130 research outputs found
CFD Study of the Impact of Variable Cant Angle Winglets on Total Drag Reduction
No full textWinglets are commonly used drag-reduction and fuel-saving technologies in today’s aviation. The primary purpose of the winglets is to reduce the lift-induced drag, therefore improving fuel efficiency and aircraft performance. Traditional winglets are designed as fixed devices attached at the tips of the wings. However, because they are fixed surfaces, they give their best lift-induced drag reduction at a single design point. In this work, we propose the use of variable cant angle winglets which could potentially allow aircraft to get the best all-around performance (in terms of lift-induced drag reduction), at different angle-of-attack values. By using computational fluid dynamics, we study the influence of the winglet cant angle and sweep angle in the performance of a benchmark wing at a Mach number of 0.8395. The results obtained demonstrate that by carefully adjusting the cant angle, the aerodynamic performance can be improved at different angles of attack
Variable cant angle winglets for improvement of aircraft flight performance
No full textTraditional winglets are designed as fixed devices attached at the tips of the wings. The primary purpose of the winglets is to reduce the lift-induced drag, therefore improving aircraft performance and fuel efficiency. However, because winglets are fixed surfaces, they cannot be used to control lift-induced drag reductions or to obtain the largest lift-induced drag reductions at different flight conditions (take-off, climb, cruise, loitering, descent, approach, landing, and so on). In this work, we propose the use of variable cant angle winglets which could potentially allow aircraft to get the best all-around performance (in terms of lift-induced drag reduction), at different flight phases. By using computational fluid dynamics, we study the influence of the winglet cant angle and sweep angle on the performance of a benchmark wing at Mach numbers of 0.3 and 0.8395. The results obtained demonstrate that by adjusting the cant angle, the aerodynamic performance can be improved at different flight conditions
Adjoint-aided Homogenisation for Flows Through Heterogeneous Membranes
No full textPorous membranes, like nets or filters, are thin structures that allow fluid to flow through their pores. Homogenisation can be used to rigorously link the flow velocity with the stresses on the membrane via several coefficients (e.g. permeability and slip) stemming from the solution of Stokes problems at the pore level. For a periodic microstructure, the geometry of a single pore determines these coefficients for the whole membrane. However, many biological membranes are not periodic, and the porous microstructure of industrial membranes can be modified to address specific needs, resulting in non-periodic patterns of solid inclusions and pores. In this case, multiple microscopic calculations are needed to retrieve the local non-periodic membrane properties, negatively affecting the efficiency of the homogenised model. In this paper, we introduce an adjoint-based procedure that drastically reduces the computational cost of these operations by computing the pore-scale solution's first- and second-order sensitivities to geometric modifications. This adjoint-based technique only requires the solution of a few problems on a reference geometry and allows us to find the homogenised solution on any number of modified geometries. This new adjoint-based homogenisation procedure predicts the macroscopic flow around a thin aperiodic porous membrane at a fraction of the computational cost of classical approaches while maintaining comparable accuracy.LFM
Effective flows across diffusio-phoretic membranes
No full textFlows enabled by phoretic mechanisms are of significant interest in several biological and biomedical processes, such as bacterial motion and targeted drug delivery. Here, we develop a homogenisation-based macroscopic boundary condition that describes the effective flow across a diffusio-phoretic microstructured membrane, where the interaction between the membrane walls and the solute particles is modelled via a potential approach. We consider two cases where potential variations occur (i) at the pore scale and (ii) only in the close vicinity of the boundary, allowing for a simplified version of the macroscopic flow description, in the latter case. Chemical interactions at the microscale are rigorously upscaled to macroscopic phoretic solvent velocity and solute flux contributions, and added to the classical permeability and diffusivity properties of the membrane. These properties stem from the solution of Stokes advection–diffusion problems at the microscale, some of them forced by an interaction potential term. Eventually, we show an application of the macroscopic model to develop minimal phoretic pumps, showcasing its suitability for efficient design and optimisation procedures.LFM
Homogenization of Flows in Porous Membranes: A Journey Across Scales
No full textPorous media are solid structures perforated by a matrix of pores, which may let a fluid flow across them. Geometrically, we can classify them as "thin" if their thickness is comparable with the size of their pores, and "bulk" otherwise. These structures can be found in various biological and man-made systems, such as cell membranes, sponges, insect feathers, flow control devices for aerodynamics and cooling applications and filtration devices. A common feature of these systems is the presence of a large difference in size between the pores and the full membrane.
From the modeling point of view, two approaches are generally considered: direct solutions of the governing equations and average models. The first strategy guarantees high accuracy but may easily become computationally unaffordable, particularly when the pores are very small compared to the membrane. The second approach models the effect of the membrane using mathematical relations between the flow far from the membrane and the pore-scale behavior. These laws often rely on empirical coefficients, thus limiting their predictive capabilities. However, the computational cost associated with them is tiny compared to direct solutions, and they find use in many engineering simulation routines. Thanks to multi-scale techniques such as homogenization, we can derive such average models from first principles and find out that the coefficients appearing inside them stem from the solution of a set of solvability conditions valid at the pore level.
Starting from the elementary case of Stokes flow across a thin membrane, developed by Zampogna & Gallaire (2020), we build further pieces of theory into this framework. Inspired by the microstructure heterogeneities found at the cellular level or in defective man-made membranes, in chapter 2, we introduce an efficient adjoint-based methodology to evaluate the effect of many geometric modifications of the microstructure at a glance. The effect of inertia at the pore level, which is relevant for applications in the flow-control domain, is introduced in chapter 3, where we also consider the presence of a solute advected by the fluid flow. These chapters use a simple but effective approximation, consisting of a unique value for the homogenized flow variables on the membrane. This approximation, however, is sub-optimal when we deal with ``contradictory'' membrane properties, found in the so-called "Janus membranes". A new, discontinuous flow description at the membrane level in the presence of solute transport is described in chapter 4. The model is subsequently used in chapter 5 to deal with diffusio-phoresis, i.e. when a difference in local solute concentration, interacting with the membrane wall, causes a fluid flow. However, in many systems such as reverse-osmosis filters and cell membranes, the pore dimensions are so small that a continuous flow description may not be accurate. In such cases, the proper simulation tool is constituted by molecular dynamics simulations. In chapter 6, we present some results of the coupling between conventional molecular dynamics simulations and homogenization. The objective of this chapter is to propose a hybrid strategy to exploit the convenient computational cost of homogenization with the accuracy of molecular dynamics simulation. In chapter 7, we summarize the main results and discuss future perspectives for our methodology.LFM
Understanding consumer buying process in collaborative consumption
No full textCollaborative consumption (CC) is a form of exchange which occurs within three actors: a platform provider, a peer service provider, and a customer. CC has gained broad attention among researchers in recent years. How consumers make buying decisions in CC has gained less attention. Drawing on a review of relevant academic research author offers insights on (1) how the five-stage model of consumer buying process can help us to understand consumer buying behavior in collaborative consumption and (2) how consumer buying process differs in CC compared to other modes of exchange. With an enhanced understanding of the consumer buying process the author introduces a framework called the five-stage buying process in CC. Finally, author gives recommendations for platform providers and peer service providers
Quasi-Linear Homogenization for Large-Inertia Laminar Transport across Permeable Membranes
No full textPorous membranes are thin solid structures that allow the flow to pass
through their tiny openings, called pores. Flow inertia may play a significant
role in several filtration flows of natural and engineering interest. Here, we
develop a predictive macroscopic model to describe solvent and solute flows
past thin membranes for non-negligible inertia. We leverage homogenization
theory to link the solvent velocity and solute concentration to the jumps of
solvent stress and solute flux across the membrane. Within this framework, the
membrane acts as a boundary separating two distinct fluid regions. These jump
conditions rely on several coefficients, stemming from closure problems at the
microscopic pore scale. Two approximations for the advective terms of
Navier-Stokes and advection-diffusion equations are introduced to include
inertia in the microscopic problem. The approximate inertial terms couple the
micro- and macroscopic fields. Here, this coupling is solved numerically using
an iterative fixed-point procedure. We compare the resulting models against
full-scale simulations, with a good agreement both in terms of averaged values
across the membrane and far-field values. Eventually, we develop a strategy
based on unsupervised machine learning to improve the computational efficiency
of the iterative procedure. The extension of homogenization toward weak-inertia
flow configurations as well as the performed data-driven approximation may find
application in preliminary analyses as well as optimization procedures toward
the design of filtration systems, where inertia effects can be instrumental in
broadening the spectrum of permeability and selectivity properties of these
filters.Comment: 28 pages, 30 figure
Trial of healthy relationship initiatives for the very early years (THRIVE), evaluating Enhanced Triple P for Baby and Mellow Bumps additional social and care needs during pregnancy and their infants who are at higher risk of maltreatment : study protocol for a randomised controlled trial
No full textTHRIVE was funded by the National Institute for Health Research Public Health Research Programme (PHR Project: 11/3002/01). The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care. Intervention Subvention Funding was provided by the CSO and Scottish Government (GN12KH589 THRIVE). Neither the trial funders nor Sponsor (NHS Greater Glasgow & Clyde Health Board (Reference GN12KH589)) will have any involvement in the implementation of the study design or the analysis of the data. The Sponsor will, however, play an active role in the delivery of the interventions, through employing and managing group facilitators. The Sponsor will also be the grant holder of the subvention funding, granted by the CSO and the Scottish Government to deliver the groups. Approval for all documentation to be used with the trial must be granted by the Sponsor as it will be delivered to NHS patients. Likewise, permission must be sought from the trial funders prior to any public engagement regarding the trial including conference presentations or academic articles.Peer reviewe
Correction to: Enhancing maternal and infant wellbeing: study protocol for a feasibility trial of the Baby Triple P Positive Parenting programme for mothers with severe mental health difficulties (the IMAGINE study)
No full textFollowing publication of the original article [1], the authors reported that Elizabeth Camacho was omitted from the author name list
- …
