Search Results (6)

Negative inlet pre-swirl has been identified as a potentially effective method to improve the theoretical work that has been performed. However, it should be noted that a large negative inlet swirl may adversely affect the pressure ratio of the compressor due to the different centrifugal forces generated by the movement of the airflow within the large-angle pre-swirl guide vane flow channel. In order to achieve a large inlet negative pre-swirl, a new guide vane with a contraction channel is proposed for a 40° pre-swirl angle fan. This contraction guide vane is of the tandem type, and it includes a first-stage enlarged guide vane and a second-stage contraction guide vane channel. Comprehensive CFD numerical simulations and experimental studies have been conducted to analyze the key design parameters, and the total pressure loss and efficiency of the new guide vanes were analyzed and compared under various operating conditions. It was found that this new guide vane can significantly reduce the total pressure loss coefficients. Compared with the conventional guide vanes, the inlet velocity distribution is more uniform development of inlet velocities, and a significant reduction in flow separation is found for this new guide vane. The guide vane with a ring width ratio of 1.5 reduced 53.11% of the total pressure loss coefficient. In addition, the efficiency of the fan has been shown to increase by more than 2.29% under various operating conditions, due to the improved internal flow of the fan under large flow conditions, under all operating conditions, with an overall improvement in the total pressure ratio of about 5%. Full article

This paper introduces a lightweight flame detection algorithm, enhancing the accuracy and speed of gas-flame state recognition in low-pressure environments using an improved YOLOv8n model. This method effectively resolves the aforementioned problems. Firstly, GhostNet is integrated into the backbone to form the GhostConv module, reducing the model’s computational parameters. Secondly, the C2f module is improved by integrating RepGhost, forming the C2f_RepGhost module, which performs deep convolution, extends feature dimensions, and simplifies the inference structure. Additionally, the CBAM attention mechanism is added to enhance the model’s ability to capture fine-grained features of flames in both channel and spatial dimensions. The replacement of CIoU with WIoU improves the sensitivity and accuracy of the model’s regression loss. Experimental results on a simulated dataset of the theoretical testbed indicate that compared to the original model, the proposed improvements achieve good performance in low-pressure flame state detection. The model’s parameter count is reduced by 12.64%, the total floating-point operations are reduced by 12.2%, and the detection accuracy is improved by 21.2%. Although the detection frame rate slightly decreases, it still meets real-time detection requirements. The experimental results demonstrate that the feasibility and effectiveness of the proposed algorithm have been significantly improved. Full article

In order to improve the wear and corrosion resistance and enhance the tribological and mechanical properties of gray cast iron, the laser surface cladding technique was employed to fabricate double-layer coatings with different Ni/WC ratios on the surface of gray cast iron. The effects of laser processing parameters and the type of Ni-based alloy on the microstructure and properties of the gray cast iron matrix and laser-clad layer were investigated. A 316L stainless steel transition layer was introduced between the gray cast iron substrate and the Ni/WC coating to prevent the cladding layer from cracking. The tribological and mechanical properties of the laser-clad coatings were characterized with various tests at the macro- and micro-scales; the residual stresses on the coating surfaces were measured, and electrochemical tests were also carried out. The microstructures of the clad layers were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that the laser-clad layers exhibit excellent vibration and noise reduction performance, which is partially due to the reduction and stabilization of the coefficients of friction (COFs) and the high levels of compressive residual stress on the surface of the laser-clad layers. The wear and corrosion resistance of the laser-clad layers are significantly improved, and the maximum wear loss of the laser-clad coating was about only 5% of that of the unclad gray cast iron substrate. This research has significance for the laser surface modification of cast iron, steel, and other metals, which is an increasingly important topic, especially in the automotive friction brake industry. Full article

Laser surface modification is a widely used technology to improve the properties of functional surfaces. In this study, the properties of gray cast iron are modified by laser surface modification, and the influence of laser quenching on the properties of cast iron in terms of frictional vibration and noise, friction and wear, internal structure, residual stress, hardness, and corrosion resistance is investigated. The experimental results show that, after high-power laser quenching, the frictional vibrations and noise of most gray cast iron specimens are decreased, but the coefficients of friction against a bearing steel counterface are increased and more stable. The surface and sub-surface hardness of all laser-quenched cast iron specimens is significantly increased. The residual stresses on the surface of the cast iron specimens are significantly increased and changed from tensile to compressive residual stresses. Experimental modal testing results show that the modal damping ratios of the laser-treated specimens are increased significantly, although their modal frequencies are not significantly changed. In addition, through the metallographic observation, XRD (X-ray diffraction) analysis, and TEM (transmission electron microscopy) observation, it is found that the microstructures of the cast iron specimen after high-power laser modification become fine-grained, and the pearlite and ferrite in the matrix become fine martensite, which leads to the improvement of the dynamical, tribological, and chemical properties of cast iron after laser modification. Full article

Laser surface treatment is a very useful technology for the fabrication of functional surfaces. In this study, novel antifouling surfaces are fabricated by laser cladding of TC4 and Ni60 mixed materials in various mass ratios on the surfaces of 316L stainless steel substrates. Parametric studies are carried out to investigate the effects of the mixed powder mass ratios and laser cladding parameters on the antifouling performance of the laser clad coatings (LCCs). The antifouling mechanism of the LCCs is investigated by using the water contact angle/surface energy measurement, scanning electron microscope (SEM) surface observation, and phase composition analysis via XRD (X-ray diffractometer) testing. The experimental results show that the LCCs with Ni60/TC4 mass ratio of 3/7 has better antifouling performance in this study. The antifouling performance of the LCC decreases with the increase in laser scanning speed. Surface energy and surface topography have a significant effect on the antifouling performance of LCCs. In order to get the optimal antifouling performance of LCCs, the Ni60/TC4 mass ratio and laser cladding parameters should be optimized. Full article

Various textures are fabricated by a picosecond laser machine on the surfaces of circular stainless steel specimens. Vibrational and tribological effects of laser surface textures are investigated by means of a tribometer and a data acquisition and signal processing (DASP) system. Experimental results show that surface textures can reduce the coefficients of friction (COFs), enhance the wear resistance, and improve the dynamical performance of frictional surfaces. In this study, the surface with micro circular dimples in diameter of 150 μm or textured area density of 25% has the best tribological and dynamical performance. Compared with the non-textured surface, the surface with circular dimples in diameter of 150 μm and 15% textured area density has 27% reduction of COFs, 95% reduction of frictional vibrations, and 66% reduction of frictional noise. The frictional vibrations and noise in the sliding contacts can be effectively reduced by adding graphene to the lubrication oil, and the surface textures enhance the frictional noise reduction performance of lubrication. Full article