Sensitive versus Rough Dependence in Initial Conditions in Atmospheric Flow Regimes

2016 ◽  
Author(s):  
Yanguang Li
Keyword(s):  
Initial Conditions ◽  
Flow Regimes ◽  
Atmospheric Flow

scholarly journals Sensitive versus Rough Dependence under Initial Conditions in Atmospheric Flow Regimes

Atmosphere ◽  
2016 ◽  
Vol 7 (12) ◽  
pp. 157 ◽  
Author(s):  
Anthony Lupo ◽  
Y. Li ◽  
Z. Feng ◽  
Neil Fox ◽  
Jordan Rabinowitz ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Flow Regimes ◽  
Atmospheric Flow

A Functional Scaling Relationship for Laminar to Turbulent Flow Regimes

2011 ◽  
Author(s):  
George Papadopoulos
Keyword(s):  
Turbulent Flow ◽  
Stokes Equations ◽  
Initial Conditions ◽  
Flow Characteristics ◽  
Flow Region ◽  
Flow Regimes ◽  
Transitional Flow ◽  
Turbulent Regime ◽  
Flow Profile ◽  
Scaling Relationship

A dimensional analysis that is based on the scaling of the two-dimensional Navier-Stokes equations is presented for correlating bulk flow characteristics arising from a variety of initial conditions. The analysis yields a functional relationship between the characteristic variable of the flow region and the Reynolds number for each of the two independent flow regimes. A linear relationship is realized for the laminar regime, while a nonlinear relationship is realized for the turbulent regime. Both relationships incorporate mass-flow profile characteristics to fully capture the effects of initial conditions on the variation of the characteristic variables. The union of these two independent relationships is formed utilizing the concept of flow intermittency to further expand into a generic scaling relationship that incorporates transitional flow effects to fully encompass solutions spanning the laminar to turbulent flow regimes. The results of the analysis are discussed within the context of several flow phenomena (e.g. pipe flow, jet flow & separated flow) resulting from various initial and boundary conditions.

scholarly journals Regionally Enhanced Global (REG) 4D-Var

2018 ◽  
Vol 146 (12) ◽  
pp. 4015-4038
Author(s):  
Michael A. Herrera ◽  
Istvan Szunyogh ◽  
Adam Brainard ◽  
David D. Kuhl ◽  
Karl Hoppel ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Prediction Models ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Computational Cost ◽  
Limited Area ◽  
Atmospheric Flow ◽  
Forecast Performance ◽  
Limited Area Model ◽  
Area Model

Abstract A regionally enhanced global (REG) data assimilation (DA) method is proposed. The technique blends high-resolution model information from a single or multiple limited-area model domains with global model and observational information to create a regionally enhanced analysis of the global atmospheric state. This single analysis provides initial conditions for both the global and limited-area model forecasts. The potential benefits of the approach for operational data assimilation are (i) reduced development cost, (ii) reduced overall computational cost, (iii) improved limited-area forecast performance from the use of global information about the atmospheric flow, and (iv) improved global forecast performance from the use of more accurate model information in the limited-area domains. The method is tested by an implementation on the U.S. Navy’s four-dimensional variational global data assimilation system and global and limited-area numerical weather prediction models. The results of the monthlong forecast experiments suggest that the REG DA approach has the potential to deliver the desired benefits.

Flow regimes of large-velocity-ratio coaxial jets

1997 ◽  
Vol 345 ◽  
pp. 357-381 ◽  
Author(s):  
H. REHAB ◽  
E. VILLERMAUX ◽  
E. J. HOPFINGER
Keyword(s):  
Flow Structure ◽  
Initial Conditions ◽  
Near Field ◽  
Velocity Ratio ◽  
Low Frequency ◽  
Flow Regimes ◽  
Entrainment Rate ◽  
Recirculation Bubble ◽  
Jet Mixing ◽  
Coaxial Jets

An investigation of the near-field flow structure of coaxial jets with large outer to inner velocity ratio ru has been conducted. Since in all cases ru>1, the outer jet dominates the near-field flow structure. Two flow regimes are identified depending on whether ru is larger or smaller than a critical value ruc. When ru<ruc, the fast annular jet periodically pinches the central, slow jet near the end of the inner potential cone. The pinching frequency corresponds to the outer-jet mode. The length of the inner potential cone is strongly dependent on ru and behaves like A/ru, where A depends weakly on the initial conditions. When ru>ruc, the inner potential cone is truncated and is followed by an unsteady recirculation bubble with low-frequency oscillation.The transition from one regime to another is explained by a simple model whose ingredients are the turbulent entrainment rate, governed by the outer-jet mixing layers and mass conservation. This model satisfactorily predicts the dependence of the inner potential cone length on ru and the critical velocity ratio ruc. The recirculation bubble has a wake-type instability. It oscillates at a low frequency and a large amplitude compared to the Kelvin–Helmholtz mode. Angular cross-correlations in the plane parallel to the jet outlet show moreover that this oscillation displays an azimuthal precession such that the rotation time of the phase of the oscillation equals the oscillation period. These salient features are discussed in the framework of the nonlinear delayed saturation (NLDS) model.

Coastal Atmospheric Circulation around an Idealized Cape during Wind-Driven Upwelling Studied from a Coupled Ocean–Atmosphere Model

2011 ◽  
Vol 139 (3) ◽  
pp. 809-829 ◽  
Author(s):  
Natalie Perlin ◽  
Eric D. Skyllingstad ◽  
Roger M. Samelson
Keyword(s):  
Atmospheric Circulation ◽  
Wind Stress ◽  
Coastal Upwelling ◽  
Initial Conditions ◽  
Temperature Inversion ◽  
Ocean Current ◽  
Atmospheric Flow ◽  
Near Surface ◽  
Ocean Atmosphere ◽  
Atmosphere Model

Abstract The study analyzes atmospheric circulation around an idealized coastal cape during summertime upwelling-favorable wind conditions simulated by a mesoscale coupled ocean–atmosphere model. The domain resembles an eastern ocean boundary with a single cape protruding into the ocean in the center of a coastline. The model predicts the formation of an orographic wind intensification area on the lee side of the cape, extending a few hundred kilometers downstream and seaward. Imposed initial conditions do not contain a low-level temperature inversion, which nevertheless forms on the lee side of the cape during the simulation, and which is accompanied by high Froude numbers diagnosed in that area, suggesting the presence of the supercritical flow. Formation of such an inversion is likely caused by average easterly winds resulting on the lee side that bring warm air masses originating over land, as well as by air warming during adiabatic descent on the lee side of the topographic obstacle. Mountain leeside dynamics modulated by differential diurnal heating is thus suggested to dominate the wind regime in the studied case. The location of this wind feature and its strong diurnal variations correlate well with the development and evolution of the localized lee side trough over the coastal ocean. The vertical extent of the leeside trough is limited by the subsidence inversion aloft. Diurnal modulations of the ocean sea surface temperatures (SSTs) and surface depth-averaged ocean current on the lee side of the cape are found to strongly correlate with wind stress variations over the same area. Wind-driven coastal upwelling develops during the simulation and extends offshore about 50 km upwind of the cape. It widens twice as much on the lee side of the cape, where the coldest nearshore SSTs are found. The average wind stress–SST coupling in the 100-km coastal zone is strong for the region upwind of the cape, but is notably weaker for the downwind region, estimated from the 10-day-average fields. The study findings demonstrate that orographic and diurnal modulations of the near-surface atmospheric flow on the lee side of the cape notably affect the air–sea coupling on various temporal scales: weaker wind stress–SST coupling results for the long-term averages, while strong correlations are found on the diurnal scale.

scholarly journals The Influence of the Intermittent Behavior of the Nocturnal Atmospheric Flow on the Prediction of the Diurnal Temperature Range: A Simplified Model Analysis

2017 ◽  
Vol 2017 ◽  
pp. 1-8
Author(s):  
Leandro L. Gonzales ◽  
Felipe D. Costa ◽  
Otávio C. Acevedo ◽  
Daniel M. dos Santos ◽  
Luiz E. Medeiros ◽  
...  
Keyword(s):  
Diurnal Temperature Range ◽  
Flow Regimes ◽  
Atmospheric Model ◽  
Atmospheric Temperature ◽  
Atmospheric Concentration ◽  
Atmospheric Flow ◽  
Diurnal Temperature ◽  
Temperature Range ◽  
Intermittent Behavior ◽  
Weak Wind

The variation of the atmospheric temperature near the surface associated with anthropogenic effects is analyzed using a simplified atmospheric model. Local changes in cloud cover and four different scenarios of atmospheric concentration of carbon dioxide are considered. The results show that the highest temperature variability occurs in the weak wind and decoupled state and in the transition between flow regimes. In agreement with previous efforts, the results indicate that the reduction of diurnal temperature range is related to the existence of two distinct flow regimes in the stable boundary layer. However, in the decoupled state, the occurrence of intermittent bursts of turbulence may cause temperature variations among the different scenarios to become unpredictable. It implies that it is difficult to predict the diurnal temperature range in places where low winds are common.

Insight Into the Heel–Toe Effect of a Long Horizontal Wellbore Based on a Hybrid Numerical Method

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Pranab N. Jha ◽  
Chuck Smith ◽  
Ralph W. Metcalfe
Keyword(s):  
Dynamic Behavior ◽  
Shale Gas ◽  
Initial Conditions ◽  
Fluid Flows ◽  
Flow Regimes ◽  
Lumped Parameter Model ◽  
Axial Distance ◽  
Gas Well ◽  
Lumped Parameter ◽  
Horizontal Wellbore

Numerical simulation of flow inside a horizontal wellbore with multiple completion stages is presented. Using a hybrid method combining computational fluid dynamics and a lumped parameter model, blocking effect on the toe-end stages observed in long horizontal wells (heel–toe effect) under simplified conditions is explained. A two-dimensional channel geometry was used to model the wellbore, with side inlets representing completion stages. First, using a five-stage well with steady state flow conditions, the existence of three basic flow regimes—trickle flow, partially blocked flow and fully blocked flow—was established. Using these results, the phenomenon of blocking of upstream inlets near the toe by the downstream ones near the heel is explained. The existence of these flow regimes is consistent with well-log data obtained from a horizontal shale gas well with 31 completion stages at two different times during production. Further, to study the dynamic behavior of the completion stages when reservoir fluid flows into the wellbore, a basic reservoir depletion model was created using a pressure boundary condition at the side inlets, varying in time. A lumped-parameter model was used to account for the pressure drop between two inlets separated by large axial distance. Different characteristic time scales, related to the depletion of the reservoirs, were identified. By varying initial conditions, the dynamic behavior of the system with multiple inlets was observed and analyzed. The transition of flow regimes with depletion of reservoirs is consistent with the observed behavior of the horizontal shale gas well.

The wake of two staggered square cylinders

2016 ◽  
Vol 801 ◽  
pp. 475-507 ◽  
Author(s):  
Md. Mahbub Alam ◽  
Honglei Bai ◽  
Yu Zhou
Keyword(s):  
Experimental Study ◽  
Reynolds Number ◽  
Shear Layer ◽  
Initial Conditions ◽  
Flow Characteristics ◽  
Flow Regimes ◽  
Flow Structures ◽  
Extensive Data ◽  
Square Cylinders ◽  
Gap Flow

This work aims to provide a systematic experimental study of the wake behind two staggered square cylinders at a Reynolds number $Re=1.3\times 10^{4}$. Four distinct flow regimes, i.e. two single-street modes S-I and S-II and two double-street modes T-I and T-II, are identified based on extensive data, including Strouhal numbers $(St)$, flow structures and their downstream evolution. S-I, S-II and T-II are each further subdivided into two types. The flow characteristics in each regime are presented in terms of shear layer reattachment and impingement, vortex impingement, gap flow behaviour, interaction between cylinders and downstream evolution of the wake. A detailed discussion is made regarding how the physical aspects of the flow are connected to the initial conditions and the $St$ number.

A Functional Relationship for Modeling Laminar to Turbulent Flow Transitions

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
George Papadopoulos
Keyword(s):  
Turbulent Flow ◽  
Functional Relationship ◽  
Stokes Equations ◽  
Initial Conditions ◽  
Flow Region ◽  
Flow Regimes ◽  
Transitional Flow ◽  
Turbulent Regime ◽  
Flow Profile ◽  
Mean Flow

A dimensional analysis which is based on the scaling of the two-dimensional Navier–Stokes equations is presented for correlating bulk flow characteristics arising from a variety of initial conditions. The analysis yields a functional relationship between the characteristic variable of the flow region and the Reynolds number for each of the two independent flow regimes, laminar and turbulent. A linear relationship is realized for the laminar regime, while a nonlinear relationship is realized for the turbulent regime. Both relationships incorporate mass-flow profile characteristics to capture the effects of initial conditions (mean flow and turbulence) on the variation of the characteristic variable. The union of these two independent relationships is formed leveraging the concept of flow intermittency to yield a generic functional relationship that incorporates transitional flow effects and fully encompasses solutions spanning the laminar to turbulent flow regimes. Empirical models to several common flows are formed to demonstrate the engineering potential of the proposed functional relationship.

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