Wake Parameters Research Articles

Studying the Wake of an Island in a Macro-Tidal Estuary

Tidal flow can generate unsteady wakes, large eddies, and recirculation zones in the lee or around complex natural and artificial obstructions, such as islands, headlands, or harbours. It is essential to understand the flow patterns around such structures given the potential impacts they can have on sedimentation, the marine environment, ecology, and anthropogenic activities. In this paper, the wake around an island in a macro-tidal environment has been studied using a widely used hydro-environmental model, Telemac-2D. Current data collected using moored acoustic Doppler current profilers (ADCPs) were used to validate and refine the Telemac-2D model. Four different turbulence models and several different solver options for the k- ε model were tested in this study to assess which representation could best replicate the hydrodynamics. The classic k- ε model with the solver of conjugate residual was the most suitable method to simulate the wake in the lee of the island. The model results showed good correlation with measured data. The island wake parameter used to predict the wake behaviour and its predictions matched the model results for different tidal conditions, suggesting that the island wake parameter could be used to predict the wake behind obstacles in macro-tidal environments. The model predictions showed the development of a wake is similar between ebb and flood tides in the neap tide while showing more difference in spring tide. With the increase of velocity in the neap tide, two side-by-side vortices will appear and then changing to stable Karman Vortex Street. During the ebb phase of spring tide, the wake will develop from a stable vortex to an unstable Karman Vortex Street, while the wake remained stable with two vortices during an flood tide.

Convective Heat Transfer and Entropy Generation Around a Sphere Within Cuboidal Enclosure

The intricate three-dimensional natural convection and entropy generation of a flow between cuboidal enclosure and a spherical surface is numerically examined in this study. The sphere is maintained hot and centrally located in cubical enclosure with four cooled walls, whereas top and bottom walls are perfectly insulated. The effects of inner shape, Rayleigh numbers, and inclination angles on fluid flow and heat transfer characteristics are analyzed in detail for Rayleigh numbers ranging from to and a tilted angle of the enclosure varying from 0 to 90°. The working fluid is air so that the Prandtl number equates to 0.71. The developed mathematical model is governed by the coupled equations of continuity, momentum, and energy and is solved by a finite volume method. Based on numerical results, two correlation expressions for predicting average Nusselt number of lateral walls of the cubical enclosure and the inner sphere are proposed as a function of Rayleigh number and inclination angle under different wake parameters. By comparing inner spherical shape results with that of cylindrical shape, it can be inferred that using a spherical shape provides the highest thermal performance for heat transfer. Moreover, this comparison reveals that the inner spherical shape decelerates the unsteadiness for the considered inclinations. Results indicate also that the optimal average heat transfer rate is obtained for extreme Rayleigh number, , and an inclination of 90° for both cases of the inner sphere and lateral walls of the cuboidal enclosure. The Bejan number and total entropy generation are found to be increased by increasing the inclination angle for the considered Rayleigh numbers. Maximum local entropy generation due to heat transfer and that due to fluid friction decrease gradually by increasing the inclination angle. The results of this investigation find extensive array of applications in several engineering devices, which will be mentioned in the paper content.

THE EFFECT OF LEEWAY ANGLE ON THE PROPELLER PERFORMANCE

One of the aspects influencing the performance of wind assisted vessels is the effect of leeway (drift) angle on the propeller performance. It is known that due to leeway the delivered propeller power and propulsive efficiency can vary significantly from the straight sailing condition. This effect of leeway angle is studied using a combination of viscous flow calculations and captive model tests for one twin screw and three single screw vessels. It is observed that the changes in mean axial velocity and pre-swirl rotation in the wakefield due to a combination of leeway angle and propeller suction are sufficient to describe the trends observed in captive model tests. This knowledge is used in a proposed prediction method to model the changes in propeller thrust and torque due to leeway angle at the design stage. The prediction model combined with a fit of the average wake parameters for the studied vessel types is finally used the show the trends in propulsive efficiency and delivered propeller power at constant propeller rotation rate and ship speed for small leeway angles.

A new analytical model for dip modified velocity distribution in fully developed turbulent open channel flow

This paper presents a new analytical model to predict the streamwise time-averaged velocity profile affected by the dip phenomenon in open channel flows. The novel approach of the present study is that the Finley wake law has been used instead of Coles’ wake law for the outer layer. To validate the new analytical model, six high quality experiments were conducted in a hydraulically rough bed open channel flow by considering variations of aspect ratio, defined as the ratio of the width of the channel to the depth of flow, from 2 to 4. In these controlled experiments, the time-averaged velocities were measured using a Nortek Vectrino-plus acoustic Doppler velocimeter. In addition, 14 sets of available experimental data, including five field experiments conducted across the globe were also used to test the performance of the proposed model. The proposed model, the Finley-dip-modified-log-wake law (FDMLWL), was used to develop a semiempirical equation to compute the dip position as a function of the dip correction factor and the wake parameter. In addition, using the experimental data and FDMLWL, an empirical equation was developed to compute the dip correction factor for hydraulically smooth open channel flows. The comparison of the FDMLWL model with the experimental data belonging to hydraulically smooth, transition, and rough regimes has consistently indicated better representation of the velocity dip phenomenon. The FDMLWL model has also been compared with other analytical models available in the literature and the superior performance of the proposed model is further observed. Finally, based on the satisfactory validation between experimental data and FDMLWL, it is inferred that the proposed model is better suited for modeling zero velocity gradient at the boundary layer edge, as in open channel flows with dip phenomenon.

SAT-325 RELATIONSHIP AND PATTERN BETWEEN AMBULATORY BLOOD PRESSURE MONITORING PARAMETERS AND ESTIMATED GLOMERULAR FILTRATION RATE IN CHILDREN WITH GLOMERULAR AND NON-GLOMERULAR CONDITIONS

Ambulatory blood pressure monitoring (ABPM) is an important tool for evaluation of blood pressure (BP) among high risk children including those with renal diseases. Our study aimed to describe and compare the ABPM parameters between children with glomerular and non-glomerular renal conditions, and explore the relationship between the various ABPM parameters and the estimated glomerular filtration (eGFR). We performed a cross-sectional review of the office BP records and ABPM reports of children followed up in the paediatric nephrology clinic of Queen Elizabeth Hospital, Hong Kong from year 2013-2017. ABPM reports with <70% success rate were excluded. Among subjects with ≥1 ABPM reports, only the first available report was included for analysis. The renal diagnosis was categorized into glomerular diseases and non-glomerular disease comprising congenital anomalies of kidney and urinary tract (CAKUT), cystic kidney diseases, renovascular hypertension, neurogenic bladder / bladder dysfunction and other conditions. Altogether there were 67 patients included in the final analysis. The median age (interquartile range) of the cohort was 14.5 (5.4) years and the median BMI was 19.3 (5.0) kg/m2. Glomerular diseases accounted for 23.9% of all renal conditions and the median eGFR of the whole cohort was 96.3 (34.6) ml/min/1.73m (Table 1)2. There were 62.7% of subjects having ABPM hypertension (ABPM systolic or diastolic hypertension in either wake or sleep periods), and 40.3% of subjects were non-dippers (nocturnal dipping <10%). Office BP hypertension was found in 35.9% of subjects and 25% of subjects had masked hypertension. Only 16.7% of subjects with ABPM hypertension were receiving anti-hypertensive medications. The baseline characteristics of subjects with glomerular and non-glomerular diseases showed no significant difference, and the ABPM parameters in both wake and sleep periods were comparable between the two groups (Table 2). Most subjects with non-glomerular diagnoses had no hypertension (35.4%), whereas ambulatory hypertension (both office BP hypertension and ABPM hypertension) was the commonest BP category (37.5%) among those with glomerular conditions (p=0.934) (Figure 1). The median eGFR of children with glomerular and non-glomerular diseases showed no significant difference (p=0.538). All systolic or diastolic BP indices and BP loads in wake and sleep periods showed a significantly inverse relationship with the eGFR among children with glomerular diseases (Table 3). The relationship was stronger for glomerular than non-glomerular conditions. A lower eGFR among children with glomerular disease could be observed in those having wake or sleep ABPM hypertension (systolic or diastolic) or ABPM hypertension, as well as non-dippers. And a significant difference could be found among those with wake period diastolic hypertension (p=0.036) and sleep period systolic hypertension (p=0.044). Masked hypertension and non-dippers were common among children with renal conditions and most children with ABPM hypertension were not receiving anti-hypertensives. Both the wake and sleep period ABPM parameters demonstrated a negative correlation with eGFR among children having glomerular diseases at a relatively normal eGFR. The results indicated that regular ABPM should be performed for children with renal conditions, even without chronic kidney disease.

Engineering Wake Induction Model For Axisymmetric Multi-Kite Systems

Multi-kite airborne wind energy systems (MAWES) fly two or more kites in a high-altitude orbit that allows a main tether to unroll a generator. An engineering wake induction model could simplify the (axisymmetric) aerodynamics of such an unsteady actuator-annulus with variable thrust-coefficient, flight-radius, and downwind-direction apparent velocity, in comparison to high-fidelity wake models. To the authors’ knowledge, existing engineering models do not predict the influence of variable flight radius. The goal of this paper is to synthesize a MAWES engineering model, a closed-form function approximating the axial induction factor ã, specifically at the kite mid-span, using linearized wake parameters, as available from a dynamics solver. A vortex tube model is used to construct a plausible approximation of the induction, which is then heavily simplified for computation tractability while retaining important flow physics.

Influence of acoustic type waves on the vortex wake behind a wing in the supersonic flow

In this paper an investigation of an acoustic type waves influence on a wingtip vortex wake parameters was performed in a supersonic flow. The supersonic flow around a straight wing with sharp leading and trailing edges was considered at an attack angle of 10 degrees at Mach number of incoming flow M = 2.Perturbations were introduced into a steady state stream in the form of monochromatic plane waves with small amplitude. Numerical simulations were carried out at the Keldysh Institute of Applied Mathematics RAS using the parallel algorithm for turbulent flow simulation. For the numerical studies an approach based on the URANS method with using the SA turbulence model was applied. Numerical simulations were carried out on the supercomputing system K-60.Numerical data were obtained in the area exceeding 30 wing chords downstreamfrom a wing axis. A numerical data on the pulsation of gasdynamic parameters in the vortex wake influenced by disturbance are obtained, in particular, frequencies and disturbance ranges on the wingtip vortex axis are investigated depending on a distance from the wing - vortex generator.

Spike–Wave Discharges and Sleep–Wake States during Circadian Desynchronization: No Effects of Agomelatine upon Re-Entrainment

Rapid changes in the light–dark cycle cause circadian desynchronization between rhythms of spike–wave discharges (SWDs) and motor activity in genetic epileptic rats, and this is accompanied by an increase in epileptic activity. Given the close relationship between absence seizures and sleep–wake states, the present study assessed firstly a putative relationship between vigilance rhythms and SWDs during re-synchronization, and secondly sleep–wake patterns responsible for increased epileptic activity. Lastly, in a view of existing evidence that melatonin and its agonists accelerate re-synchronization, the effects of different doses of agomelatine upon the speed of re-synchronization of different sleep–wake states and SWDs were investigated.Simultaneous electroencephalographic and electromyographic recordings were made in symptomatic WAG/Rij rats, before, during and 10 days following an 8 h light phase delay. Agomelatine was orally administered acutely and sub-chronically, during 10 post-shift days.The magnitude of the advance after the shift and the speed of re-synchronization were specific for various rhythms. Most prominent change was the increase in REM sleep duration during the dark phase. A post-shift increase in passive wakefulness and a reduction in deep slow-wave sleep coincided with an aggravation of SWDs during the light phase. Agomelatine showed neither an effect on sleep–wake parameters and SWDs, nor affected re-synchronization.The same speed of re-synchronization of SWDs and light slow-wave sleep suggests that both are controlled by a common circadian mechanism. The redistribution of SWDs and their increase in the light phase after the shift may be of importance for patients with absence epilepsy planning long trans-meridian flight across time zones.

Wake Management in Wind Farms: An Adaptive Control Approach

Advanced wind measuring systems like Light Detection and Ranging (LiDAR) is useful for wake management in wind farms. However, due to uncertainty in estimating the parameters involved, adaptive control of wake center is needed for a wind farm layout. LiDAR is used to track the wake center trajectory so as to perform wake control simulations, and the estimated effective wind speed is used to model wind farms in the form of transfer functions. A wake management strategy is proposed for multi-wind turbine system where the effect of upstream turbines is modeled in form of effective wind speed deficit on a downstream wind turbine. The uncertainties in the wake center model are handled by an adaptive PI controller which steers wake center to desired value. Yaw angle of upstream wind turbines is varied in order to redirect the wake and several performance parameters such as effective wind speed, velocity deficit and effective turbulence are evaluated for an effective assessment of the approach. The major contributions of this manuscript include transfer function based methodology where the wake center is estimated and controlled using LiDAR simulations at the downwind turbine and are validated for a 2-turbine and 5-turbine wind farm layouts.

Later Chronotype Is Associated with Higher Alcohol Consumption and More Adverse Childhood Experiences in Young Healthy Women.

This study aimed at examining potential associations of mid sleep timing (chronotype) and social jetlag with intake of alcohol and caffeine, depressive symptoms, and body mass index (BMI) in a sample of healthy young women. Furthermore, it was explored whether these behavioral sleep–wake parameters are associated with adverse childhood experiences (ACEs). In total, 146 women (21.7 ± 1.7 years) took part in a two-week assessment on daily consumption of alcohol and caffeine. They completed questionnaires on ACEs, chronotype, sleep quality and depressive symptoms. Partial correlations and Chi-Square tests were calculated to assess the relationships between the assessed variables. Results show an association on a trend level for chronotype (r = 0.162, p = 0.053) and a significant association for social jetlag (r = 0.169, p = 0.044) with average alcohol intake. Furthermore, participants with above-median ACEs were more likely to be late chronotypes compared to the below-median group (X2(2) = 6.595, p = 0.037). We could replicate the association among late chronotype, social jetlag and higher alcohol consumption in a sample of healthy, young women. Furthermore, our results suggest a relationship between ACEs and chronotype. Although it can be hypothesized that it is rather ACEs that have an impact on chronotype, further research is needed to explore this relationship more and to shed more light on the direction of the association between chronotype and ACEs as well as on underlying mechanisms and possible mediators.

Potential and limitations of scale resolved simulations for ship hydrodynamics applications

ABSTRACTThe paper gives an overview of experience gathered by the authors in development and application of hybrid URANS/LES methods for the solution of ship hydrodynamic problems. Difficulties arising at the interface between URANS and LES are discussed and illustrated for a channel flow benchmark. A hybrid model developed by the authors is described. It was shown that pure LES has advantages over hybrid models provided a sufficient resolution can be attained for a given Re number. Advantages of hybrid models over RANS-based ones is demonstrated for the determination of wake parameters behind models of full bottomed ships JBC and KVLCC2. Difficulties with prediction of the ship resistance by hybrid methods are discussed.

Development of a LIDAR array to study and classify wakes at the U.S. Department of Energy (DOE)/Sandia National Laboratories Scaled Wind Farm Technology (SWiFT) facility

Wind turbine wake has the wind speed deficit and the increased turbulent flow to the downstream turbines as signatures. Various experiments and simulations have been performed over the years to investigate the wake parameters; however, a statistical characterization of wake states is still to be uncovered. An innovative wake measurement approach that uses five ground-based Spidar Light Detection and Ranging (LIDAR) has been developed in partnership with Texas Tech University (TTU), Sandia National Laboratories, and Pentalum Technologies to develop, test, and validate a system and methodology that enables the capture of statistically significant wake dynamics in real atmospheric conditions. This article will discuss the potential of this new direct detection remote sensing equipment for studying the wake states as well as report the validation process of the LIDAR and the feasibility of continuing to pursue the primary purpose of the initiative.

Repeated chemotherapy cycles produced progressively worse and enduring impairments in the sleep–wake profile of hospitalized breast cancer patients

ABSTRACT Cross-sectional studies, conducted previously, reported disruption of the sleep–wake rhythms of cancer patients on chemotherapy. Although few studies highlighted the effect of hospitalization on sleep, no data were obtained on the effects of longitudinal repeated chronotherapy cycles on sleep pattern of cancer patients. In this study, using the two-factor repeated-measures design, we attempted to assess longitudinally the quality and pattern in sleep–wake behavior of breast cancer in- and outpatients, who received multiple cycles of chemotherapy. We randomly selected the patients from the Regional Cancer Center, Dr. B.R. Ambedkar Memorial Hospital, Raipur, India. We used wrist-worn actigraphs to record the sleep–wake pattern both objectively and subjectively. Additionally, we administered Pittsburgh Sleep Quality Index questionnaire to each patient. Results revealed statistically significant effects of chemotherapy with and without hospitalization mostly on all objective [total sleep time, sleep onset latency, wake after sleep onset, fragmentation index, and sleep efficiency (SE)] and subjective [duration of sleep, sleep disturbance, sleep latency, daytime dysfunction due to sleepiness, SE, and overall sleep quality] sleep–wake parameters of cancer patients. Cancer patients, who received repeated chemotherapy administration followed by hospitalization on each occasion, experienced severely impaired sleep–wake cycle as compared with those who went home after receiving chemotherapy.

Axial meso-scale modeling of gas-liquid-solid fluidized beds

The meso-scale theory, based on the energy minimization multi-scale principle, has recently inspired the accurate modeling of the multi-phase flow. In this study, an axial meso-scale flow model for the gas-liquid-solid fluidized bed is established and verified by the literature models and data. Compared with the reported axial models, this model predicts the axial distribution of all three-phase hydrodynamic parameters with fewer empirical corrections. Predictions of the present model show that the operation conditions and physical properties of solid particles obviously affect the flow behaviors of phases, such as the slip velocity, entrainment of solid particles, wake shedding parameters. Solid particles entrained by bubble wake determine the formation of axial distribution in the gas-liquid-solid fluidized bed. Region with the axial structure is the transition section, length of which depends on the entrainment of solid particles. Furthermore, behaviors of the gas bubbles and the solid particles are mutually influential.

Spatio-temporal stability analysis of linear arrays of 2D density stratified wakes and jets

This paper investigates the spatio-temporal stability characteristics of multiple shear flow elements (wakes or jets) with density stratification. While the stability of single jets or wakes has been considered extensively, many applications exist where these canonical flow fields are aligned in multi-element configurations. A fundamental question is the relationship between the stability characteristics of a single element and the larger system. More fundamentally, this question involves the interaction of multiple regions of vorticity concentration and how they modify a system’s absolute stability as well as the manner in which density gradients influence the way these different regions of concentrated vorticity interact. This study presents a generalization of Yu and Monkewitz’s analysis [“The effect of nonuniform density on the absolute instability of two-dimensional inertial jets and wakes,” Phys. Fluids A 2, 1175 (1990)] for multiple jets and wakes, explicitly considering n = 2, 3, 4, and infinity elements. The velocity and density base profiles are parameterized by the density ratio, S, velocity shear ratio, λ, and the wake spatial separation parameter, L/D. The results show that the maximum absolute growth rate (ω0,i) exhibits a non-monotonic dependence on L/D. In addition, the most absolutely unstable mode switches between system-sinuous and system-varicose as the spatial separation parameter is varied, in agreement with prior experiments [I. Peschard and P. Le Gal, “Coupled wakes of cylinders,” Phys. Rev. Lett. 77, 3122 (1996)]. This transition in symmetry, as well as the specific L/D value at which a given mode dominates, can be approximately predicted using the resonant wave interaction model from Juniper et al. [“The effect of confinement on the stability of two-dimensional shear flows,” J. Fluid Mech. 565, 171 (2006)]. Furthermore, there are two distinct L/D regimes: a “near-wake regime” (L/D &amp;lt; ∼3) and a “far-wake regime.” In the near-wake regime, the system stability is a function of the number of elements, n, while in the far-wake regime, it is only the element spacing, not the number of elements that influences ω0,i.

Impact of atmospheric stability on X-band and C-band synthetic aperture radar imagery of offshore windpark wakes

C-band and X-band Synthetic Aperture Radar (SAR) data acquired by the Sentinel-1 and TerraSAR-X satellites are used to study atmospheric wakes behind offshore wind parks in the German Bight. A particular focus is on the impact of atmospheric stability on wake parameters like the wake length. Stability parameters are estimated from measurements taken at the FINO-1 observation platform. Based on a data set covering different seasons and concentrating on the first German offshore wind park Alpha Ventus (AV), it is shown that in this area stable atmospheric conditions favour longer wakes. This is first demonstrated for situations, where the wake behind AV was unperturbed by other neighbor wind parks. In this case, wakes of more than 30 km length are observed. In a second step, the more complicated situation with wake superposition from different neighboring wind parks is analysed. It is shown that in this case, the merged wakes can extend to more than 70 km downstream.The analysis is challenged by two factors. First of all, the FINO-1 platform is within the wind farm wakes for a certain range of wind directions. This means stability estimates for the upstream conditions are not straightforward to obtain in these conditions. The second complication is associated with an apparent increase in the radar cross section downstream of wind parks observed on many SAR scenes, typically within the first 10 km downstream the wind park. A semi-empirical model is proposed to explain this effect by an increased downward momentum flux associated with increased turbulence generated by the wind park. Applying numerical inversion methods, a couple of typical downstream wind speed profiles are reproduced with this model based on SAR derived estimates of the friction velocity.

Correlates of disrupted sleep–wake variables in patients with advanced cancer

ObjectivesHigh rates of sleep difficulties have been found in patients with advanced cancer. However, not much is known about factors that are associated with sleep impairments in this population and...

The Influence of Different Wake Profiles on Losses in a Low Pressure Turbine Cascade

Large eddy simulations were carried out in order to investigate the influence of unsteady incoming wakes with different profiles on the loss mechanisms of the high lift T106Alinear low-pressure turbine (LPT) cascade. Bars placed upstream of the LPT blade were set into rotation around their axis, thus generating circulation, as well as asymmetrical wake profiles. Three different rotation rates were simulated, yielding different wake parameters that were then compared to an actual turbine blade wake profile. Whereas the commonly-used non-rotating bars generated wakes with turbulent kinetic energy levels several times higher than that of an actual blade wake, the case with counter-clockwise rotation led to more rapid wake mixing. All three wakes were able to trigger boundary layer transition and thus intermittently prevent separation on the suction surface. However, the weaker the wakes, the larger and longer lasting the separation bubbles became, and an increase in profile losses could be observed. Interestingly, the configuration with the weakest wake and the largest separation bubble resulted in a reduction of the overall LPT loss.

Improved version of LeMoS hybrid model for ambiguous grid densities

Application of the LeMoS hybrid (LH) URANS/LES method for the wake parameters prediction is considered. The wake fraction coefficient is calculated for inland ship model M1926 under shallow water conditions and compared to results of PIV measurements. It was shown that due to lack of the resolved turbulence at the interface between LES and RANS zones the artificial grid induced separations can occur. In order to overcome this drawback, a shielding function is introduced into LH model. The new version of the model is compared to the original one, RANS k−ω SST and SST-IDDES models. It is demonstrated that the proposed modification is robust and capable of wake prediction with satisfactory accuracy.

Dominant features in three-dimensional turbulence structure: comparison of non-uniform accelerating and decelerating flows

The results are presented from an experimental study to investigate three-dimensional turbulence structure profiles, including turbulence intensity and Reynolds stress, of different non-uniform open channel flows over smooth bed in subcritical flow regime. In the analysis, the uniform flow profiles have been used to compare with those of the non-uniform flows to investigate their time-averaged spatial flow turbulence structure characteristics. The measured non-uniform velocity profiles are used to verify the von Karman constant κ and to estimate sets of log-law integration constant Br and wake parameter П, where their findings are also compared with values from previous studies. From κ, Br and П findings, it has been found that the log-wake law can sufficiently represent the non-uniform flow in its non-modified form, and all κ, Br and П follow universal rules for different bed roughness conditions. The non-uniform flow experiments also show that both the turbulence intensity and Reynolds stress are governed well by exponential pressure gradient parameter β equations. Their exponential constants are described by quadratic functions in the investigated β range. Through this experimental study, it has been observed that the decelerating flow shows higher empirical constants, in both the turbulence intensity and Reynolds stress compared to the accelerating flow. The decelerating flow also has stronger dominance to determine the flow non-uniformity, because it presents higher Reynolds stress profile than uniform flow, whereas the accelerating flow does not.