ORCID Identifier(s)

0000-0003-1581-7913

Graduation Semester and Year

Summer 2025

Language

English

Document Type

Thesis

Degree Name

Master of Science in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Daejong Kim

Abstract

This study presents a comparative investigation of two inherent orifice modeling approaches - single-point injection and virtual orifice distribution - for simulating flow behavior in hydrostatic and hybrid air bearings. The objective is to evaluate the accuracy and applicability of each method under varying geometric and pressure conditions. These models are critical for assessing flow resistance in orifices, guided by the Reynolds equation, which describes gas film dynamics in aerostatic bearing systems. Both choked and unchoked flow scenarios were simulated through experimental and computational methods, with air introduced into the bearing gap via orifices. In both approaches, the isentropic expansion of air is assumed to occur at the curtain area surrounding the orifice, rather than at its physical cross-section. In the single-point injection approach, pressure is calculated at a single control surface near the orifice curtain. This method is effective when the orifice diameter is smaller than the grid spacing but becomes less accurate when the orifice size exceeds this limit, resulting in issues like flow choking or abrupt pressure changes. To overcome these challenges, a virtual orifice distribution method was developed, which allocates the orifice curtain area across multiple grid points around the orifice to maintain equivalent mass flow and injected area. This technique ensures better representation of the orifice geometry and produces more realistic pressure and flow velocity distributions, especially under high-pressure conditions or with larger orifices.

Three bearing configurations were examined: flat film with stationary surface, taper-flat film with stationary surface, and taper-flat film with a moving surface. The two orifice models were validated against high-fidelity Computational Fluid Dynamics (CFD) results generated using ANSYS Fluent. The findings show that the single-point injection model provides accurate predictions for mass flow rate and pressure distribution in flat film geometries, closely aligning with CFD data. However, it underperforms in capturing load capacity in geometries involving taper and surface motion. The virtual orifice model, though it avoids flow choking, consistently underpredicts mass flow and shows better load estimation only in complex, dynamic configurations, such as the taper-flat film with moving surface. Overall, this study concludes that model selection should depend on the geometry and intended performance metric. The single-point model is well-suited for flow-focused predictions in simple cases, while the virtual orifice model offers advantages in capturing distributed pressure in dynamically influenced geometries. These insights provide practical guidelines for selecting appropriate modeling strategies in the design and simulation of air-lubricated thrust bearing systems.

Disciplines

Aerodynamics and Fluid Mechanics | Computer-Aided Engineering and Design | Other Aerospace Engineering | Other Mechanical Engineering | Structures and Materials

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