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During the process of five-axis free-form milling, tool orientation and surface curvature of the workpiece have significant effects on tool wear. Five-axis milling experiments are carried out on 17-4PH stainless steel using a carbide ball end mill. The influence of tool orientation on the amount of wear, cutting force, and chip morphology of the ball end cutter was investigated. The results show that tool wear is slighter at a tool inclination angle of approximately 15°, reducing tool wear by up to 29.55% compared with other angles. The inclination angle also has great effects on the milling force and torque signals, a suitable tool inclination angle makes the milling force and torque signals smooth, and the standard deviation is only 0.94 N and 0.017 N·m, respectively. In addition, the chips can reflect the stability of the machining process to some extent. On this basis, different workpiece surfaces were selected to investigate the effect of workpiece surface characteristics on tool wear. The results show that more severe tool wear and higher milling force signals on curved surfaces occurred with smaller radii of curvature. An appropriate tool orientation in relation to the curvature of the workpiece surface can significantly reduce tool wear; concave surfaces are suitable for machining with small angle of inclination, e.g., 5° ~ 10°, whereas convex surfaces are suitable for machining with larger angle of inclination, e.g., 20° ~ 25°. [ABSTRACT FROM AUTHOR]

We have investigated the effects of rib surface curvature of a superhydrophobic wall in both laminar and turbulent channel flows. Direct numerical simulation is performed for laminar flows and large eddy simulation is performed for turbulent flows. The parametric study shows that a convex rib surface leads to a lower flow ratethan a flat rib for all Reynolds numbers. A concave rib surface firstly increases and then decreases the flow rate as the curvature angle becomes larger, where an optimal curvature angle exists to maximise flow rate. The value of the optimal curvature angle varies with the Reynolds number. A curved rib surface can modify the distribution of the mean velocity and turbulent statistics near the SH wall. Analysis shows that the overall effect of a curved rib surface on the flow rate is the combination of the wetted area augmentation and the change to the spanwise flow interaction, which depends on the curvature angle and the Reynolds number. The SH wall does not change the fundamental structures of near-wall vortices in turbulent flows. The ridge-groove pattern formed by the curved rib surface can provide additional drag reduction similar to that arising from the surface riblets. [ABSTRACT FROM AUTHOR]

Due to the increasing energy cost, the efficiency of the industrial dryer as the energyintensive processes should be improved. The designer should optimize the design parameters of industrial drying equipment to achieve the minimum drying energy consumption. SST k-ω turbulence model is used to simulate a real geometry for industrial drying applications. For the optimization of the impinging round jet, the specific drying energy consumption is set as the objective function to be minimized. The jet to surface distance, jet to jet spacing, jet inlet velocity, jet angle, and surface velocity are chosen as the design parameters. The SHERPA search algorithm is used to search for the optimal point from the weighted sum of all objectives method. One correlation is developed and validated for the specific drying energy consumption. It is found that the SST k-ω turbulence model succeeded with reasonable accuracy in reproducing the experimental results. The minimum specific energy consumption correlates with high values of the jet to jet spacing, jet angle, and surface velocity and low values of the nozzle to surface distance and jet inlet velocity. The agreement in the prediction of the specific drying energy consumption between the numerical simulation and correlation is found to be reasonable and all the data points deviate from the correlation by less than 7%. [ABSTRACT FROM AUTHOR]

Thermal protection effect of reactive fire protection systems on small‐scale steel components with curved surfaces Intumescent fire protection coatings, also referred to as reactive fire protection systems, are often used to protect steel components from heating up too quickly in the event of a fire. The products are particularly suitable due to profile‐following application as well as the comparatively low coating thickness. If exposed to fire, the intumescent coating foams up and forms a thermal protective layer around the steel profile. This slows down the heating of the steel and delays the temperature‐related loss of strength, which improves the fire resistance of the steel component. From fire tests it is known that the performance of intumescent coatings on steel profiles with a curved surface is usually worse than on comparable components with a flat surface. The following article presents the theoretical background as well as the results from fire tests on small‐scale specimens to show the influence of surface curvature on the thermal protective effect of intumescent fire protection coatings. The systematic investigations show that with increasing surface curvature, the performance of the intumescent coating tends to decrease. When assessing the thermal protective effect of an intumescent coating, the surface curvature of a steel component should be considered. Focusing solely on the profile factor of a steel profile is generally not sufficient. The research forms the basis for the development of screening tests to assess the suitability of intumescent coatings for curved surfaces, enabling a pre‐selection of products for this application. [ABSTRACT FROM AUTHOR]

Jet impingements enhance the heat and mass transfer rate in industrial drying machines. The designer should optimize the design parameters of industrial drying equipment to achieve maximum heat transfer rate. The heat transfer between multiple jets and a moving curved surface is more difficult to study due to the changing boundaries and the effect of surface curvature but is also very relevant in industrial drying applications. SST k-ω turbulence model is used to simulate a real geometry for industrial drying applications. The SST k-ω turbulence model succeeded with reasonable accuracy in reproducing the experimental results. The jet to surface distance, jet to jet spacing, jet inlet velocity, jet angle, and surface velocity are chosen as the design parameters. For the optimization of the impinging round jet, the average Nu number on the moving curved surface is set as the objective functions to be maximized. The SHERPA search algorithm is used to search for the optimal point from the weighted sum of all objectives method. One correlation is developed and validated for the average Nu number. It is found that the maximum average Nu number correlates with high values of jet inlet velocity (Vj), jet angle (ϑ) and jet to jet spacing (S/d) and low values of the jet to surface distance (H/d) and relative surface velocity (VR). The agreement in the prediction of the average Nu number between the numerical simulation and correlation is found to be reasonable and all the data points deviate from the correlation by less than 4%. [ABSTRACT FROM AUTHOR]

Tool orientation has an important effect on the surface quality of a free-form surface during ball end milling process, and the selection of tool orientation is important to ensure the surface quality. In this work, a series of milling experiments were performed by using a carbide ball end mill on a workpiece of TC17 titanium alloy. The purpose of this study was to determine the tool orientation producing optimal surface integrity. The results showed that the surface roughness in both directions was better when the rotational angle was within the range of 0°~90° and with a constant inclination angle. In addition, inclination angle had little effect on the roughness in the feed direction, whereas a much larger or smaller angle led to greater roughness in the step direction. The tool orientation strongly affected the surface morphology. Compressive residual stress was detected on all machined surfaces. The maximum surface residual stress was obtained when the rotational angle was 90°, and the surface residual stress decreased as the inclination angle increased. On this basis, four curved surface models with different curvatures were established according to the features of a blade, and the effects of inclination angle and cutter path orientation on surface integrity were studied. The results indicated that the surface roughness produced with an upward orientation varied more than that produced with a downward orientation for a steep curved surface; the value of the roughness was small for a horizontal orientation and when the machine surface was very smooth. The machined surface for a flat curved surface was smoother, and there were no obvious differences in surface morphology between the two cutter path orientations. For steep curved surfaces, the cutter path orientation had no obvious influence on the residual stress, and a greater value was obtained when the surface was much steeper. For flat curved surfaces, the residual stress had no obvious variation resulting from small changes of the inclination angle. [ABSTRACT FROM AUTHOR]

The controlling mechanisms of the radiation extinction of the flame spreading over cylinders in low flow velocity conditions are investigated with an analytical approach. Attention is focused on the interaction among solid surface curvature, solid surface radiation, and gas-phase volumetric radiation heat loss in the flame spread process. The analysis uses a classical thermal model, which considers the heat balance on the unburned fuel surface near the flame front. A non-dimensional number that evaluates the effects of volumetric radiation heat loss and finite rate chemistry on the flame temperature is also proposed. It is found that solid surface radiation cannot be a dominant mechanism for the radiation extinction of a flame spreading over a thin cylinder. Furthermore, in the case of flame spread over a cylinder, flame spread rate significantly increases with decreasing opposed flow velocity due to curvature effect, thus the consideration of the relative gas flow velocity seen by the spreading flame becomes essential in low flow velocity conditions. However, when the volumetric radiation heat loss in the gas phase is taken into account in the thermal model, flame spread rate for a thin cylinder once increases with decreasing opposed flow velocity and then turns to decrease. As a result, the flame spread rate of a thin cylinder shows a peak value in low flow velocity conditions. This trend is in good agreement with previous microgravity experiments (Fujita et al., 2002 [1]). Moreover, the limit condition of flame spread appears as a bifurcation point where the stable and unstable solutions of flame spread rate coincide in the low flow velocity condition. The analytical results indicate that it is essential to consider the volumetric radiation heat loss in the gas phase to predict the flame spread over a curved surface in low flow velocity conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • MLSPT-induced tri-directional RS as a function of curvature was investigated. • RS difference between both convex and concave surfaces was identified. • MLSPT-induced CRS mathematic model as a function of curvature was proposed. • Influence mechanisms of surface curvature on MLSPT-induced CRS were revealed. To improve the application of laser shock peening (LSP) to curved surfaces, the effects of surface curvature on tri-directional (radial, axial, and depth) residual stress distributions in the LSPed 316L stainless steel specimens were investigated in the present work. Both residual stress fields of convex and concave surfaces were experimentally and theoretically measured and compared using finite element analysis. Results showed that the compressive residual stress decreased with increasing the surface curvature, and the surface curvature had a significant influence on the thickness of plastic deformation layer. Furthermore, a mathematic model of compressive residual stress as a function of surface curvature was proposed to predict the compressive residual stress fields of LSPed curved surfaces. [ABSTRACT FROM AUTHOR]

A numerical investigation is performed to study the serrated trenched-hole film cooling performance on the convex and the concave surfaces, with the use of a plenum coolant-fed mode. In current study, the relevant curvature of curved surface is varied as 2r 1 /d = 30, 60 and 90 at the convex side, 2r 2 /d = 90, 120 and 180 at the concave side. In addition, three coolant injection angles (such as θ = 30°, 35° and 45°) are considered in a specific curved channel. The blowing ratio defined in terms of the local primary flow velocity is ranged from 0.25 to 1.5. From the present study, a critical parameter (I 0), in the form of I cos2 θ , is preliminarily identified to be around 0.5 for the serrated trenched-hole film cooling. When I cos2 θ < I 0 , the film cooling effectiveness on the convex surface is better than that on the flat surface and concave surfaces. The situation is opposite when I cos2 θ > I 0. In particular, this critical value for the serrated trenched-hole film cooling is obviously less than the unity that previously identified in the cylindrical-hole film cooling situation. The relevant curvature shows nearly rare influence on the film cooling effectiveness under small blowing ratios, either on the convex surface or the concave surface. However, under high blowing ratios, it has a pronounced impact on the film cooling effectiveness, in particular at the concave side. Under M = 1.5, the area-averaged adiabatic film cooling effectiveness in the region between s/d = 10 and s/d = 20 is increased up to 33% by the smallest relevant curvature case with respect to the biggest relevant curvature case. The coolant injection angle plays an important role on the mutual interaction of jet-in-corssflow of the serrated trenched-hole film cooling. The reduction in the coolant injection angle leads to an obvious film cooling enhancement, either on the convex surface or the concave surface. Moreover, the enhancing effect led by the reduction of coolant injection angle behaves more pronouncedly as the blowing ratio increases. [ABSTRACT FROM AUTHOR]

The aim of the present study is to reveal fundamental cavitation erosion characteristics of the curved surface. The submerged waterjet was used to produce cavitation. An experimental work was performed on a standard cavitation erosion test rig. The Al 5083 specimens with three curvature radii, 7.0, 9.0 and 10.0 mm, were selected as the target specimens. The flat surfaces were tested for comparison. The mass loss of the eroded specimens was measured. The cumulative erosion rate was calculated. Morphology of the eroded surfaces was observed using techniques of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The root mean square (RMS) surface roughness of the eroded specimen was obtained. The results indicate that the curvature radius has a significant effect on the cavitation erosion intensity. The surface with the largest radius of curvature exhibits the weakest resistance to the cavitation erosion. No explicit relevance is recognized between the curvature radius and the extent of the cavitation erosion. In the early stage of the cavitation erosion, the central region of the target surface is less eroded. As the cavitation erosion progresses, the mass removal in the central area manifests a layer-by-layer pattern. Large erosion pits are evidenced in such a region. The specimen of R = 9.0 mm, with the highest resistance to the cavitation erosion, is featured by a sharp decline of the skewness of surface height distribution in the early stage of the cavitation erosion. • Cavitation erosion of curved surface was studied on a cavitating waterjet test rig. • Cavitation erosion was compared among surfaces with different curvature radii. • The surface with the largest curvature radius is featured by the highest mass loss. • The material removal from the eroded surface manifests a layer-by-layer pattern. • Negative skewness is predominant as the resistance to cavitation erosion is weak. [ABSTRACT FROM AUTHOR]