Search results

1 – 10 of over 2000
To view the access options for this content please click here
Article
Publication date: 3 July 2017

Florian Schueltke and Eike Stumpf

Laminarization of commercial aircraft surfaces is the most promising technology to reduce fuel consumption and ecological impact. As laminar flow highly depends on cross…

Abstract

Purpose

Laminarization of commercial aircraft surfaces is the most promising technology to reduce fuel consumption and ecological impact. As laminar flow highly depends on cross-flow effects, there is the question in which way simple estimations and simplifications for application in conceptual aircraft design can be used to capture these cross-flow influences. This paper aims to show the accuracy of 2D methods for estimating laminar flow regions on 3D wing objects.

Design/methodology/approach

Several methods, relating 3D and 2D flow conditions, are analyzed with regard to capture cross-flow influences. The 3D pressure distributions depending on utilized transformation method are compared to Reynolds-averaged Navier–Stokes (RANS) solutions. With the most precise transformation method, the laminar flow area on a conventional wing of a short range aircraft is determined and compared to the laminar area obtained with the RANS pressure distributions as input. Further, hybrid laminar flow control component sizing is carried out to obtain the net benefit in fuel reduction of simplified method compared to RANS method for a conventional short range aircraft.

Findings

In this particular case, the solutions calculated with the simplified methods show high deviations from those obtained with RANS.

Originality/value

This investigation underlines the need of proper methods for fast and accurate estimation of cross-flow effects to be able to assess the full potential of laminar flow control within conceptual aircraft design.

Details

Aircraft Engineering and Aerospace Technology, vol. 89 no. 4
Type: Research Article
ISSN: 1748-8842

Keywords

To view the access options for this content please click here
Article
Publication date: 23 January 2019

Konrad Nering and Kazimierz Rup

For internal flows with small values of the Reynolds number, there is often at a considerable distance from the pipe inlet cross-section a change of the flow form from…

Abstract

Purpose

For internal flows with small values of the Reynolds number, there is often at a considerable distance from the pipe inlet cross-section a change of the flow form from laminar to turbulent. To describe this phenomenon of laminar-turbulent transition in the pipe, also parallel-plate channel flow, a modified algebraic intermittency model was used. The original model for bypass transition developed by S. Kubacki and E. Dick was designed for simulating bypass transition in turbomachinery.

Design/methodology/approach

A modification of mentioned model was proposed. Modified model is suitable for simulating internal flows in pipes and parallel-plate channels. Implementation of the modified model was made using the OpenFOAM framework. Values of several constants of the original model were modified.

Findings

For selected Reynolds numbers and turbulence intensities (Tu), localization of laminar breakdown and fully turbulent flow was presented. Results obtained in this work were compared with corresponding experimental results available in the literature. It is particularly worth noting that asymptotic values of wall shear stress in flow channels and asymptotic values of axis velocity obtained during simulations are similar to related experimental and theoretical results.

Originality/value

The modified model allows precision numerical simulation in the area of transitional flow between laminar, intermittent and turbulent flows in pipes and parallel-plate channels. Proposed modified algebraic intermittency model presented in this work is described by a set of two additional partial differential equations corresponding with k-omega turbulence model presented by Wilcox (Wilcox, 2006).

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article
Publication date: 1 November 2002

A. Behzadmehr, N. Galanis and A. Laneville

Upward mixed convection flow of air in a uniformly heated vertical tube was studied numerically using the three‐dimensional elliptic conservation equations and the Launder…

Downloads
1008

Abstract

Upward mixed convection flow of air in a uniformly heated vertical tube was studied numerically using the three‐dimensional elliptic conservation equations and the Launder and Sharma low Reynolds number kε turbulence model. For Re=1,000 the fully developed flow field undergoes two transitions as the Grashof number increases: thus, this flow field is laminar for Gr<8×106, turbulent for 8×106<Gr<5×107 and again laminar for Gr>5×107. In the entry region, turbulent kinetic energy decays monotonically for Gr≤3×106 and Gr≥7.1×107. For Gr between these two values it initially increases from the imposed inlet condition and then decreases towards its calculated fully developed value. The mean velocity profiles as well as the axial evolution of the skin friction coefficient are presented for representative values of Gr.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 12 no. 7
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article
Publication date: 19 March 2020

Ryszard Szwaba, Piotr Kaczyński and Piotr Doerffer

The purpose of this paper is to study experimentally the effect of transition and also the roughness height on the flow structure of the shock wave boundary layer…

Abstract

Purpose

The purpose of this paper is to study experimentally the effect of transition and also the roughness height on the flow structure of the shock wave boundary layer interaction in the blades passage of a compressor cascade.

Design/methodology/approach

A model of a turbine compressor passage was designed and assembled in a transonic wind tunnel. In the experiment, the distributed roughness with different heights and locations was used to induce transition upstream of the shock wave.

Findings

Recommendation regarding the roughness parameters for the application depends on what is more important as goal, whether the reduction of losses or unsteadiness. In case if more important are the losses reduction, a good choice for the roughness location seems to be the one close to the shock wave position.

Research limitations/implications

The knowledge gained by this paper will enable the implementation of an effective laminar flow technology for engines in which the interaction of a laminar boundary layer with a shock wave takes place in the propulsion system and causes severe problems.

Originality/value

The paper focuses on the influence of the boundary layer transition induced by different roughness values and locations on aerodynamic performance of a compressor cascade. Very valuable results were obtained in the roughness application for the boundary layer transition control, demonstrating a positive effect in changing the nature of the interaction and also some negative influence in case of oversized roughness height, which cannot be found in the existing literature.

Details

Aircraft Engineering and Aerospace Technology, vol. 92 no. 4
Type: Research Article
ISSN: 1748-8842

Keywords

To view the access options for this content please click here
Article
Publication date: 26 September 2019

S. Hoseinzadeh, P.S. Heyns and H. Kariman

The purpose of this paper is to investigate the heat transfer of laminar and turbulent pulsating Al203/water nanofluid flow in a two-dimensional channel. In the laminar

Abstract

Purpose

The purpose of this paper is to investigate the heat transfer of laminar and turbulent pulsating Al203/water nanofluid flow in a two-dimensional channel. In the laminar flow range, with increasing Reynolds number (Re), the velocity gradient is increased. Also, the Nusselt number (Nu) is increased, which causes increase in the overall heat transfer rate. Additionally, in the change of flow regime from laminar to turbulent, average thermal flux and pulsation range are increased. Also, the effect of different percentage of Al2O3/water nanofluid is investigated. The results show that the addition of nanofluids improve thermal performance in channel, but the using of nanofluid causes a pressure drop in the channel.

Design/methodology/approach

The pulsatile flow and heat transfer in a two-dimensional channel were investigated.

Findings

The numerical results show that the Al2O3/Water nanofluid has a significant effect on the thermal properties of the different flows (laminar and turbulent) and the average thermal flux and pulsation ranges are increased in the change of flow regime from laminar to turbulent. Also, the addition of nanofluid improves thermal performance in channels.

Originality/value

The originality of this work lies in proposing a numerical analysis of heat transfer of pulsating Al2O3/Water nanofluid flow -with different percentages- in the two-dimensional channel while the flow regime change from laminar to turbulent.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article
Publication date: 14 October 2020

Ali Cemal Benim and Sai Bhagavan Maddala

The purpose of this paper is the numerical investigation of the friction laws for incompressible flow in undulated channels, with emphasis on the applicability of the…

Abstract

Purpose

The purpose of this paper is the numerical investigation of the friction laws for incompressible flow in undulated channels, with emphasis on the applicability of the hydraulic diameter concept. A focal point of the study is the derivation of correlations to increase the accuracy of the hydraulic diameter approach.

Design/methodology/approach

Calculations are performed for laminar and turbulent flow, for Reynolds number ranges between 10–2,000 and 5,000–100,000. For turbulent flow, the shear stress transport (SST) model is used. A simple, sawtooth-like undulation shape is considered, where the channel geometry can be described by means of three length parameters. Letting each to take three values, totally 27 geometries are analyzed.

Findings

It is observed that the hydraulic diameter concept applied via analytical or empirical expressions to obtain friction coefficients does not lead to accurate results. For laminar flow, the maximum deviations of analytical values from predicted are about 70%, while 20% deviation is observed on average. For turbulent flow, deviations of Blasius correlation from predicted ones are smaller, but still remarkable with about 20% for maximum deviation and about 10% on average.

Originality/value

Applicability of the hydraulic diameter concept to undulated channels was not computationally explored. A further original ingredient of the work is the derivation of correlations that lead to improved accuracy in calculating the friction coefficient using hydraulic diameter. For laminar flow, the maximum and average deviations of present correlations from numerical predictions are below 5% and 2%, respectively. For turbulent flow, these numbers turn out to be approximately 12% for the maximum deviation and about 2% for the average.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 31 no. 6
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article
Publication date: 20 April 2012

Weifeng Wu, Jian Li, Ting Li, Quanke Feng and Xiaoling Yu

The purpose of this paper is to find a solution of laminar liquid flow in asymmetric narrow channels. In many cases, an intuitive solution is much more useful and…

Abstract

Purpose

The purpose of this paper is to find a solution of laminar liquid flow in asymmetric narrow channels. In many cases, an intuitive solution is much more useful and necessary for engineering applications, although numerical solutions can be obtained.

Design/methodology/approach

The Navier‐Stokes equations of laminar liquid flow in asymmetric narrow channels are simplified based on geometric characteristics of narrow channels, physical characteristics of liquid and boundary conditions. The simplified Navier‐Stokes equations are solved theoretically. Verification of the obtained results is carried out based on comparing with the Jeffery‐Hamel flow, which is an exact solution of liquid flow in convergent or divergent channels proposed by Jeffery.

Findings

This paper proposed an intuitive solution of laminar liquid flow in asymmetric narrow channels. Obtained results show that the solution can provide a fairly precise flowrate, when a ratio between the width of the channel and the curvature of the boundary of the asymmetry channel is smaller than 0.2936/Re. Furthermore, the obtained solution of pressure distribution along the channel shows high enough accuracy, even though the Reynolds number reaches to higher than 105.

Research limitations/implications

Because the authors assumed the width of the channel is far smaller than the curvature of the boundary of the asymmetric channel, the obtained results could only fit finite cases. Because the Navier‐Stocks equations were finally simplified into one‐dimensional, it is impossible to forecast separation flows; so the obtained results will fail when the Re number is too big. However, experiments should be carried out further to verify these problems.

Originality/value

This paper proposes an intuitive solution of laminar liquid flow in asymmetric narrow channels, including the pressure distribution along the channel.

Details

Industrial Lubrication and Tribology, vol. 64 no. 3
Type: Research Article
ISSN: 0036-8792

Keywords

To view the access options for this content please click here
Article
Publication date: 19 July 2019

Dhanush Vittal Shenoy, Mostafa Safdari Shadloo, Jorge Peixinho and Abdellah Hadjadj

Fluid flows in pipes whose cross-sectional area are increasing in the stream-wise direction are prone to separation of the recirculation region. This paper aims to…

Abstract

Purpose

Fluid flows in pipes whose cross-sectional area are increasing in the stream-wise direction are prone to separation of the recirculation region. This paper aims to investigate such fluid flow in expansion pipe systems using direct numerical simulations. The flow in circular diverging pipes with different diverging half angles, namely, 45, 26, 14, 7.2 and 4.7 degrees, are considered. The flow is fed by a fully developed laminar parabolic velocity profile at its inlet and is connected to a long straight circular pipe at its downstream to characterise recirculation zone and skin friction coefficient in the laminar regime. The flow is considered linearly stable for Reynolds numbers sufficiently below natural transition. A perturbation is added to the inlet fully developed laminar velocity profile to test the flow response to finite amplitude disturbances and to characterise sub-critical transition.

Design/methodology/approach

Direct numerical simulations of the Navier–Stokes equations have been solved using a spectral element method.

Findings

It is found that the onset of disordered motion and the dynamics of the localised turbulence patch are controlled by the Reynolds number, the perturbation amplitude and the half angle of the pipe.

Originality/value

The authors clarify different stages of flow behaviour under the finite amplitude perturbations and shed more light to flow physics such as existence of Kelvin–Helmholtz instabilities as well as mechanism of turbulent puff shedding in diverging pipe flows.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 30 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

To view the access options for this content please click here
Article
Publication date: 1 May 1930

J.W. Maccoll

THIS paper aims at giving the most important results of modern German research upon the motion of incompressible fluids. Before dealing with the latest developments, I…

Abstract

THIS paper aims at giving the most important results of modern German research upon the motion of incompressible fluids. Before dealing with the latest developments, I have thought it advisable to give a short account of the older researches upon which the present work is based. It is hoped that this résumé will give a fairly complete survey of the methods that have led to the present insight into the hydrodynamical mechanism.

Details

Aircraft Engineering and Aerospace Technology, vol. 2 no. 5
Type: Research Article
ISSN: 0002-2667

To view the access options for this content please click here
Article
Publication date: 11 January 2008

Ton Hoang Mai, Catalin Viorel Popa and Omar Kholai

The aim of this study is to present numerical analyses for combined effects of the inlet temperature (ΔT+) and the wall‐to‐fluid thermal capacitance ratio (a*) on the…

Abstract

Purpose

The aim of this study is to present numerical analyses for combined effects of the inlet temperature (ΔT+) and the wall‐to‐fluid thermal capacitance ratio (a*) on the laminar mixed convection unsteady flows in a vertical pipe.

Design/methodology/approach

The full Navier‐Stokes and energy, coupled, unsteady state, two‐dimensional governing equations for ascending laminar mixed convection in a vertical pipe are solved numerically using a finite‐difference scheme.

Findings

The results show that the thermohydraulic flow behaviour is highly dependent on both parameters (ΔT+, a*). Moreover, the unsteady characteristics of the flow can involve oscillatory and reversed flow phenomena yielding the unstable flows. For the heating case, the reversed flow appears below the wave instability and the unsteady vortex is always significant in the vicinity of the wall, whatever ΔT+ and a*<100. For the cooling case, the reversed flow appears in the central region of the pipe; it develops on top of the wave instability.

Practical implications

This study should be very useful to improve heat transfer equipment.

Originality/value

The paper shows clearly the combined effects of both parameters (ΔT+, a*) on the laminar mixed convection flow.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 18 no. 1
Type: Research Article
ISSN: 0961-5539

Keywords

1 – 10 of over 2000