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15 pages, 3841 KiB

Open AccessArticle

Numerical Bifurcation Analysis of a Film Flowing over a Patterned Surface through Enhanced Lubrication Theory

by Nicola Suzzi and Giulio Croce

Fluids 2021, 6(11), 405; https://doi.org/10.3390/fluids6110405 - 09 Nov 2021

Cited by 1 | Viewed by 1199

The bifurcation analysis of a film falling down an hybrid surface is conducted via the numerical solution of the governing lubrication equation. Instability phenomena, that lead to film breakage and growth of fingers, are induced by multiple contamination spots. Contact angles up to [...] Read more.

The bifurcation analysis of a film falling down an hybrid surface is conducted via the numerical solution of the governing lubrication equation. Instability phenomena, that lead to film breakage and growth of fingers, are induced by multiple contamination spots. Contact angles up to

75^{\circ}

are investigated due to the full implementation of the free surface curvature, which replaces the small slope approximation, accurate for film slope lower than

30^{\circ}

. The dynamic contact angle is first verified with the Hoffman–Voinov–Tanner law in case of a stable film down an inclined plate with uniform surface wettability. Then, contamination spots, characterized by an increased value of the static contact angle, are considered in order to induce film instability and several parametric computations are run, with different film patterns observed. The effects of the flow characteristics and of the hybrid pattern geometry are investigated and the corresponding bifurcation diagram with the number of observed rivulets is built. The long term evolution of induced film instabilities shows a complex behavior: different flow regimes can be observed at the same flow characteristics under slightly different hybrid configurations. This suggest the possibility of controlling the rivulet/film transition via a proper design of the surfaces, thus opening the way for relevant practical application. Full article

(This article belongs to the Special Issue Lubrication Flows)

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15 pages, 3770 KiB

Open AccessArticle

Performance Investigation of MQL Parameters Using Nano Cutting Fluids in Hard Milling

by Tran Minh Duc, Tran The Long and Ngo Minh Tuan

Fluids 2021, 6(7), 248; https://doi.org/10.3390/fluids6070248 - 06 Jul 2021

Cited by 14 | Viewed by 2729

Abstract

Machining difficult-to-cut materials is one of the increasingly concerned issues in the metalworking industry. Low machinability and high cutting temperature generated from the contact zone are the main obstacles that need to be solved in order to improve economic and technical efficiency but [...] Read more.

Machining difficult-to-cut materials is one of the increasingly concerned issues in the metalworking industry. Low machinability and high cutting temperature generated from the contact zone are the main obstacles that need to be solved in order to improve economic and technical efficiency but still have to ensure environmental friendliness. The application of MQL method using nano cutting fluid is one of the suggested solutions to improve the cooling and lubricating performance of pure-MQL for machining difficult-to-cut materials. The main objective of this paper is to investigate the effects of nanofluid MQL (NFMQL) parameters including the fluid type, type of nanoparticles, air pressure and air flow rate on cutting forces and surface roughness in hard milling of 60Si₂Mn hardened steel (50–52 HRC). Analysis of variance (ANOVA) was implemented to study the effects of investigated variables on hard machining performance. The most outstanding finding is that the main effects of the input variables and their interaction are deeply investigated to prove the better machinability and the superior cooling lubrication performance when machining under NFMQL condition. The experimental results indicate that the uses of smaller air pressure and higher air flow rate decrease the cutting forces and improve the surface quality. Al₂O₃ nanoparticles show the better results than MoS₂ nanosheets. The applicability of soybean oil, a type of vegetable oil, is proven to be enlarged in hard milling by suspending nanoparticles, suitable for further studies in the field of sustainable manufacturing. Full article

(This article belongs to the Special Issue Lubrication Flows)

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20 pages, 1054 KiB

Open AccessArticle

Squeeze Flow of Stress Power Law Fluids

by Lorenzo Fusi and Andrea Ballotti

Fluids 2021, 6(6), 194; https://doi.org/10.3390/fluids6060194 - 21 May 2021

Cited by 3 | Viewed by 2309

Abstract

In this paper, we studied the squeeze flow between circular disks of a new class of fluids defined by an implicit relation referred to as stress power law fluids. The constitutive response of these fluids was written expressing the symmetric part of the [...] Read more.

In this paper, we studied the squeeze flow between circular disks of a new class of fluids defined by an implicit relation referred to as stress power law fluids. The constitutive response of these fluids was written expressing the symmetric part of the velocity gradient as a tensorial function of the Cauchy stress. We assumed that the aspect ratio between the gap separating the disks and the radius was small so that a lubrication expansion could be adopted. We wrote the general problem and looked for a solution that could be written in terms of the small aspect ratio parameter. We obtained a sequence of problems that could be solved iteratively at each order, and we focused on the leading and first order, deriving explicit expressions for the velocity field, stress, and pressure. Full article

(This article belongs to the Special Issue Lubrication Flows)

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