Sorin Cioc

A Deterministic Elastohydrodynamic Lubrication Model of High-Speed Rotorcraft Transmission Components

This paper describes a deterministic approach to analyze elastohydrodynamic lubrication (EHL) of helicopter transmission gear surfaces with asperities. A thermal, non-Newtonian, model, accompanied by three specialized models is used to study the mechanisms of film generation, pressure distribution and temperature distributions within the fluid and on the surface, in an EHL line contact. A two-slope viscosity-pressure model is used to avoid overestimation of the viscosity of the lubricant under heavy loads. The three-dimensional roughness description of an actual gear tooth surface is measured using a non-contact surface profiler. The pressure distribution, film thickness distribution and the temperature rise at the contact surface are predicted as a function of the gear operating conditions including normal load, lubricant temperature and rolling/sliding speed. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002

Application of the CE/SE Method to One-Dimensional Flow in Fluid Film Bearings

A numerical scheme that has been successfully used to solve a wide variety of compressible flow problems, titled the space-time conservation element and solution element method, is extended to predict the effects of gaseous cavitation in moderate to heavily loaded bearings. The formulation of the one-dimensional problem is presented. The numerical results obtained for different types of bearings are compared with other numerical solutions to demonstrate the superior ability of the method to solve such problems. Presented at the 56th Annual Meeting in Orlando, Florida May 20–24, 2001

Dynamic Modeling of a Dual Clearance Squeeze Film Damper—Part I: Test Rig and Dynamic Model with One Damper

This paper presents a description of a dual clearance squeeze film damper (SFD) test rig and a dynamic model of a single SFD. The purpose of a dual SFD is to provide protection at high levels of vibration, when conventional devices are no longer effective. An experimental facility was designed and built for tire study of SFD behavior within mechanically controlled orbits. It can be used for both single and dual squeeze film dampers. In Part 1 of this paper, measured and computed responses are presented while operating as a single squeeze film device. Numerical and experimental results for undamped cases are presented, i.e., when no oil film is present in the damper. Subsequently, the effects of the oil film are considered. Good agreement was obtained between experimental data and predictions. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002

Application of the CE/SE method to wave journal bearings

The space-time conservation element and solution element (CE/SE) method, successfully used to solve a wide variety of compressible flow problems, is extended for the first time to predict the effects of gaseous cavitation in moderate to heavily loaded wave hearings, including misaligned cases. Elrods formulation is used for a two-dimensional, finite length hearing, and the intricacies of the CEISE scheme applied to solve this problem are presented. The numerical results obtained are compared with other numerical solutions to demonstrate the ability of the method to solve such problems. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002

Computation of Pressurized Gas Bearings Using CE/SE Method

A numerical scheme that has been successfully used to solve a wide variety of compressible flow problems, including flows with large and small discontinuities, entitled the space-time conservation element and solution element (CE/SE) method, is extended to compute compressible viscous flows in pressurized thin fluid films. This method is applied to calculate the pressure distribution in a hybrid gas journal bearing. The formulation of the problem is presented, including the modeling of the feeding system. The numerical results obtained are compared with experimental data. Good agreement between the computed results and the test data were obtained, and thus, validate the CE/SE method to solve such problems. Presented at the 57th Annual Meeting in Houston, Texas May 19–23, 2002

Application of the CE/SE method to two‐dimensional flow in fluid film bearings

A numerical scheme that has been successfully used to solve a wide variety of compressible flow problems, entitled the space‐time conservation element and solution element (CE/SE) method, is extended to predict the effects of gaseous cavitation in moderate to heavily loaded bearings. The formulation of the two‐dimensional, finite length, bearing problem is presented. The numerical results obtained are compared with other numerical solutions to demonstrate the superior ability of the method to solve such problems.

Detailed Study of Fluid Flow and Heat Transfer in the Abrasive Grinding Contact Using Computational Fluid Dynamics Methods

This paper introduces a set of research oriented computational fluid dynamics (CFD) 3D models used to simulate the fluid flow and heat transfer in a grinding process. The most important features of these models are described and some representative simulation results are presented, along with comparisons to published experimental data. Distributions of temperatures, pressures, velocities, and liquid volume fractions in and around the grinding region are obtained in great detail. Such results are essential in studying the influence of the fluid on the grinding process, as well as in determining the best fluid composition and supply parameters for a given application. The simulation results agree well with experimental global flow rates, temperature, and pressure values, showing the feasibility of CFD simulations in grinding applications.

A Study of the Steady-State Performance of a Pressurized Air Wave Bearing at Concentric Position

The steady-state performance of a pressurized air wave bearing in concentric position is predicted using a commercial computational fluid dynamics (CFD) code. This code solves the three-dimensional compressible Navier-Stokes equations in the turbulent regime, taking into account the real geometry of both the bearing fluid film and the supply regions. The code can provide detailed information about the flow (pressure, turbulent kinetic energy distributions, velocity profiles, etc.) in all bearing regions including the supply holes. This approach does not involve a correction of the flow rate with an empirical discharge coefficient. The predicted values of the supply flow rates are compared to the experimental values obtained with a dedicated wave bearing test rig located at NASA Glenn Research Center in Cleveland, Ohio.

Dynamic Modeling of a Dual Clearance Squeeze Film Damper. Part II

Squeeze film dampers (SFD) have been used for many years to control the vibrations of the shafts in high-speed rotating machinery. Dual squeeze film dampers are essentially a combination of two SFDs separated by a sleeve. Normal operation utilizes only one oil film, as in a conventional damper, and the sleeve is fixed in place. However, under high load conditions, the sleeve is released and both oil films become operational. An experimental facility was designed and built to study both single and dual SFD behavior within mechanically controlled orbits. The first part of this paper presents a description of this test rig and provides a dynamic model of a single SFD. In this portion of the paper, we present results obtained while the inner sleeve is released and both oil films are operational. Here the inner sleeve is not supported by any mechanical device; the anti-rotational effect is provided by the opposed actions of the inner oil film and of the outer oil film. The modeling covers the inner and the outer oil films, the elastic fixtures, the unbalanced shaft, and the sleeve. Numerical results are compared with the experimental data. Presented at the ASME/STLE Tribology Conference, in Long Beach, California October 24-27, 2004 Review led by Luis San Andres

Calculation of the Flow in High-Speed Gas Bearings Including Inertia Effects Using the CE/SE Method

In the classical Reynolds equation, inertia effects are neglected. Gas bearings working at very high speeds may encounter flow discontinuities (shock waves), which require the inclusion of inertia terms within the momentum equations. In order to solve the resulting system of equations, a numerical method capable of capturing flow discontinuities is necessary, and the space-time conservation element/solution element (CE/SE) is such a method. In addition, it does not incorporate any other assumptions or special numerical treatment. Results obtained using this method are compared with experimental data and theoretical results, as well as with results obtained by neglecting inertia effects.