Browsing by Author "Sahu, Krishnkant"

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    Effects of Grooved Surfaces and Lubrication Media on the Performance of Hybrid Gas Journal Bearings
    (2025) Kumar Tomar, Adesh; Sahu, Krishnkant; Sharma, Satish C.; Marian, Max
    Gas bearings are attractive for sustainable, high-speed, and cryogenic applications, where gases replace liquid lubricants. This study numerically analyzed hybrid gas journal bearings lubricated with hydrogen, nitrogen, air, and helium, and quantifies the impact of circumferential micro-grooves. The compressible Reynolds equation was solved by the finite element method with constant-flow valve restrictors, while Gauss–Seidel iterations were used for convergence. The model was verified against published theoretical and experimental data with maximum deviations below 6%, and mesh independence is confirmed. The parametric results show that the gas type and texturing jointly controlled static and dynamic performance. Helium (highest viscosity) yielded the largest minimum film thickness, whereas hydrogen (lowest viscosity) attained higher peak pressures at a lower film thickness for a given load. Grooves redistributed pressure and reduced both the maximum pressure and the minimum film thickness, but they also lowered the frictional torque. Quantitatively, the hydrogen-lubricated grooved bearing reduced the frictional torque by up to 50% compared with the non-grooved air-lubricated bearing at the same load. Relative to air, hydrogen increased stiffness and damping by up to 10% and 50%, respectively, and raised the stability threshold speed by 110%. Conversely, grooves decreased the stiffness, damping, and stability threshold speed compared with non-grooved surfaces, revealing a trade-off between friction reduction and dynamic stability. These findings provide design guidance for selecting gas media and surface texturing to tailor hybrid gas journal bearings to application-specific requirements.
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    Slot-entry herringbone grooved hybrid conical bearings under piezo-viscous lubrication
    (2025) Tomar, Adesh Kumar; Sahu, Krishnkant; Sharma, Satish C.; Marian, Max
    This study investigates the effect of herringbone groove geometry and piezoviscous shear-thinning fluid (PVSTF) behavior on the performance of slot-entry hybrid conical journal bearings (SHCJBs). Using a modified Reynolds equation solved via finite element analysis and the Gauss–Seidel method, the influence of groove angles (30°, 60°, and 90°), semi-cone angles, and lubricant type on key tribological parameters is examined. The results indicate that a 30° groove angle in combination with PVSTF yields the highest stiffness coefficients and stability margins, while also reducing frictional torque compared to non-grooved designs and Newtonian lubricants. These findings provide design guidance for optimizing bearing geometry and lubricant selection, with applicability to high-performance rotating machinery.