On recent developments in marginal separation theory

Braun, Stefan; Scheichl, Stefan

doi:10.1098/rsta.2013.0343

Cited by 19 publications

(11 citation statements)

References 23 publications

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“…Scaling the innovation fits perfectly along the demand curve will even lead to revenue in the amount of the integral underneath the curve. To make this possible several methods of business informatics can be used to extract, collect and analyze data, emulating variability and evolutionary processes during product development and research processes [1,2,3].…”

Section: Plastic Part Solutions For Agile Industry Applicationmentioning

confidence: 99%

New approach for the efficient attainment of flame retardancy using multi component injection molding

Schneider¹,

Hübner²,

Bourbigot³

2019

AIP Conference Proceedings

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The injection molding process yields many possibilities to create innovative plastic part solutions. Based on extensive research in distinct subject areas and the cross-disciplinary interconnection between different academic disciplines lately an interesting new approach for the efficient and effective attainment of flame retardancy could be identified: Multi component injection molding, where two or more plastic melts are injected next to or within each other during one cycle, can be used to produce innovative flame retardant plastic parts. These parts have an optimized skin/core structure with the core part consisting of the pristine polymer while the flame retardant polymer system is located in the skin. Such a structure proves to be ideal, because it allows for a faster protection dynamic.This broadening of the field of application of standard injection molding machines is made possible by the use of intermediate plates with individually suitable modular technological inserts. The modular inserts required for this kind of application comprise hot runners including shut off and control functions to separate and join melt flows from different injection units into one cavity. These modules make for the combination of the sequential and simultaneous injection of melts. In that account first trials which prove the concept to be viable have been conducted. Promising results will be shown as well as the principles of laboratory and industrial scale implementation of the underlying production process, while further research still is ongoing. In conclusion the paper will point out the advantages, possibilities and application potential given by this new approach. Cost savings will be given by the supersession of costly special machinery as well as achieved material savings and increased part quality and process stability.

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Section: Plastic Part Solutions For Agile Industry Applicationmentioning

confidence: 99%

New approach for the efficient attainment of flame retardancy using multi component injection molding

Schneider¹,

Hübner²,

Bourbigot³

2019

AIP Conference Proceedings

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“…The uniform flow pattern around a fixed plate continues to be actively studied both experimentally [13,14] and theoretically with the aim of improving the methods of laminarization of flow on the wing and turbulence description [15]. Much attention is paid to analysis of the flow in the region of the boundary layer separation from the plate [16], as well as calculation of the velocity field taking into account the complex multilevel flow structure [17]. The boundary layer separation from a plate with a sharpened leading edge leads to the formation of a sequence of leading-edge vortices with their properties studied for several values of the angles of attack in [18].…”

Section: Introductionmentioning

confidence: 99%

2D Hydrodynamics of a Plate: From Creeping Flow to Transient Vortex Regimes

Chashechkin

Zagumennyi²

2021

Fluids

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Based on the numerical and experimental visualization methods, the flow patterns around a uniformly moving plate located at an arbitrary angle of attack are studied. The study is based on the fundamental equations of continuity, momentum and stratifying substance transport for the cases of strong and weak stratified fluids, as well as potential and actually homogeneous ones. The visualization technique and computation codes were compiled bearing in mind conditions of internal waves, vortices, upstream, and downstream wakes registration, as well as the resolution of ligaments in the form of thin interfaces in schlieren flow images. The analysis was carried out in a unified mathematical formulation for a wide range of plate motion parameters, including slow diffusion-induced flows and fast transient vortex flows. The patterns of formation and subsequent evolution of the basic structural components, such as upstream disturbances, downstream wake, internal waves, vortices, and ligaments, are described both at start of motion and subsequent uniform movement of the plate. Calculations of forces acting on the obstacle in the flow were carried out to study effects of variations in fluid properties, flow conditions and plate parameters on the dynamic characteristics of the obstacle. The numerical and experimental results on the flow patterns around a plate are in a good agreement with each other for different flow regimes.

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“…Regularization methods in this regard were not yet known and moreover the computing power available at that time was still insufficient to solve the occasionally delicate nonlinear evolution equations numerically. Of course, high-end computing power is available now, and as far as the ill-posedness is concerned, we believe these difficulties can be overcome as well [ 28 ].…”

Section: Introductionmentioning

confidence: 99%

The triple-deck stage of marginal separation

2021

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The method of matched asymptotic expansions is applied to the investigation of transitional separation bubbles. The problem-specific Reynolds number is assumed to be large and acts as the primary perturbation parameter. Four subsequent stages can be identified as playing key roles in the characterization of the incipient laminar–turbulent transition process: due to the action of an adverse pressure gradient, a classical laminar boundary layer is forced to separate marginally (I). Taking into account viscous–inviscid interaction then enables the description of localized, predominantly steady, reverse flow regions (II). However, certain conditions (e.g. imposed perturbations) may lead to a finite-time breakdown of the underlying reduced set of equations. The ensuing consideration of even shorter spatio-temporal scales results in the flow being governed by another triple-deck interaction. This model is capable of both resolving the finite-time singularity and reproducing the spike formation (III) that, as known from experimental observations and direct numerical simulations, sets in prior to vortex shedding at the rear of the bubble. Usually, the triple-deck stage again terminates in the form of a finite-time blow-up. The study of this event gives rise to a noninteracting Euler–Prandtl stage (IV) associated with unsteady separation, where the vortex wind-up and shedding process takes place. The focus of the present paper lies on the triple-deck stage III and is twofold: firstly, a comprehensive numerical investigation based on a Chebyshev collocation method is presented. Secondly, a composite asymptotic model for the regularization of the ill-posed Cauchy problem is developed.

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On recent developments in marginal separation theory

Cited by 19 publications

References 23 publications

New approach for the efficient attainment of flame retardancy using multi component injection molding

New approach for the efficient attainment of flame retardancy using multi component injection molding

2D Hydrodynamics of a Plate: From Creeping Flow to Transient Vortex Regimes

The triple-deck stage of marginal separation

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