scholarly journals An Investigation of Aerodynamic Effects of Body Morphing for Passenger Cars in Close-Proximity

Fluids ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 64
Author(s):  
Geoffrey Le Good ◽  
Max Resnick ◽  
Peter Boardman ◽  
Brian Clough
Keyword(s):  
Large Scale ◽  
Aerodynamic Drag ◽  
Autonomous Vehicle ◽  
Small Scale ◽  
Bluff Bodies ◽  
Passenger Cars ◽  
Current Trends ◽  
Close Proximity ◽  
Potential Energy Saving ◽  
The Individual

The potential energy-saving benefit for vehicles when travelling in a ‘platoon’ formation results from the reduction in total aerodynamic drag which may result from the interaction of bluff bodies in close-proximity. Early investigations of platooning, prompted by problems of congestion, had shown the potential for drag reduction but was not pursued. More recently, technologies developed for connected-autonomous vehicle control have provided a renewed interest in platooning particularly within the commercial vehicle industry. To date, most aerodynamics-based considerations of platooning have been conducted to assess the sensitivity of drag-saving to vehicle spacing and were based on formations of identically shaped constituents. In this study, the interest was the sensitivity of drag-saving to the shape of the individual platoon constituents. A new reference car, the Resnick model, was specially designed to include front and rear-end add-on sections to make distinct changes in profile form and simulate large-scale body morphing. The results of wind tunnel tests on small-scale models suggested that current trends in low-drag styling may not provide the ideal shape for platoon constituent members and that optimised forms are likely to be dependent upon position in the platoon.

Nonlinear interactions in turbulence with strong irrotational straining

1997 ◽  
Vol 337 ◽  
pp. 333-364 ◽  
Author(s):  
N.K.-R. KEVLAHAN ◽  
J.C.R. HUNT
Keyword(s):  
Large Scale ◽  
Order Term ◽  
Initial Energy ◽  
Perturbation Series ◽  
Small Scale ◽  
Bluff Bodies ◽  
Leading Order ◽  
Viscous Effects ◽  
First Case ◽  
Maximum Amplification

The rate of growth of the nonlinear terms in the vorticity equation are analysed for a turbulent flow with r.m.s. velocity u0 and integral length scale L subjected to a strong uniform irrotational plane strain S, where (u0/L)/S=ε[Lt ]1. The rapid distortion theory (RDT) solution is the zeroth-order term of the perturbation series solution in terms of ε. We use the asymptotic form of the convolution integrals for the leading-order nonlinear terms when β= exp(−St)[Lt ]1 to determine at what time t and beyond what wavenumber k (normalized on L) the perturbation series in ε fails, and hence derive the following conditions for the validity of RDT in these flows. (a) The magnitude of the nonlinear terms of order ε depends sensitively on the amplitude of eddies with large length scales in the direction x2 of negative strain. (b) If the integral of the velocity component u2 is zero the leading-order nonlinear terms increase and decrease in the same way as the linear terms, even those that decrease exponentially. In this case RDT calculations of vorticity spectra become invalid at a time tNL∼L/u0k−3 independent of ε and the power law of the initial energy spectrum, but the calculation of the r.m.s. velocity components by RDT remains accurate until t= TNL∼L/u0, when the maximum amplification of r.m.s. vorticity is ω/S∼εexp(ε−1)[Gt ]1. (c) If this special condition does not apply, the leading-order nonlinear terms increase faster than the linear terms by a factor O(β−1). RDT calculations of the vorticity spectrum then fail at a shorter time tNL∼(1/S) ln(ε−1k−3); in this case TNL∼(1/S) ln(ε−1) and the maximum amplification of r.m.s. vorticity is ω/S∼1. (d) Viscous effects dominate when t[Gt ](1/S) ln(k−1(Re/ε)1/2). In the first case RDT fails immediately in this range, while in the second case RDT usually fails before viscosity becomes important. The general analytical result (a) is confirmed by numerical evaluation of the integrals for a particular form of eddy, while (a), (b), (c) are explained physically by considering the deformation of differently oriented vortex rings. The results are compared with small-scale turbulence approaching bluff bodies where ε[Lt ]1 and β[Lt ] 1.These results also explain dynamically why the intermediate eigenvector of the strain S aligns with the vorticity vector, why the greatest increase in enstrophy production occurs in regions where S has a positive intermediate eigenvalue; and why large-scale strain S of a small-scale vorticity can amplify the small-scale strain rates to a level greater than S – one of the essential characteristics of high-Reynolds-number turbulence.

Wessex in Context

2010 ◽  
Author(s):  
Niall Sharples
Keyword(s):  
Large Scale ◽  
Daily Basis ◽  
Small Scale ◽  
Internal Dynamic ◽  
Archaeological Record ◽  
Human Relationships ◽  
Architectural Form ◽  
Individual Agency ◽  
The People ◽  
The Individual

In this book I have attempted to create a new agenda for the study of Britain in the last millennium BC. The book consciously sets out, in its structure and content, to direct attention away from the nature of the archaeological record towards the nature of past human societies. This does not mean I am not interested in the archaeological record, and readers will have noted there is a considerable amount of detail in the text, perhaps too much for some people; but the data has to be examined in relation to the people who lived in a particular place at a particular time: ‘the archaeologist is digging up, not things, but people’ (Wheeler 1954b: v). The objective has been to outline the overall constraints of place and time (Chapter 2) and to see how these created a distinctive archaeological record that differed not only from other areas of Britain, but which varied significantly within the region. I examine how people created communities (Chapter 3) and explore how the mechanisms used to organize human relationships, within that society, changed through time. These changes were partly brought about through events outside their control, but always in a way that was affected by their own particular circumstances. I consider how the most ubiquitous architectural form in later prehistory, the house, was used to structure social relationships on a daily basis in relation to the family, and how this provided a template for thinking about the world (Chapter 4). The analysis concludes with an examination of how these societies considered individual freedom and connectedness, and how the complex variability of individual agency provides an internal dynamic to social change that was influenced by external events, but not led by them (Chapter 5). When I originally conceived of this book the structure was reversed: I started with the individual and worked up to the organization of the larger landscapes. At first sight this may sound a more sensible way of presenting the evidence, moving from small-scale structures to large-scale processes, but during the writing of the book I found this did not seem to work.

scholarly journals Simulated and observed horizontal inhomogeneities of optical thickness of Arctic stratus

2018 ◽  
Vol 18 (17) ◽  
pp. 13115-13133 ◽  
Author(s):  
Michael Schäfer ◽  
Katharina Loewe ◽  
André Ehrlich ◽  
Corinna Hoose ◽  
Manfred Wendisch
Keyword(s):  
Wind Velocity ◽  
Optical Thickness ◽  
Large Scale ◽  
Atmospheric Model ◽  
Sensitivity Study ◽  
Small Scale ◽  
Airborne Measurements ◽  
Cloud Properties ◽  
Scale Structures ◽  
The Individual

Abstract. Two-dimensional horizontal fields of cloud optical thickness τ derived from airborne measurements of solar spectral, cloud-reflected radiance are compared with semi-idealized large eddy simulations (LESs) of Arctic stratus performed with the Consortium for Small-scale Modeling (COSMO) atmospheric model. The measurements were collected during the Vertical Distribution of Ice in Arctic Clouds (VERDI) campaign carried out in Inuvik, Canada, in April/May 2012. The input for the LESs is obtained from collocated airborne dropsonde observations of a persistent Arctic stratus above the sea-ice-free Beaufort Sea. Simulations are performed for spatial resolutions of 50 m (1.6 km × 1.6 km domain) and 100 m (6.4 km × 6.4 km domain). Macrophysical cloud properties, such as cloud top altitude and vertical extent, are well captured by the COSMO simulations. However, COSMO produces rather homogeneous clouds compared to the measurements, in particular for the simulations with coarser spatial resolution. For both spatial resolutions, the directional structure of the cloud inhomogeneity is well represented by the model. Differences between the individual cases are mainly associated with the wind shear near cloud top and the vertical structure of the atmospheric boundary layer. A sensitivity study changing the wind velocity in COSMO by a vertically constant scaling factor shows that the directional, small-scale cloud inhomogeneity structures can range from 250 to 800 m, depending on the mean wind speed, if the simulated domain is large enough to capture also large-scale structures, which then influence the small-scale structures. For those cases, a threshold wind velocity is identified, which determines when the cloud inhomogeneity stops increasing with increasing wind velocity.

Appropriate technologies for the future

1980 ◽  
Vol 209 (1174) ◽  
pp. 183-186 ◽  
Keyword(s):  
Food Production ◽  
Large Scale ◽  
Low Cost ◽  
Health Needs ◽  
Small Scale ◽  
Cost Of Energy ◽  
Prophylactic Measures ◽  
The Future ◽  
The Individual ◽  
The Third World

Crystal ball gazing is a hazardous occupation: the sharper the picture, the greater the possibility of error. In the future, appropriate technologies that will raise standards of health and diminish the prevalence of disease in the Third World must take cognizance of such factors as burgeoning population growth, impossibly high cost of energy sources, a widening gap between food requirements and food production, increasing urbanization, and inherent difficulties of control of disease vectors and water-borne diseases. The technologies that must be made available will be both large-scale and small-scale, low-cost and simple, improving life for the individual and the community, mediated by appropriately trained and adequately supervised polycompetent auxiliaries. The present reappraisal of health needs in the context of food (seeds, soils, irrigation, protection against loss of the harvested products) and of prevention of disease by appropriate prophylactic measures and its treatment, will necessitate hard thinking and greater cooperation between all concerned.

scholarly journals Some Observations on Shape Factors Influencing Aerodynamic Lift on Passenger Cars

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 44
Author(s):  
Jeff Howell ◽  
Steve Windsor ◽  
Martin Passmore
Keyword(s):  
Wind Tunnel ◽  
High Performance ◽  
Aerodynamic Drag ◽  
Small Scale ◽  
Shape Features ◽  
Passenger Cars ◽  
Shape Factors ◽  
Front End ◽  
Factors Influencing ◽  
Aerodynamic Lift

The car aerodynamicist developing passenger cars is primarily interested in reducing aerodynamic drag. Considerably less attention is paid to the lift characteristics except in the case of high-performance cars. Lift, however, can have an effect on both performance and stability, even at moderate speeds. In this paper, the basic shape features which affect lift and the lift distribution, as determined from the axle loads, are examined from wind tunnel tests on various small-scale bodies representing passenger cars. In most cases, the effects of yaw are also considered. The front-end shape is found to have very little effect on overall lift, although it can influence the lift distribution. The shape of the rear end of the car, however, is shown to be highly influential on the lift. The add-on components and other features can have a significant effect on the lift characteristics of real passenger cars and are briefly discussed. The increase in lift at yaw is, surprisingly, almost independent of shape, as shown for the simple bodies. This characteristic is less pronounced on real passenger cars but lift increase at yaw is shown to rise with vehicle length.

scholarly journals Enhancing Kidney Vasculature in Tissue Engineering—Current Trends and Approaches: A Review

Biomimetics ◽  
2021 ◽  
Vol 6 (2) ◽  
pp. 40
Author(s):  
Charlotta G. Lebedenko ◽  
Ipsita A. Banerjee
Keyword(s):  
Tissue Engineering ◽  
Large Scale ◽  
Kidney Diseases ◽  
Kidney Tissue ◽  
Small Scale ◽  
Current Trends ◽  
Large Size ◽  
Microphysiological Systems ◽  
Primary Obstacle ◽  
Kidney Stem Cells

Chronic kidney diseases are a leading cause of fatalities around the world. As the most sought-after organ for transplantation, the kidney is of immense importance in the field of tissue engineering. The primary obstacle to the development of clinically relevant tissue engineered kidneys is precise vascularization due to the organ’s large size and complexity. Current attempts at whole-kidney tissue engineering include the repopulation of decellularized kidney extracellular matrices or vascular corrosion casts, but these approaches do not eliminate the need for a donor organ. Stem cell-based approaches, such as kidney organoids vascularized in microphysiological systems, aim to construct a kidney without the need for organ donation. These organ-on-a-chip models show complex, functioning kidney structures, albeit at a small scale. Novel methodologies for developing engineered scaffolds will allow for improved differentiation of kidney stem cells and organoids into larger kidney grafts with clinical applications. While currently, kidney tissue engineering remains mostly limited to individual renal structures or small organoids, further developments in vascularization techniques, with technologies such as organoids in microfluidic systems, could potentially open doors for a large-scale growth of whole engineered kidneys for transplantation.

scholarly journals Relation between Large-Scale Circulation and European Winter Temperature: Does It Hold under Warmer Climate?

2010 ◽  
Vol 23 (13) ◽  
pp. 3752-3760 ◽  
Author(s):  
K. Goubanova ◽  
L. Li ◽  
P. Yiou ◽  
F. Codron
Keyword(s):  
Large Scale ◽  
Winter Temperature ◽  
Small Scale ◽  
Large Scale Circulation ◽  
Local Climate ◽  
Temperature Changes ◽  
Weather Regimes ◽  
High Resolution Models ◽  
The Individual ◽  
The Impact

Abstract The idea of using large-scale information to predict local climate variability is widely exploited in climate change impact studies as an alternative to computationally expensive high-resolution models. This approach implies the hypothesis that the statistical relationship between large-scale climate states and local variables defined for the present-day climate remains valid in the altered climate. In this paper, the concept of weather regimes is used to deduce a relationship between large-scale circulation and European winter temperature. The change in temperature with increased greenhouse gases is, however, not homogeneous among the individual regimes. As a result, the impact of the weather regimes on local temperature changes varies in the future, limiting its usefulness for refining temperature changes to the small scale.

scholarly journals Statistical Analysis of Dynamic Subgrid Modeling Approaches in Large Eddy Simulation

Aerospace ◽  
2021 ◽  
Vol 8 (12) ◽  
pp. 375
Author(s):  
Mohammad Khalid Hossen ◽  
Asokan Mulayath Variyath ◽  
Jahrul M. Alam
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Large Scale ◽  
Joint Probability ◽  
Energy Dissipation Rate ◽  
Statistical Characteristics ◽  
Small Scale ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Individual

In large eddy simulation (LES) of turbulent flows, dynamic subgrid models would account for an average cascade of kinetic energy from the largest to the smallest scales of the flow. Yet, it is unclear which of the most critical dynamical processes can ensure the criterion mentioned above. Furthermore, evidence of vortex stretching being the primary mechanism of the cascade is not out of the question. In this article, we study essential statistical characteristics of vortex stretching. Our numerical results demonstrate that vortex stretching rate provides the energy dissipation rate necessary for modeling subgrid-scale turbulence. We have compared the interaction of subgrid stresses with the filtered quantities among four models using invariants of the velocity gradient tensor. The individual and the joint probability of vortex stretching and strain amplification show that vortex stretching rate is highly correlated with the energy cascade rate. Sheet-like flow structures are correlated with viscous dissipation, and vortex tubes are more stretched than compressed. The overall results indicate that the stretching mechanism extracts energy from the large-scale straining motion and passes it onto small-scale stretched vortices.

scholarly journals Small-scale turbulence characteristics of two-dimensional bluff body wakes

2002 ◽  
Vol 459 ◽  
pp. 67-92 ◽  
Author(s):  
R. A. ANTONIA ◽  
T. ZHOU ◽  
G. P. ROMANO
Keyword(s):  
Porous Body ◽  
Large Scale ◽  
Bluff Body ◽  
Inertial Range ◽  
Small Scale ◽  
Bluff Bodies ◽  
Two Dimensional ◽  
The Difference ◽  
Scale Turbulence ◽  
Made In

Measurements have been made in nominally two-dimensional turbulent wakes generated by five different bluff bodies. Each wake has a different level of large-scale organization which is reflected in different amounts of large-scale anisotropy. Structure functions of streamwise (u) and lateral (v) velocity fluctuations at approximately the same value of Rλ, the Taylor microscale Reynolds number, indicate that inertial-range scales are significantly affected by the large-scale anisotropy. The effect is greater on v than u and more pronounced for the porous-body wakes than the solid-body wakes. In particular, ‘relative’ values of the scaling (or power-law) exponents indicate that the magnitude of the transverse exponents can exceed that of the longitudinal ones in the porous-body wakes. This is supported by the inertial-range behaviour of the spectra of u and v. The difference between the transverse and longitudinal exponents appears to depend on the large-scale anisotropy of the flow, as measured by the ratio of the variances of v and u and ratio of the integral length scales of v and u. The spanwise vorticity spectra are much less affected by the anisotropy than the spectra of u and v.

scholarly journals UCalMiCeL – UNIFIED INTRINSIC AND EXTRINSIC CALIBRATION OF A MULTI-CAMERA-SYSTEM AND A LASERSCANNER

2017 ◽  
Vol IV-2/W3 ◽  
pp. 17-24 ◽  
Author(s):  
M. Hillemann ◽  
B. Jutzi
Keyword(s):  
Large Scale ◽  
Calibration Method ◽  
Bundle Adjustment ◽  
Sensor System ◽  
Small Scale ◽  
Camera System ◽  
Extrinsic Calibration ◽  
Camera Systems ◽  
The Individual ◽  
Calibration Approach

Unmanned Aerial Vehicle (UAV) with adequate sensors enable new applications in the scope between expensive, large-scale, aircraftcarried remote sensing and time-consuming, small-scale, terrestrial surveyings. To perform these applications, cameras and laserscanners are a good sensor combination, due to their complementary properties. To exploit this sensor combination the intrinsics and relative poses of the individual cameras and the relative poses of the cameras and the laserscanners have to be known. In this manuscript, we present a calibration methodology for the <i>Unified Intrinsic and Extrinsic Calibration of a Multi-Camera-System and a Laserscanner (UCalMiCeL)</i>. The innovation of this methodology, which is an extension to the calibration of a single camera to a line laserscanner, is an unifying bundle adjustment step to ensure an optimal calibration of the entire sensor system. We use generic camera models, including pinhole, omnidirectional and fisheye cameras. For our approach, the laserscanner and each camera have to share a joint field of view, whereas the fields of view of the individual cameras may be disjoint. The calibration approach is tested with a sensor system consisting of two fisheye cameras and a line laserscanner with a range measuring accuracy of 30&amp;thinsp;<i>mm</i>. We evaluate the estimated relative poses between the cameras quantitatively by using an additional calibration approach for Multi-Camera-Systems based on control points which are accurately measured by a motion capture system. In the experiments, our novel calibration method achieves a relative pose estimation with a deviation below 1.8&amp;deg; and 6.4&amp;thinsp;<i>mm</i>.

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