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The purpose of this paper is to compare the thermal resistances between optimized gallium- and water-based heat sinks to show which one is superior.

Taking the thermal resistances of heat sinks as the goal function, an optimization process is programmed based on the genetic algorithm. The optimal channel/fin widths and the corresponding thermal resistances of gallium- and water-based heat sinks are obtained and compared with/without a laminar flow constraint. The analytic model and CFD method are applied in different situations to ensure sufficient accuracy.

The results show that in the laminar regime, the thermal resistance of optimized gallium-based heat sink is lower than the water-based counterpart in most cases, but the latter becomes better if it is long enough or the channel is sufficient high. Without the laminar constraint, the thermal resistance of the optimized gallium-based heat sink can be decreased by 33-45 per cent compared with the water-based counterparts. It is interesting to find that when the heat sink is long or the channel height is short, the optimal geometry of gallium-based heat sink is a mini gap.

This paper demonstrates that the cooling performance of gallium-based heat sink can be significantly improved by optimization without the laminar flow constraint.

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.

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.

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

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.

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 k–ε 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.

AN important step towards a European laminar aircraft has been made by flight testing of a modified wing on a Fokker 100. During the tests which started on 12 November, laminar flow was achieved for a range of flight conditions. The initial results confirm that the expected drag reduction of up to 15% is attainable. This was revealed at a special presentation on 28 November at the Fokker facilities in the Netherlands.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.