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This paper studies the effect of the dimple cross-sectional profile on the behavior of gas parallel slider bearings using the numerical method. The numerical method is performed in MATLAB software. The influence of geometrical parameters of dimples on the dimensionless average pressure is studied for different dimple cross-sectional profiles. The geometrical parameters of dimples include dimple depth, dimple area density, transversal textured ratio, and longitudinal textured ratio. It is found that the hydrodynamic lubrication of dimple-textured gas parallel slider bearings is controlled by the dimple depth, dimple area density, transversal textured ratio, longitudinal textured ratio, and dimple cross-sectional profile. Furthermore, the impact of sliding speed on the hydrodynamic lubrication is studied for different dimple cross-sectional profiles. The results indicate that the optimum sliding speed for maximizing the hydrodynamic pressure is controlled by the dimple cross-sectional profile. [ABSTRACT FROM AUTHOR]

• Dimpled airfoils, arranged in-line, exhibit a reduction in noise across a wide range of frequencies. • The noise reduction in in-line configurations demonstrates an upward trend, correlating with higher jet velocities and resulting in reductions of approximately 3.5–5.5 dB compared to the baseline. • In the case of the dimpled airfoil, there is a discernible decrease in coherence within the flow field compared to the baseline. This paper presents systematic and comprehensive experimental investigations into the use of circular dimples to reduce broadband noise on airfoils. The dimples are introduced on the suction surface of symmetric NACA airfoils with different thickness ratios for the control of broadband noise over a wide range of frequencies. The effects of dimple arrangements (inline and staggered) and their locations (1/3rd and 1/5th of the chord from the leading edge) on the noise characteristics are studied in detail to determine the best dimple arrangement, location, and airfoil geometry for low noise. Results indicate that the inline arrangement of dimples positioned at 1/3rd of the chord from the leading edge provides significant noise reductions of about 6–8 dB, particularly from mid to high frequencies. When the dimples are shifted to 1/5th of the chord from the leading edge, the degree of noise reduction decreases, which indicates that the noise reduction performance of airfoils decreases when the dimples are introduced near the leading edge. Further, it reveals that the inline arrangement of dimples on thicker airfoils provides superior noise reductions (6–8 dB) as compared to thinner airfoils (4–6 dB). Flow visualization reveals that the flow field is inconsistent throughout the span of the dimpled surface due to the evolution of small vortices from the dimple corner. It enhances mixing and accelerates flow structures passing over the dimpled surface, which is indicated by the presence of a high degree of spanwise decoherence/phase lag in the hotwire measurements. The presence of higher spanwise decoherence/phase lag due to the presence of the inconsistent flow field leads to significant reductions of far-field noise in dimpled airfoils. Further, the inline arrangement of dimples exhibits much higher levels of noise reduction as compared to staggered ones, due to the presence of a greater degree of spanwise decoherence/phase lag resulting from the substantial disruption of the flow field in the spanwise direction. [ABSTRACT FROM AUTHOR]

The effect of cold working on hydrogen embrittlement of Monel-400 alloy has been investigated in this report. Monel-400 alloy having 50 and 60% cold working has been selected for this study. A part of these cold-worked materials is annealed. A series of slow strain rate tensile tests of the cold-worked as well as annealed materials are carried out in two different environmental conditions—air and with hydrogen charging in 3.5% NaCl solution. Alloy with 60% cold working exhibits the highest reduction in ductility with hydrogen charging. The reduction in ductility is lower for the annealed materials compared to that of cold-worked materials when tested with hydrogen charging. The results lead to infer that (i) the alloy becomes more detrimental to hydrogen embrittlement with the increase in percentage cold working, which reduces ductility significantly with increasing strength under hydrogen charging, (ii) annealing of cold-worked materials decreases their susceptibility to hydrogen embrittlement, and (iii) hydrogen damage promotes brittle fracture for the cold-worked materials. [ABSTRACT FROM AUTHOR]