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Article

Zhenyuan Tang and Decheng Wan

The jet impingement usually accompanying large interface movement is studied by the in-house solver MLParticle-SJTU based on the modified moving particle semi-implicit…

Abstract

Purpose

The jet impingement usually accompanying large interface movement is studied by the in-house solver MLParticle-SJTU based on the modified moving particle semi-implicit (MPS) method, which can provide more accurate pressure fields and deformed interface shape. The comparisons of the pressure distribution and the shape of free surface between the presented numerical results and the analytical solution are investigated. The paper aims to discuss these issues.

Design/methodology/approach

To avoid the instability in traditional MPS, a modified MPS method is employed, which include mixed source term for Poisson pressure equation (PPE), kernel function without singularity, momentum conservative gradient model and highly precise free surface detection approach. Detailed analysis on improved schemes in the modified MPS is carried out. In particular, three kinds of source term in PPE are considered, including: particle number density (PND) method, mixed source term method and divergence-free method. Two typical kernel functions containing original kernel function with singularity and modified kernel function without singularity are analyzed. Three kinds of pressure gradient are considered: original pressure gradient (OPG), conservative pressure gradient (CPG) and modified pressure gradient (MPG). In addition, particle convergence is performed by running the simulation with various spatial resolutions. Finally, the comparison of the pressure fields by the modified MPS and by SPH is presented.

Findings

The modified MPS method can provide a reliable pressure distribution and the shape of the free surface compared to the analytical solution in a steady state after the water jet impinging on the wall. Specifically, mixed source term in PPE can give a reasonable profile of the shape of free surface and pressure distribution, while PND method adopted in the traditional MPS is not stable in simulation, and divergence-free method cannot produce rational pressure field near the wall. Two kernel functions show similar pressure field, however, the kernel function without singularity is preferred in this case to predict the profile of free surface and pressure on the wall. The shape of free surface by CPG and MPG is agreement with the analytical solution, while a great discrepancy can be observed by OPG. The pressure peak by MPG is closer to the analytical solution than that by CPG, while the pressure distribution on the right hand side of the pressure peak by latter is better match with the analytical solution than that by former. Besides, fine spatial resolution is necessary to achieve a good agreement with analytical results. In addition, the pressure field by the modified MPS is also quite similar to that by SPH, and this can further validate the reliable of current modified MPS.

Originality/value

The present modified MPS appears to be a stable and reliable tool to deal with the impinging jet flow problems involving large interface movement. Mixed source term in PPE is superior to PND adopted in the traditional MPS and divergence-free method. The kernel function without singularity is preferred to improve the computational accuracy in this case. CPG is a good choice to obtain the shape of free surface and the pressure distribution by jet impingement.

Details

Engineering Computations, vol. 32 no. 4
Type: Research Article
ISSN: 0264-4401

Keywords

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Article

S. Madhu and M. Balasubramanian

The purpose of this study is for solving many issues in production that includes processing of complex-shaped profile, machining of high-strength materials, good surface

Abstract

Purpose

The purpose of this study is for solving many issues in production that includes processing of complex-shaped profile, machining of high-strength materials, good surface finish with high-level precision and minimization of waste. Among the various advanced machining processes, abrasive jet machining (AJM) is one of the non-traditional machining techniques used for various applications such as polishing, deburring and hole making. Hence, an overview of the investigations done on carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GRFP) composites becomes important.

Design/methodology/approach

Discussion on various approaches to AJM, the effect of process parameters on the glass fiber and carbon fiber polymeric composites are presented. Kerf characteristics, surface roughness and various nozzle design were also discussed.

Findings

It was observed that abrasive jet pressure, stand-off distance, traverse rate, abrasive size, nozzle diameter, angle of attack are the significant process parameters which affect the machining time, material removal rate, top kerf, bottom kerf and kerf angle. When the particle size is maximum, the increased kinetic energy of the particle improves the penetration depth on the CFRP surface. As the abrasive jet pressure is increased, the cutting process is enabled without severe jet deflection which in turn minimizes the waviness pattern, resulting in a decrease of the surface roughness.

Research limitations/implications

The review is limited to glass fiber and carbon fiber polymeric composites.

Practical implications

In many applications, the use of composite has gained wide acceptance. Hence, machining of the composite need for the study also has gained wide acceptance.

Social implications

The usage of composites reduces the usage of very costly materials of high density. The cost of the material also comes down.

Originality/value

This paper is a comprehensive review of machining composite with abrasive jet. The paper covers in detail about machining of only GFRP and CFRP composites with various nozzle designs, unlike many studies which has focused widely on general AJM of various materials.

Details

World Journal of Engineering, vol. 18 no. 2
Type: Research Article
ISSN: 1708-5284

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Article

Jun Sun, Xinlong Zhu, Liang Zhang, Xianyi Wang, Chunmei Wang, Hu Wang and Xiaoyong Zhao

Current lubrication analyses of misaligned journal bearings were generally performed under some given preconditions. To make the lubrication analysis closer to the actual…

Abstract

Purpose

Current lubrication analyses of misaligned journal bearings were generally performed under some given preconditions. To make the lubrication analysis closer to the actual situation and usable to the journal bearing design, the purpose of this paper was to calculate the lubrication characteristics of misaligned journal bearings considering the viscosity-pressure effect of the oil, the surface roughness and the elastic deformation of the journal bearing at the same time.

Design/methodology/approach

The lubrication of bearings was analyzed using the average Reynolds equation. The deformation of the bearing surface under oil film pressure was calculated by a compliance matrix method. The compliance matrix was established by finite element analysis of the bearing housing. The viscosity-pressure and viscosity–temperature equations were used in the analysis.

Findings

The oil viscosity-pressure relationship has a significant effect on the lubrication of misaligned journal bearings. The surface roughness will affect the lubrication of misaligned journal bearings when the eccentricity ratio and angle of journal misalignment are all large. The directional parameter of the surface has an obvious effect on the lubrication of misaligned journal bearings. The deformation of the bearing surface has a remarkable effect on the lubrication of misaligned journal bearings.

Originality/value

The lubrication characteristics of misaligned journal bearings were calculated considering the viscosity-pressure effect of the oil, the surface roughness and the elastic deformation of the journal bearing at the same time. The results of this paper are helpful to the design of the bearing.

Details

Industrial Lubrication and Tribology, vol. 66 no. 3
Type: Research Article
ISSN: 0036-8792

Keywords

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Article

Qiyin Lin, Zhengying Wei, Ning Wang and Wei Chen

The purpose of this paper is to study the influence of large-area texture/slip surface, especially the area and position of large-area texture surface on journal bearing…

Abstract

Purpose

The purpose of this paper is to study the influence of large-area texture/slip surface, especially the area and position of large-area texture surface on journal bearing, and improve the tribological performances of journal bearing.

Design/methodology/approach

A modified texture/slip numerical boundary condition with double parameters is presented and is applied onto the region where surface textures locate to represent the impact of actual texture/slip surface. A phase change condition is used to analyze cavitation phenomena.

Findings

The global/cumulative texture effect can be represented by applying texture/slip condition onto the region where it locates. The area and position of texture/slip surface would significantly affect the cavitation and load-carrying capacity. Texture/slip surface would not affect the pressure and load-carrying capacity when it locates at cavitation zone. The effect of texture/slip surface on load-carrying capacity would be beneficial if it locates at the pressure rise region, but its effect would be adverse if it locates at the pressure drop region. Well-designed texture/slip surface can improve tribological performances.

Originality/value

The developed texture/slip boundary condition can be a suitable and useful tool to analyze the effect of large-area texture/slip surface and especially to optimize the area and position of large-area texture surface. This approach can be complementary to conventional approach which is used to analyze the influence of textures’ real configurations and parameters.

Details

Industrial Lubrication and Tribology, vol. 67 no. 3
Type: Research Article
ISSN: 0036-8792

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Article

Haniff Abdul Rahman, Jaharah A. Ghani, Wan Mohd Faizal Wan Mahmood and Mohammad Rasidi Mohammad Rasani

This study aims to simulate the influence of surface texturing produced via turning process toward pressure distribution and load capacity generation using computational…

Abstract

Purpose

This study aims to simulate the influence of surface texturing produced via turning process toward pressure distribution and load capacity generation using computational fluid dynamics (CFD).

Design/methodology/approach

The dimple geometry was obtained via turning process, to be used for future application on piston skirt surfaces. Two cases were studied: a preliminary study using single periodic dimple assuming linear dimple distribution and an application study using multiple periodic dimples to address actual dimple orientation following the turning process.

Findings

For the first case, the dimple was proven to generate load capacity with regard to untextured surface, owing to the asymmetric pressure distribution. Increasing the Reynolds number, dimple width and dimple depth was found to increase load capacity. For the second case, although load capacity increases via surface texturing, the value was 97.4 per cent lower relative to the first case. This confirmed the importance of doing multiple dimple simulations for real applications to achieve more realistic and accurate results.

Originality/value

A new concept of dimple fabrication using a low-cost turning process has been developed, with a potential to increase the tribological performance under hydrodynamic lubrication. Previous CFD simulations to simulate these benefits have been done using a single periodic dimple, assuming equal distribution array between dimples. However, due to the different orientations present for dimples produced using turning process, a single periodic dimple simulation may not be accurate, and instead, multiple dimple simulation is required. Therefore, present research was conducted to compare the results between these two cases and to ensure the accuracy of CFD simulation for this type of dimple.

Details

Industrial Lubrication and Tribology, vol. 71 no. 4
Type: Research Article
ISSN: 0036-8792

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Article

Sudipto Ray and S.K. Roy Chowdhury

The paper's aim is to predict numerically the contact temperatures between two rough sliding bodies and to compare with the experimental results.

Abstract

Purpose

The paper's aim is to predict numerically the contact temperatures between two rough sliding bodies and to compare with the experimental results.

Design/methodology/approach

An elastic contact algorithm is used to analyze the normal contact between two nominally smooth surfaces. The algorithm evaluates real contact area using digitized roughness data and the corresponding contact pressure distribution. Using finite element method a steady state 3D temperature distribution at the interface between the sliding bodies is obtained. Using infrared (IR) imaging technique, experiments were carried out to measure the contact temperature distribution between rough rubbing bodies with a systematic variation of surface roughness and operating variables.

Findings

Contact temperature distributions over a wide range of normal load, sliding velocity and surface roughness have been obtained. It was seen that the maximum contact temperature expectedly increases with surface roughness (Sa values), normal load and sliding velocity. The results also indicate that the “hot spots” are located exactly at the positions where the contact pressures are extremely high. Temperatures can be seen to fall drastically at areas where no asperity contacts were established. The temperature contours at different depths were also plotted and it was observed that the temperatures fall away from the actual contact zone and relatively high temperatures persist at the “hot spot” zones much below the contact surface. Finally it is encouraging to find a good correlation between the numerical and experimental results and this indicates the strength of the present analysis.

Research limitations/implications

Experimental accuracy can be improved by using a thermal imaging camera that measures emissivity in situ and uses it to find the contact temperature. The spatial resolution and the response time of the camera also need to be improved. This can improve the correlation between numerical and experimental results.

Practical implications

One of the major factors attributed to the failure of sliding components is the frictional heating and the resulting flash temperatures at the sliding interface. However, it is not easy to measure such temperatures owing to the inherent difficulties in accessing the contact zone. Besides, thermal imaging techniques can be applied only with such tribo‐pairs where at least one of the contacting materials is transparent to IR radiation. In practice, such cases are a rarity. However, the good correlation observed between the numerical and experimental results in this work would give the practicing engineer a confidence to apply the numerical model directly and calculate contact temperatures for any tribo‐material pairs that are generally seen around.

Originality/value

A good correlation between the numerical and experimental results gives credence to the fact that the numerical model can be used to predict contact temperatures between any sliding tribo‐pairs.

Details

Industrial Lubrication and Tribology, vol. 63 no. 5
Type: Research Article
ISSN: 0036-8792

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Article

M.M. De Guzman, C.A.J. Fletcher and J.D. Hooper

The detailed flow behaviour around a four—hole Cobra Pitot pressureprobe, developed by the Commonwealth Scientific and Industrial ResearchOrganization, Australia, (CSIRO)…

Abstract

The detailed flow behaviour around a four—hole Cobra Pitot pressure probe, developed by the Commonwealth Scientific and Industrial Research Organization, Australia, (CSIRO), to determine the pressure and the velocity components in three dimensional single‐phase/multi‐phase fluid flow, is investigated computationally. The incompressible steady state Navier—Stokes equations are solved numerically using a general purpose computational fluid dynamics (CFD) code developed at CANCES. Computational results are presented for representative probe pitch and yaw angles at a Reynolds number = 2 × 103, emphasising the pressure distribution and flow separation patterns on the probe tip adjacent to the pressure ports. Quantitative comparison of the computational simulation to experimental results is done by comparing experimental calibration data to numerically computed pressure responses. The topological features of the near tip flow behaviour are visualised using critical point concepts and three dimensional streamlines. Additional qualitative comparison to experiment is discussed using data from a preliminary experimental investigation using surface oil film visualisation techniques, where available. Conclusions are drawn concerning the near tip flow behaviour, the good level of agreement between the numerical results and experimental data and the effectiveness of using a computational analysis to provide accurate detail useful for engineering design purposes.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 4 no. 5
Type: Research Article
ISSN: 0961-5539

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Article

Ashwani Assam, Nikhil Kalkote, Nishanth Dongari and Vinayak Eswaran

Accurate prediction of temperature and heat is crucial for the design of various nano/micro devices in engineering. Recently, investigation has been carried out for…

Abstract

Purpose

Accurate prediction of temperature and heat is crucial for the design of various nano/micro devices in engineering. Recently, investigation has been carried out for calculating the heat flux of gas flow using the concept of sliding friction because of the slip velocity at the surface. The purpose of this study is to exetend the concept of sliding friction for various types of nano/micro flows.

Design/methodology/approach

A new type of Smoluchowski temperature jump considering the viscous heat generation (sliding friction) has recently been proposed (Le and Vu, 2016b) as an alternative jump condition for the prediction of the surface gas temperature at solid interfaces for high-speed non-equilibrium gas flows. This paper investigated the proposed jump condition for the nano/microflows which has not been done earlier using four cases: 90° bend microchannel pressure-driven flow, nanochannel backward facing step with a pressure-driven flow, nanoscale flat plate and NACA 0012 micro-airfoil. The results are compared with the available direct simulation Monte Carlo results. Also, this paper has demonstrated low-speed preconditioned density-based algorithm for the rarefied gas flows. The algorithm captured even very low Mach numbers of 2.12 × 10−5.

Findings

Based on this study, this paper concludes that the effect of inclusion of sliding friction in improving the thermodynamic prediction is case-dependent. It is shown that its performance depends not only on the slip velocity at the surface but also on the mean free path of the gas molecule and the shear stress at the surface. A pressure jump condition was used along with the new temperature jump condition and it has been found to often improve the prediction of surface flow properties significantly.

Originality/value

This paper extends the concept of using sliding friction at the wall for micro/nano flows. The pressure jump condition was used which has been generally ignored by researchers and has been found to often improve the prediction of surface flow properties. Different flow properties have been studied at the wall apart from only temperature and heat flux, which was not done earlier.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 8
Type: Research Article
ISSN: 0961-5539

Keywords

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Article

Dandan Qiu, Lei Luo, Songtao Wang, Bengt Ake Sunden and Xinhong Zhang

This study aims to focus on the surface curvature, jet to target spacing and jet Reynolds number effects on the heat transfer and fluid flow characteristics of a slot jet…

Abstract

Purpose

This study aims to focus on the surface curvature, jet to target spacing and jet Reynolds number effects on the heat transfer and fluid flow characteristics of a slot jet impinging on a confined concave target surface at constant jet to target spacing.

Design/methodology/approach

Numerical simulations are used in this research. Jet to target spacing, H/B is varying from 1.0 to 2.2, B is the slot width. The jet Reynolds number, Rej, varies from 8,000 to 40,000, and the surface curvature, R2/B, varies from 4 to 20. Results of the target surface heat transfer, flow parameters and fluid flow in the concave channel are performed.

Findings

It is found that an obvious backflow occurs near the upper wall. Both the local and averaged Nusselt numbers considered in the defined region respond positively to the Rej. The surface curvature plays a positive role in increasing the averaged Nusselt number for smaller surface curvature (4-15) but affects little as the surface curvature is large enough (> 15). The thermal performance is larger for smaller surface curvature and changes little as the surface curvature is larger than 15. The jet to target spacing shows a negative effect in heat transfer enhancement and thermal performance.

Originality/value

The surface curvature effects are conducted by verifying the concave surface with constant jet size. The flow characteristics are first obtained for the confined impingement cases. Then confined and unconfined slot jet impingements are compared. An ineffective point for surface curvature effects on heat transfer and thermal performance is obtained.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 29 no. 8
Type: Research Article
ISSN: 0961-5539

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Article

Ming-min Liu, L.Z. Li and Jun Zhang

The purpose of this paper is to discuss a data interpolation method of curved surfaces from the point of dimension reduction and manifold learning.

Abstract

Purpose

The purpose of this paper is to discuss a data interpolation method of curved surfaces from the point of dimension reduction and manifold learning.

Design/methodology/approach

Instead of transmitting data of curved surfaces in 3D space directly, the method transmits data by unfolding 3D curved surfaces into 2D planes by manifold learning algorithms. The similarity between surface unfolding and manifold learning is discussed. Projection ability of several manifold learning algorithms is investigated to unfold curved surface. The algorithms’ efficiency and their influences on the accuracy of data transmission are investigated by three examples.

Findings

It is found that the data interpolations using manifold learning algorithms LLE, HLLE and LTSA are efficient and accurate.

Originality/value

The method can improve the accuracies of coupling data interpolation and fluid-structure interaction simulation involving curved surfaces.

Details

Multidiscipline Modeling in Materials and Structures, vol. 13 no. 2
Type: Research Article
ISSN: 1573-6105

Keywords

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