Turbulent Shear Research Articles

The coupled dynamics of internal waves and hairpin vortices in stratified plane Poiseuille flow

A simulation of stably stratified plane Poiseuille flow at a moderate Reynolds number ( $\textit {Re}_\tau = 550$ ) and Richardson number ( $\textit {Ri}_\tau = 480$ ) is presented. For the first time, the dynamics in the channel core are shown to be described as a series of internal waves that approximately obey a linear wave dispersion relationship. For a given streamwise wavenumber $k_x$ there are two internal wave solutions, a dominant low frequency mode and a weaker-amplitude high-frequency mode, respectively corresponding to ‘backward’ and ‘forward’ propagating internal waves relative to the mean flow. Analysis of linearised equations shows that the dominant low-frequency mode appears to arise due to a particularly sensitive response of the mean flow profiles to incoherent forcing. Instantaneous visualisations reveal that hairpin vortices dominate the outer region of the channel flow, neighbouring the buoyancy dominated channel core. These hairpins are fundamentally different from those observed in canonical unstratified boundary layer flows, as they arise via quasi-linear local processes far from the wall, governed by background shear. Outer region ejection events are common and can be induced by high amplitude waves. Ejected hairpins are transported into the channel core, in turn ‘ringing’ the prevailing strong buoyancy gradient and thus generating high-amplitude internal waves, high dissipation and wave breaking, induced by spanwise vortex stretching and baroclinic vorticity generation. Such spontaneous and sustained generation of quasi-linear internal waves by wall-bounded sheared turbulence may provide novel idealised solutions for, and insight into, large-scale turbulent mixing in a wide range of environmental and industrial flows.

Sediment suspension affected by submerged rigid vegetation under waves, currents and combined wave–current flows

Laboratory experiments and mathematical analyses were carried out to investigate and quantify the impacts of submerged rigid vegetation on sediment suspension under waves, currents and combined wave–current flows. Mimic canopies constructed from wooden cylinders were used in the experiments with three configurations (sparse, dense and vertically varying density). It was found that more sediment was suspended within the vegetation canopies, where smaller velocities and higher turbulence were observed, indicating that vegetation-induced turbulence rather than mean flow was the main driver of sediment suspension over vegetated beds. Meanwhile, higher sediment concentration near the bed was observed within a denser canopy, especially in the case of vertically varying vegetation density. The near-bed suspended sediment concentration could be described by an exponential formulation using an effective bed shear velocity considering different turbulence components (i.e. vegetation wake turbulence, bed shear turbulence and near-bed coherent structures). The formula was applicable in both vegetated and bare beds with different hydrodynamic conditions. To predict the vertical distributions of sediment suspension, two theoretical models of turbulent diffusion were improved by incorporating the vertically varying turbulent intensity in the water column.

Wind Energy Resource Assessment for Cook Islands With Accurate Estimation of Weibull Parameters Using Frequentist and Bayesian Methods

Wind energy resource assessments at two islands in the Cook Islands are carried out in the present work. The wind data were collected for one year from sites on Mauke and Rarotonga Islands in the Cook Islands and the daily, monthly and seasonal average wind speeds, the diurnal variations of the wind shear coefficient, average temperature and turbulence intensity were estimated. Eleven frequentist methods and a Bayesian technique were used to determine the Weibull parameters and the wind power density (WPD) for each site. The best method was determined using the goodness of fit test and error measures. The average wind speeds were 4.65 m/s and 3.86 m/s at 34 m above ground level for the sites on Mauke and Rarotonga respectively. Based on the goodness of fit tests and error measures, the Least Squares Method performed best for estimating the Weibull parameters at the Mauke site, while for the Rarotonga site, the median and quartiles method performed the best. For both the sites, the Bayesian method, which is being used for the first time for wind resource assessments, ranked second of the twelve methods, indicating good potential for this method. The annual energy production (AEP) was also determined which was calculated to be 2192.34 MWh from a total of ten Vergnet 275 kW turbines at the two sites. Finally, an economic analysis, carried out for the two sites, indicated a payback period of 7.72 years.

Effect of tidal resuspension with oyster biodeposits on nutrient and oxygen dynamics

To test the effect of biodeposit resuspension on nutrient and oxygen dynamics, we performed a 30 d experiment in three 1000 l shear turbulence resuspension mesocosm (STURM) tanks (R) and three 1000 l non-resuspension (NR) tanks. All tanks contained defaunated muddy sediment and brackish estuarine water, received daily additions of oyster biodeposits, and had similar water column root mean square turbulent velocities (~1 cm s-1), energy dissipation rates (~0.08 cm2 s-3), and tidal cycles (4 h mixing-on; 2 h mixing-off). While bottom shear stress was low in NR tanks, high instantaneous bottom shear produced sediment and biodeposit resuspension in R tanks during the mixing-on cycles. Resuspension and biodeposit addition resulted in complex nutrient and oxygen dynamics in the water column as well as altered seabed fluxes. Modeled biodeposit diagenesis demonstrated that added resuspended biodeposit nitrogen in R tanks was nitrified, resulting in high water column nitrate and nitrite concentrations, as well as increasing water column dissolved oxygen demand. Water column dissolved oxygen concentrations were 2.3 times lower in the R tanks than in the NR tanks, whereas deposited organic matter from biodeposits resulted in sediment dissolved oxygen uptake 3 times higher in NR versus R tanks. Sediment dissolved inorganic nitrogen uptake in NR tanks and efflux in R tanks, respectively, were mediated by microphytobenthos abundance and biodeposit deposition. Seabed and water column biogeochemical processes, as mediated by biodeposit resuspension, controlled the nutrient and oxygen balances. Biodeposit resuspension is important when evaluating oysters as support for eutrophication control.

Unsteady turbulent flow developing inside and around different parts of fluttering trawl net in flume tank

Fluttering motions of a trawl are affected by its geometrical shape, natural underwater flows, and unsteady turbulent flow inside and around it. Thus, knowledge of the interaction between fluttering motions and the turbulent flow developing inside and around the different parts of the trawl is essential for understanding the hydrodynamic performance and selectivity of fishing gear. This paper assesses the coupled dynamics of the fluttering motions of different parts of a trawl and their hydrodynamics behavior. The analysis is based on three-dimensional electromagnetic current velocity meter measurements carried out inside and around different parts of a 1/18 scaled bottom trawl model. Instantaneous flow velocity fields and turbulent flow parameters were analyzed from obtained flow data. Moreover, fast Fourier transform and wavelet transform analysis were conducted to analyze the time–frequency contents of instantaneous flow velocity fields and fluctuating parts. The motions of different parts of the trawl net were oscillatory quasi-periodic and related to low frequency activity. The mean velocity ratios inside and around trawl wing, square, trawl body, and codend were 0.92, 0.89, 0.86, and 0.84, respectively. These results demonstrate the existence of unsteady turbulent flow inside and around different parts of the trawl. This unsteady turbulent flow corresponds to turbulent boundary layer flow, turbulent flow because of trawl wake, and vortex shedding. The dominant frequencies of these unsteady turbulent flows showed low frequency activities and wavelet energy was transferred from small-scale to large-scale motions under unsteady shear turbulence. In addition, knowledge of unsteady turbulent flow is greatly important for better understanding the hydrodynamic forces acting on a trawl and its geometrical shape as well as for implementing various selective devices and mesh shapes to reduce juvenile by-catch.

Flow aeration by an offset aerator: Air entrainment, bubbly flow turbulence, and adaptive-window cross-correlation processing

Chute aerators are used to induce flow aeration to prevent cavitation damages to flood discharge structures. The aerated chute flows are traditionally studied in terms of the air concentration distributions and air entrainment rate, whereas further detailed characterization of the bubbly flow associated with the turbulence modification has been missing. Herein the air–water flow turbulence was studied experimentally for a simple offset aerator model in a sloping chute. Advanced interfacial turbulence analyses were applied to the air–water flow measurement results using a dual-tip phase-detection probe. The new adaptive-window cross-correlation approach was first applied to the turbulence intensity estimate in both regions upstream and downstream the impact point. The overall spatial distributions of basic air–water flow properties agreed favorably with literature, and highlighted different patterns of air–water flow development in different sections of the flow. The turbulence level of the bubbly flow, and the bubble-turbulence interactions, were quantitatively described with the interfacial turbulence intensity, correlation turbulent length scale, and some measures of the bubble clustering behaviors. The interfacial turbulence intensity was obtained in the same order of magnitude as the common water-phase turbulence intensity observations, except for the impact zone. The results revealed the shear flow development and turbulence dissipation in the bottom layer of the aerated chute flow, which affected the local average bubble counts, the relative motions of neighboring bubbles, the diffusive transport of bubbly eddy structures, and consequently the near-wall bubble distributions critical for the protection of chute surface from cavitation erosion.

Effect of heat source on statistics and scaling in compressible homogeneous shear turbulence

The effects of heat sources on the velocity and pressure spectra, Mach number scaling of one-point statistics, and small-scale structures of compressible homogeneous shear turbulence are numerically studied. The dilatational components of flow fields are significantly enhanced by a strong heat source at low turbulent Mach numbers Mt and are dominated by an acoustic mode, leading to a strong acoustic equilibrium between the dilatational velocity and pressure. As the magnitude of the heat source increases, the scaling behaviors of the dilatational components of kinetic energy and dissipation rate change from Mt4 and approach a state that is nearly independent of the turbulent Mach number. Furthermore, a strong heat source has a significant effect on small-scale structures at low turbulent Mach numbers. The conditional probability density functions of the normalized eigenvalues of a strain rate tensor become more dependent on the dilatation owing to the effect of the heat source. For low turbulent Mach numbers with strong heat sources, the ratio of the normalized eigenvalues of the strain rate tensor tends to −1:0:0 and −0.2:0.25:1 in the strong compression and strong expansion regions, respectively, and the dilatational vortex stretching term can significantly enhance the enstrophy production.

Collisional properties of cm-sized high-porosity ice and dust aggregates and their applications to early planet formation

ABSTRACT In dead zones of protoplanetary discs, it is assumed that micrometre-sized particles grow Brownian, sediment to the mid-plane and drift radially inward. When collisional compaction sets in, the aggregates collect slower and therefore dynamically smaller particles. This sedimentation and growth phase of highly porous ice and dust aggregates is simulated with laboratory experiments in which we obtained mm- to cm-sized ice aggregates with a porosity of 90 per cent as well as cm-sized dust agglomerates with a porosity of 85 per cent. We modelled the growth process during sedimentation in an analytical calculation to compute the agglomerate sizes when they reach the mid-plane of the disc. In the mid-plane, the dust particles form a thin dense layer and gain relative velocities by, e.g. the streaming instability or the onset of shear turbulence. To investigate these collisions, we performed additional laboratory drop tower experiments with the high-porosity aggregates formed in the sedimentary-growth experiments and determined their mechanical parameters, including their sticking threshold velocity, which is important for their further collisional evolution on their way to form planetesimals. Finally, we developed a method to calculate the packing-density-dependent fundamental properties of our dust and ice agglomerates, the Young’s modulus, the Poisson ratio, the shear viscosity, and the bulk viscosity from compression measurements. With these parameters, it was possible to derive the coefficient of restitution which fits our measurements. In order to physically describe these outcomes, we applied a collision model. With this model, predictions about general dust-aggregate collisions are possible.

Improved Supersonic Turbulent Flow Characteristics Using Non-Linear Eddy Viscosity Relation in RANS and HPC-Enabled LES

A majority of the eddy viscosity models for supersonic turbulent flow are based on linear relationship between Reynolds stresses and mean strain rate. The validity of these models can be improved by introducing non-linearity in relation as RANS models offer advantages in terms of reduced turnaround times typical of industry applications. With these benefits, the present work utilizes quadratic constitutive relation (QCR) with Menter’s k omega SST model to characterize the flowfield of rectangular jets. The sensitivity of this model with QCR, weighted towards diffusion, dissipation, and a combination of both, is addressed. Viscous large eddy simulations (LES) with WALE subgrid scale models are employed for qualitative comparisons using a commercial solver. Massively parallel LES are enabled by the new in-house 1088-core computing cluster at the University of Cincinnati and are also used for benchmarking. The nearfield results are validated with available experimental data and show good agreement in both fidelities. Flow characteristics, including the shear layer profiles, Reynolds stresses, and turbulence kinetic energy (TKE) and its production are compared. LES reveal higher TKE production in the regions with highest Reynolds stresses. It is comparatively lower in QCR RANS. As a special case of TKE analysis in jets, a preliminary investigation of retropropulsion is outlined for rectangular nozzles for the first time. Improved flow behavior by implementation of a non-linear relationship between Reynolds stresses and mean strain rate is demonstrated.

Analysis and Numerical Simulation of no Reacting Swirling Flow by Using URANS Approach

In this paper, we investigate the no-reacting swirling flow by using the numerical simulation based to the unsteady Reynolds-averaged Navier-Stokes approach. The numerical simulation was realized by using a computational fluid dynamics CFD code. The governing equations are solved by using the finite volume method with two classical models of turbulence K-epsilon and Shear Stress K-ω. The objective of this paper is therefore to evaluate the performance of the two models in predicting the recirculation zones in a swirled turbulent flow. The current models are validated by comparing the numerical results of the axial, radial and tangential velocities to the experimental data from literature.

Research on the Influence of Shear Turbulence on the Aerodynamic Loads Characteristics of Wind Turbine

In order to accurately analysis the aerodynamic loads characteristics of the wind turbine under different turbulent wind conditions, the horizontal homogeneity in the flow field without a wind turbine and the numerical accuracy of the homogeneous flow field with a wind turbine were validated against the experimental results. The aerodynamic loads of the wind turbine were studied under the conditions of the uniform wind with a uniform turbulence intensity, the uniform wind with a shear turbulence intensity, the shear wind with a uniform turbulence intensity and the shear wind with a shear turbulence intensity. The results show that the increasing turbulence intensity leads to a small reduction in the torque of the wind turbine. Compared with uniform wind, shear inflow leads to a sine or cosine variation in the aerodynamic performance of the wind turbine and a reduction in the wind turbine’s thrust and torque. Compared with uniform turbulence intensity, shear turbulence intensity leads to a reduction in the wind turbine’s thrust and torque, and a more obvious phase lag effect, but it has little influence on the yawing moment and pitching moment.

Investigation of pulsatile flow structure in closed-type cavity

Pulsatile flow in a channel with sudden expansion and contraction, referred to as a closed-type cavity, is experimentally and numerically investigated in the range of Re = 50–1650, covering laminar and transitional flow regimes. Investigations are performed in the range of pulsation frequencies corresponding to Wo = 0.28–0.62 and at a constant pulsation amplitude. Pulsation frequency influence to time-averaged recirculation zone length and the development of recirculation zone as well as upper and corner eddies during the pulse cycle at different pulsation frequencies are investigated. A fixed amplitude from zero to maximum velocity is chosen to investigate flow behaviour throughout a whole pulsation cycle. The results show that the pulsation effect on the recirculation zone length is insignificant in the laminar flow regime at investigated frequencies. However, in the transitional flow regime, recirculation zone length was shortened, regardless of the Wo. The analysis of recirculation zone and upper eddy dynamics during the pulse cycle revealed that their growth rate depends on Wo. The development lag effect is observed at certain velocity phase angles. The analysis of shear rate and turbulence intensity profiles revealed that increased instabilities are determined by the interaction of recirculation zone, upper eddy and the forward-facing step during the pulse cycle.

An Integrated Spatio-Temporal Features Analysis Approach for Ocean Turbulence Using an Autonomous Vertical Profiler

Turbulent energy cascade and intermittency are very important characteristics in the turbulent energy evolution process. However, understanding the temporal–spatial features of kinetic energy transfer and quantifying the correlations between different scales of turbulent energy remains an outstanding challenge. To deeply understand the spatial–temporal features in the energy transfer process, an integrated features identification and extraction method is proposed to quantitatively investigate the correlations using the ocean shear turbulence measured by an autonomous vertical reciprocating profiler (AVRP). The proposed integrated method mainly contains two parallel features analysis modules: first, temporal multiscale features structures of the nonlinear and nonstationary turbulent cascade are identified by Variational Mode Decomposition (VMD); then, the ocean microstructure shear fluctuation data are decomposed into a series of intrinsic mode functions (IMFs), which are characterized by different time scales and frequency bandwidths. The local features of energy transfer are identified when the local intermittency peaks overlap and the phase-synchronization case occurs between two neighboring scales; second, the spatial statistical characteristics of the turbulent energy dissipation are quantitatively studied. The cumulative probability distribution functions (CPDFs) of kinetic energy dissipation are approximated well by a normal distribution, indicating that the turbulent dissipation process exhibits a robust spatial scaling correlation and a few intense dissipation locations dominate the integrated process. Finally, the proposed integrated method is evaluated through experiments using an autonomous vertical reciprocating profiler deployed in the South China Sea. Preliminary experimental results show that the proposed novel method is useful to improve our understanding of turbulent energy transfer and the evolution process in the ocean dynamic systems.

Lithium depletion and angular momentum transport in F-type and G-type stars in Galactic open clusters

Context. Open clusters provide unambiguous clues to understand the evolution of 7Li at the surface of low-mass stars and its possible correlation with stellar rotation, which is a challenge for both stellar hydrodynamics and Galactic chemical evolution. Aims. We aim to quantify the efficiency of the transport processes for both angular momentum and chemicals that are required to explain simultaneously the observed behaviour of surface 7Li (and 9Be) and rotation as well as the internal rotation profiles inferred from helio- and asteroseismology in F- and G-type main sequence stars. Methods. We apply the model for the transport of angular momentum and chemicals that we tailored in a previous work for solar-type stars to an extended range of initial masses and metallicities corresponding to F- an G-type stars in a sample of 20 Galactic open clusters. We evaluate its ability to explain the 7Li, 9Be, and rotation periods observations. This model includes atomic diffusion, rotation-induced processes (for which we tested different prescriptions for shear turbulence), penetrative convection with a rotational dependence, parametric viscosity and turbulence, and magnetic braking. Results. Over the entire range of masses, metallicities, and ages explored, we reproduce the evolution of the surface rotation rates and predict, for the first time, the observed anti-correlation between the surface rotation rate and 7Li depletion as a consequence of the penetrative convection prescription. The 7Li behaviour and its evolution with time is well reproduced for G-type stars. However, the ability of the model to reproduce the so-called 7Li dip centred around ∼6600 K strongly depends on the adopted prescriptions for shear turbulence. It also requires a stellar mass dependence for the parametric viscosity adopted for the transport of angular momentum, similar to the behaviour predicted for the generation and luminosity of internal gravity waves generated by stellar convective envelopes. Finally, the model predicts internal rotation profiles in good agreement with asteroseismic constraints in main sequence stars. Conclusions. We provide an efficient way to model G-type stars of different ages and metallicities successfully. However, the 7Li and 9Be dip constraints urgently call for further hydrodynamical studies to better model turbulence in stars, and for the exploration of physical processes such as tachocline mixing for the transport of chemicals and internal gravity waves for the transport of angular momentum. Finally, additional data for the internal rotation and for 9Be in main sequence low-mass stars are definitively needed.

Statistical analysis of wind resource and energy potential assessment of Sanghar site, Sindh Pakistan

PurposeThe purpose of this paper is to assess the wind resource and energy potential of the Sanghar site for minimizing the dependence on fossil fuels and improving the environment.Design/methodology/approachThe Sanghar site wind shear coefficient and turbulence intensity factor are investigated for a period of a year. The two-parameter k and c Weibull distribution function is used to analyze the wind speed of the Sanghar site. The standard deviation, coefficient of variation, wind power density and energy density; and capacity factor was assessed for a period of a year. The economic assessment of energy/kWh is investigated for the selection of appropriate wind turbines.FindingsThe mean wind shear of the Sanghar site was found to be 0.2509. The mean wind speed was found to be 4.766, 5.534 and 6.121 at 20, 40 and 60 m above the ground level. The mean value of the k parameter was observed to be 2.433, 2.777 and 2.862 at 20, 40 and 60 m for a period of a year. The Weibull c m/s parameter was found to be 5.377, 6.245 and 6.906 m/s at 20, 40 and 60 m. The major portion of values of standard deviation was found to be in between 0.1 to 2.00 at 20, 40 and 60 m. The mean wind power density values were observed to be 88.33, 93.5 and 110.16 W/m2 at 20, 40 and 60 m; respectively, for a period of a year. The mean coefficient of variation was found to be 0.1478, 0.1205 and 0.1033 at 20, 40 and 60 m; respectively. The mean energy density was found to be 476.75, 683.08 and 866.33 kWh/m2 at 20, 40 and 60 m; respectively. The mean capacity factor for different wind turbines was ranged between 18 to 24.83 for a period of a year. The economic assessment showed that wind turbine B has the minimum cost (US$) 0.0484/kWh.Practical implicationsThe assessment provides the solution to sustainable energy generation which reduces the consumption of fuel and the effect of fluctuating price of fuel in the world market on local consumers.Social implicationsWind energy may have social implications including environmentally friendly, consistent supply of energy during the peak summer season, less unit per cost, etc.Originality/valueThe Sanghar site is new and assessed for the first time in this research work. The Sanghar site is suitable for installing utility wind turbines for energy generation at the lowest cost.

Dynamic iterative approximate deconvolution models for large-eddy simulation of turbulence

Dynamic iterative approximate deconvolution (DIAD) models with Galilean invariance are developed for subgrid-scale (SGS) stress in the large-eddy simulation (LES) of turbulence. The DIAD models recover the unfiltered variables using the filtered variables at neighboring points and iteratively update model coefficients without any a priori knowledge of direct numerical simulation (DNS) data. The a priori analysis indicates that the DIAD models reconstruct the unclosed SGS stress much better than the classical velocity gradient model and approximate deconvolution model with different filter scales ranging from viscous to inertial regions. We also propose a small-scale eddy viscosity (SSEV) model as an artificial dissipation to suppress the numerical instability based on a scale-similarity-based dynamic method without affecting large-scale flow structures. The SSEV model can predict a velocity spectrum very close to that of DNS data, similar to the traditional implicit large-eddy simulation. In the a posteriori testing, the SSEV-enhanced DIAD model is superior to the SSEV model, dynamic Smagorinsky model, and dynamic mixed model, which predicts a variety of statistics and instantaneous spatial structures of turbulence much closer to those of filtered DNS data without significantly increasing the computational cost. The types of explicit filters, local spatial averaging methods, and initial conditions do not significantly affect the accuracy of DIAD models. We further successfully apply DIAD models to the homogeneous shear turbulence. These results illustrate that the current SSEV-enhanced DIAD approach is promising in the development of advanced SGS models in the LES of turbulence.

Development and validation of the MAVR-TA code for analyzing the release and transport of fission products during a severe accident at a VVER NPP. Part 2 – Modelling of the fission products transport in the primary circuit and inside the containment

This paper provides information on the models of the MAVR-TA code, associated with modeling of the fission products transport in the primary circuit and inside the containment. The paper provides information on the system of the equations which is solved to describe the fission products transport in the primary circuit and inside the containment. The velocity equations for 6 deposition processes (sedimentation, thermophoresis, diffusiophoresis, Brownian diffusion, turbulent diffusion and turbulent impaction) and 4 agglomeration processes (Brownian agglomeration, gravitational agglomeration, turbulent shear and inertial agglomerations) are provided. This paper also provides information about MAVR-TA code validation for MARVIKEN ATT-2b experiment and FALCON ISP-1 and ISP-2 experiments for the primary circuit and MAVR-TA code validation for PHEBUS-FP and VANAM-M3 experiments for the containment.

Statistical analysis of wind resource and energy potential assessment of Quaidabad site, Sindh Pakistan

Purpose Pakistan is an energy starving country that needs continuous supply of energy to keep up its economic speed. The aim of this paper is to assess the wind resource and energy potential of Quaidabad site for minimizing the dependence on fuels and improving the environment. Design/methodology/approach The Quaidabad site wind shear coefficient and turbulence intensity factor are investigated. The two-parameter k and c Weibull distribution function is used to analyze the wind speed of site. The standard deviation of the site is also assessed for a period of a year. The wind power density and energy density are assessed for a period of a year. The economic assessment of energy/kWh is investigated for selection of appropriate wind turbine. Findings The mean wind shear coefficient was observed to be 0.2719, 0.2191 and 0.1698 at 20, 40 and 60 m, respectively, for a period of a year. The mean wind speed is found to be 2.961, 3.563, 3.907 and 4.099 m/s at 20, 40, 60 and 80 m, respectively. The mean values of k parameters were observed to be 1.563, 2.092, 2.434 and 2.576 at 20, 40, 60 and 80 m, respectively, for a period of a year. The mean values of c m/s parameter were found to be 3.341, 4.020, 4.408 and 4.625 m/s at 20, 40, 60 and 80 m, respectively, for a period of a year. The major portion of values of standard deviation was found to be in between 0.1 and 2.00 at 20, 40, 60 and 80 m. The wind power density (W/m2) sum total values were observed to be 351, 597, 792 and 923 W/m2 at 20, 40, 60 and 80 m, respectively, for a period of a year. The mean coefficient of variation was found to be 0.161, 0.130, 0.115 and 0.105 at 20, 40, 60 and 80 m, respectively. The sum total energy density was observed to be 1,157, 2,156, 2,970 and 3,778 kWh/m2 at 20, 40, 60 and 80 m, respectively. The economic assessment is showing that wind turbine E has the minimum cost US$0.049/kWh. Originality/value The Quaidabad site is suitable for installing the utility wind turbines for energy generation at the lowest cost.

Bubble refinement by non-invasive rotating flow

Gas–liquid flow widely exists in industrial processes. Bubble refinement is of importance because smaller bubbles lead to higher efficiency of the gas–liquid interaction. Here, the novel rotating flow is designed for bubble refinement without using invasive parts. The drag force along the flow direction and the additional shear-lift force applied on the mother bubble allow it to detach from the orifice more easily with smaller size. In addition, the non-invasive rotating flow generates a large velocity gradient in both the shear and normal directions, resulting in turbulent shear and normal stress, causing the rising mother bubbles to break up in either the shear or normal direction. As a result, the number of bubbles increases to 408 compared to 9 under the static condition. Approximately 50% of the bubbles in the liquid are less than 3.60 mm in size and the Sauter mean bubble diameter is reduced from 10.45 to 4.77 mm, a decrease of 54.41%. The bubble refinement mechanism in the non-invasive rotating flow applies to other occasions where no invasive parts are needed.

Effect of overlying water pH, temperature, and hydraulic disturbance on heavy metal and nutrient release from drinking water reservoir sediments.

How environmental factors impact the release of pollutants from sediment is critical to ensure the safety of drinking water, especially when the seasons change. Here, we investigated the effect of water pH, temperature, and hydraulic disturbance on the release of heavy metals and nutrients from the sediment of drinking water reservoir. The results show that lower initial water pH promoted the Zn release, while low temperature enhanced the Mn flux after 15days. Meanwhile, continuous disturbance caused more metals releasing from sediment than intermittent disturbance due to greater shear stress and turbulence effect. However, intermittent high-speed disturbance greatly altered the dynamic release of Zn from L-shaped curve to U-shape in water column. Moreover, lower water pH caused higher ammonium in water but lower nitrate since H+ restrained the nitrification. Yet, higher temperature inhibited the release of ammonium from sediment, which might relate to the accelerated mineralization of organic nitrogen and elevated dissolved oxygen caused by the algae growth. Notably, hydraulic disturbance with various intensity and duration greatly influenced the fluxes of various species of nitrogen and soluble phosphate in water column, because the disturbance facilitated the nitrogen and phosphorus exchanges between sediment-water and water-air interfaces. PRACTITIONER POINTS: Lower water pH induced Zn release, while low temperature gradually enhanced Mn level. More metals were released from sediment under continuous disturbance than intermittent disturbance. Lower water pH caused higher ammonium nitrogen in water but lower nitrate nitrogen. Higher temperature inhibited the release of ammonium nitrogen from sediment. Hydraulic disturbance greatly changed the release of different species of nitrogen and soluble phosphate from sediment.