Regional Flow Research Articles

Hydrogeological analysis of topography-driven groundwater flow in a low temperature geothermal aquifer system in the Julian Alps, Slovenia

Abstract Groundwater flow and heat distribution was investigated in the regional karstic-fissured aquifer-aquitard system near Lake Bled in the Slovenian, eastern Julian Alps. The area features thermal springs with temperatures of 19–23 °C which are exploited by abstraction wells. The occurrence of low-temperature geothermal systems, which are common in the Alps, are associated with specific hydrogeological conditions, such as vertical hydraulic connectivity between different geological formations, relatively large elevation differences along flow paths, and the concentrated upwelling of geothermal water to the surface. The occurrence of the low-temperature geothermal field is explained by the presence of a hydraulically conductive fault along with a regional groundwater flow pattern that supports deep groundwater circulation. Hydraulic measurements and temperature data were collected from springs and wells in the area to support the analysis of flow patterns, together with the construction of a basin-scale 2D numerical flow and heat transport simulation. The diverse topographic and geological conditions result in a multi-scale groundwater flow system. The discharge of thermal waters in the Lake Bled area is a consequence of the upwelling of deep groundwater induced by a combination of the ~ 650 m difference in hydraulic head and hydrogeological heterogeneity and anisotropy, related to faulting of the geological formations. In addition, individual flow subsystems were found to significantly affect the natural heat distribution and travel times within the basin-scale system. The study highlights the combination of a basin scale approach taking into consideration local to regional-scale heterogeneities and faults in order to better understand the hydrogeological behaviour of Alpine groundwater systems.

Role of strike-slip faults on the regional groundwater flow in the complex aquifer system of Lake Suwa watershed, Japan

Role of strike-slip faults on the regional groundwater flow in the complex aquifer system of Lake Suwa watershed, Japan

Flow and heat transfer characteristics of a squealer tip with bent rail in turbine blades

Squealer tip is an effective method for reducing heat transfer and leakage losses of blade tips in gas turbines and is currently being extensively researched and developed. In this study, the squealer tip has been innovatively developed by introducing bent rails, and three types of squealer structures with bent rails were proposed: the bent pressure-side rail scheme (Case_P), the bent suction-side rail scheme (Case_S), and the bent double-side rail scheme (Case_PS). This study first compared the performance of the proposed novel schemes with the traditional squealer tip scheme with vertical rails (Baseline) in terms of tip heat transfer and flow control by analyzing parameters such as the tip heat transfer coefficient (h), leakage flow rate (LFR), and total pressure loss (Cpt) under fixed bending values (S). Subsequently, the effects of different bending values (S) on the three novel schemes were investigated. The results show that, in terms of heat transfer, both Case_P and Case_S can effectively reduce the tip h, but their mechanisms are entirely different. Case_P primarily relies on the increasing separation bubble size at pressure-side rail edge and gradually expanded low-energy flow region in the pressure-side rail corner. In contrast, in Case_S, it is mainly because the cavity flow enters the suction-side gap more smoothly due to the bent suction-side rail. In terms of aerodynamics, the bent pressure-side rail of Case_P significantly inhibits the entering velocity of leakage flow, thereby reducing the LFR and Cpt; however, Case_S causes the LFR to increase. In Case_PS, the heat transfer and leakage phenomena resemble a combination of Case_P and Case_S. With the increase in S, the tip h in the three schemes all decreases, and the tip heat transfer in Case_PS is more comprehensively reduced because it incorporates all the flow factors that reduce h from the other two schemes. In Case_PS, the rail types that both hinder and increase LFR coexist, resulting in the LFR remaining relatively stable with varied S.

Strong turbulent flow in the subauroral region in the Antarctic can deteriorate satellite-based navigation signals

In the subauroral zone at the boundary of the auroral oval in the evening and night hours during geomagnetic disturbances, a narrow (about 1°–2°) and extended structure (several hours in longitude) is formed. It is known as a polarization jet (PJ) or the subauroral ion drift (SAID). The PJ/SAID is a fast westward ion drift and is one of the main signatures of a geomagnetic disturbance in the subauroral ionosphere at the altitudes of the F-layer, when the geomagnetic AE index reaches more than 500 nT. Plasma speed in the PJ/SAID can reach several kilometres per second, and the size of plasma irregularities inside it can reach scales from tens of meters to several hundred meters. Such high velocities and structured plasma can affect trans-ionospheric radio waves and lead to scintillations in the received signal. We show that at the moment of auroral activity intensification, an increase in the magnitude of phase scintillation index (σϕ) as well as loss of satellite signals lock were observed in the region of the PJ/SAID equatorward of the auroral oval over Dronning Maud Land (Queen Maud Land) in Antarctica. We find that fluctuations inside the PJ/SAID can lead to serious deterioration of radio communication or navigational services. We emphasize the importance of considering the geometry of the beam passing from the GNSS satellite to the receiver on the ground. We highlight the mutual contribution of the PJ/SAID and the diffuse aurora boundary, which are almost impossible to separate in practice. Our results demonstrate the importance of considering the subauroral zone, where very dynamic plasma formations can occur with a strong flow and various-scale irregularities inside that lead to serious interference in satellite communications.

Microplastics Settling in Turbid Water: Impacts of Sediments-Induced Flow Patterns on Particle Deposition Rates.

When microplastics (MPs) enter water bodies, they undergo various transport processes, including sedimentation, which can be influenced by factors such as particle size, density, and interactions with other particles. Surface waters contain suspended natural particles (e.g., clay and silt), which may impact MP settling rates. Here, we investigated how the presence of suspended sediments (SS) influenced the deposition patterns and rates of MPs in turbid waters. We systematically analyzed the settling velocities of particles, including different MP sizes and SS concentrations, in a plexiglass column with a camera array. For each experimental variant, we collected data on thousands of individual MPs, strengthening the statistical analysis of the particles' velocities. Simultaneous measurements of the SS flow and MPs trajectories revealed that the SS induced complex flow patterns, with MPs spending more time in downwelling flow regions, thereby accelerating MPs sedimentation. This effect was more pronounced when SS were aggregated. Additionally, we found that smaller MP fragments were more affected by the fluctuations than spheres or larger fragments. Collectively, our results provide valuable data for future MP fate models and help to understand the sedimentation processes of MPs in natural waters, which is crucial for assessing their environmental transport and impact.

Features of Supersonic Flow Around a Blunt Body in the Area of Junction with a Flat Surface

This work studies the influence of a growing boundary layer on the process of supersonic flow around an aerodynamic body. The task is to select and implement in an experiment the parameters of a supersonic flow and to study the flow pattern near the surface of an aerodynamic body at different viscosity values for the incoming flow. Visualization of the shock wave configuration in front of the body and studying the change in the pressure field in the flow region under these conditions is the main goal of this work. The experiment was carried out on an experimental stand created on the basis of a shock tube. The aerodynamic body under study (a semi-cylinder pointed along a circle or an ellipse) was placed in a supersonic nozzle. The model was clamped by lateral transparent walls, which were simultaneously a source of boundary layer growth and the viewing windows for visualizing the flow. For selected modes with Reynolds numbers from 8200 to 45,000, schlieren flow patterns and pressure distribution fields near the surface of the streamlined models and the plate of the growing boundary layer were obtained. The data show a complex, unsteady flow pattern realized near the model which was caused by the viscous-inviscid interaction of the boundary layer with the bow shock wave near the wall.

Competing pathways of intracranial aneurysm growth: linking regional growth distribution and hemodynamics.

The complex mix of factors, including hemodynamic forces and wall remodeling mechanisms, that drive intracranial aneurysm growth is unclear. This study focuses on the specific regions within aneurysm walls where growth occurs and their relationship to the prevalent hemodynamic conditions to reveal critical mechanisms leading to enlargement. The authors examined hemodynamic models of 67 longitudinally followed aneurysms, identifying 88 growth regions. These regions (of enlargement) were pinpointed through alignment and distance mapping between baseline and follow-up models. Aneurysm wall subdivisions were created based on saccular anatomy and flow-related characteristics, which were used to assess local hemodynamics. The distribution of growing regions across these subdivisions was then studied and stratified by aneurysm location and morphology to reveal distinct growth patterns. Statistical significance was evaluated using the Kruskal-Wallis and Mann-Whitney tests. Growth predominantly occurred in the body (p < 0.0001) of aneurysms, with anterior communicating artery (ACom) (p < 0.0001) and lateral (p = 0.002) aneurysms showing a significantly greater tendency for growth in this region. In comparison, middle cerebral artery (MCA) (p < 0.0001) and bifurcation (p = 0.0001) aneurysms demonstrated growth in both the dome and the body. Notable differences in growth distribution across saccular regions included ACom versus MCA (neck, p = 0.038), bifurcation versus lateral (neck, p = 0.008), and so forth. The central flow region saw the most growth (p < 0.0001); although not significant, ACom (p = 0.196) and lateral (p = 0.218) aneurysms showed a tendency for growth in inflow and central zones, while MCA (p = 0.001) and bifurcation (p < 0.0001) aneurysms were more likely to grow in the central flow region. Two primary mechanisms seem to influence aneurysm growth: high-flow impingement jets in the neck, body, and inflow zones leading to wall degeneration/thinning, mainly in ACom aneurysms; and slow, oscillatory flow conditions in the dome and central flow zones promoting wall remodeling/thickening, mainly in MCA aneurysms. This latter mechanism is also observed as secondary flows in ACom aneurysms. These findings emphasize the need to understand the distinct and sometimes concurrent mechanisms of aneurysm growth, advocating for targeted monitoring and interventions that mitigate rupture risks by considering the unique hemodynamic environments within different aneurysm regions and locations.

Three-dimensional electrical structure in the northwestern sector of the Sichuan-Yunnan diamond block

The Sichuan-Yunnan diamond block is a significant region of material flow from the Tibetan Plateau. However, its northwest electrical boundary remains undefined. Our study conducted a magnetotelluric profile from Chazha to Luomai across the geological boundary of the Sichuan-Yunnan block in its northwest sector. Using the nonlinear conjugate gradient three-dimensional inversion method, we obtained the deep electrical structure across the northern part of the block. Our findings reveal distinct segmental characteristics in the electrical structure along the profile. Marked by a high-resistivity zone along the Dedeng-Batang-Riyu fault, two high-conductivity layers exist in the upper-middle crust of the southwestern and central sections of the profile, at depths of 5–20 km and 10–30 km, respectively. Thus, our study suggests that the northwest boundary of the Sichuan-Yunnan diamond block, contrary to previous studies that considered it a transitional boundary, is located at the Dedeng-Batang-Riyu fault. Here, the boundary is a high-resistivity barrier, electrically isolating the Qiangtang block in the southwest from the Sichuan-Yunnan block in the northeast. The two significant high-conductivity zones in the upper-middle crust appear within the block’s interior, contrasting with previous assumptions of lower crustal flow.

Using hydrogeological data to characterise regional Chalk flow processes in East Kent

The Chalk of southern England is known to be a dual porosity - dual permeability porous medium, with a very low permeability and high porosity matrix. It has a fracture system providing the transmissivity and a low unconfined storage coefficient of up to two %. Conceptualisation of regional aquifers is carried out to support regional modelling studies. In such studies, observation well piezometry is of primary importance in understanding the hydrogeology of an area. While flow gauging provides an understanding of surface water responses, observation wells provide spatial detail of the groundwater response within each catchment. During review of the Environment Agency's East Kent Chalk groundwater model, geomorphological and hydrogeological data were used to characterise the area in two zones; the primary and secondary dipslopes, in the first part of this paper. The second part of the paper considers quality control and classification of the piezometry responses with respect to permanent and ephemeral Chalk streams and the Chalk escarpment. The third part of the paper looks at an analysis of lag between rainfall and recharge to the water table. This analysis can help to understand processes in the unsaturated zone and aid their incorporation into groundwater models.

Two-fluid flow of blood in a curved stenotic artery under pulsating condition.

The present article focuses on the analysis of the two-phase flow of blood via a stenosed artery under the influence of a pulsatile pressure gradient. The core and plasma regions of flow are modeled using the constitutive relations of Herschel-Bulkley and the Newtonian fluids, respectively. The problem is modeled in a cylindrical coordinate system. A modest stenosis assumption is used to simplify the non-dimensional governing equations of the flow issue. An explicit finite difference approach is used to solve the resultant nonlinear system of differential equations while accounting for the provided boundary conditions. After the necessary adjustments have been made to the crucial non-dimensional parameters, an analysis of the data behind the huge image, such as axial velocity, temperature field, concentration wall shear stress, flow rate, and flow impedance, is conducted. The current study shows that the curvature of blood vessels plays a significant role in influencing blood velocity. Specifically, a unit increase in the curvature radius results in a 24% rise in blood velocity.

Endothelial cells under disturbed flow release extracellular vesicles to promote inflammatory polarization of macrophages and accelerate atherosclerosis

BackgroundExtracellular vesicles (EVs) derived from endothelial cells (ECs) are increasingly recognized for their role in the initiation and progression of atherosclerosis. ECs experience varying degrees and types of blood flow depending on their specific arterial locations. In regions of disturbed flow, which are predominant sites for atherosclerotic plaque formation, the impact of disturbed flow on the secretion and function of ECs-derived EVs remains unclear. This study aims to assess the role of disturbed flow in the secretion of EVs from ECs and to evaluate their proatherogenic function.ResultsOur comprehensive experiments revealed that disturbed flow facilitated the secretion of ECs-derived EVs both in vivo and in vitro. Mechanistically, the MAPK pathway transduces mechanical cues from disturbed flow in ECs, leading to increased secretion of EVs. Pharmacological inhibition of the MAPK pathway reduced the secretion of EVs even under disturbed flow conditions. Interestingly, under disturbed flow stimulation, ECs-derived EVs promoted monocyte accumulation and enhanced their invasion of the endothelium. More important, these EVs initiated the inflammatory polarization of macrophages from the M2 to the M1 phenotype. However, the phenotypic switching of vascular smooth muscle cells was not affected by exposure to these EVs.ConclusionsTaken together, targeting the MAPK signaling pathway holds potential as a novel therapeutic strategy for inhibiting the secretion of EC-derived EVs and mitigating the inflammatory polarization of macrophages, ultimately ameliorating the progression of atherosclerosis.Graphical

Responses of Typical Riparian Vegetation to Annual Variation of River Flow in a Semi-Arid Climate Region: Case Study of China’s Xiliao River

Responses of Typical Riparian Vegetation to Annual Variation of River Flow in a Semi-Arid Climate Region: Case Study of China’s Xiliao River

Convective forces contribute to post‐traumatic degeneration after spinal cord injury

AbstractSpinal cord injury (SCI) initiates a complex cascade of chemical and biophysical phenomena that result in tissue swelling, progressive neural degeneration, and formation of a fluid‐filled cavity. Previous studies show fluid pressure above the spinal cord (supraspinal) is elevated for at least 3 days after injury and contributes to a phase of damage called secondary injury. Currently, it is unknown how fluid forces within the spinal cord itself (interstitial) are affected by SCI and if they contribute to secondary injury. We find spinal interstitial pressure increases from −3 mmHg in the naive cord to a peak of 13 mmHg at 3 days post‐injury (DPI) but relatively normalizes to 2 mmHg by 7 DPI. A computational fluid dynamics model predicts interstitial flow velocities up to 0.9 μm/s at 3 DPI, returning to near baseline by 7 DPI. By quantifying vascular leakage of Evans Blue dye after a cervical hemi‐contusion in rats, we confirm an increase in dye infiltration at 3 DPI compared to 7 DPI, suggestive of higher fluid velocities at the time of peak fluid pressure. In vivo expression of the apoptosis marker caspase‐3 is strongly correlated with regions of interstitial flow at 3 DPI, and exogenously enhancing interstitial flow exacerbates tissue damage. In vitro, we show overnight exposure of neuronal cells to low pathological shear stress (0.1 dynes/cm2) significantly reduces cell count and neurite length. Collectively, these results indicate that interstitial fluid flow and shear stress may play a detrimental role in post‐traumatic neural degeneration.

Optical Coherence Tomography Angiography in Patients With the Boston Keratoprosthesis Type 1.

To report on optical coherence tomography angiography (OCTA) in patients with a type 1 Boston keratoprosthesis (KPro) and determine its feasibility through assessment of imaging artifacts. KPro and non-KPro subjects were matched for age, gender, and glaucoma diagnosis. OCTA images of the peripapillary optic nerve were obtained, reviewed by 2 readers masked to the diagnosis for artifacts and usability, and used for microvascular measurements. KPro subjects (n = 18) had worse visual acuity than non-KPro (n = 36) subjects (LogMAR mean ± standard deviation 0.36 ± 0.30 vs. 0.07 ± 0.11, P < 0.001) and a greater proportion were monocular (56% vs. 3%, P < 0.001). OCTA from KPro eyes had more artifacts per scan than images from non-KPro eyes (4 ± 2 vs. 2 ± 2, P < 0.001). About 33% of KPro images were useable based on having image quality score above 40 and artifact in less than 10% of the peripapillary region. Worse visual acuity (odds ratio [OR] 0.01, 95% confidence interval [CI] 2 x 10-4-0.30, P = 0.02) and KPro (OR 0.19, 95% CI 0.05-0.63, P = 0.008) were associated with lowered likelihood of usability. Useable OCTA from 3 KPro eyes with glaucoma demonstrated microvascular defects in the inferior peripapillary region and lower vessel density and flow compared with 3 KPro eyes without glaucoma. This is the first study assessing OCTA in KPro patients and identified a higher incidence of artifacts that may be associated with the KPro optic. About 33% of KPro images were useable for microvascular measurements, supporting further OCTA research in this population to assess vascular pathology of glaucoma.

Numerical analysis on heat transfer enhancement of Al2O3 and CuO-water nanofluids in annular curved tubes

The present investigation presents numerically the thermo-hydraulic performance of annular curved tubes in the turbulent flow region. The three-dimensional (3D) computational fluid dynamic (CFD) model was developed by using a commercial ANSYS 14.5 package to get additional insights on the thermo-hydraulic performance on a level of detail that is not always available in experiment results. The turbulent k-ε realize model was employed to examine the effect of Al2O3-water and CuO-water nanofluids on the heat transfer and fluid flow characteristics at different key design parameters. Three coil geometry shapes (including helical, spiral, and conical), five annular cross-section shapes (including circular, elliptical, square, rectangular, and triangular), and three cross-section areas were also investigated in this study. The numerical simulations were carried out at Reynolds numbers of 4700 to 26,700 and nanofluid volume concentrations, φ of 1%, 3%, and 5%, with constant wall temperature (CWT) heat transfer boundary conditions. The result showed that the addition of Al2O3 (45 nm) and CuO (29 nm) nanoparticles to water improves the heat transfer coefficient by 48.8%, 25.7%, and 8.4% and 37.1%, 20%, and 8.7%, respectively, at φ of 5%, 3%, and 1%, while the penalty of pressure drop is approximately negligible. The heat transfer rate per unit pumping power for helical design achieved 21.6% and 5.34% higher than conical and spiral designs, respectively, for the same curvature ratio, cross-section area, and coil length. Also, the circular shape achieved a higher heat transfer enhancement than elliptical, square, rectangular, and triangular shapes by 4%, 14.6%, 17.8%, and 30.1%, respectively. The maximum thermo-hydraulic performance index reached 1.68 and 1.58 for both Al2O3-water and CuO-water nanofluids, respectively, at φ of 5%.

Течение ньютоновской жидкости в смесителях различных конфигураций

The flow of a viscous incompressible fluid in agitators with solid and anchor blades is analyzed. Mathematical formulation for the problem involves Navier-Stokes and continuity equations in the plane approximation. A solution algorithm is developed based on the control volume method and a SIMPLE correction procedure. The differential equations are discretized with unstructured triangular meshes that take into account the geometric features of the flow region. Tests were performed to verify the approximation convergence and to estimate the order of accuracy of the numerical scheme, as well as to verify the original calculation program. Parametric studies were carried out for Reynolds numbers in range of 0.1-100, which is characteristic of the technology of fluid materials processing in industrial mixers. Distributions of the kinematic and dynamic characteristics of the flow were obtained, and the flow patterns, whose specific feature is the presence of circulation zones in paddle agitators of different configurations, were demonstrated. Calculations are done to determine the position of marker particles and the evolution of reference lines, which give a visual representation of the process and demonstrate the presence of areas of uniform and non-uniform mixing. A quantitative mixing quality parameter is introduced to compare agitators of different configurations with each other and to consider the process of mixing over time. The process is evaluated quantitatively by the values of the integral of the dissipative function, which shows the energy consumption, and by the value of the quantitative parameter of the inhomogeneity of the marker particle distribution. The latter allows a more detailed study of the mixing process over the volume over time.

Simulation of Flow Around a Finite Rectangular Prism: Influence of Mesh, Model, and Subgrid Length Scale.

This study investigates the flow field around a finite rectangular prism using both experimental and computational methods, with a particular focus on the influence of the turbulence approach adopted, the mesh resolution employed, and different subgrid length scales. Ten turbulence modelling and simulation approaches, including both 'scale-modelling' Reynolds-Averaged Navier-Stokes (RANS) models and 'scale-resolving' Delayed Detached Eddy Simulation (DDES), were tested across six different mesh resolutions. A case with sharp corners allows the location of the flow separation to be fixed, which facilitates a focus on the separated flow region and, in this instance, the three-dimensional interaction of three such regions. The case, therefore, readily enables an assessment of the 'grey-area' issue, whereby some DDES methods demonstrate delayed activation of the scale-resolving model, impacting the size of flow recirculation. Experimental measurements were shown to agree well with reference data for the same geometry, after which particle image velocimetry (PIV) data were gathered to extend the reference dataset. Numerical predictions from the RANS models were generally quite reasonable but did not show improvement with further refinement, as one would expect, whereas DDES clearly demonstrated continuous improvement in predictive accuracy with progressive mesh refinement. The shear-layer-adapted (SLA) subgrid length scale (ΔSLA) displayed consistently superior performance compared to the more widely used length scale based on local cell volume, particularly for moderate mesh resolutions commonly employed in industrial settings with limited resources. In general, front-body separation and reattachment exhibited greater sensitivity to mesh refinement than wake resolution. Finally, in order to correlate the observed DDES mesh requirements with the observations from the converged RANS solutions, an approximation for the Taylor microscale was explored as a potential tool for mesh sizing.

From sea to sky: understanding the sea surface temperature impact on an atmospheric blocking event using sensitivity experiments with the ICOsahedral Nonhydrostatic (ICON) model

Abstract. Blocked weather regimes are an important phenomenon in the Euro-Atlantic region and are frequently linked to extreme weather events. Despite their importance for surface weather, the correct prediction of blocking events remains challenging. Previous studies indicated a link between the misrepresentation of blocking events in numerical weather prediction models and sea surface temperature (SST) biases, particularly in the Gulf Stream region. However, the pathway that links SST in the Gulf Stream region and the downstream upper-level flow is not yet fully understood. To deepen our physical understanding of the link between the Gulf Stream SST and downstream atmospheric blocking, we perform sensitivity experiments with varying SST conditions for an atmospheric blocking event in February 2019. This blocking event, which was associated with a winter heat wave with unprecedented temperatures in western Europe, was both preceded and accompanied by several rapidly intensifying extratropical cyclones originating in the Gulf Stream region and crossing the North Atlantic. Those cyclones and their associated rapidly ascending air streams, so-called warm conveyor belts (WCBs), played a crucial role in the development of the upper-level ridge and the blocking event. The ascent of these WCBs, which connect the lower and upper troposphere, was enhanced by moisture uptake during cold air outbreaks (CAOs) in the Gulf Stream region. In this study, we employ sensitivity experiments with the ICOsahedral Nonhydrostatic Weather and Climate Model (ICON) to assess the impact of intense air–sea interactions during CAOs on WCBs and the downstream ridge. In total five different experiments are used, including idealized and weakened SST gradients and one with increased absolute SST in the Gulf Stream region. Using Eulerian and Lagrangian perspectives, we demonstrate that the SST gradient in the Gulf Stream region affects moisture availability and air temperature in the WCB inflow region and, consequently, WCB ascent. In our case study, stronger SST gradients lead to increased specific humidity and warmer temperatures in the lower troposphere, resulting in more pronounced WCB ascent, while weaker SST gradients are associated with reduced WCB activity. The differences in WCB ascent and outflow properties induced by weakened SST gradients, such as reduced cross-isentropic ascent and outflow heights, subsequently influence the upper-level flow and weaken the downstream ridge. Moreover, experiments with weaker SST gradients show a decrease in cyclone intensity, and vice versa, stronger cyclones are found in experiments with warmer SSTs. To summarize, our results suggest that different SST and SST gradient representations affect the large-scale atmospheric flow via the WCB airstream. Specifically, moisture availability regulated by SST and SST gradients in the WCB inflow region influences subsequent WCB ascent and outflow characteristics, which, in turn, influence the upper-level ridge downstream. The SST in the Gulf Stream region affects WCB characteristics consistently from the inflow, over the ascent to the outflow phase.

Heat transfer in the entrance region of annular laminar flow with constant and different heat flux on two walls

AbstractHeat transfer differs in the regions where the flow is developed and developing thermally. These regions can be differentiated by using the thermal entry length. Many researchers have presented correlations to determine the thermal entry length for natural and forced convection. In this study, heat transfer in the entrance region of a concentric annuli is investigated. It is accepted that beginning from the inlet of annuli the flow is developed hydrodynamically and it is developing thermally. Heat transfer is investigated where the internal or external surfaces of the annuli are at constant but different heat fluxes. The fluid velocity is assumed to be constant or radially variable. Due to thermal boundary conditions, one thermal boundary layer appears on the outer cylinder surface, another on the inner cylinder surface. The edge of two boundary layers will be adiabatic and naturally, the temperature of fluid between the two edges will be equal to free stream temperature. Transformation, Separation of Variables method, eigenvalue problem, Sturm‐Liouville system, Bessel differential equation and properties of orthogonal functions are used in solution of the problem. Exact and analytical solutions of the momentum and energy equations are presented. Velocity and temperature distributions, local Nusselt numbers and convection heat transfer coefficients are calculated for the internal and external surfaces of annuli.

Boundary-Layer Evolution over the Lower Surface of a Wind-Turbine Airfoil

The boundary-layer evolution over rotor-blade airfoils can be significantly affected by changes in the flow conditions. Because this sensitivity would have a major impact on the wind-turbine performance, it is crucial to evaluate it at the large Reynolds numbers characteristic of modern wind-turbine rotor blades. This work extends earlier wind-tunnel investigations on a DU 91-W2-250 airfoil by examining the transition behavior on its pressure surface at angles-of-attack from −14 to 20 deg and chord Reynolds numbers up to 12 million. Large regions of laminar flow were identified at positive angles-of-attack using temperature-sensitive paint, which also enabled an estimation of the development of turbulent separation at negative incidence. The global surface temperature distributions were supplemented by pressure tap data, which also provided an input for linear stability computations of the laminar boundary layer that supported and complemented the experimental findings. This systematic analysis elucidated not only the effect of Reynolds number and airfoil incidence on laminar-turbulent transition, but also a localized, facility-specific variation in the transition front. The observed boundary-layer evolution substantiated the discussion of the development of the aerodynamic coefficients, which were measured in previous investigations and were well reproduced in the present work.