to soil moisture status, 30days antecedent rainfall and rainfall event intensity. Drain flow response in all treatments was seen to deteriorate in time with the strongest responses evident in early events. Flow hydrographs showed strong variation in flow characteristics, within and across treatments and across events. If the predicted increase in short-term extreme rainfall events materialises then such systems will have to operate in increasingly adverse conditions. This will require changes in system design to improve the effectiveness of mole and gravel mole drainage.

Analysis of Supercritical Flow In Suddenly Expanding Channel

The experimental analysis is carried out to study the variation of flow characteristics namely sequent depth ratio (Y2 / Y1), Relative height of jump (hj / Y1), relative energy loss (EL / E1), Efficiency (E2 / E1), Relative length of jump (Lj / Y1) and relative length of roller (Lr / Y1) of the hydraulic jump for suddenly expanding channel for different B1 / B2 (expansion) ratio. Dimension of baffle blocks and end sill are also considered as the third variable. Explanations of the variation of these characteristics with approach Froude number is presented based on experiments. Empirical models are presented using Buckinham's π-theorem; these models are tested, validated and compared with other authors result. Modifications in energy dissipation as a result of application of appurtenances are obtained showing usefulness to its dimensions.

A Numerical Study on the Physics of Flow Over a Flat Plate with Backward Facing Step

Some of the results of a numerical investigation of the flow field characteristics of a transonic compressible flow over a flat plate with backward facing step of different heights are presented. The study has been performed by solving Two-Dimensional Navier-Stokes equations. The system of governing equations has been solved, using an explicit Harten-Yee Non- MUSCL Modified flux type TVD scheme and a zero-equation algebraic turbulence model to calculate the eddy viscosity coefficient. The results presented in this paper are computed for fixed Mach number, M=0.8 and for different step heights, h=2.5, 5 and 7.5mm. The details on pressure, temperature and velocity field, together with recirculation length, expansion shock, reattached shock, interaction of shock wave are reported. The variations of flow characteristics due to change of step heights are also presented.