Search results

1 – 10 of 70
To view the access options for this content please click here
Article

TEJWANT SINGH

The theoretical derivation of the start‐up laminar flow of incompressible viscous fluid in a long pipe as suggested by Szymanski, could not be verified experimentally…

Abstract

The theoretical derivation of the start‐up laminar flow of incompressible viscous fluid in a long pipe as suggested by Szymanski, could not be verified experimentally. This leads to the checking of assumption of constant pressure gradient across the ends of the pipe, on the basis of which the theoretical development was made. Recently, the problem was again investigated for viscous fluid by Otis. In the present paper, the laminar start‐up flow of elastico‐viscous fluid in a pipe, without assuming constant pressure gradient across its ends, has been investigated. The non‐linear governing equations are solved numerically and the effects of start‐up flow parameters and elastico‐viscous parameter on the velocity distribution have been studied.

Details

Engineering Computations, vol. 9 no. 1
Type: Research Article
ISSN: 0264-4401

Keywords

To view the access options for this content please click here
Article

Nathi Ram and Satish C. Sharma

The present work aimed to study analytically the influence of wear on the performance of a capillary-compensated hole-entry hybrid misaligned journal bearing system…

Abstract

Purpose

The present work aimed to study analytically the influence of wear on the performance of a capillary-compensated hole-entry hybrid misaligned journal bearing system operating in a turbulent regime. The numerically simulated results are presented for the chosen values of restrictor design parameter, Reynolds numbers, wear depth and misalignment parameters.

Design/methodology/approach

The wear caused on the bearing surface due to start/stop operations is modeled using the Dufrane’s abrasive wear model. The modified Reynolds equation based on Constantinescu’s lubrication theory is solved using finite element method together with capillary restrictor flow equation.

Findings

It is found that the value of minimum fluid-film thickness increases significantly for a constant value of restrictor design parameter when unworn aligned bearing operates in turbulent regime vis-à-vis laminar regime. Further, it has also been observed that when a worn bearing operates in laminar/turbulent regimes, the reduction in the value of minimum fluid-film thickness is more due to journal misalignment as compared to the aligned bearing operates in laminar regime.

Originality/value

The present work is original concerning the performance of worn hole-entry hybrid misaligned journal bearing system operating in turbulent regime. The results are expected to be quite useful for the bearing designer.

Details

Industrial Lubrication and Tribology, vol. 66 no. 4
Type: Research Article
ISSN: 0036-8792

Keywords

To view the access options for this content please click here
Article

Maged A.I. El‐Shaarawia and Ali A. Al‐Ugla

The paper seeks to focus on obtaining the transient torque required to rotate the inner cylinder in open ended vertical concentric annuli for a fluid of Pr = 0.7 in the…

Abstract

Purpose

The paper seeks to focus on obtaining the transient torque required to rotate the inner cylinder in open ended vertical concentric annuli for a fluid of Pr = 0.7 in the laminar natural convection flow regime over a wide range of the controlling parameter Gr2/Ta. The inner wall is heated and subjected to an impulsive rotation while the outer one is stationary and maintained adiabatic.

Design/methodology/approach

The governing transient boundary‐layer equations are numerically solved using an iterative linearized finite‐difference scheme.

Findings

The transient induced flow rate and absorbed heat for different annulus heights are presented. High rotational speed (i.e. low values of Gr2/Ta) increases the flow rate and heat absorbed in short annuli. However, for considerably tall annuli, Gr2/Ta has slight effect on the flow and heat absorbed. The steady‐state time is tangibly influenced by Gr2/Ta in considerably short annuli and very slightly affected for considerably tall annuli.

Practical implications

The investigated problem can simulate the start‐up period of naturally cooled small vertical electric motors.

Originality/value

The paper presents results not available in the literature for the effect of Gr2/Ta on the developing velocities, pressure, flow‐rate induced, absorbed heat by fluid and required torque in vertical concentric annuli with impulsively rotated inner walls under the transient free‐convection heat transfer mode.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 19 no. 2
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article

T.S. LEE, R.S. TAN and X.P. XU

The time development of the symmetrical standing zones of recirculation, which is formed in the early stages of the impulsively started laminar flow over the square…

Abstract

The time development of the symmetrical standing zones of recirculation, which is formed in the early stages of the impulsively started laminar flow over the square cylinder, have been studied numerically. The Reynolds number considered ranges from 25 to 1,000. Main flow characteristics of the developing recirculation region aft of the square cylinder and its interaction with the separating shear layer from the leading edges are studied through the developing streamlines. Other flow characteristics are analysed in terms of pressure contours, surface pressure coefficient, wake length and drag coefficient. Four main‐flow types and three subflow types of regimes are identified through a detailed analysis of the evolution of the flow characteristics. Typically, for a given Reynolds number, it is noted that flow starts with no separation (type I main‐flow). As time advances, symmetrical standing zone of recirculation develops aft of the square cylinder (type II main‐flow). The rate of growth in width, length and structure of the aft end eddies (sub‐flow (a)) depends on the Reynolds number. In time, separated flow from the leading edges of the square cylinder also develops (type III main‐flow) and forms growing separation bubbles (sub‐flow (b)) on the upper and lower surfaces of the square cylinder. As time advances, the separation bubbles on the upper and lower surfaces of the cylinder grow towards downstream regions and eventually merge with the swelling symmetrical eddies aft of the cylinder. This merging of the type II and type III flows created a complex type IV main‐flow regime with a disturbed tertiary flow zone (sub‐flow (c)) near the merging junction. Eventually, depending on the Reynolds number, the flow develops into a particular category of symmetrical standing recirculatory flow of specific characteristics.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 6 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article

M.A.I. El‐Shaarawi, M.A. Al‐Nimr and M.A. Hader

The paper presents a finite‐difference scheme to solve thetransient conjugated heat transfer problem in a concentricannulus with simultaneously developing hydrodynamic and…

Abstract

The paper presents a finite‐difference scheme to solve the transient conjugated heat transfer problem in a concentric annulus with simultaneously developing hydrodynamic and thermal boundary layers. The annular forced flow is laminar with constant physical properties. Thermal transient is initiated by a step change in the prescribed isothermal temperature of the inner surface of the inside tube wall while the outer surface of the external tube is kept adiabatic. The effects of solid‐fluid conductivity ratio and diffusivity ratio on the thermal behaviour of the flow have been investigated. Numerical results are presented for a fluid of Pr = 0.7 flowing in an annulus of radius ratio 0.5 with various values of inner and outer solid wall thicknesses.

Details

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

Keywords

To view the access options for this content please click here
Article

M.A.I. EL‐SHAARAWI and M.A. AL‐ATTAS

A finite‐difference scheme is developed for solving the boundary layer equations governing the unsteady laminar free convection flow in open ended vertical concentric…

Abstract

A finite‐difference scheme is developed for solving the boundary layer equations governing the unsteady laminar free convection flow in open ended vertical concentric annuli. The initial condition considered for the creation of the thermal transient corresponds to a step change in temperature at the inner annulus boundary while the outer wall is maintained adiabatic. Numerical results for a fluid of Pr = 0.7 in an annulus of radius ratio 0.5 are presented. The results show the developing velocity and pressure fields with respect to space and time. Also, the important relationship between the annulus height and the induced flow rate is presented for various values of the time parameter starting from quiescence to the final steady state.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 2 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article

Ali J. Chamkha

The problem of unsteady laminar fully‐developed flow and heat transfer of an electrically‐conducting and heat‐generating or absorbing fluid with variable properties…

Abstract

The problem of unsteady laminar fully‐developed flow and heat transfer of an electrically‐conducting and heat‐generating or absorbing fluid with variable properties through porous channels in the presence of uniform magnetic and electric fields is formulated. The general governing equations which include such effects as magnetic field, electric field, porous medium inertia and heat generation or absorption effects are non‐dimensionalized and solved numerically by the implicit finite‐difference methodology. A representative set of numerical results for the transient and steady‐state velocity and temperature profiles, the skin‐friction coefficients at both the upper and lower walls of the channel as well as the heat transfer coefficient at the lower wall are presented graphically and discussed. Favorable comparisons with previously published work are performed and the results are in excellent agreement. A comprehensive parametric study is performed to show the effects of the Hartmann number, electric field parameter, inverse Darcy number, inertia parameter, heat generation or absorption coefficient, exponents of variable properties and the Eckert number on the solutions.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 11 no. 5
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article

Etienne Muller, Dominique Pelletier and André Garon

This paper aims to focus on characterization of interactions between hp-adaptive time-integrators based on backward differentiation formulas (BDF) and adaptive meshing…

Abstract

Purpose

This paper aims to focus on characterization of interactions between hp-adaptive time-integrators based on backward differentiation formulas (BDF) and adaptive meshing based on Zhu and Zienkiewicz error estimation approach. If mesh adaptation only occurs at user-supplied times and results in a completely new mesh, it is necessary to stop the time-integration at these same times. In these conditions, one challenge is to find an efficient and reliable way to restart the time-integration. The authors investigate what impact grid-to-grid interpolation errors have on the relaunch of the computation.

Design/methodology/approach

Two restart strategies of the time-integrator were used: one based on resetting the time-step size h and time-integrator order p to default values (used in the initial startup phase), and another designed to restart with the time-step size h and order p used by the solver prior to remeshing. The authors also investigate the benefits of quadratically interpolate the solution on the new mesh. Both restart strategies were used to solve laminar incompressible Navier–Stokes and the Unsteady Reynolds Averaged Naviers-Stokes (URANS) equations.

Findings

The adaptive features of our time-integrators are excellent tools to quantify errors arising from the data transfer between two grids. The second restart strategy proved to be advantageous only if a quadratic grid-to-grid interpolation is used. Results for turbulent flows also proved that some precautions must be taken to ensure grid convergence at any time of the simulation. Mesh adaptation, if poorly performed, can indeed lead to losing grid convergence in critical regions of the flow.

Originality/value

This study exhibits the benefits and difficulty of assessing both spatial error estimates and local error estimates to enhance the efficiency of unsteady computations.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article

T.S. Lee

Characteristics of the development of an impulsively started flow around an expanded trapezoidal cylinder were studied numerically. A stream function‐vorticity formulation…

Abstract

Characteristics of the development of an impulsively started flow around an expanded trapezoidal cylinder were studied numerically. A stream function‐vorticity formulation in a body coordinate system was used to describe the unsteady flow field. The inflow Reynolds number considered ranges from 25 to 1,000. Pressure contours, surface pressure coefficient and drag coefficient were studied through the streamline flow field. Main‐flow and sub‐flow regimes are identified through an analysis of the evolution of the flow characteristics. Typically, for a given expanded trapezoidal cylinder, it is noted that flow starts with minimum separation at the aft end. As time advances, symmetrical standing zone of recirculation develops aft of the cylinder. The rate of growth in width, length and structure of the aft end eddies depends on the Reynolds number. As time advances and at higher Reynolds numbers, separated flow from the leading edges of the trapezoidal cylinder develops along the upper and lower inclined surfaces of the trapezoidal cylinder. The separation bubbles on the upper and lower inclined surfaces of the cylinder grow towards the downstream regions with time and eventually merge with the swelling symmetrical eddies aft of the cylinder. This merging of the flows created a complex flow regime with a disturbed tertiary flow zone near the merging junction. For the flows considered here, eventually, depending on the Reynolds number and the expanded angle of the trapezoidal cylinder, the flow field develops into a specific category of symmetrical standing recirculatory flow with its own distinct characteristics.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 8 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article

Yogesh Jaluria

This paper aims to discuss inverse problems that arise in a variety of practical thermal processes and systems. It presents some of the approaches that may be used to…

Abstract

Purpose

This paper aims to discuss inverse problems that arise in a variety of practical thermal processes and systems. It presents some of the approaches that may be used to obtain results that lie within a small region of uncertainty. Therefore, the non-uniqueness of the solution is reduced so that the final design and boundary conditions may be determined. Optimization methods that may be used to reduce the uncertainty and to select locations for experimental data and for minimizing the error are presented. A few examples of thermal systems are given to illustrate the applicability of these methods and the challenges that must be addressed in solving inverse problems.

Design/methodology/approach

In most analytical and numerical solutions, the basic equations that describe the process, as well as the relevant and appropriate boundary conditions, are known. The interest lies in obtaining a unique solution that satisfies the equations and boundary conditions. This may be termed as a direct or forward solution. However, there are many problems, particularly in practical systems, where the desired result is known but the conditions needed for achieving it are not known. These are generally known as inverse problems. In manufacturing, for instance, the temperature variation to which a component must be subjected to obtain desired characteristics is prescribed, but the means to achieve this variation are not known. An example of this circumstance is the annealing, tempering or hardening of steel. In such cases, the boundary and initial conditions are not known and must be determined by solving the inverse problem to obtain the desired temperature variation in the component. The solutions, thus, obtained are generally not unique. This is a review paper, which discusses inverse problems that arise in a variety of practical thermal processes and systems. It presents some of the approaches or strategies that may be used to obtain results that lie within a small region of uncertainty. It is important to realize that the solution is not unique, and this non-uniqueness must be reduced so that the final design and boundary conditions may be determined with acceptable accuracy and repeatability. Optimization techniques are often used for minimizing the error. This review presents several methods that may be applied to reduce the uncertainty and to select locations for experimental data for the best results. A few examples of thermal systems are given to illustrate the applicability of these methods and the challenges that must be addressed in solving inverse problems. By considering a variety of systems, the paper also shows the importance of solving inverse problems to obtain results that may be used to model and design thermal processes and systems.

Findings

The solution of inverse problems, which frequently arise in thermal processes, is discussed. Different strategies to obtain the conditions that lead to the desired result are given. The goal of these approaches is to reduce uncertainty and obtain essentially unique solutions for different circumstances. The error of the method can be checked against known conditions to see if it is acceptable for the given problem. Several examples are given to illustrate the use of these methods.

Originality/value

The basic strategies presented here for solving inverse problems that arise in thermal processes and systems, as well as the optimization techniques used to reduce the domain of uncertainty, are fairly original. They are used for certain challenging problems that have not been considered in detail earlier. Several methods are outlined for considering different types of problems.

Details

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

Keywords

1 – 10 of 70