G. Talmage

Prediction of Rotor Dynamic Coefficients in Gas Lubricated Foil Journal Bearings with Corrugated Sub-Foils

A finite element foil bearing model that incorporates radial and circumferential deflections of a corrugated sub-foil into the prediction of rotor dynamic coefficients is presented. The corrugated sub-foil is treated as a continuous structure that supports the top-foil. Radial and circumferential deflections are coupled in the sub-foil model. The Coulomb friction between the top-foil, sub-foil, and the bearing shell is modeled as an equivalent viscous friction. The foil deflections, the film thickness, and gas pressure are then perturbed to calculate the rotor dynamic coefficients. The results are presented demonstrating the effects of frequency, orbit size, and friction coefficient on the rotor dynamic coefficients and the energy dissipation rate.

A fully coupled finite element formulation for elastically supported foil journal bearings

Foil gas journal bearings consist of a compliant metal shell structure that supports a rigid journal by means of a gas film. The prediction of steady operating characteristics such as minimum film thickness, load capacity, and drag require the coupled solution of the shell structure and the gas flow. A general fully coupled finite element approach is presented. A single four noded finite element that incorporates the elastically supported shell structure of the foil and the gas film modeled by a compressible Reynolds equation is developed. The resulting system of nonlinear finite elements is solved by the Newton Raphson method. Presented at the 58th Annual Meeting in New York City April 28–May 1, 2003

Liquid-metal MHD flow in rectangular ducts with thin conducting or insulating walls: laminar and turbulent solutions

Abstract This paper treats the steady, fully-developed flow of a liquid metal in a rectangular duct of constant cross-section with a uniform, transverse magnetic field. Thin conducting wall boundary conditions at the top/bottom walls (perpendicular to the magnetic field) are extended to allow electrical currents to return through either the wall or the Hartmann layers. Hence, a unified analysis of flows in ducts with wall conductance ratios in the range of interest of fusion blanket applications, namely, from thin conducting to insulating wall ducts, is conducted. The flow in laminar and turbulent regimes is investigated through a composite core-side-layer spectral collocation solution which explicitly resolves the flow in the side layers (parallel to the magnetic field) even for very large Hartmann numbers. Turbulent profiles are obtained through an iterative scheme in which turbulence is introduced through an eddy viscosity model from the renormalization group theory of turbulence [Yakhot, V. and Orsag, S.A., J. Sci. Comput. , 1986, 1 (1), 3]. The transition from a flow in a duct with thin conducting walls to one with insulating walls is clearly displayed by varying the wall conductance ratio from 0.05 to 0 for Hartmann numbers in the range 10 3 –10 5 . In turbulent regime, Reynolds numbers vary in the range 5 × 10 4 –5 × 10 5 . For thin conducting wall duct flows, turbulence is concentrated in the increased side layers while the core remains unperturbed. In insulating wall ducts, the flow remains in the laminar regime within the considered range of Reynolds numbers.

A Pseudospectral-Finite Difference Analysis of an Infinitely Wide Slider Bearing with Thermal and Inertial Effects

A pseudospectral-finite difference solution of the thermal hydraulic flow through an infinitely wide convergent slider bearing configuration is presented. The model includes both thermal and inertial effects. The approach combines a collocation technique with orthogonal polynomial representations of velocities, temperatures and prop erty variations through the thickness of the lubricant film with finite difference representations of derivatives in the stream wise direction. The technique is motivated by the need for general analyses of fluid film bearings which incorporate the before-mentioned effects. Results will be presented that separately demonstrate inertial and thermal effects in laminar flows.

Turbulence and the feasibility of self-cooled liquid metal blankets for fusion reactors

Magnetohydrodynamics (MHD) considerations are of paramount importance in the design and performance of self-cooled liquid-metal (LM) blankets; the interaction between the magnetic field and the flowing LM can have a significant effect on the pressure drop, the heat transfer rate, and the corrosion rate. The purpose of the present work is to assess the implications that the recent experimental findings might have on the performance of self-cooled LM blankets. The assessment is done by considering the poloidal blanket concept, which uses a vanadium alloy for the structure. Material strength and LM compatibility considerations limit the first-wall (FW) and FW/LM interface temperature to 750/sup 0/C. When the FW is subjected to a 0.5 MW/m/sup 2/ heat flux, a temperature drop of approx. 100/sup 0/C will be established across it, restricting the FW/LM interface temperature to T/sub int/ approx. 650/sup 0/C. It is concluded that the enhanced two-dimensional turbulence might significantly increase the attractiveness of self-cooled LM blankets by enabling (a) the design of simpler and, possibly, cheaper blankets, and (b) the attainment of lower pumping power requirements and higher energy conversion efficiency.

Heat transfer in laminar and turbulent liquid-metal MHD flows in square ducts with thin conducting or insulating walls

Abstract The heat transfer in fully-developed liquid-metal flows in a square duct with a uniform, transverse magnetic field is analyzed. Velocity profiles obtained for laminar and turbulent regimes [Cuevas, S., Picologlou, B. F., Walker, J. S. and Talmage, G., Int. J. Engng Sci. , 1997, 35 , 485] are employed to solve the heat transfer equation through finite differences, in a duct with one side wall (parallel to the magnetic field) uniformly heated and three adiabatic walls. Turbulent effects are introduced through eddy viscous and thermal diffusivity models from the renormalization group theory of turbulence [Yakhot, V. and Orszag, S. A., J. Sci. Comput. , 1986, 1 (1), 3]. Analysis focuses in determining how the structure of the side-layer flow, influenced by the wall conductance ratio and Hartmann and Peclet numbers in the ranges of interest of fusion blanket applications, affects the heat transfer processes. Numerical calculations for liquid lithium show that for thin conducting wall duct cases, the laminar MHD heat transfer mechanism, characterized by high-velocity side-wall jets, appears to be more efficient than turbulent mixing in the boundary layer for a given Peclet number.

Comparison of Lubrication Models for Plane Slider Bearings

Accurate models of lubricant films are necessary to predict the performance of bearings under complex operating conditions. This investigation compares load predictions of the Reynolds equation and bulk flow model to that predicted by a three dimensional pseudo-spectral technique which incorporates thermal and inertial effects. Four different operating regimes along with their associated dimensionless parameters are identified. Three of these regimes are discussed, namely: laminar isothermal, turbulent isothermal, and turbulent thermal. The results provide insight into the conditions under which the Reynolds equation and bulk flow model are in good correlation with the pseudo-spectral technique. Presented at the 54th Annual Meeting in Las Vegas, Nevada May 23–27, 1998

Liquid‐metal flows in sliding electrical contacts with arbitrary magnetic‐field orientations

In certain situations, liquid‐metal sliding electrical contacts for high‐current and low‐voltage electrical machines may prove a viable alternative to solid metal brushes. Before it can be ascertained whether such an option is feasible, the problems inherent in a liquid‐metal flow through a narrow gap between a fixed and a moving surface with free surfaces beyond each gap end must be explored. The flow occurs in the presence of an arbitrarily oriented magnetic field. By assuming that the secondary flow is negligible, the problem reduces to a fully developed magnetohydrodynamic (MHD) duct flow problem. In the parameter range presented here, the liquid‐metal flow can be laminar or turbulent, requiring that both regimes be analyzed. The numerical results from the mathematical model presented herein for laminar flow with arbitrary Hartmann number M and with arbitrary magnetic‐field orientation indicate that, even with an O(1) Hartmann number, the flow is already beginning to evolve into the distinct regions p...

Liquid-metal MHD energy conversion in fusion reactors

The purpose of the present work is to assess the viability of a novel approach to high-temperature fusion blanket power conversion - liquid-metal magnetohydrodynamics (LMMHD). The following power-conversion LMMHD PCSs and lithium-cooled blanket LMMHD PCSs. LMMHD PCSs might enable converting high-temperature blanket energy into electricity at efficiencies of the order of 60%. Being free of moving parts, at least in the high-temperature range, the LMMHD PCS technology appears to be better suited than PCS technology based on turbomachinery. Indeed, certain LMMHD PCSs could be designed to be completely static and practically hermetically sealed. This provides a simple system, with expected high reliability, facilitated maintenance, and tritium control. Moreover, in none of the LMMHD PCSs considered is there a need for lithium-to-water heat exchange, thus avoiding safety and tritium handling difficulties.

Heat transfer in liquid metals with electric currents and magnetic fields: The conduction case☆

Abstract There are two volumetric heat sources in a liquid-metal sliding electrical contact for a homopolar device: Joulean heating and viscous dissipation. The Joulean heating is created by the presence of electric currents; the viscous dissipation results from the motion of the liquid metal and is enhanced by magnetohydrodynamic (MHD) effects. In a homopolar device, the liquid metal is confined to a small gap between the perimeter of a rotating disk and the surrounding static surface. The maximum temperature achieved within the liquid metal is significantly larger for an MHD flow than for an ordinary hydrodynamic flow, a flow in the absence of a magnetic field. Information concerning the temperature distribution within the liquid metal and solid parts of a homopolar device will result in the design of efficient and operational sliding electrical contacts.