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Article
Publication date: 23 March 2010

D.W. Marshall, S.J. Newman and C.B. Williams

The purpose of this paper is to investigate the effect a variety of different boundary layers have on a wing in ground‐effect.

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Abstract

Purpose

The purpose of this paper is to investigate the effect a variety of different boundary layers have on a wing in ground‐effect.

Design/methodology/approach

Experiments were carried out in the University of Southampton's 3′×2′ wind tunnel. A variable length splitter plate was designed and manufactured in order to generate four boundary‐layer thicknesses at a selected measurement position. A single element inverted GA(W)‐1 aerofoil was then introduced to the flow at varying heights above the plate. Laser Doppler anemometry (LDA) and surface static pressure measurements (both on the aerofoil surface and on the splitter plate) were recorded.

Findings

The flow beneath the wing is found to be affected considerably by the presence of the boundary layer. As the boundary‐layer thickness is increased, the under‐wing pressure is observed to increase, hence resulting in decreased suction. Further, the LDA results indicate a modification to the wake profile. In particular, at low wing heights, the wake is observed to become entrained in the boundary layer, to differing degrees dependant on the boundary layer present and the wing height.

Research limitations/implications

The acquisition of force values from the tests will have allowed further understanding of the “real world” implications of the presence of the boundary‐layer thicknesses on a wing in ground‐effect but this is not possible in the test facility used.

Practical implications

The aerodynamics of a wing in ground‐effect are of great interest for both lifting surfaces for aircraft and downforce generation in motorsport applications. The implications of this paper enhance the importance of understanding the boundary conditions present when wind tunnel testing for these applications.

Originality/value

Although the influence of the boundary layer on low ground clearance objects has been well documented, the methods used here, in particular the use of the pressure tapped splitter plate and LDA, allow a further insight into the explanations behind this influence.

Details

Aircraft Engineering and Aerospace Technology, vol. 82 no. 2
Type: Research Article
ISSN: 0002-2667

Keywords

Article
Publication date: 1 September 1955

T.R. Nonweiler

WRITING an introduction to an article by Mr S. B. Gates on Trailing‐Edge Flaps, which appeared in these columns in 1937, the Editor felt constrained to admit his bewilderment over…

Abstract

WRITING an introduction to an article by Mr S. B. Gates on Trailing‐Edge Flaps, which appeared in these columns in 1937, the Editor felt constrained to admit his bewilderment over the number and variety of types of high‐lift aid which then existed. Without intending any disrespect, I imagine that the progress of years must have added to his embarrassment. It has certainly added to the number of devices in use and under test.

Details

Aircraft Engineering and Aerospace Technology, vol. 27 no. 9
Type: Research Article
ISSN: 0002-2667

Article
Publication date: 20 June 2016

Karen Ingerslev

This paper reports from a qualitative case study of a change initiative undertaken in a Danish public hospital setting during national healthcare reforms. The purpose of this…

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Abstract

Purpose

This paper reports from a qualitative case study of a change initiative undertaken in a Danish public hospital setting during national healthcare reforms. The purpose of this paper is to challenge understandings of innovations as defined by being value-adding per se. Whether the effects of attempting to innovate are positive or negative is in this paper regarded as a matter of empirical investigation.

Design/methodology/approach

Narrative accounts of activities during the change initiative are analysed in order to elucidate the effects of framing the change initiative as innovation on which boundaries are created and crossed.

Findings

Framing change initiatives as innovation leads to intended as well as unanticipated boundary crossings where healthcare practitioners from different organizations recognize a shared problem and task. It also leads to unintended boundary reinforcements between “us and them” that may exclude the perspectives of patients or stakeholders when confronting complex problems in healthcare. This boundary reinforcement can lead to further fragmentation of healthcare despite the stated intention to create more integrated services.

Practical implications

The paper suggests that researchers as well as practitioners should not presume that intentions to innovate will by themselves enhance creativity and innovation. When analysing the intended, unintended as well as unanticipated consequences of framing change initiatives as innovation, researchers and practitioner gain nuanced knowledge about the effects of intending to innovate in complex settings such as healthcare.

Originality/value

This paper suggests the need for an analytical move from studying the effects of innovation to studying the effects of framing complex problems as a call for innovation.

Details

Journal of Health Organization and Management, vol. 30 no. 4
Type: Research Article
ISSN: 1477-7266

Keywords

Article
Publication date: 28 May 2020

Mahantesh M. Nandeppanavar, M.C. Kemparaju, R. Madhusudhan and S. Vaishali

The steady two-dimensional laminar boundary layer flow, heat and mass transfer over a flat plate with convective surface heat flux was considered. The governing nonlinear partial…

Abstract

Purpose

The steady two-dimensional laminar boundary layer flow, heat and mass transfer over a flat plate with convective surface heat flux was considered. The governing nonlinear partial differential equations were transformed into a system of nonlinear ordinary differential equations and then solved numerically by Runge–Kutta method with the most efficient shooting technique. Then, the effect of variable viscosity and variable thermal conductivity on the fluid flow with thermal radiation effects and viscous dissipation was studied. Velocity, temperature and concentration profiles respectively were plotted for various values of pertinent parameters. It was found that the momentum slip acts as a boost for enhancement of the velocity profile in the boundary layer region, whereas temperature and concentration profiles decelerate with the momentum slip.

Design/methodology/approach

Numerical Solution is applied to find the solution of the boundary value problem.

Findings

Velocity, heat transfer analysis is done with comparing earlier results for some standard cases.

Originality/value

100

Details

Multidiscipline Modeling in Materials and Structures, vol. 16 no. 5
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 2 January 2018

Mahmood Khalid, Khalid A. Juhany and Salah Hafez

The purpose of this paper is to use a computational technique to simulate the flow in a two-dimensional (2D) wind tunnel where the effect of the solid walls facing the model has…

Abstract

Purpose

The purpose of this paper is to use a computational technique to simulate the flow in a two-dimensional (2D) wind tunnel where the effect of the solid walls facing the model has been addressed using a porous geometry so that interference arriving at the solid walls are duly damped and a flow suction procedure has been adopted at the side wall to minimize the span-wise effect of the growing side wall boundary layer.

Design/methodology/approach

A CFD procedure based on discretization of the Navier–Stokes equations has been used to model the flow in a rectangular volume with appropriate treatment for solid walls of the confined volume in which the model is placed. The rectangular volume was configured by stacking O-Grid sections in a span-wise direction using geometric growth from the wall. A porous wall condition has been adapted to counter the wall interference signatures and a separate suction procedure has been implemented for reducing the side wall boundary layer effects.

Findings

It has been shown that through such corrective measures, the flow in a wind tunnel can be adequately simulated using computational modeling. Computed results were compared against experimental measurements obtained from IAR (Institute for Aerospace, Canada) and NAL (National Aeronautical Laboratory, Japan) to show that indeed appropriate corrective means may be adapted to reduce the interference effects.

Research limitations/implications

The solutions seemed to converge a lot better using relatively coarser grids which placed the shock locations closer to the experimental values. The finer grids were more stiff to converge and resulted in reversed flow with the two equation k-w model in the region where the intention was to draw out the fluid to thin down the boundary layer. The one equation Spalart–Allmaras model gave better result when porosity and wall suction routines were implemented.

Practical implications

This method could be used by industry to point check the results against certain demanding flow conditions and then used for more routine parametric studies at other conditions. The method would prove to be efficient and economical during early design stages of a configuration.

Originality/value

The method makes use of an O-grid to represent the confined test section and its dual treatment of wall interference and blockage effects through simultaneous application of porosity and boundary layer suction is believed to be quite original.

Details

Aircraft Engineering and Aerospace Technology, vol. 90 no. 1
Type: Research Article
ISSN: 1748-8842

Keywords

Article
Publication date: 14 May 2019

Ravisha M., I.S. Shivakumara and Mamatha A.L.

The onset of convection in a ferrofluid-saturated porous layer has been investigated using a local thermal nonequilibrium (LTNE) model by allowing the solid phase to transfer heat…

Abstract

Purpose

The onset of convection in a ferrofluid-saturated porous layer has been investigated using a local thermal nonequilibrium (LTNE) model by allowing the solid phase to transfer heat via a Cattaneo heat flux theory while the fluid phase to transfer heat via usual Fourier heat-transfer law. The flow in the porous medium is governed by modified Brinkman-extended Darcy model. The instability of the system is discussed exactly for stress-free boundaries, while for rigid-ferromagnetic/paramagnetic boundaries the results are obtained numerically using the Galerkin method. The presence of Cattaneo effect introduces oscillatory convection as the preferred mode of instability contrary to the occurrence of instability via stationary convection found in its absence. Besides, oscillatory ferroconvection is perceived when the solid thermal relaxation time parameter exceeds a threshold value and increase in its value is to hasten the oscillatory onset. The effect of different boundary conditions on the instability of the system is noted to be qualitatively same. The paper aims to discuss these issues.

Design/methodology/approach

The investigators would follow the procedure of Straughan (2013) to obtain the expression for Rayleigh number. The Brinkman-extended Darcy model is used to describe the flow in a porous medium. The investigators have used a Galerkin method to obtain the numerical results for rigid-ferromagnetic/paramagnetic boundaries, while the instability of the system is discussed exactly for stress-free boundaries.

Findings

The Cattaneo–LTNE porous ferroconvection has been analyzed for different velocity and magnetic boundary conditions. The Brinkman-extended Darcy model is used to describe the flow in a porous medium. The effect of different types of velocity and magnetic boundary conditions on the instability of the system has been highlighted. The instability of the system is discussed exactly for stress-free boundaries, while for rigid-ferromagnetic/paramagnetic boundaries the results are obtained numerically using the Galerkin method.

Originality/value

The novelty of the present paper is to combine LTNE and second sound effects in solids on thermal instability of a ferrofluid-saturated porous layer by retaining the usual Fourier heat-transfer law in the ferrofluid. The Brinkman-extended Darcy model is used to describe the flow in a porous medium. The effect of different types of velocity and magnetic boundary conditions on the instability of the system is discussed.

Details

Multidiscipline Modeling in Materials and Structures, vol. 15 no. 4
Type: Research Article
ISSN: 1573-6105

Keywords

Article
Publication date: 13 July 2021

Shayan Naseri Nia, Faranak Rabiei and M.M. Rashidi

This paper aims to use the Lattice Boltzmann method (LBM) to numerically simulate the natural convection heat transfer of Cu-water nanofluid in an L-shaped enclosure with curved…

Abstract

Purpose

This paper aims to use the Lattice Boltzmann method (LBM) to numerically simulate the natural convection heat transfer of Cu-water nanofluid in an L-shaped enclosure with curved boundaries.

Design/methodology/approach

LBM on three different models of curved L-shape cavity using staircase approach is applied to perform a comparative investigation for the effects of curved boundary on fluid flow and heat transfer. The staircase approximation is a straightforward and efficient approach to simulating curved boundaries in LBM.

Findings

The effect of curved boundary on natural convection in different parameter ranges of Rayleigh number and nanoparticle volume fraction is investigated. The curved L-shape results are also compared to the rectangular L-shape results that were also achieved in this study. The curved boundary LBM simulation is also validated with existing studies, which shows great accuracy in this study. The results show that the top curved boundary in curved L-shape models causes a notable increase in the Nusselt number values.

Originality/value

Based on existing literature, there is a lack of comparative studies which would specifically examine the effects of curved boundaries on natural convection in closed cavities. Particularly, the application of curved boundaries to an L-shape cavity has not been examined. In this study, curved boundaries are applied to the sharp corners of the bending section in the L-shape and the results of the curved L-shape models are compared to the simple rectangular L-shape model. Hence, a comparative evaluation is performed for the effect of curved boundaries on fluid flow in the L-shape enclosure.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 32 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 March 1999

G. Chen and H.A. Hadim

The objective of the present work was to perform a detailed numerical study of laminar forced convection in a three‐dimensional square duct packed with an isotropic granular…

Abstract

The objective of the present work was to perform a detailed numerical study of laminar forced convection in a three‐dimensional square duct packed with an isotropic granular material and saturated with a Newtonian fluid. Hydrodynamic and heat transfer results are reported for three different thermal boundary conditions. The flow in the porous medium was modeled using the semi‐empirical Brinkman‐Forchheimer‐extended Darcy model which also included the effects of variable porosity and thermal dispersion. Empirical models for variable porosity and thermal dispersion were determined based on existing three‐dimensional experimental measurements. Parametric studies were then conducted to investigate the effects of particle diameter, Reynolds number, Prandtl number and thermal conductivity ratio. The results showed that channeling phenomena and thermal dispersion effects are reduced considerably in a three‐dimensional duct compared with previously reported results for a two‐dimensional channel. It was found that the Reynolds number affects mainly the velocity gradient in the flow channeling region, while the particle diameter affects the width of the flow channeling region. As the Reynolds number increases or as the particle diameter decreases (i.e., when the inertia and thermal dispersion effects are enhanced), the Nusselt number increases. The effects of varing the Prandtl number on the magnitude of the Nusselt number were found to be more significant than those of the thermal conductivity ratio. Finally, the effects of varing the duct aspect ratio on the friction factor can be neglected for small particle diameter (Dp ≤ 0.01) or for high particle Reynolds number (Red ≥ 1000) due to the dominant bulk damping resistance from the porous matrix (Darcy term) or strong inertia effects (Forchheimer term), respectively.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 9 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 May 1993

MICHAEL J. NUSCA

An aerothermodynamic design code for axisymmetric projectiles has been developed using a viscous‐inviscid interaction scheme. Separate solution procedures for the inviscid and the…

Abstract

An aerothermodynamic design code for axisymmetric projectiles has been developed using a viscous‐inviscid interaction scheme. Separate solution procedures for the inviscid and the viscous (boundary layer) fluid dynamic equations are coupled by an iterative solution procedure. Non‐equilibrium, equilibrium and perfect gas boundary layer equations are included. The non‐equilibrium gas boundary layer equations assume a binary mixture (two species; atoms and molecules) of chemically reacting perfect gases. Conservation equations for each species include finite reaction rates applicable to high temperature air. The equilibrium gas boundary layer equations assume infinite rate reactions, while the perfect gas equations assume no chemical reactions. Projectile near‐wall and surface flow profiles (velocity, pressure, density, temperature and heat transfer) representing converged solutions to both the inviscid and viscous equations can be obtained in less than two minutes on minicomputers. A technique for computing local reverse flow regions is included. Computations for yawed projectiles are accomplished using a coordinate system transformation technique that is valid for small angle‐of‐attack. Computed surface pressure, heat transfer rates and aerodynamic forces and moments for 1.25 &le Mach No. &le 10.5 are compared to wind tunnel and free flight measurements on flat plate, blunt‐cone, and projectile geometries such as a cone‐cylinder‐flare.

Details

Engineering Computations, vol. 10 no. 5
Type: Research Article
ISSN: 0264-4401

Keywords

Article
Publication date: 9 August 2022

Hanieh Javadi Khasraghi, Xuan Wang, Jun Sun and Bahar Javadi Khasraghi

To obtain optimal deliverables, more and more crowdsourcing platforms allow contest teams to submit tentative solutions and update scores/rankings on public leaderboards. Such…

Abstract

Purpose

To obtain optimal deliverables, more and more crowdsourcing platforms allow contest teams to submit tentative solutions and update scores/rankings on public leaderboards. Such feedback-seeking behavior for progress benchmarking pertains to the team representation activity of boundary spanning. The literature on virtual team performance primarily focuses on team characteristics, among which network closure is generally considered a positive factor. This study further examines how boundary spanning helps mitigate the negative impact of network closure.

Design/methodology/approach

This study collected data of 9,793 teams in 246 contests from Kaggle.com. Negative binomial regression modeling and linear regression modeling are employed to investigate the relationships among network closure, boundary spanning and team performance in crowdsourcing contests.

Findings

Whereas network closure turns out to be a negative asset for virtual teams to seek platform feedback, boundary spanning mitigates its impact on team performance. On top of such a partial mediation, boundary spanning experience and previous contest performance serve as potential moderators.

Practical implications

The findings offer helpful implications for researchers and practitioners on how to break network closure and encourage boundary spanning with the establishment of facilitating structures in crowdsourcing contests.

Originality/value

The study advances the understanding of theoretical relationships among network closure, boundary spanning and team performance in crowdsourcing contests.

Details

Information Technology & People, vol. 36 no. 6
Type: Research Article
ISSN: 0959-3845

Keywords

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