The bump-type gas foil bearing (GFB) is widely used in various high-speed oil-free turbomachinery due to its extra features such as high-speed capability without any external oil lubricant. Under the high-speed condition, the performance characteristics of GFB are majorly dependent on its design parameter. Thus, this paper briefly analyzes and optimizes the design parameters of bump-type GFB to improve its performance characteristic. The numerical simulation of bump-type GFB is performed in ANSYS software. The effect of various design parameters such as foil thickness, bump half-length, bump pitch, and bump angle on the output responses are analyzed using a response surface methodology based CCD design matrix. Here, the output responses are structural stiffness and the equivalent stress in foil bearing. To optimize it, the multi-objective GRA technique is used. These results show that the foil thickness is the most influencing and the bump angle is the least influencing design parameter. The optimal value of foil thickness, bump angle, bump half-length and bump pitch are 0.14mm, 63.75 deg., 1.55mm and 4.6mm respectively. At these optimal design parameters, the deviation between the predicted regression model and the numerical results are within 3.5%. Moreover, with these optimal design parameters, the structural stiffness of foil bearings increases by 68.4% and stress distribution reduces by 44.22% compared to the general configuration of foil bearings.

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In this paper, the bump-type foil bearing is considered to analyze and optimize its performance characteristics with various foil materials. For the study, the operating parameters such as friction coefficient F1, F2 and loading pressure P are considered variable input parameters. The response surface methodology-based BBD model is used to design and analyze these variable parameters. The structural stiffness and equivalent stress of bump-type foil bearings are considered as the output responses in the present study. The multiobjective GRA technique is used to evaluate the optimum value of operating parameters for each foil material and compare its results. These results show that the loading pressure is the most influencing operating parameter on the output responses, followed by friction coefficient F1 and then F2. By the GRA technique, the Inconel X750 is found to be the most significant foil material, followed by Spring Steel EN42J for bump-type foil bearings. Moreover, it is also observed that the dissimilar foil material in bump-type foil bearings provides better results compared to similar foil material. The combination of stainless steel 316 (bump foil) and phosphor bronze (top foil) offers better results than similar foil results. In addition, the fabrication cost of bump-type foil bearings should be reduced with dissimilar foil materials.

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Due to corrosive environment, material loss in a localized area leads to formation of a corrosion pit. It diminishes the structural integrity and performance of product. To predict and analyze the effect of corrosion pit on the performance of gas foil bearings (GFBs), FEM analysis of bump-type GFBs is carried out. The effect of corrosion pit is investigated for three different shapes: circular, square and triangular. In this study, the FEM analysis of bump-type GFBs is performed in ANSYS software. Firstly, the influence of a corrosion pit is analyzed for various shapes under different pressure loading. These results show that the presence of a corrosion pit developed high-stress crack intensity, which can result in crack initiation in foil bearings. As pressure loading increased, the stress crack intensity in foil bearings increased. Among different pit shapes, the circular pit shape induces the maximum stress crack intensity in foil bearings, which shows that the crack initiation in foil bearings is observed for a circular pit. Then, the influence of a corrosion pit on the structural stiffness of foil bearings is evaluated for various foil materials under different friction coefficients. These results show that the influence of friction coefficient in foil bearings is increased within the presence of a corrosion pit.