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Flexible systems bending in steady flows are known to experience a lesser drag compared to their rigid counterpart. Through a careful dimensional analysis, an analytical expression of the Vogel exponent quantifying this reduction of drag is derived for cantilever beams, within a framework based on spatial self-similar modelling of the flow and structural properties at the clamped edge of the structure. Numerical computations are performed on various situations, including systems involving more complex distributions of the flow or structural parameters. The scaling of drag versus flow velocity for large loadings is shown to be well predicted by fitting the system properties by simple power laws at the scale of the length on which significant bending occurs. Ultimately, the weak sensitivity of the Vogel exponent to the parameters of the system provides an explanation to the rather reduced scattering of the Vogel exponents around − 1 observed on most natural systems in aquatic or aerial vegetation. [ABSTRACT FROM AUTHOR]

Both numerical and experimental studies were conducted to evaluate the performance of an omni-flow wind turbine designed to provide renewable electricity on the top of urban buildings like skyscrapers. The numerical approach was based on Finite Volume Method (FVM) and the turbulence flow was studied with several commonly used Reynolds-averaged Navier–Stokes turbulence models. The results of the study were evaluated with the wind tunnel test results over a range of tip speed ratios. The numerical results showed the effect of blade number on both power output and starting capability. Although both the power and torque coefficient were improved significantly by the optimisation of the blade number, there was only a slight change when the blade number was greater than twenty. The results from wind tunnel testing also showed excellent starting capability with a starting wind velocity as low as 1.6 m/s. A numerical simulation was also conducted for the wind turbine working under non-uniform flow conditions. The numerical results have shown that the peak power coefficient of such a wind turbine under non-uniform flow, was lower than that under the uniform flow. Additionally, the applied thrust on a blade was subject to frequent and periodical changes. However, the effect of the change of thrust in magnitude and frequency was not significant. Therefore the omni-flow wind turbine has the potential to meet the challenge of unpredictable wind velocity and direction as a consequence of the urban environment. [ABSTRACT FROM AUTHOR]

Studying open channel flow and sediment transport in narrow flumes under non-uniform flow conditions, both sidewall and non-uniformity corrections are required for bed-shear stress. This research first reviews conventional predictive methods for bed-shear stress, including the flow-depth method, the hydraulic radius method and Einstein's sidewall correction. It then presents a novel procedure for sidewall and non-uniformity corrections based on a recent cross-sectional velocity distribution model. These methods are compared with data from the log-law under uniform and non-uniform, sub- and supercritical flow conditions, indicating that (i) the flow-depth and the hydraulic radius methods specify the upper and lower bounds for bed-shear stress; (ii) although Einstein's procedure causes a paradox for smooth flumes, it agrees with data from rough beds; and (iii) the proposed is better than Einstein's for subcritical flow, but the latter has advantage for supercritical flow. As an application, sediment inception under non-uniform flow conditions is also discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Non-uniform flow and drag force through the grass were studied semi-analytically. [•] Max. shear stress exists either at the top of the grass layer or on the ground. [•] An inflection point appears near the interface for the submerged case as expected. [•] The flow profile of the mixed type grass is successfully and smoothly plotted. [•] A new approach to better understand the mechanism of vegetated flows was proposed. [ABSTRACT FROM AUTHOR]

The reported experimental study assesses the effects of flow non-uniformity on the momentum flux in straight compound channels. Two flumes were used, featuring vertical and sloping banks. Starting with uniform flow condition, various imbalances in the upstream discharge distribution were introduced. This resulted in a time-averaged lateral flow and advective transport of momentum, which interacted with the shear-layer turbulence generated by the compound geometry. To investigate this interaction, the three contributions to transverse momentum flux (depth-averaged flow, shear-layer turbulence and dispersive term of spanwise velocity) are assessed. The first two contributions were strengthened by the sloping banks, while the third becomes important for the case of the vertical bank. With a lateral flow towards the main channel, the first contribution rises at the expense of the second. With a lateral flow towards the floodplain, the first two contributions have the same order of magnitude, and the Boussinesq approach is invalidated. [ABSTRACT FROM AUTHOR]

Abstract: This work combines the computational fluid dynamics (CFD) solutions and laser absorption spectroscopy technology to simulate the process of the mass flux measurement in supersonic scramjet inlet/isolator. The effects of non-uniform flows on the absorption line shape were analyzed in detail. Using an optimal line selection, the accuracy of the mass flux measurement with tunable diode laser absorption spectroscopy (TDLAS) has been improved. Simulated results indicated that the TDLAS-based mass flux had a good performance with error of less than 2% at the isolator where 6% of path length contains the boundary layers. In contrast, large deviation appeared between the simulation data and CFD results when the sensor location was near the cowl lip of the inlet, due to the large gradient of temperature, pressure and velocity in y direction. [Copyright &y& Elsevier]

Culvert design must account for a large range of flow rates but most of the time culverts convey flows that are smaller than the design flow. Repeated high flows passing through the culverts lead to a gradual increase of the sediment deposits in the culvert vicinity, eventually resulting in reduced flow and sediment capacity. Sedimentation at culverts is quite an involved process due to the combined effect of flow non-uniformity and unsteadiness, as well as of the flow-sediment interaction. This paper reports results from a series of laboratory experiments aimed at understanding the hydro and morpho-dynamic changes occurring in the vicinity of a three-box culvert. For this purpose, velocity and turbulence characteristics upstream of the culvert were mapped globally and locally during the transition from an original flatbed to equilibrium sediment transport condition using contemporary acoustics, light detection and ranging, and image-based technologies. The experimental results reveal flow complexities not currently accounted for in the design of the multi-barrel culverts, but which can be detrimental for their long-term operation. Considerations on practical approaches to efficiently model the complexities were formulated. [ABSTRACT FROM AUTHOR]

Abstract: Flow simulation in inlet ducts along with several turning vanes used in electrostatic precipitator (ESP) are analysed to understand the flow pattern at its exit locations. The geometry of inlet duct has been extracted from the Plant Design Manufacturing System (PDMS) and refined with turning vanes placed at several locations. The domain of duct geometry around turning vanes are decomposed with several volumes and filled with hexahedral elements with the help of stat-of-art mesh generator – Hypermesh. The resulting computational grid has been used in TASCflow solver to predict its flow pattern in the duct. Simulation for the specified conditions predicts uneven flow distribution in the ESP inlet duct. Due to large flow recirculation and turbulent losses in the duct, non-uniform averaged mass flow rates are noticed at duct exit locations. Simulation results suggest that the improvement of flow distribution in the duct through optimization can be tried by placing more turning/splitter vanes in the inlet duct. In order to ensure that the results obtained from TASCflow are meaningful and in right direction, in the absence of measurement data, simulation was benchmarked with other industry standard commercial flow solvers. The observations made from these popular solvers confirm the findings obtained using the TASCflow solver. The analysis with multiple solvers indicates that Fluent provides quick results, while better visualization can be made using CFX solver. The Star-CD solver, which captures the turbulent losses accurately takes more time for convergence provides alternatives. [Copyright &y& Elsevier]

The article presents a study that develops analytical model for the three-dimensional transport and dispersion of contaminants in a radial flow field within finite-thickness aquifer. The model was compared with Laplace transform finite difference (LTFD) model to verify its accuracy. The study considered a hypothetical convergent flow tracer test to show the application capability of the model. It says that the model can be used in checking numerical solution of a three-dimensional dispersion.

The article presents a study on non uniform flow effect on the turbulence and velocity intensities over a cobble bed flume. The study employs measurements of Reynolds shear stress, mean longitudinal flow velocity and turbulence intensity determination. Results of the study show the dependence of the maximum values Reynolds shear stress and turbulence intensities on the intermediate submergence scale as well as on the accelerating and decelerating flow structures.

Abstract: This paper investigates energy losses in compound channel under non-uniform flow conditions. Using the first law of thermodynamics, the concepts of energy loss and head loss are first distinguished. They are found to be different within one sub-section (main channel or floodplain). Experimental measurements of the head within the main channel and the floodplain are then analyzed for geometries with constant or variable channel width. Results show that head loss differs from one sub-section to another: the classical 1D hypothesis of unique head loss gradient appears to be erroneous. Using a model that couple 1D momentum equations, called “Independent Sub-sections Method (ISM)”, head losses are resolved. The relative weights of head losses related to bed friction, turbulent exchanges and mass transfers between sub-sections are estimated. It is shown that water level and the discharge distribution across the channel are influenced by turbulent exchanges for (a) developing flows in straight channels, but only when the flow tends to uniformity; (b) flows in skewed floodplains and symmetrical converging floodplains for small relative flow depth; (c) flows in symmetrical diverging floodplains for small and medium relative depth. Flow parameters are influenced by the momentum flux due to mass exchanges in all non-prismatic geometries for small and medium relative depth, while this flux is negligible for developing flows in straight geometry. The role of an explicit modeling of mass conservation between sub-sections is eventually investigated. [Copyright &y& Elsevier]

Abstract: Results are reported herein of an open channel flow laboratory based study of the development of ripples on a fine silica sand bed, and under non-uniform turbulent subcritical flow conditions. The hydraulic model used included a diverging channel, which resulted in a variation of hydraulic and sediment transport parameters along the channel. Sediment supply limitation occurred during experimentation, impacting bed form development. The overall aim of this study was to improve the understanding and modelling capability of the development of bed forms under limited sediment supply and non-uniform flow conditions. In particular, the applicability of an existing empirical model capable of predicting ripple development was tested for the conditions of this study, using measured ripple dimensions. The ripple height and length results were extracted from detailed bed profile records, obtained using an acoustic Doppler probe traversed longitudinally over the sediment bed, at various experimentation time intervals. It was found that the non-uniform flow conditions affected the development rate of the bed forms, while sediment supply limitation impacted their steady state dimensions. The measured steady state ripple dimensions were lower, on average, than the corresponding equilibrium dimensions predicted using existing empirical equations. Non-uniform flow also caused the simultaneous occurrence of bed forms at different stages of development along the hydraulic model, where 3D and 2D ripples and incipient bed forms were recorded. Such a scenario can occur in estuarine and coastal flows, due to changing hydraulic conditions and/or a limitation of sediment supply. The ripple development model tested was verified for the conditions of this study, with its accuracy being shown to depend on an accurate determination of steady state parameters. [Copyright &y& Elsevier]

Abstract: Commercial use of membrane adsorbers in the biotechnology industry is increasing. Here the system time lag created by membrane adsorber peripherals and the membrane adsorber flow distribution headers has been modeled using an anion exchange membrane and bovine serum albumin (BSA). The system time lag was modeled as a zero order and first order time lag. The zero and first order time lags have been removed from the breakthrough curve. The method used does not involve fitting a mathematical expression to the breakthrough curve. Further no assumptions are made regarding the shape of the breakthrough curve in the absence of the time lag. The method has been used to calculate the Langmuir isotherm parameters. The membrane capacity was found to be twice as large as the capacity determined after removal of the time lag. The Langmuir constant was five times as large for the system without accounting for the time lag. Errors in fitting isotherm parameters can significantly impact frontal analysis and membrane adsorber scale-up. The Langmuir isotherm calculated under dynamic conditions with the system time lag removed, was in agreement with the static adsorption isotherm. [Copyright &y& Elsevier]

Abstract: Existing analytical solutions to 2D and 3D contaminant transport problems are limited by the mathematically convenient assumption of uniform flow. An approximate method is developed herein for coordinate mapping of 2D (vertically-averaged) transport solutions to non-uniform steady-state irrotational and divergence-free flow fields in single-layer aquifers. The method enables existing analytical transport solutions to be applied to aquifer systems with wells, non-uniform saturated thickness, surface water features, and (to a limited degree) heterogeneous hydraulic conductivity and recharge. This mass-conservative coordinate mapping approach is inexact in its approximation of the dispersion process but is still sufficiently accurate for many simple flow systems. The degree of model error is directly proportional to the variation of velocity magnitude within the domain. These mapped analytical solutions are compared to numerical simulation results and the coordinate mapping errors are investigated. The methods described herein may be used in the traditional capacity of analytical transport models, i.e., screening and preliminary site assessment, without sacrificing accuracy by assuming locally uniform flow conditions or applying an ad-hoc coordinate transformation. The solutions benefit from the traditional advantages of analytical methods, particularly the removal of artifacts due to spatial and temporal discretization: no time-stepping or numerical discretization is required. [Copyright &y& Elsevier]

Abstract: This study investigates turbulence structures in steady and non-uniform flows. Equations of Reynolds shear stress and turbulent velocity fluctuations are derived and their physical interpretations are explained. The theoretical results show that, different from previous studies, the variation of water surface can generate the wall-normal velocity, resulting in deviations of Reynolds shear stress and turbulence intensities from those in uniform flows. A self-similarity relationship is found between the Reynolds shear stress and turbulence intensities in non-uniform flows. The existence of self-similarity indicates that the effect of non-uniformity does not influence the mixing length. An empirical equation has been proposed to express the relationship based on experimental data available in the literature. Good agreement is achieved between the measured and predicted turbulence intensities by applying the self-similarity relationship. [Copyright &y& Elsevier]

Summary: The importance of channel non-uniformity to natural hydrogeomorphic and ecological processes in gravel-bed rivers is becoming increasingly known, but its use in channel rehabilitation lags behind. Many projects still use methods that assume steady, uniform flow and simple channel geometries. One aspect of channel non-uniformity that has not been considered much is its role in controlling backwater conditions and thus potentially influencing patterns of physical habitat and channel stability in sequences of riffles and pools. In this study, 2D hydrodynamic models of two non-uniform pool–riffle–pool configurations were used to systematically explore the effects of four different downstream water surface elevations at three different discharges (24 total simulations) on riffle–pool ecohydraulics. Downstream water surface elevations tested included backwater, uniform, accelerating, and critical conditions, which are naturally set by downstream riffle-crest morphology but may also be re-engineered artificially. Discharges included a fish-spawning low flow, summer fish-attraction flow, and a peak snowmelt pulse. It was found that the occurrence of a significant area of high-quality fish spawning habitat at low flow depends on riffles being imposed upon by backwater conditions, which also delay the onset of full bed mobility on riffles during floods. The assumption of steady, uniform flow was found to be inappropriate for gravel-bed rivers, since their non-uniformity controls spatial patterns of habitat and sediment transport. Also, model results indicated that a “reverse domino” mechanism can explain catastrophic failure and re-organization of a sequence of riffles based on the water surface elevation response to scour on downstream riffles, which then increases scour on upstream riffles. [Copyright &y& Elsevier]

Abstract: Advective transport from a finite line contamination source to an extraction well with regional flow depends on interplay of radial and regional flows, a scheme commonly encountered in capture zone delineation. We have investigated travel-time distribution from a finite line contamination source and the associated breakthrough curves (BTCs) observed at an extraction well. The resulting travel-time distribution and BTCs depend on dimensionless source length, dimensionless pumping rate, and inclined angle of the source with respect to the regional flow, where the dimensionless terms are lumped parameters involving source length, pumping rate, distance between the source and the extraction well, aquifer thickness, and regional flow discharge. The observed concentration at the extraction well increases with time in a sub-linear manner. When the source orientation is perpendicular to the regional flow, the dimensionless first arrival time only depends on the dimensionless pumping rate whereas the dimensionless steady-state arrival time depends on both the dimensionless pumping rate and the dimensionless source length. The steady-state concentration at the extraction well is sensitive to the dimensionless source length and the inclined angle of the source with respect to the regional flow, but not sensitive to the dimensionless pumping rate. Two special cases where the extraction well is very close to the source and the regional flow can be negligible have also been discussed. [Copyright &y& Elsevier]

Abstract: A numerical experiment is carried out to investigate the suitability of a Boussinesq-type momentum model for simulating transcritical flows at short length transitions in open channel flow measuring structures. Two one-dimensional Boussinesq-type equation models, which incorporate different degrees of dynamic pressure corrections, are considered for this purpose. A finite difference method is employed to discretise and solve the equations. The models are then applied to simulate different test cases for flows in such channels with predominant non-hydrostatic pressure distribution effects. A comparison of the computed results with the corresponding experimental data is presented. Results of this study reveal that the proposed model, which includes a higher-order correction for the effect of the centrifugal pressure, describes well even relatively abrupt changes from sub- to super-critical flow state. [Copyright &y& Elsevier]

In this study, the effects of non-uniform flow due to: (i) inflow from tributaries and (ii) the presence of a downstream control structure (such as a weir or a barrage), on the optimal waste load allocation decision and the resulting cost-equity trade-off relationships, have been investigated. These effects are illustrated with in the framework of a typical cost-equity multi-objective optimization model for optimal waste load allocation in rivers. This framework consists of an embedded river water quality simulator with gradually varied flow and transport (BOD-DO) modules and a cost- equity multi-objective optimization model. A multi-objective evolutionary algorithm known as Non- dominated Sorting Genetic Algorithm-II is used for solving the optimization problem. The optimal fraction removal levels, the treatment cost and the system inequity measure are under predicted in certain reaches of the river, if the uniform flow assumption is made, while actually non-uniform flow conditions exist. This effect is quite pronounced when the flow non-uniformity results from a downstream control structure such as a weir. [ABSTRACT FROM AUTHOR]

Two-dimensional experiments investigating sediment transport and turbulence structure in sustained turbidity currents that cross breaks in slope are presented as analogue illustrations for natural flows. The results suggest that in natural flows, turbulence generation at slope breaks may account for increased sand transport into basins and that the formation of a hydraulic jump may not be necessary to explain features such as the occurrence of submarine plunge pools and the deposition of coarser-grained beds in the bottomsets of Gilbert-type fan deltas. Experimental flows were generated on 0°, 3°, 6° and 9° slopes of equal length which terminated abruptly on a horizontal bed. Two-component velocities were measured on the slope, at the slope break and downstream of the slope break. Flows were depositional and non-uniform, visibly slowing and thickening with distance downstream. One-dimensional continuous wavelet transforms of velocity time series were used to produce time-period variance maps. Peaks in variance were tested against a background red-noise spectrum at the 95% level; a significant period banding occurs in the cross-wavelet transform at the slope break, attributed to increased formation of coherent flow structures (Kelvin–Helmholtz billows). Variance becomes distributed at progressively longer periods and the shape of the bed-normal-velocity spectral energy distribution changes with distance downstream. This is attributed to a shift towards larger turbulent structures caused by wake stretching. Mean velocity, Reynolds shear stress and turbulent kinetic energy profiles illustrate the mean distribution of turbulence through the currents. A turbulent kinetic energy transfer balance shows that flow non-uniformity arises through the transfer of mean streamwise slowing to mean bed-normal motion through the action of Reynolds normal stresses. Net turbulence production through the action of normal stresses is achieved on steeper slopes as turbulence dissipation due to mean bed-normal motion is limited. At the slope break, an imbalance between the production and dissipation of turbulence occurs because of the contrasting nature of the wall and free-shear boundaries at the bottom and top of the flows, respectively. A rapid reduction in mean streamwise velocity predominately affects the base of the flows and steeper proximal slope flows have to slow more at the break in slope. The increased turbulent kinetic energy, limited bed-normal motion and strong mixing imposed by steep proximal slopes means rapid slowing enhances turbulence production at the break in slope by focusing energy into coherent flow structures at a characteristic period. Thus, mean streamwise slowing is transferred into turbulence production at the slope break that causes increased transport of sediment and a decrease in deposit mass downstream of the slope break. The internal effects of flow non-uniformity therefore can be separated from the external influence of the slope break. [ABSTRACT FROM AUTHOR]

Backward location and travel time probabilities, which provide information about the former location of contamination in an aquifer, can be used to identify unknown contamination sources. Backward location probability describes the possible upgradient positions of contamination at a known time in the past, and backward travel time probability describes the time required for contamination to travel from a known upgradient location to an observation point. These probabilities are related to adjoint states of resident concentration, and their governing equation is the adjoint of a forward contaminant transport model. Using adjoint theory to obtain the appropriate governing equation, we extend the backward probability model for conservative solutes to more general non-uniform and transient flow fields. In particular, we address three important extensions, spatially-varying porosity, transient flow and temporally-varying porosity, and internal distributed sources and sinks of solute and water. For the first time we learn that forward and backward location and travel time probabilities are not necessarily equivalent to adjoint states, but are related to them. The extensions are illustrated using a vertically-integrated groundwater model, creating transient flow by a step change in pumping and using areal recharge as an internal distributed source. Both the movement and spread of probabilities are affected. With internal sources of water, there are two interpretations of backward probability, depending on whether or not the source of water is also a source of solute. The results demonstrate how the backward probability model can be applied to other, perhaps more important, non-uniform and transient flow conditions, with time- and space-varying water storage, such as time-varying pumping or unsaturated (or saturated–unsaturated) flow and transport with spatially- and temporally-varying moisture content. [Copyright &y& Elsevier]

The tip clearance has an important effect on the performance of an engine compressor. While the impact of tip clearance on a concentric compressor has been widely explored in previous research, the flow field distribution of an eccentric compressor has only been minimally explored. Both the steady and unsteady computational fluid dynamics (CFD) methods have been widely used in the studies of concentric axial-compressors, and they have similar simulation results in terms of flow field. However, they have been rarely applied to axial-compressors with non-uniform tip clearance to investigate their flow field. In this paper, ANSYS CFX is used as CFD software, and both steady and unsteady CFD methods are applied to study a single rotor of ROTOR67 to investigate the compressor characteristic line and flow field under different eccentricity conditions. The results show that non-uniform tip clearance creates a non-uniform flow field at the inlet and tip regions over the whole operating range. The circumferential position where the flow coefficient and the axial velocity are the smallest occurs at a position close to the maximum tip clearance and is located on the side deviating toward the direction of rotation of the rotor. Compared with steady CFD, unsteady CFD has better predictive capability for the flow field distribution in axial compressors with non-uniform tip clearance. [ABSTRACT FROM AUTHOR]

• A quasi-three-dimensional model for performance of micro-channel SHP is developed. • Refrigerant flow among tubes is modeled as uneven flow with fixed direction in tube. • Air flow is modeled as uneven inlet flow with fixed direction across heat exchanger. • The model predicts micro-channel SHP heat capacity with average deviation below 5%. Micro-channel separated heat pipes (micro-channel SHPs), which may cycle without inputting additional electrical power, have shown their advantages of energy saving and compact structure, and they are preferred in the cooling of electronic equipment with narrow inner space. The non-uniformly distributed refrigerant flow among multiple flat tubes and air flow among multiple fins of micro-channel heat exchangers may have a significant effect on the performance of SHPs. In this study, a quasi-three-dimensional distributed parameter model of micro-channel SHPs is proposed for predicting the effects of non-uniformly distributed refrigerant and air flows on the performance. The model is developed by modeling all the components of a micro-channel SHP, i.e. an evaporator, an ascending tube, a condenser and a descending tube, respectively. In the model, the refrigerant flow is described as uneven flow among tubes and the flow direction is fixed inside each tube; the air flow is modelled as the flow with two-dimensional uneven distribution at the windward of heat exchanger and with the fixed direction across the heat exchanger; the three-dimensional partition method is applied to the control volume partition of flat tubes and fins. The proposed model is validated by experiments, and the results show that the deviations between simulated and experimental data of the heat transfer capacity, the temperature difference of micro-channel SHP, the outlet air temperature of evaporator and the outlet air temperature of condenser are 4.6%, 0.9 °C, 1.1 °C and 0.4 °C, respectively. [ABSTRACT FROM AUTHOR]

Li, Q. and Hong, B.G., 2020. Numerical calculation of non-uniform flow field in water area at the end of a breakwater. In: Bai, X. and Zhou, H. (eds.), Advances in Water Resources, Environmental Protection, and Sustainable Development. Journal of Coastal Research, Special Issue No. 115, pp. 494-497. Coconut Creek (Florida), ISSN 0749-0208. The control of ship motion in harbor water is a frontier problem in unmanned ship research. In harbor waters, affected by the shore type, the varied flow pattern has a great influence on ship motion. In this paper, numerical calculation method was used to study the influence of non-uniform flow on ship motion. a control-volume-based finite-difference scheme of the three-dimensional rectangular coordinate system was used for solving the two-phase transient Navier-Stokes equations. The dynamic process of water interaction with the ship and its (ship) free surface was investigated with the help of volume of fluid (VOF) technique. Moreover, the flow field and mechanical characteristics of the ship in the breakwater were analyzed under the action of cross flow. The force analysis of ship with respect to time and space such as the ship sailing out of breakwater with certain sail-angle and speed characteristics are also investigated. Finally, these numerical results were compared with that of experimental data which has a nice correlation with each other. [ABSTRACT FROM AUTHOR]