Search results
1 – 10 of over 2000Xu Wang, Ping Liu and Fumei Wang
Understanding the friction property between fabric and skin is an important issue in both product design and comfort evaluation. The purpose of this paper is to present a new type…
Abstract
Purpose
Understanding the friction property between fabric and skin is an important issue in both product design and comfort evaluation. The purpose of this paper is to present a new type of tester to evaluate the friction between skin and clothing.
Design/methodology/approach
The proposed fabric‐skin friction tester consists of test host, friction equipment, control box, and computer processing system. The suitable testing conditions (tension, friction velocity, and sample width) are recommended by comparing the parameters and actual test circumstance.
Findings
As the stress history characteristic of skin, the friction test should be repeated since the second time for each fabric and skin friction pair. The fluctuation of single friction curve and dispersion degree of several friction curves in repeated trials are both smallest under the recommended test conditions (200 cN tension, 500 mm/min friction velocity and 10 cm wide sample) for woven fabric.
Originality/value
The proposed fabric‐skin friction tester is adapted to measure the dynamical friction properties between human skin and clothing. This is original in comparison to the conventional research method usually found in the literature.
Details
Keywords
Massimo Miozzi, Alessandro Capone, Christian Klein and Marco Costantini
The purpose of this study is the characterization of the dramatic variation in the flow scenario occurring at incipient stall conditions on a NACA0015 hydrofoil at moderate…
Abstract
Purpose
The purpose of this study is the characterization of the dramatic variation in the flow scenario occurring at incipient stall conditions on a NACA0015 hydrofoil at moderate Reynolds numbers via the experimental analysis of time- and space-resolved skin-friction maps. The examined flow conditions are relevant for a variety of applications, including renewable energy production and unmanned and micro-aerial vehicles.
Design/methodology/approach
Grounding on the global temperature data acquired via temperature-sensitive paint, the proposed methodology adopts two approaches: one to obtain time-resolved, relative skin-friction vector fields by means of an optical-flow-based algorithm and the other one to extract quantitative, time-averaged skin-friction maps after minimization of the dissimilarity between the observed passive transport of temperature fluctuations and that suggested by the Taylor hypothesis.
Findings
Through the synergistic application of the proposed methods, the time-dependent evolution of the incipient stall over the hydrofoil suction side is globally described by firstly identifying the trailing edge separation at an angle of attack (AoA) AoA = 11.5°, and then by capturing the onset of upstream oriented, mushroom-like structures at AoA = 13°. The concomitant occurrence of both scenarios is found at the intermediate incidence AoA = 12.2°.
Originality/value
The qualitative, time-resolved skin-friction topology, combined with the quantitative, time-averaged distribution of the streamwise friction velocity, enables to establish a portrait of the complex, three-dimensional, unsteady scenario occurring at the examined flow conditions, thus providing new, fundamental information for a deeper understanding of the incipient stall development and for its control.
Details
Keywords
Rajesh Vemula, A J Chamkha and Mallesh M. P.
The purpose of this paper is to focus on the numerical modelling of transient natural convection flow of an incompressible viscous nanofluid past an impulsively started…
Abstract
Purpose
The purpose of this paper is to focus on the numerical modelling of transient natural convection flow of an incompressible viscous nanofluid past an impulsively started semi-infinite vertical plate with variable surface temperature.
Design/methodology/approach
The problem is governed by the coupled non-linear partial differential equations with appropriate boundary conditions. A robust, well-tested, Crank-Nicolson type of implicit finite-difference method, which is unconditionally stable and convergent, is used to solve the governing non-linear set of partial differential equations.
Findings
The local and average values of the skin-friction coefficient (viscous drag) and the average Nusselt number (the rate of heat transfer) decreased, while the local Nusselt number increased for all nanofluids, namely, aluminium oxide-water, copper-water, titanium oxide-water and silver-water with an increase in the temperature exponent m. Selecting aluminium oxide as the dispersing nanoparticles leads to the maximum average Nusselt number (the rate of heat transfer), while choosing silver as the dispersing nanoparticles leads to the minimum local Nusselt number compared to the other nanofluids for all values of the temperature exponent m. Also, choosing silver as the dispersing nanoparticles leads to the minimum skin-friction coefficient (viscous drag), while selecting aluminium oxide as the dispersing nanoparticles leads to the maximum skin-friction coefficient (viscous drag) for all values of the temperature exponent m.
Research limitations/implications
The Brinkman model for dynamic viscosity and Maxwell-Garnett model for thermal conductivity are employed. The governing boundary layer equations are written according to The Tiwari-Das nanofluid model. A range of nanofluids containing nanoparticles of aluminium oxide, copper, titanium oxide and silver with nanoparticle volume fraction range less than or equal to 0.04 are considered.
Practical implications
The present simulations are relevant to nanomaterials thermal flow processing in the chemical engineering and metallurgy industries. This study also provides an important benchmark for further simulations of nanofluid dynamic transport phenomena of relevance to materials processing, with alternative computational algorithms (e.g. finite element methods).
Originality/value
This paper is relatively original and illustrates the influence of variable surface temperature on transient natural convection flow of a viscous incompressible nanofluid and heat transfer from an impulsively started semi-infinite vertical plate.
Details
Keywords
Sampath Kumar V.S. and N.P. Pai
The purpose of this paper is to study the effect of injection and suction on velocity profile, skin friction and pressure distribution of a Casson fluid flow between two parallel…
Abstract
Purpose
The purpose of this paper is to study the effect of injection and suction on velocity profile, skin friction and pressure distribution of a Casson fluid flow between two parallel infinite rectangular plates approaching or receding from each other with suction or injection at the porous plates.
Design/methodology/approach
The governing Navier–Stokes equations are reduced to the fourth-order non-linear ordinary differential equation through the similarity transformations. The approximated analytic solution based on the Homotopy perturbation method is given and also compared with the classical finite difference method.
Findings
From this study, the authors observed that the skin friction is less in non-Newtonian fluids compared to Newtonian fluids. The use of non-Newtonian fluids reduces the pressure in all the cases compared to Newtonian and hence load-carrying capacity will be more. As γ value increases velocity, skin friction and pressure decreases. When γ is fixed, it is observed that skin friction and pressure is minimum for A=0.5 and maximum when A=−0.5. The result of this study also shows that the effect of suction on the velocity profiles, pressure and skin friction is opposite to the effect of injection.
Originality/value
The present work analyzes the characteristic of non-Newtonian fluid having practical and industrial applications.
Details
Keywords
EVER since I first began to study Aeronautics I have been annoyed by the vast gap which has existed between the power actually expended on mechanical flight and the power…
Abstract
EVER since I first began to study Aeronautics I have been annoyed by the vast gap which has existed between the power actually expended on mechanical flight and the power ultimately necessary for flight in a correctly‐shaped aeroplane. Every year, during my summer holiday, this annoyance is aggravated by contemplating the effortless flight of the sea birds and the correlated phenomenon of the beauty and grace of their forms.
O.M. Haddad, M.A. Al‐Nimr and M.A. Abu‐Ayyad
Numerical solutions are presented for steady two‐dimensional symmetric flow past a parabolic cylinder embedded in porous media. For this study, the full Navier–Stokes equations…
Abstract
Numerical solutions are presented for steady two‐dimensional symmetric flow past a parabolic cylinder embedded in porous media. For this study, the full Navier–Stokes equations (combined with the Brinkman–Forchheimer‐extended Darcy model) and energy equation in parabolic coordinates were solved. A second order accurate finite difference scheme on a non‐uniform grid was used. A wide range of Reynolds number (Re) is studied for different values of Prandtl number (Pr). It is found that the pressure, skin friction and Nusselt number decreases as the Darcy number (Da) decreases and/or the Inertia parameter (Λ) increases.
Details
Keywords
Nawar Mohammed Ridha Hashim, Mohd. Zamri Yusoff and Hussein Ahmed Mohammed
The purpose of this paper is to numerically study the phenomenon of separation and subsequent reattachment that happens due to a sudden contraction or expansion in flow geometry…
Abstract
Purpose
The purpose of this paper is to numerically study the phenomenon of separation and subsequent reattachment that happens due to a sudden contraction or expansion in flow geometry, in addition, to investigating the effect of nanoparticles suspended in water on heat transfer enhancement and fluid flow characteristics.
Design/methodology/approach
Turbulent forced convection flow over triple forward facing step (FFS) in a duct is numerically studied by using different types of nanofluids. Finite volume method is employed to carry out the numerical investigations. with nanoparticles volume fraction in the range of 1-4 per cent and nanoparticles diameter in the range 30-75 nm, suspended in water. Several parameters were studied, such as the geometrical specification (different step heights), boundary conditions (different Reynolds [Re] numbers), types of fluids (base fluid with different types of nanoparticles), nanoparticle concentration (different volume fractions) and nanoparticle size.
Findings
The numerical results indicate that the Nusselt number increases as the volume fraction increases, but it decreases as the diameter of the nanoparticles of nanofluids increases. The turbulent kinetic energy and its dissipation rate increase as Re number increases. The velocity magnitude increases as the density of nanofluids decreases. No significant effect of increasing the three steps heights on Nusselt along the heated wall, except in front of first step where increasing the first step height leads to an increase in the recirculation zone size adjacent to it.
Research limitations/implications
The phenomenon of separation and subsequent reattachment happened due to a sudden contraction or expansion in flow geometry, such as forward facing and backward facing steps, respectively, can be recognized in many engineering applications where heat transfer enhancement is required. Some examples include cooling systems for electronic equipment, heat exchanger, diffusers and chemical process. Understanding the concept of these devices is very important from the engineering point of view.
Originality/value
Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions, the traditional fluids or by enhancing thermal conductivity of the fluid. Great attention has been paid to increase the thermal conductivity of base fluid by suspending nano-, micro- or larger-sized particles in fluid. The products from suspending these particles in the base fluid are called nanofluids. Many studies have been conducted to investigate the heat transfer and fluid flow characteristics over FFS. This study is the first where nanofluids are employed as working fluids for flow over triple FFS.
Details
Keywords
Gangqiang Zhang, Xiangqiong Zeng, Tianhui Ren and Emile van der Heide
The purpose of this paper is to investigate the tribological performance of graphene oxide (GO) sheets as water-based lubricant additive when ultra-high molecular weight…
Abstract
Purpose
The purpose of this paper is to investigate the tribological performance of graphene oxide (GO) sheets as water-based lubricant additive when ultra-high molecular weight polyethylene (UHMWPE) plates slid against 316L stainless steel ball using a reciprocating tribometre.
Design/methodology/approach
The factors influencing the tribological performance were considered, including the viscosity of the GO dispersion, normal load, sliding velocity and the roughness of UHMWPE. The surface microstructure and properties of UHMWPE were studied by means of scanning electron microscopy, laser confocal microscopy, Raman spectroscopy and contact angle measurements.
Findings
The results revealed that the GO dispersion reduced friction and sliding-wear. The surface images of the wear UHMWPE plates indicated that GO sheets were prone to adsorption on the surface and form a thin physical tribofilms at the substrate.
Originality/value
Based on the experimental findings for the evolution of the microstructure morphology and the development of subsurface cracks, less debris and cracking can be observed in the UHMWPE plates lubricated by GO dispersion.
Details
Keywords
Khursheed Muhammad, Tasawar Hayat and Bashir Ahmad
This study aims to explore the combined impacts of velocity and thermal slips on hybrid nanomaterial (GO+Ag+kerosene oil) bounded between two parallel infinite walls (plates)…
Abstract
Purpose
This study aims to explore the combined impacts of velocity and thermal slips on hybrid nanomaterial (GO+Ag+kerosene oil) bounded between two parallel infinite walls (plates). Both the walls are separated by a distance. The upper wall is subjected to squeezing with velocity, while the lower wall stretches with velocity. A uniform magnetic field acts normally to the flow. Moreover, heat transmission is analyzed in the presence of Joule heating. Heat transport characteristics are investigated by imposing the Cattaneo–Christov (C–C) heat flux model. The behavior of velocities, skin friction and temperature under sundry variables are examined graphically.
Design/methodology/approach
The obtained partial differential equations (PDEs) related to the considered problem are nondimensionalized by choosing appropriated variables. These nondimensional PDEs are then solved by the numerical technique, finite difference method (FDM). For implementation of this method, the obtained nondimensional PDEs are converted into finite difference equations (FDEs) using forward difference (FD) toolkits.
Findings
Velocity of the hybrid nanomaterial decreases with higher Hartman number and velocity slip parameter, while it increases with increase in Reynolds and squeezing numbers. Temperature of the hybrid nanomaterial increases for large Hartman number, Eckert number and squeezing parameter, while it is reduced by higher thermal slip parameter, thermal relaxation time parameter and nanoparticle volume fractions for graphene oxide (GO) and silver (Ag). Skin friction is controlled through higher Reynolds number, while it intensifies with nanoparticle volume fractions for GO and Ag.
Originality/value
Here, the authors have investigated 2D flow of hybrid nanomaterial bounded between two parallel walls. The lower and upper walls are subjected to stretching and squeezing, respectively. The authors guarantee that all outcomes and numerical technique (FDM) results are original, neither submitted nor published in any journal before.
Details
Keywords
Jitendra Kumar Singh and Srinivasa C.T.
The purpose of this paper is to deal with an unsteady natural convection flow of a rotating fluid past an exponential accelerated vertical plate. The effect of Hall current…
Abstract
Purpose
The purpose of this paper is to deal with an unsteady natural convection flow of a rotating fluid past an exponential accelerated vertical plate. The effect of Hall current, ion-slip and magnetic field is considered. Two types of plate temperature, namely, uniform and ramped temperature are considered to model heat transfer analysis.
Design/methodology/approach
The Laplace transform technique is employed to find the closed form solutions for velocity, temperature and concentration.
Findings
The effects of flow governing parameters on the velocity profile, temperature profile, concentration profile, skin friction, Nusselt and Sherwood numbers are discussed and presented through graphs and tables. It is found that fluid velocity in the primary flow direction decreases with the increase in the magnetic parameter.
Originality/value
First time in the literature, the authors obtained closed form solution to natural convection flow of a rotating fluid past an exponential accelerated vertical plate.
Details