Discontinuous Grooves Research Articles

Spanwise-Discontinuous Grooves for Separation Delay and Drag Reduction of Bodies with Vortex Shedding

Suitably shaped grooves, placed transverse to the flow, can delay flow separation over curved surfaces. When grooves are fully extruded in the spanwise direction, they may reduce the drag of boat-tailed bodies with vortex shedding, but with the drawback of increasing the spanwise correlation of the vortex shedding. We investigate herein the effect of spanwise-discontinuous grooves through Large Eddy Simulations. A systematic analysis is carried out on the effect of the number, N, of grooves that are present for N equally long portions of the total spanwise length of the boat-tail. Discontinuous grooves further reduce the drag compared with the full-spanwise-extruded groove. Increasing N produces an improvement of the flow-control-device performance, whose maximum value is reached for N=3, corresponding to a spanwise extension of the groove roughly equal to the body crossflow dimension. Above this value, no further improvements are found. The maximum drag reduction is equal to 25.7% of the drag of the boat-tail without grooves and to 17.7% of the one of the boat-tail with the full-spanwise-extruded groove. The lowest drag value occurs for the least correlated vortex-shedding in the spanwise direction. The reduction in the correlation is mainly related to a flow separation line that is less regular in the spanwise direction.

Spontaneous spreading of nanodroplets on partially wetting surfaces with continuous grooves: Synergy of imbibition and capillary condensation

The wetting behavior of nanodroplets deposited on hydrophilic textured surfaces with discontinuous and continuous grooves was investigated by many-body dissipative particle dynamics. For surfaces with discontinuous grooves, the apparent contact angle (θa) can be described by the Wenzel model with an effective area ratio. However, for surfaces with continuous grooves, θa of nanodroplets depends on roughness topology, and spontaneous spreading of nanodroplets can take place even for partially wetting surfaces (θY > 0). That is, the partial-to-total wetting transition can occur on hydrophilic surfaces as surface textures change from discontinuous to continuous grooves. The dynamics of the spreading can be characterized by the apparent radius and groove radius (Rg). While the former is time-invariant at early stage, the latter follows the power law Rg ~ t1/4. This spreading of nanodroplets along continuous grooves can be explained from the synergy of spontaneous imbibition into continuous grooves, arrest by sharp edges, and capillary condensation for resuming the flow.

Discontinuous grooves in thrust air bearings designed with CAPSO algorithm

Spiral groove thrust air bearings suffer from low load capacity. Although there have been studies on optimizing the groove geometry of spiral groove thrust air bearings to enhance the load capacity, all of them found so far have focused on continuous grooves only. Here, a novel groove optimization method, which allows the flexibility of generating either continuous or discontinuous grooves, is introduced for maximizing the load capacity of spiral groove thrust air bearings. In the proposed method, computational fluid dynamics is combined with the chaos-enhanced accelerated particle swarm optimization algorithm to search for the optimal groove geometry. A case study is given where the optimization of an initial spiral groove thrust air bearing is implemented. The optimized grooves are found to be discontinuous and of new geometry. Numerical analysis shows that the optimized discontinuous grooves can achieve higher load capacity than the optimized continuous grooves, the conventional herringbone, and the initial spiral grooves. The effect of the proposed method is further verified in experiments.

Tribological properties of surface topography in ultrasonic vibration-assisted grinding of zirconia ceramics

In order to clarify the friction phenomenon of zirconia ceramics in the dental prosthodontics, tribological properties of surface topography in ultrasonic vibration-assisted grinding (UVAG) are studied in this work. The mechanism of material removal is researched to introduce the discontinuous grooves in UVAG theoretically. The UVAG experiments are conducted on zirconia ceramics. Through investigating and comparing experimental results, it is found that UVAG surface has better tribological properties compared with diamond grinding surface. 3D surface roughnesses of UVAG surface are improved when suitable spindle speed, large feed, small cutting depth, and large vibration amplitude are adopted. Surface topography in UVAG changes from thorn scaly to discontinuous shallow furrow when feed increases and spindle speed decreases. The discontinuous grooves are most apparent when vibration amplitude is maximum. Furthermore, the friction coefficient is experimentally studied. The results indicate that there is no significant difference among all the friction coefficients in UVAG. Proper cutting and vibration parameters can improve the average friction coefficient.

Machined Surface Morphology and Generation Mechanism of NbC Particle Reinforced Iron-Base Composites

In this paper, the morphology of machined surface in turning NbC particle reinforced iron-base composites was investigated. It indicates that since the dispersive distribution of reinforcing particles, the machined surface is likely to occur various defects such as tool traces, small pits, discontinuous grooves or micro-cracks. Moreover, the surface generation mechanism was discussed. There exist three different behaviors for reinforcing particles such as brittle breakage, pressed into or flaking off the machined surface during machining. Generally, particles of small diameter are likely to be pressed into the matrix and the machining defects are relatively slight. However, particles of large diameter are likely to break or flake off, which makes surface integrity deteriorate.

Pressure Distributions along Vertical Hydrodynamic Herringbone-Grooved Journal Bearings

The pressure distributions generated along vertical hydrodynamic herringbone-grooved journal bearings were experimentally and numerically investigated at rotational speeds ranging from 203 to 2110 rpm. A test rig was designed and constructed for this purpose and four journals (shafts) with different herringbone-grooved patterns and radial gaps were tested: Journal 1 (with symmetrical and discontinuous grooves and 0.25-mm clearance gap), Journal 2 (with symmetrical and discontinuous grooves and 0.35-mm clearance gap), Journal 3 (with symmetrical and four continuous grooves), and Journal 4 (with asymmetrical and three continuous grooves). The journals were made of aluminum with diameters of 46.00 mm, and the sleeve was made of a transparent Plexiglas pipe for visual observation of the lubricant in the gap between the journal and the sleeve. Pressure taps were installed along the sleeve to obtain the pressure distributions using a pressure transducer. Numerical simulations were performed for these four herringbone-grooved journal bearings using commercially available computational fluid dynamic software. The computational simulations agree in trends with the experimental results and theoretical expectations. Review led by Greg Kostrzewsky

The effects of continuous and discontinuous groove edges on cell shape and alignment

Nanofabricated model surfaces and digital image analysis of cell shape were used to address the importance of a continuous sharp edge in the alignment of cells to shallow surface grooves. The grooved model surfaces had either continuous or discontinuous edges of various depths (40–400 nm) but identical surface chemistry and groove/ridge dimensions (15 μm wide). Epithelial cells were cultured on the model surfaces for 10 and 24 h. Fluorescence microscopy combined with image analysis were used to quantify cell area and alignment and to make cell shape classifications of individual cells. The degrees of alignment of cells and the percentages of elongated cell classes increased with groove depth on samples with continuous grooves. Two main differences, with regard to cell response, were observed between the continuous and discontinuous grooved surfaces. First, significantly fewer cells aligned to surface grooves with discontinuous edges than to grooves with continuous edges. Second, there were lower percentages of the elongated cell classes on discontinuous grooves than on continuous ones. We concluded that grooved surfaces with continuous edges are more potent in aligning and inducing elongated cells. The results from the present study suggest that a mechanism of alignment involving orientation along a continuous edge is likely.

Morphological Characteristics of Neuromuscular Junctions of the Opossum (Didelphis albiventris) Extraocular Muscles: A Scanning-Electron-Microscopic Study

Three types of neuromuscular junctions were described in the extraocular muscles of the opossum. The present study demonstrates the three-dimensional characteristics of these neuromuscular junctions after HCl connective tissue digestion. Adult opossum of both sexes were used and the neuromuscular junctions of the extraocular muscles were examined after removal of the intramuscular connective tissue and basal layer. This material was examined with a scanning electron microscope. Two types of ‘en plaque’ neuromuscular junction were described: the continuous type revealed elongated and branched primary synaptic grooves separated from each other by sarcolemma protuberances with different sizes, and the discontinuous or punctiform type which presents very shallow and discontinuous grooves when compared with the former. The multiple neuromuscular junctions were observed as two or three junctions associated with the same muscular fiber. The multiple junctions were present in thin fibers (around 11 μm caliber); the en plaque junctions were associated with large diameter fibers (around 21 μm). This study confirms and reveals the detailed morphological characteristics of the three neuromuscular junction types previously described by transmission electron microscope in the extraocular muscles of opossum.

Microstructural changes in GeSbTe film during repetitious overwriting in phase-change optical recording

Microstructural changes that occur in a GeSbTe film during repetitious overwriting in phase-change optical recording were investigated. The GeSbTe active layer was melted by a focused laser diode (LD) beam during each overwriting process over amorphous mark formation. The repetitious solidification and liquefaction process in such a short time as 50–200 ns resulted in microstructural changes in the active layer: a segregation, sink, and void formations. The sink was formed in the low-density active layer due to the shrinking of the volume during the resolidification process. Sink formation could be suppressed when a high-density active layer, having more than 80% of the bulk density, was used. Such a high-density GeSbTe film, however, resulted in a void formation of the size of 0.1 μm. The voids were thought to be nucleated by residual vacancies and Ar precipitation, since the active layer contained a high concentration of Ar impurities, due to the atomic peening effect. The subsequent void coalescence and migration processes across the beam scanning direction could result in the formation of thermally discontinuous grooves at the edges of the written marks. The voids could also migrate along the LD beam scanning direction, accompanied by a material flow of the active layer in the opposite direction. These phenomena were also found to depend on the material used to fabricate the protective layers which sandwiched the active layer. A TaOx protective layer enhanced the void migration across the track, resulting in the removal of voids from the center of the track. Use of the ZnS:SiO2 compound protective layer confined voids to the center of the track. The ZnS:SiO2 protective layer also promoted the formation of thermally discontinuous grooves at the edges of amorphous marks. The material flow along the track resulted in a thicker active layer at the start of the consecutive LD irradiation, and also in a high void density region at the final edge of the irradiation having a length on the order of 10 μm. This tendency was found for both the ZnS:SiO2 and TaOx sandwiching media.

Dietary management reverses grooving and abnormal polarization of hair shafts in argininosuccinase deficiency

We have observed that the fragile hair of two untreated patients with argininosuccinic aciduria showed abnormal alternating zones of bright and dark banding by polarizing microscopy. Scanning electron microscopy documented discontinuous grooves with a 50 to 100 microns periodicity. Results of amino acid analysis of the hair were essentially normal. After the patients were treated with a low-protein, arginine-supplemented diet, the hair assumed a normal appearance. Five patients already treated with diet showed no hair abnormalities. The pathogenesis of the hair changes in unknown, but our findings suggest that products generated in the disease can adversely affect metabolically active tissue such as hair.

Stream Fluting and Stream Erosion

Swiftly moving sand or silt-laden water currents sometimes abrade grooves, elongated in the direction of flow, in boulders and in the bedrock of the channel. Discontinuous grooves of irregular pattern result from turbulence of the water flow. In this article the grooves are termed flutes, and the process of their formation is called stream fluting. The importance of fluting in fluvial erosion is discussed. The process is analyzed on the basis of excellent examples observed in the inner gorge of the Grand Canyon of the Colorado River.