scholarly journals Far Wake and Its Relation to Aerodynamic Efficiency

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3641
Author(s):  
Sidaard Gunasekaran ◽  
Aaron Altman
Keyword(s):  
Reynolds Stress ◽  
Initial Conditions ◽  
The United States ◽  
Free Shear Layer ◽  
Algebraic Models ◽  
Aerodynamic Efficiency ◽  
Wing Geometry ◽  
Image Pairs ◽  
Wing Performance ◽  
Far Wake

Correlations were found between the aerodynamic efficiency and the mean and fluctuating quantities in the far wake of a wall-to-wall SD7003 model and an AR 4 flat plate. This correlation was described algebraically by modeling the wake signature as a function of wing geometry and initial conditions. The model was benchmarked against experimental results to elicit the wing performance as a function of angle of attack by interrogating the wake. In these algebraic models, the drag coefficient along with other initial conditions of the turbulent generator (either airfoil or wing) were used to reconstruct the Reynolds Stress distribution and the momentum deficit distribution in the turbulent wake. Experiments were undertaken at the United States Air Force Research Labs Horizontal Free Surface Water Tunnel (AFRL/HFWT). These experiments build on previous results obtained at the University of Dayton Low Speed Wind Tunnel (UD-LSWT) on a cylinder, an AR 7 SD7062 wing, and a small remote control twin motor aircraft. The Reynolds stress and the momentum deficit of the turbulent generators were experimentally determined using Particle Image Velocimetry (PIV) with a minimum of 1000 image pairs averaged at each condition. The variation of an empirical factor (γ) used to match the Reynolds stress and momentum deficit distributions showed striking correlation to the variation of drag and aerodynamic efficiency of the turbulent generator. This correlation suggests that the wing performance information is preserved in the free shear layer 10 chord lengths downstream of the trailing edge (TE) of the wing irrespective of the dimensionality of the flow.

The effect of initial conditions on the development of a free shear layer

1966 ◽  
Vol 26 (2) ◽  
pp. 225-236 ◽  
Author(s):  
P. Bradshaw
Keyword(s):  
Turbulent Mixing ◽  
Initial Conditions ◽  
Mixing Layer ◽  
Initial Boundary ◽  
Shear Layers ◽  
Free Shear Layer ◽  
Turbulent Mixing Layer ◽  
Free Shear Layers ◽  
Final Approach ◽  
Reynolds Number Effects

The distance between the separation point and the final approach to a fully developed turbulent mixing layer is found to be of the order of a thousand times the momentum-deficit thickness of the initial boundary layer, whether the latter be laminar or turbulent. There are correspondingly large shifts in the virtual origin of the mixing layer, resulting in spurious Reynolds-number effects which cause considerable difficulties in tests of model jets or blunt-based bodies, and which are probably responsible for the disagreements over the influence of Mach number on the development of free shear layers. These effects are explained.

scholarly journals Impact of Assimilating Dropsonde Observations from MPEX on Ensemble Forecasts of Severe Weather Events

2016 ◽  
Vol 144 (10) ◽  
pp. 3799-3823 ◽  
Author(s):  
Glen S. Romine ◽  
Craig S. Schwartz ◽  
Ryan D. Torn ◽  
Morris L. Weisman
Keyword(s):  
United States ◽  
Initial Conditions ◽  
Positive Impact ◽  
The United States ◽  
Early Morning ◽  
Severe Weather ◽  
Synoptic Scale ◽  
Ensemble Forecasts ◽  
Forecast Performance ◽  
Weather Events

Over the central Great Plains, mid- to upper-tropospheric weather disturbances often modulate severe storm development. These disturbances frequently pass over the Intermountain West region of the United States during the early morning hours preceding severe weather events. This region has fewer in situ observations of the atmospheric state compared with most other areas of the United States, contributing toward greater uncertainty in forecast initial conditions. Assimilation of supplemental observations is hypothesized to reduce initial condition uncertainty and improve forecasts of high-impact weather. During the spring of 2013, the Mesoscale Predictability Experiment (MPEX) leveraged ensemble-based targeting methods to key in on regions where enhanced observations might reduce mesoscale forecast uncertainty. Observations were obtained with dropsondes released from the NSF/NCAR Gulfstream-V aircraft during the early morning hours preceding 15 severe weather events over areas upstream from anticipated convection. Retrospective data-denial experiments are conducted to evaluate the value of dropsonde observations in improving convection-permitting ensemble forecasts. Results show considerable variation in forecast performance from assimilating dropsonde observations, with a modest but statistically significant improvement, akin to prior targeted observation studies that focused on synoptic-scale prediction. The change in forecast skill with dropsonde information was not sensitive to the skill of the control forecast. Events with large positive impact sampled both the disturbance and adjacent flow, akin to results from past synoptic-scale targeting studies, suggesting that sampling both the disturbance and adjacent flow is necessary regardless of the horizontal scale of the feature of interest.

scholarly journals LDAS-Monde Sequential Assimilation of Satellite Derived Observations Applied to the CONtiguous US: An ERA-5 Driven Reanalysis of the Land Surface Variables

2018 ◽  
Author(s):  
Clément Albergel ◽  
Simon Munier ◽  
Aymeric Bocher ◽  
Bertrand Bonan ◽  
Yongjun Zheng ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Initial Conditions ◽  
The United States ◽  
Agricultural Drought ◽  
Reference Network ◽  
Surface Model ◽  
Area Index ◽  
Medium Range Weather Forecast ◽  
The Impact

LDAS-Monde, an offline land data assimilation system with global capacity, is applied over the CONtiguous US (CONUS) domain to enhance monitoring accuracy for water and energy states and fluxes. LDAS-Monde ingests satellite-derived Surface Soil Moisture (SSM) and Leaf Area Index (LAI) estimates to constrain the Interactions between Soil, Biosphere, and Atmosphere (ISBA) Land Surface Model (LSM) coupled with the CNRM (Centre National de Recherches Météorologiques) version of the Total Runoff Integrating Pathways (CTRIP) continental hydrological system (ISBA-CTRIP). LDAS-Monde is forced by the ERA-5 atmospheric reanalysis from the European Center For Medium Range Weather Forecast (ECMWF) from 2010 to 2016 leading to a 7-yr, quarter degree spatial resolution offline reanalysis of Land Surface Variables (LSVs) over CONUS. The impact of assimilating LAI and SSM into LDAS-Monde is assessed over North America, by comparison to satellite-driven model estimates of land evapotranspiration from the Global Land Evaporation Amsterdam Model (GLEAM) project, and upscaled ground-based observations of gross primary productivity from the FLUXCOM project. Also, taking advantage of the relatively dense data networks over CONUS, we also evaluate the impact of the assimilation against in-situ measurements of soil moisture from the USCRN network (US Climate Reference Network) are used in the evaluation, together with river discharges from the United States Geophysical Survey (USGS) and the Global Runoff Data Centre (GRDC). Those data sets highlight the added value of assimilating satellite derived observations compared to an open-loop simulation (i.e. no assimilation). It is shown that LDAS-Monde has the ability not only to monitor land surface variables but also to forecast them, by providing improved initial conditions which impacts persist through time. LDAS-Monde reanalysis has a potential to be used to monitor extreme events like agricultural drought, also. Finally, limitations related to LDAS-Monde and current satellite-derived observations are exposed as well as several insights on how to use alternative datasets to analyze soil moisture and vegetation state.

Sensitivity of U.S. Drought Prediction Skill to Land Initial States

2020 ◽  
Vol 21 (12) ◽  
pp. 2793-2811 ◽  
Author(s):  
Chul-Su Shin ◽  
Bohua Huang ◽  
Paul A. Dirmeyer ◽  
Subhadeep Halder ◽  
Arun Kumar
Keyword(s):  
United States ◽  
Soil Moisture ◽  
Initial Conditions ◽  
The United States ◽  
Prediction Skill ◽  
Severe Drought ◽  
Eastern United States ◽  
Drought Prediction ◽  
Forecast Lead Time ◽  
Initial States

AbstractIn addition to remote SST forcing, realistic representation of land forcing (i.e., soil moisture) over the United States is critical for a prediction of U.S. severe drought events approximately one season in advance. Using “identical twin” experiments with different land initial conditions (ICs) in the 32-yr (1979–2010) CFSv2 reforecasts (NASA GLDAS-2 reanalysis versus NCEP CFSR), sensitivity and skill of U.S. drought predictions to land ICs are evaluated. Although there is no outstanding performer between the two sets of forecasts with different land ICs, each set shows greater skill in some regions, but their locations vary with forecast lead time and season. The 1999 case study demonstrates that although a pattern of below-normal SSTs in the Pacific in the fall and winter is realistically reproduced in both reforecasts, GLDAS-2 land initial states display a stronger east–west gradient of soil moisture, particularly drier in the eastern United States and more consistent with observations, leading to warmer surface temperature anomalies over the United States. Anomalies lasting for one season are accompanied by more persistent barotropic (warm core) anomalous high pressure over CONUS, which results in better prediction skill of this drought case up to 4 months in advance in the reforecasts with GLDAS-2 land ICs. Therefore, it is essential to minimize the uncertainty of land initial states among the current land analyses for improving U.S. drought prediction on seasonal time scales.

scholarly journals Microcomputers in the Teaching of Astronomy

1990 ◽  
Vol 105 ◽  
pp. 159-170 ◽  
Author(s):  
Robert J. Dukes
Keyword(s):  
United States ◽  
Computer Simulations ◽  
Initial Conditions ◽  
The United States ◽  
Homework Exercise

There are many ways to use computers in teaching. This paper discusses one of those ways: as an adjunct to the introductory astronomy course as taught in the United States.The computer allows the demonstration of phenomena in a graphic dynamic manner, so its use can enable students to gain a deeper understanding of the material than they might when they passively listen to a lecture, look at slides, or study a textbook. In a very real sense, material presented in a computer is similar to that presented by film or video, but with one major difference: viewing movies is essentially a passive experience while interacting with a computer is an active one. Using computer simulations, the user can vary initial conditions and observe the effect of changes. This ability is the case whether the person doing the interacting is the instructor during a lecture or the student during a lab or while independently executing a homework exercise.

scholarly journals Hydrologic Prediction over the Conterminous United States Using the National Multi-Model Ensemble

2014 ◽  
Vol 15 (4) ◽  
pp. 1457-1472 ◽  
Author(s):  
Kingtse C. Mo ◽  
Dennis P. Lettenmaier
Keyword(s):  
United States ◽  
Initial Conditions ◽  
Dominant Role ◽  
The United States ◽  
Hydrologic Model ◽  
Forecast Skill ◽  
Model Ensemble ◽  
Infiltration Capacity ◽  
Forecast Period ◽  
Ensemble Mean

Abstract The authors analyzed the skill of monthly and seasonal soil moisture (SM) and runoff (RO) forecasts over the United States performed by driving the Variable Infiltration Capacity (VIC) hydrologic model with forcings derived from the National Multi-Model Ensemble hindcasts (NMME_VIC). The grand ensemble mean NMME_VIC forecasts were compared to ensemble streamflow prediction (ESP) forecasts derived from the VIC model forced by resampling of historical observations during the forecast period (ESP_VIC), using the same initial conditions as NMME_VIC. The forecast period is from 1982 to 2010, with the forecast initialized on 1 January, 1 April, 5 July, and 3 October. Overall, forecast skill is seasonally and regionally dependent. The authors found that 1) the skill of the grand ensemble mean NMME_VIC forecasts is comparable with that of the individual model that has the highest skill; 2) for all forecast initiation dates, the initial conditions play a dominant role in forecast skill at 1-month lead, and at longer lead times, forcings derived from NMME forecasts start to contribute to forecast skill; and 3) the initial conditions dominate contributions to skill for a dry climate regime that covers the western interior states for all seasons and the north-central part of the country for January. In this regime, the forecast skill for both methods is high even at 3-month lead. This regime has low mean precipitation and precipitation variations, and the influence of precipitation on SM and RO is weak. In contrast, a wet regime covers the region from the Gulf states to the Tennessee and Ohio Valleys for forecasts initialized in January and April, the Southwest monsoon region, the Southeast, and the East Coast in summer. In these dynamically active regions, where rainfall depends on the path of the moisture transport and atmospheric forcing, forecast skill is low. For this regime, the climate forecasts contribute to skill. Skillful precipitation forecasts after lead 1 have the potential to improve SM and RO forecast skill, but it was found that this mostly was not the case for the NMME models.

scholarly journals Aerodynamic Optimization of an Over-the-Wing-Nacelle-Mount Configuration

2011 ◽  
Vol 2011 ◽  
pp. 1-13 ◽  
Author(s):  
Daisuke Sasaki ◽  
Kazuhiro Nakahashi
Keyword(s):  
Interference Effect ◽  
Jet Engines ◽  
Aerodynamic Design ◽  
Aerodynamic Optimization ◽  
High Lift ◽  
Aerodynamic Efficiency ◽  
Wing Geometry ◽  
Aerodynamic Interference ◽  
Drag Ratio ◽  
Lift To Drag Ratio

An over-the-wing-nacelle-mount airplane configuration is known to prevent the noise propagation from jet engines toward ground. However, the configuration is assumed to have low aerodynamic efficiency due to the aerodynamic interference effect between a wing and a nacelle. In this paper, aerodynamic design optimization is conducted to improve aerodynamic efficiency to be equivalent to conventional under-the-wing-nacelle-mount configuration. The nacelle and wing geometry are modified to achieve high lift-to-drag ratio, and the optimal geometry is compared with a conventional configuration. Pylon shape is also modified to reduce aerodynamic interference effect. The final wing-fuselage-nacelle model is compared with the DLR F6 model to discuss the potential of Over-the-Wing-Nacelle-Mount geometry for an environmental-friendly future aircraft.

Toward a turbulent constitutive relation

1970 ◽  
Vol 41 (2) ◽  
pp. 413-434 ◽  
Author(s):  
J. L. Lumley
Keyword(s):  
Reynolds Stress ◽  
Time Scale ◽  
Ad Hoc ◽  
Initial Conditions ◽  
Equilibrium Structure ◽  
Mean Velocity ◽  
Equilibrium Time ◽  
Universal Structure ◽  
High Reynolds ◽  
Stress Dependent

In an attempt to explain the failure of the various pure homogeneous strain experiments to reach equilibrium (and consequently to support the contention of Townsend of an equilibrium structure of the Reynolds stress dependent only on geometry), the nature of the general Reynolds stress-mean velocity relation is examined. It is shown that if homogeneous flows become asymptotically independent of initial conditions, and if the Reynolds stress bearing structure can be characterized by a single time scale (i.e.–at sufficiently high Reynolds number) then these flows behave like classical non-linear viscoelastic media, with the Reynolds stress structure dependent on the (strain-rate) (time scale) product. Thus, the existence of an equilibrium structure implies the existence of an equilibrium time scale and a universal value of the product. The ideas permitting Reynolds stress and mean velocity to be related are applied to the dissipative structure in homogeneous flows, and it is found that in such flow the time scale never ceases to grow, so that these flows can never reach an equilibrium structure. With the aid of an ad-hoc assumption these flows are examined in some detail, and the results of experiments are predicted with considerable accuracy. It is suggested that (inhomogeneous) flows having an equilibrium time scale may, in the homogeneous limit, be expected to display a universal structure. The small departure from universality induced by the large eddies associated with inhomogeneity may be adequately predicted by this same ad-hoc model.

scholarly journals The Roles of Radiative Forcing, Sea Surface Temperatures, and Atmospheric and Land Initial Conditions in U.S. Summer Warming Episodes

2016 ◽  
Vol 29 (11) ◽  
pp. 4121-4135 ◽  
Author(s):  
Liwei Jia ◽  
Gabriel A. Vecchi ◽  
Xiaosong Yang ◽  
Richard G. Gudgel ◽  
Thomas L. Delworth ◽  
...  
Keyword(s):  
United States ◽  
Radiative Forcing ◽  
Heat Waves ◽  
Initial Conditions ◽  
The United States ◽  
Sea Surface ◽  
Temperature Anomalies ◽  
Summer Heat ◽  
Summer Warming ◽  
Direct Radiative Forcing

Abstract This study investigates the roles of radiative forcing, sea surface temperatures (SSTs), and atmospheric and land initial conditions in the summer warming episodes of the United States. The summer warming episodes are defined as the significantly above-normal (1983–2012) June–August 2-m temperature anomalies and are referred to as heat waves in this study. Two contrasting cases, the summers of 2006 and 2012, are explored in detail to illustrate the distinct roles of SSTs, direct radiative forcing, and atmospheric and land initial conditions in driving U.S. summer heat waves. For 2012, simulations with the GFDL atmospheric general circulation model reveal that SSTs play a critical role. Further sensitivity experiments reveal the contributions of uniform global SST warming, SSTs in individual ocean basins, and direct radiative forcing to the geographic distribution and magnitudes of warm temperature anomalies. In contrast, for 2006, the atmospheric and land initial conditions are the key drivers. The atmospheric (land) initial conditions play a major (minor) role in the central and northwestern (eastern) United States. Because of changes in radiative forcing, the probability of areal-averaged summer temperature anomalies over the United States exceeding the observed 2012 anomaly increases with time over the early twenty-first century. La Niña (El Niño) events tend to increase (reduce) the occurrence rate of heat waves. The temperatures over the central United States are mostly influenced by El Niño/La Niña, with the central tropical Pacific playing a more important role than the eastern tropical Pacific. Thus, atmospheric and land initial conditions, SSTs, and radiative forcing are all important drivers of and sources of predictability for U.S. summer heat waves.

Initial Conditions and Emergence of Corporate Reorganization in the United States and England

2020 ◽  
pp. 21-46
Author(s):  
Sarah Paterson
Keyword(s):  
United States ◽  
Twentieth Century ◽  
Initial Conditions ◽  
Explanatory Power ◽  
The United States ◽  
Institutional Logics ◽  
Corporate Reorganization ◽  
Selective Review ◽  
The Us ◽  
The Way

This chapter is a scene-setting exercise, offering a brief and highly selective review of almost one hundred years of corporate reorganization in the US and England. It seeks to provide some explanation for the very different ways in which corporate reorganization developed in each jurisdiction. Overall, its purpose is to help to sketch out the conditions which prevailed when the account in the book really begins in the 1970s, and how they offer significant explanatory power for the way in which corporate reorganization law and practice emerges in each jurisdiction. Specifically, the chapter investigates the relatively stable corporate reorganization law and practice which prevailed in each jurisdiction for much of the twentieth century, and, in each case, the institutional logics, practices, and identities which gave rise to it.

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