The impact of upstream blocking, drainage flow and the geostrophic pressure gradient on the persistence of cold-air pools

2003 ◽  
Vol 129 (587) ◽  
pp. 117-137 ◽  
Author(s):  
G. Zängl
Keyword(s):  
Pressure Gradient ◽  
Drainage Flow ◽  
Cold Air ◽  
The Impact

scholarly journals Dynamical Aspects of Wintertime Cold-Air Pools in an Alpine Valley System

2005 ◽  
Vol 133 (9) ◽  
pp. 2721-2740 ◽  
Author(s):  
Günther Zängl
Keyword(s):  
Pressure Gradient ◽  
Cold Pool ◽  
Drainage Flow ◽  
Dynamical Mechanism ◽  
Cold Air ◽  
Ambient Wind ◽  
Alpine Valley ◽  
Ambient Flow ◽  
Alpine Foreland

Abstract This study presents high-resolution numerical simulations in order to examine the dynamical mechanisms controlling the persistence of wintertime cold-air pools in an Alpine valley system. First, a case study of a cold-pool episode is conducted, the formation of which was related to the passage of a warm front north of the Alps. While the preexisting cold air was rapidly advected away in the Alpine foreland, a persistent cold pool was maintained in the inner-Alpine part of the valley system, associated with sustained horizontal temperature differences of up to 10 K over a distance of 30 km. The case study is complemented by a series of semi-idealized simulations, combining realistic topography with idealized large-scale flow conditions. These simulations consider a range of different ambient wind directions in order to investigate their impact on the cold-pool persistence. The results indicate that the most important dynamical mechanism controlling the persistence of cold-air pools in deep Alpine valleys is cold-air drainage toward the Alpine foreland. The preferred direction for such a drainage flow is down the pressure gradient imposed by the (geostrophically balanced) ambient flow. Thus, for a given valley geometry and a given strength of the ambient flow, the probability for persistent cold-air pools mainly depends on the ambient wind direction. If the direction of the imposed pressure gradient matches a sufficiently wide connection to the foreland (a valley or a low pass), then a drainage flow will lead to a rapid removal of the cold air. However, the presence of pronounced lateral constrictions in the connecting valley may strongly reduce the drainage efficiency. Cold-pool erosion by turbulent vertical mixing seems to play a comparatively minor role in deep valley systems as considered in this study.

Blade coating analysis of viscous nanofluid having Cu–water nanoparticles using flexible blade coater

2020 ◽  
Vol 36 (4) ◽  
pp. 348-367 ◽  
Author(s):  
Marya Kanwal ◽  
Xinhua Wang ◽  
Hasan Shahzad ◽  
Yingchun Chen ◽  
Hui Chai
Keyword(s):  
Pressure Gradient ◽  
Shooting Method ◽  
Volume Fraction ◽  
Volumetric Flow Rate ◽  
Lubrication Approximation ◽  
Nanoparticle Volume Fraction ◽  
Porous Substrate ◽  
Flow Equations ◽  
The Impact ◽  
Blade Coating

This article presents the blade coating analysis of viscous nanofluid passing over a porous substrate using a flexible blade coater. Water-based copper nanoparticles are considered to discuss the blade coating process. The lubrication approximation theory is applied to develop the flow equations. The analytical solution is obtained for velocity, volumetric flow rate, and pressure gradient, while shooting method is applied to obtain the pressure, thickness, and load. Different models for dynamic viscosity have been applied to observe the impact of related parameters on pressure, pressure gradient, and velocity. These results are presented graphically. Interesting engineering quantities such as load, deflection, and thickness are computed numerically and are shown in the tabulated form. It is found that nanoparticle volume fraction increases the pressure gradient, pressure and has minor effects on velocity. For model 1, an increase in the volume fraction reduces the coating thickness, load, and deflection, while model 2 has opposite effects on the mentioned quantities. Also, model 2 has a greater impact on pressure and pressure gradient when compared to model 1.

scholarly journals Investigation of productivity decline in inter-salt argillaceous dolomite reservoir due to formation damage and threshold pressure gradient: Laboratory, mathematical modeling and application

2016 ◽  
Vol 35 (1) ◽  
pp. 33-53 ◽  
Author(s):  
Dan Wu ◽  
Binshan Ju ◽  
Shiqiang Wu ◽  
Eric Thompson Brantson ◽  
Yingkun Fu ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Effective Stress ◽  
Stress Sensitivity ◽  
Microscopic Model ◽  
Oil Well ◽  
Threshold Pressure ◽  
Threshold Pressure Gradient ◽  
Well Productivity ◽  
Sensitivity Experiments ◽  
The Impact

The inter-salt argillaceous dolomite reservoirs in the central region of China contain large abundance of oil resources with ultra-low permeability and porosity. However, the oil wells in this area show a very quick reduction with the decline of formation pressure. This article aims to investigate the main possible reasons that affect oil well productivity in the target oilfield. This study begins with analysis of capillary microscopic model, core stress sensitivity experiments, and non-Darcy percolation experiments. The impact of effective stress on permeability and porosity of the reservoir was revealed in this article. The novel productivity model and productivity evaluation model which couples stress sensitivity and threshold pressure gradient were proposed. The analysis of capillary microscopic model shows stress sensitivity of permeability to be much greater than that of porosity during the process of depressurization. The core stress sensitivity experiments results indicate that permeability and effective stress show index relationship while porosity and effective stress show binomial relationship. Damage rate and recovery rate of permeability and porosity were put forward to describe the degree of influence of stress sensitivity on permeability and porosity. The models were used to investigate the factors that affect single well productivity for the target oilfield. Application of the proposed model to this tight oilfield indicates that, the degree of influence of stress sensitivity is much greater than that of threshold pressure gradient. In addition, the greater the stress sensitivity coefficient and threshold pressure gradient are, the greater the productivity reduction will be.

Effect of oil starvation on the isothermal impact problem

2017 ◽  
Vol 232 (10) ◽  
pp. 1332-1339
Author(s):  
Duohuan Wu ◽  
Jing Wang ◽  
Peiran Yang ◽  
Ton Lubrecht
Keyword(s):  
Film Thickness ◽  
Pressure Gradient ◽  
Thickness Distribution ◽  
Elastohydrodynamic Lubrication ◽  
Maximum Pressure ◽  
Numerical Techniques ◽  
Minimum Film Thickness ◽  
The Impact ◽  
Impact Motion ◽  
Impact Problem

In this study, the effect of oil starvation on isothermal elastohydrodynamic lubrication of an impact motion is explored with the aid of numerical techniques. During the impact process, on comparison with the fully lubricated results, the pressure and film thickness are much lower and the entrapped film shape does not happen. The rebound is delayed by the oil starvation assumption. During the rebound process, a periphery entrapment is seen in the starved film thickness distribution. Under the starved condition, the maximum pressure gradient is higher. The central film thickness and minimum film thickness exhibit different variations compared with the results by fully flooded assumption.

Warm-Air Intrusions in Arizona’s Meteor Crater

2012 ◽  
Vol 51 (6) ◽  
pp. 1010-1025 ◽  
Author(s):  
Bianca Adler ◽  
C. David Whiteman ◽  
Sebastian W. Hoch ◽  
Manuela Lehner ◽  
Norbert Kalthoff
Keyword(s):  
Surface Layer ◽  
Atmospheric Stability ◽  
Crater Floor ◽  
Drainage Flow ◽  
Cold Air ◽  
Stable Surface ◽  
Isothermal Layer ◽  
Stable Surface Layer ◽  
Strong Winds ◽  
Spatial And Temporal Characteristics

AbstractEpisodic nighttime intrusions of warm air, accompanied by strong winds, enter the enclosed near-circular Meteor Crater basin on clear, synoptically undisturbed nights. Data analysis is used to document these events and to determine their spatial and temporal characteristics, their effects on the atmospheric structure inside the crater, and their relationship to larger-scale flows and atmospheric stability. A conceptual model that is based on hydraulic flow theory is offered to explain warm-air-intrusion events at the crater. The intermittent warm-air-intrusion events were closely related to a stable surface layer and a mesoscale (~50 km) drainage flow on the inclined plain outside the crater and to a continuous shallow cold-air inflow that came over the upstream crater rim. Depending on the upstream conditions, the cold-air inflow at the crater rim deepened temporarily and warmer air from above the stable surface layer on the surrounding plain descended into the crater, as part of the flowing layer. The flow descended up to 140 m into the 170-m-deep crater and did not penetrate the approximately 30-m-deep crater-floor inversion. The intruding air, which was up to 5 K warmer than the crater atmosphere, did not extend into the center of the crater, where the nighttime near-isothermal layer in the ambient crater atmosphere remained largely undisturbed. New investigations are suggested to test the hypothesis that the warm-air intrusions are associated with hydraulic jumps.

scholarly journals Left ventricular diastolic function in hypertensive patients with atrial fibrillation

2012 ◽  
Vol 18 (2) ◽  
pp. 142-147 ◽  
Author(s):  
F. L. Bartosh ◽  
L. F. Bartosh ◽  
T. S. Adonina
Keyword(s):  
Atrial Fibrillation ◽  
Blood Flow ◽  
Pressure Gradient ◽  
Diastolic Function ◽  
Left Ventricular Diastolic Function ◽  
Left Ventricular ◽  
Hypertensive Patients ◽  
Mean Values ◽  
Ventricular Diastolic Function ◽  
The Impact

Objective. To study the features of the impact of atrial fibrillation on left ventricular diastolic function in hypertensive patients. Design and methods. We examined three groups of patients: hypertensive patients with atrial fibrillation, hypertensive patients with sinus rhythm and patients with idiopathic form of atrial fibrillation. All patients underwent cardiac ultrasound examination (Vivid 7 Dimension, General Electric). Results. The integral of blood flow linear velocity (VTI), period of pressure gradient half decrease (PHT) between left chambers of heart and time of transmitral blood flow (TE) were greater in patients of second and third groups compared to first group. They did not differ in second and third groups. The time of isovolumic relaxation (IVRT) was 0,102 ± 0,015; 0,091 ± 0,012 and 0,073 ± 0,013 seconds in first, second and third groups, respectively. The differences between all groups are significant (p = 0,001). The mean values of maximal (Vmax) and middle velocity (VMN), maximal (Gmax) and middle (GMN) pressure gradient between left heart chambers did not differ between groups. Conclusion. Atrial fibrillation contributes the development of left ventricular diastolic dysfunction: it reduces VTI, decelerates IVRT and shortens PHT significantly.

scholarly journals SPATIOTEMPORAL EVALUATION OF NOCTURNAL COLD AIR DRAINAGE OVER A SIMPLE SLOPE USING THERMAL INFRARED IMAGERY

2016 ◽  
Vol XLI-B8 ◽  
pp. 265-269
Author(s):  
V. Ikani ◽  
K. Chokmani ◽  
L. Fathollahi ◽  
H. Granberg ◽  
R. Fournier
Keyword(s):  
Temperature Gradient ◽  
Infrared Camera ◽  
Thermal Infrared ◽  
Infrared Analysis ◽  
Agricultural Field ◽  
Drainage Flow ◽  
Cold Air ◽  
Drainage Flows ◽  
Infrared Measurement ◽  
Thermal Infrared Imagery

Measurements of climatic processes such as cold air drainage flows are problematic over mountainous areas. Observation of cold air drainage is not available in the existing observation network and it requires a special methodology. The main objective of this study was to characterize the cold air drainage over regions with a slope. A high resolution infrared camera, a meteorological station and Digital Elevation Model (DEM) were used. The specific objective was to derive nocturnal cold air drainage velocity over the slope. To address these objectives, a number of infrared measurement campaigns were conducted during calm and clear sky conditions over an agricultural zone (blackcurrant farm) in Canada. Using thermal infrared images, the nocturnal surface temperature gradient were computed in hourly basis. The largest gradient magnitudes were found between 17h -20h. The cooling rates at basin area were two times higher in comparison to the magnitudes observed within slope area. The image analysis illustrated this considerable temperature gradient of the basin may be partly due to transport of cold air drainage into the basin from the slope. The results show that thermal imagery can be used to characterize and understand the microclimate related to the occurrence of radiation frost in the agricultural field. This study provided the opportunity to track the cold air drainage flow and pooling of cold air in low lying areas. The infrared analysis demonstrated that nocturnal drainage flow displayed continuous variation in terms of space and time in response to microscale slope heterogeneities. In addition, the analysis highlighted the periodic aspect for cold air drainage flow.

scholarly journals Study of Slip Effects in Reverse Roll Coating Process Using Non-Isothermal Couple Stress Fluid

Coatings ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1249
Author(s):  
Hasan Shahzad ◽  
Xinhua Wang ◽  
Muhammad Bilal Hafeez ◽  
Zahir Shah ◽  
Ahmed Mohammed Alshehri
Keyword(s):  
Pressure Gradient ◽  
Flow Rate ◽  
Couple Stress ◽  
Velocity Ratio ◽  
Closed Form Solution ◽  
Couple Stress Fluid ◽  
Slip Parameter ◽  
Roll Coating ◽  
Stress Parameter ◽  
The Impact

The non-isothermal couple stress fluid inside a reverse roll coating geometry is considered. The slip condition is considered at the surfaces of the rolls. To develop the flow equations, the mathematical modelling is performed using conservation of momentum, mass, and energy. The LAT (lubrication approximation theory) is employed to simplify the equations. The closed form solution for velocity, temperature, and pressure gradient is obtained. While the pressure and flow rate are obtained numerically. The impact of involved parameters on important physical quantities such as temperature, pressure, and pressure gradient are elaborated through graphs and in tabular form. The pressure and pressure gradient decreases for variation of the couple stress parameter and velocity ratio parameter K. While the variation of the slip parameter increases the pressure and pressure gradient inside the flow geometry. Additionally, flow rate decreases for the variation of the slip parameter as fluid starts moving rapidly along the roller surface. The most important physical quantity which is responsible for maintaining the quality of the coating and thickness is flow rate. For variation of both the couple stress parameter and the slip parameter, the flow rate decreases compared to the Newtonian case, consequently the coating thickness decreases for the variation of the discussed parameter.

scholarly journals Imposed pressure driven flow in peristalsis

2020 ◽  
Vol 12 (11) ◽  
pp. 168781402097106
Author(s):  
Ishrat Fatima ◽  
Saleem Asghar
Keyword(s):  
Biological Sciences ◽  
Velocity Field ◽  
Pressure Gradient ◽  
Forward Direction ◽  
Peristaltic Motion ◽  
Boundary Perturbation Method ◽  
Physical Importance ◽  
The One ◽  
Pressure Driven Flow ◽  
The Impact

Peristaltic transport phenomena are of great significance in biological sciences. The physiological transport of fluid takes place under the action of peristalsis generated as a pressure gradient. The peristaltic waves generate a pressure gradient which is responsible for the fluid flow in the forward direction. The further properties of this phenomena can be seen if an imposed pressure gradient is applied in addition to the one appearing due to peristaltic waves. This situation has not been discussed in the literature that needs further attention. The effects of the wavy boundaries and imposed pressure on the velocity of the flow field are analyzed. Here we impose a question: what happens if an imposed pressure gradient is also applied? This question of physical importance has not been addressed; and thus, remains the topic of this study. In previous papers of peristaltic motion, the flow generated by peristaltic waves only has been examined while in this study we will discuss the contribution of imposed pressure gradient on velocity field. The analytical results for the velocity field are obtained using the boundary perturbation method. The study shows that the impact of the wavy boundaries on the flow increases with the increase in corrugation parameter and imposed pressure.

The role of a tropopause polar vortex in the generation of the January 2019 extreme Arctic outbreak

2021 ◽  
Author(s):  
Samuel P. Lillo ◽  
Steven M. Cavallo ◽  
David B. Parsons ◽  
Christopher Riedel
Keyword(s):  
Great Lakes ◽  
Polar Vortex ◽  
Direct Consequence ◽  
The United States ◽  
The Arctic ◽  
Cold Air ◽  
Middle Latitudes ◽  
Cold Air Outbreak ◽  
Lake Effect ◽  
The Impact

AbstractAn extreme Arctic cold air outbreak took place across the Midwest, Great Lakes, and Northeast during 29 January to 1 February 2019. The event broke numerous long-standing records with wide-reaching and detrimental societal impacts. This study found that this rare and dangerous cold air out-break (CAO) was a direct consequence of a tropopause polar vortex (TPV) originating at high latitudes and subsequently tracking southward into the United States. The tropopause depression at the center of this TPV extended nearly to the surface. Simulations using the atmospheric component of the Model for Prediction Across Scales (MPAS) were conducted revealing excellent predictability at 6-7 days lead times with the strength, timing, and location of the CAO linked to the earlier characteristics of the TPV over the Arctic. Within the middle latitudes, the TPV subsequently developed a tilt with height. Warming and the destruction of potential vorticity also took place as the TPV passed over the Great Lakes initiating a lake effect snow storm. The climatological investigation of CAOs suggests that TPVs frequently play a role in CAOs over North America with a TPV located within 1000 km of a CAO 85% of the time. These TPVs tended to originate in the Northern Canadian Arctic and are ejected equatorward into the Great Lakes/Upper-midwest and then to the northeast over Labrador. This study also provides insight into how the impact of Arctic circulations on middle latitudes may vary within the framework of a rapidly changing Arctic.

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