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The purpose of the current research is to study the turbulent flow through microchannels having a micropost in aligned and staggered arrangements.

Numerical calculations are performed on the basis of the finite volume approach, which is based on the SIMPLEC algorithm. In this work, the slip velocity, flow velocity distribution and friction factor for the two micropost patterns are examined at friction Reynolds numbers of R_eτ = 395 and 590, relative module widths of W_m = 0.1 and 1 and cavity fraction range of F_c = 0.1 to 0.9.

Results reveal that for the two micropost patterns, as the friction Reynolds number, relative module width or cavity fraction increases, the slip velocity increases and friction factor decreases. It is found that the aligned micropost configuration leads to higher slip velocity and lower friction factor. Numerical findings indicate that the existence of the continuous cavity surface along the flow direction could be a significant criterion to realize if the velocity distribution deviates from that of the smooth channel. It is also shown that the turbulent flows are capable of producing more drag reduction than the laminar ones.

Previous studies have shown that microchannels consisting of a micropost pattern in aligned and staggered arrangements could be viewed as a promising alternative in the microscale flows for the heat removal purposes. Therefore, understanding the fluid flow through microchannels consisting of these configurations (which is a prerequisite to better understand thermal performance of such microchannels) is a significant issue, which is the subject of the present work.

The purpose of this paper is to investigate the performance of an ultra-thin film lubricated conjunction through the elastohydrodynamic lubrication of point contacts for various ridge shapes and sizes located within the contact zone including flat-top, triangle and cosine wave profiles, considering the influence of surface forces of solvation and Van der Waals’ in addition to the hydrodynamic effect to predict an optimum geometric characteristics for surface texture for lubricated conjunctions.

Surface features are simulated in a variety of sizes and shapes including flat-top, triangle and cosine wave profiles. While estimating the elastic deformation of the contacting surfaces, surface forces of solvation and Van der Waals’ are taken into account. The Reynolds equation is solved using the Newton–Raphson method to get the pressure profile and film thickness including the elastic deformation, and surface feature.

The geometrical characteristics of the ridge, its placement in relation to the contact zone and its height all have a significant impact on the performance of ultra-thin film lubricated conjunction. When the triangular-shaped ridge is present in contact, it forecasts even sharper peaks in film thickness and pressure. More friction, wear and eventually contact fatigue are brought on by this more acute pressure and film thickness peaks. The flat-top ridge shape shows a better performance for lubricated conjunction where, the minimum film thickness value is comparable to that obtained for the case of a smooth contact surface. This behavior is attributed to the effect of intermolecular force of solvation. An increase in the size of the ridge results in a step increase in the film thickness for different ridge shapes, particularly for the flat-topped ridge pattern.

Evaluation of the performance of elastohydrodynamic lubricated ultra-thin film conjunction related to film thickness and pressure profile for various ridge surface features of different amplitudes, shapes and sizes located through the contact zone considering the influence of surface forces of solvation and Van der Waals’ in addition to the hydrodynamic effect.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2023-0062/

The purpose of this paper is to study the behavior of a single ridge passing through elastohydrodynamic lubrication of point contacts problem for different ridge shapes and sizes, including flat-top, triangular and cosine wave pattern to get an optimal ridge profile.

The time-dependent Reynolds’ equation is solved using Newton–Raphson technique. Several shapes of surface feature are simulated and the film thickness and pressure distribution are obtained at every time step by simultaneous solution of the Reynolds’ equation and film thickness equation, including elastic deformation. Film thickness and pressure distribution are chosen to be the criteria in the comparisons.

The geometrical characteristics of the ridge play an important role in the formation of lubricant film thickness profile and the pressure distribution through the contact zone. To minimize wear, friction and fatigue life, an optimal ridge profile should have smooth shape with small ridge size. Obtained results are compared with other published numerical results and show a good agreement.

The study evaluates the performance of different surface features of a single ridge with different shapes and sizes passing through elastohydrodynamic of point contact problem in relation to film thickness and pressure profile.

The purpose of this study is to introduce an alternative construction for microfluidic micromixers, where the effect of the extruded filaments in the fused deposition modeling (FDM) technique is used to enhance mixing performance identified as a challenge in microfluidic micromixers.

A simple Y-shaped micromixer was designed and printed using FDM technique. Experimental and numerical studies were conducted to investigate the effect of the extruded filaments on the flow behavior. The effects of the extruded width (LW), distance between adjacent filaments (b) and filament height (h₁) are investigated on the mixing performance and enhancing mixing in the fabricated devices. The performance of fabricated devices in mixing two solutions was tested at flow rates of 5, 10, 20, 40, 80 and 150 µL/min.

The experimental results showed that the presence of geometrical features on microchannels, because of the nature of the FDM process, can act as ridges and generate a lateral transform through the transverse movement of fluids along the groove. The results showed the effect of increasing ridge height on the transverse movement of the fluids and, therefore, chaotic mixing over the ridges. In contrast, in the shallow ridge, diffusion is the only mechanism for mixing, which confirms the numerical results.

The study presents an exciting aspect of FDM for fabrication of micromixers and enhance mixing process. In comparison to other methods, no complexity was added in fabrication process and the ridges are an inherent property of the FDM process.

The purpose of this paper is to introduce the concept of stationary inlet zone bump (IZB) for film thickness enhancement in unidirectional pure sliding elastohydrodynamic lubrication (EHL) line contacts and to investigate the effects of maximum Hertzian pressure (load) and piezo-viscous response on the effectiveness of IZB.

The numerical analysis involves the solution of Reynolds and elasticity equations. The well-established Doolittle–Tait equations are used herein to determine the lubricant viscosity and density as functions of local pressure, while the Carreau model is used to describe the lubricant rheology. The IZB is assumed to have a sinusoidal profile and it is present on the stationary surface. The governing equations are discretized using finite difference scheme and solved using the Newton–Raphson technique.

Two test oils, L7808 and SR600, with linear and exponential piezo-viscous responses in the inlet zone are considered here for comparison. The effectiveness of IZB in terms of film thickness enhancement is found to be more for SR600. Besides, IZB is found to be more effective at lower values of maximum Hertzian pressure. The bump needs to shift downstream at higher load to be as effective as at lower load.

This is the first paper to simulate EHL characteristics in the presence of a stationary IZB and to study the effect of various parameters on EHL effectiveness. The film thickness enhancement obtained here is remarkable and hence it is a novel and valuable contribution.

To the Editor. DEAR SIR, In the June issue of AIRCRAFT ENGINEERING, Mr V. D. Naylor rightly asserts that, according to one‐dimensional theory, the velocity at the throat of a Laval nozzle is the local sonic velocity, whether friction is present or not. However his proof rests on an expansion law pvn=constant, when n≠y, and the throat velocity which he obtains differs according to the value of n. Both the assumption and the conclusion are false. The confusion which has existed on this point is, therefore, deepened.

The dent is one of typical surface defects on the surfaces of the machine elements and it is not in fact inerratic. This work aims to investigate the effect of a single dent with a marginal bump on the film shape in elastohydrodynamic lubrication (EHL) point contacts.

The experimental investigations of a single dent with marginal bump were carried out using multi-beam interferometry in EHL point contacts. In the meantime, its numerical simulation was also finished using multi-level method and multilevel multi-integration method. The effects of the entrainment velocity and the applied load as well as the slide-roll ratio on the film were chiefly discussed. Meanwhile, the comparison of films between smooth and dented surfaces was conducted under simple sliding conditions.

Under pure sliding conditions, the minimum film thickness presents itself near the marginal bump at lower entrainment velocity. The inlet dimple before the marginal bump is subjected to the operating conditions. Under pure rolling conditions, the shape of the dent is almost unchanged when it is passing through the contact region at lower entrainment velocity. The dent depth hardly depends on the applied load under static conditions. However, larger load enhances the inlet dimple and the elastic deformation of the dent with the marginal bump under pure sliding conditions.

This work is helpful to understanding the effect of the marginal bump before the single dent on point contact EHL films.

Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Technical Reports and Translations of the United States National Aeronautics and Space Administration and publications of other similar Research Bodies as issued.

We present in this paper an efficient finite element analysis for different types of waveguides . The computations are performed with “edge elements” . These finite elements avoid all the “spurious modes”, the non‐physical numerical fields obtained from the solution of eigenvalue problems with classical finite elements formulations.Both dielectric‐loaded waveguides and ridged waveguides (waveguides with sharp edges) are analyzed. Comparisons of our results with previously published ones show theaccuracy of the numerical technique.

An aircraft structural member such as a wing or fuselage is provided with a series of suction ducts formed in transversely disposed structural elements and embodying porous portions through which suction of the boundary layer is effected. The skin consists of outer and inner sheets 2, 13 connected by transverse channel members or, as shown in no. 1, by corrugated sheets 12, the outer sheet 2 being locally thickened at intervals for the reception of strips 1 of sintered bronze, rolled gauze or perforated material. The portion of the sheet 2 below each strip 1, and the walls of the associated duct 5 are perforated, the ducts being placed in communication with one or more suction pumps. In an alternative construction the strips 1 are replaced by sets of spanwise rows of fine, closely spaced perforations in the sheet 2. These rows of perforations may, in a further arrangement, be formed in shallow recessed grooves in the outer surface of the sheet 2, which is covered with a thin continuous sheet of porous material, such as steel or nickel alloy gauze. In another construction, FIG. 2, the outer sheet 2a is formed with ridges 22 defining rectangular or polygonal recesses, a continuous outer layer 2b of porous material being secured by gluing or bonding to the ridges 22. In the case of a wing the members constituting the ducts 5 act as stringers, while in the case of a fuselage they serve as frames. The porosity of the inserts, or the capacity of the pumps may be varied to modify the degree of suction over different portions of the surface.