Thermohydrodynamic Analysis of Compliant Flexure Pivot Tilting Pad Gas Bearings

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Kyuho Sim ◽  
Daejong Kim
Keyword(s):  
Boundary Conditions ◽  
Energy Equation ◽  
Numerical Procedure ◽  
Computational Method ◽  
Temperature Fields ◽  
Linear Perturbation ◽  
Gas Bearings ◽  
Thermal Boundary Conditions ◽  
Thermal Growth ◽  
Tilting Pad

A new thermohydrodynamic (THD) analysis for compliant flexure pivot tilting pad gas bearings is presented. Unlike many previous THD analyses on oil-lubricated bearings and gas bearings, the new THD analysis solves the rotor and bearing pad temperatures as well as the gas film temperature simultaneously upon adequate thermal boundary conditions on the bearing shell and rotor ends are given. All the previous studies assume that the rotor and bearing temperatures are given as thermal boundary conditions to solve 2D or 3D energy equation in the bearing film. The developed computational method is unique because these boundary conditions are found internally through global energy balance around the bearing. A numerical procedure involves solving the generalized Reynolds equation, 3D energy equation, and heat flux equations around the bearings simultaneously through iterative process. Furthermore, rotor thermal and centrifugal expansions are also considered during the iteration. Parametric studies were performed for the various temperature fields, i.e., rotor temperature, gas film temperature, and pad temperature as a function of nominal clearance, external load, and various thermal boundary conditions. Nominal clearance showed the most significant influence on overall THD behavior. The analyses also show that the rotor-bearing system can go to thermal runaway if adequate cooling mechanism does not exist. Linear perturbation analysis was also performed to investigate the thermal effects on the rotordynamic performance. Rotor thermal growth and increased viscosity increased direct stiffness and damping coefficients compared to the isothermal case.

Experimental and Analytical Studies on Flexure Pivot Tilting Pad Gas Bearings With Dampers Applied to Radially Compliant Pads

2009 ◽  
Author(s):  
Daejong Kim ◽  
Aaron Rimpel
Keyword(s):  
Simulation Method ◽  
Analysis Tool ◽  
Primary Analysis ◽  
Successful Operation ◽  
Gas Bearings ◽  
Viscoelastic Dampers ◽  
Thermal Growth ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
First Time

Hydrodynamic flexure pivot tilting pad gas bearings (FPTPGBs) can enable successful operation of oil-free microturbomachinery, and FPTPGBs with radially compliant pads (FPTPGB-Cs) permit rotor centrifugal and/or thermal growth to exceed original bearing clearances and achieve higher speeds. This work presents the experimental and analytical study of such bearings and the application of dampers behind the pad radial compliance structure. A time domain orbit simulation method was implemented as the primary analysis tool to predict rotor-bearing response to imbalance, the presence and location of critical speeds, etc., and compare with test results. Experiments demonstrate the stable hydrodynamic operation of FPTPGBs with a ∼28.6 mm, 0.8 kg rotor above 120 krpm for the first time. The rotor-bearing system was intentionally destabilized in tests by increasing bearing clearances, and viscoelastic dampers added behind the FPTPGB pads delayed the onset of subsynchronous vibrations (from 43 krpm without damper to above 50 krpm with damper). Midrange subsynchronous vibrations of the destabilized system initiated at ∼20 krpm were suppressed by ∼25 krpm due to the stabilizing effect of rotor centrifugal growth. The viscoelastic dampers had a negligible effect on suppressing these midrange subsynchronous vibrations in experiments, but this was not demonstrated in simulations, presumed to be due to much lower stiffness contribution of the damper at lower frequencies.

Experimental and Analytical Studies on Flexure Pivot Tilting Pad Gas Bearings With Dampers Applied to Radially Compliant Pads

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
Aaron Rimpel ◽  
Daejong Kim
Keyword(s):  
Simulation Method ◽  
Analysis Tool ◽  
Primary Analysis ◽  
Successful Operation ◽  
Gas Bearings ◽  
Viscoelastic Dampers ◽  
Thermal Growth ◽  
Tilting Pad ◽  
Rotor Bearing ◽  
First Time

Hydrodynamic flexure pivot tilting pad gas bearings (FPTPGBs) can enable successful operation of oil-free microturbomachinery and FPTPGBs with radially compliant pads permit rotor centrifugal and/or thermal growth to exceed original bearing clearances and achieve higher speeds. This work presents the experimental and analytical study of such bearings and the application of dampers behind the pad radial compliance structure. A time domain orbit simulation method was implemented as the primary analysis tool to predict the rotor-bearing response to imbalance, the presence and location of critical speeds, etc., and to compare with test results. Experiments demonstrate the stable hydrodynamic operation of FPTPGBs with an ∼28.6 mm, 0.8 kg rotor above 120 krpm, for the first time. The rotor-bearing system was intentionally destabilized in tests by increasing bearing clearances and the viscoelastic dampers added behind the FPTPGB pads delayed the onset of subsynchronous vibrations (from 43 krpm without damper to above 50 krpm with damper). Midrange subsynchronous vibrations of the destabilized system initiated at ∼20 krpm were suppressed by ∼25 krpm due to the stabilizing effect of rotor centrifugal growth. The viscoelastic dampers had a negligible effect on suppressing these midrange subsynchronous vibrations in experiments, but this was not demonstrated in simulations, presumed to be due to much lower stiffness contribution of the damper at lower frequencies.

scholarly journals An Efficient Numerical Procedure for Thermohydrodynamic Analysis of Cavitating Bearings

1996 ◽  
Vol 118 (3) ◽  
pp. 555-563 ◽  
Author(s):  
D. Vijayaraghavan
Keyword(s):  
Experimental Data ◽  
Film Thickness ◽  
Boundary Conditions ◽  
Radial Direction ◽  
Heat Dissipation ◽  
Numerical Procedure ◽  
Hydrodynamic Performance ◽  
Numerical Examples ◽  
Thermal Boundary Conditions ◽  
Theoretical Predictions

In this paper, an efficient and accurate numerical procedure to determine the thermo-hydrodynamic performance of cavitating bearings is described. This procedure is based on the earlier development of Elrod for lubricating films, in which the properties across the film thickness are determined at Lobatto points and their distributions are expressed by collocated polynomials. The cavitated regions and their boundaries are rigorously treated. Thermal boundary conditions at the surfaces, including heat dissipation through the metal to the ambient, are incorporated. Numerical examples are presented comparing the predictions using this procedure with earlier theoretical predictions and experimental data. With a few points across the film thickness and across the journal and the bearing in the radial direction, the temperature profile is very well predicted.

Three-Dimensional Natural Convection in a Vertical Porous Layer With a Hexagonal Honeycomb Core

1992 ◽  
Vol 114 (4) ◽  
pp. 924-927 ◽  
Author(s):  
Y. Asako ◽  
H. Nakamura ◽  
Y. Yamaguchi ◽  
M. Faghri
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Porous Layer ◽  
Numerical Solutions ◽  
Transfer Problem ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Honeycomb Core ◽  
Thermal Boundary Conditions

Numerical solutions are obtained for a three-dimensional natural convection heat transfer problem in a vertical porous layer with a hexagonal honeycomb core. The porous layer is assumed to be long and wide such that the velocity and temperature fields repeat themselves in successive enclosures. The natural convection problem is solved for only one honeycomb enclosure with periodic thermal boundary conditions. The porous layer is assumed to be homogeneous and isotropic and the flow is obtained by using the Darcian model. The numerical methodology is based on an algebraic coordinate transformation technique, which maps the hexagonal cross section onto a rectangle. The transformed governing equations are solved with the SIMPLE algorithm. The calculations are performed for the Darcy–Rayleigh number in the range of 10 to 103 and for eight values of the aspect ratio (H/L = 0.25, 0.333, 0.5, 0.7, 1, 1.4, 2, and 5). Two types of thermal boundary condition for the honeycomb core wall are considered: conduction and adiabatic honeycomb core wall thermal boundary conditions. The results are presented in the form of average and local heat transfer coefficients and are compared with the corresponding values for two and three-dimensional rectangular enclosures.

Calculation of Stiffness and Damping Properties of Gas Bearings

1968 ◽  
Vol 90 (4) ◽  
pp. 793-803 ◽  
Author(s):  
J. W. Lund
Keyword(s):  
Static Load ◽  
Journal Bearing ◽  
Computational Method ◽  
Gas Bearings ◽  
Rotating Speed ◽  
Damping Coefficients ◽  
Tilting Pad ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearing ◽  
Gas Bearing

The dynamic characteristics of a gas bearing can be represented by a set of spring and damping coefficients (impedances) which are functions of the static load on the bearing, the rotating speed and the whirl frequency of the journal. For a rotor supported in gas bearings, these coefficients can be used directly in a critical speed calculation or an unbalance response calculation. In addition, the coefficients can be employed in a stability investigation. The paper gives the computational method for obtaining the spring and damping coefficients and, also, describes how they are used in rotor calculations and stability studies. Numerical results are given in graphical and tabular form for a tilting pad journal bearing and a three-lobe journal bearing.

scholarly journals Graphene and CNT impact on heat transfer response of nanocomposite cylinders

2020 ◽  
Vol 9 (1) ◽  
pp. 41-52 ◽  
Author(s):  
Kamran Behdinan ◽  
Rasool Moradi-Dastjerdi ◽  
Babak Safaei ◽  
Zhaoye Qin ◽  
Fulei Chu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Micromechanical Model ◽  
Thermal Response ◽  
Polymeric Materials ◽  
Nanocomposite Materials ◽  
Functionally Graded ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Thermal Boundary Conditions

AbstractReinforcing polymers with nanofillers is an advanced approach to improve and manage the thermal behaviors of polymeric nanocomposite materials. Among the proposed nanofillers, graphene and carbon nanotube (CNT) with superior thermal conductivity are two advanced nanofillers, which have extensively been utilized to enhance the heat transfer responses of host polymeric materials. In this work, the impacts of randomly oriented graphene and CNT to steady state and transient heat transfer behaviors of functionally graded (FG) nanocomposite cylinders have been investigated using an axisymmetric model. Nanocomposite cylinders have been assumed to be under heat fluxes, heat convections or temperatures as different types of thermal boundary conditions. The thermal properties of the resulted nanocomposite materials are estimated by micromechanical model. Moreover, the governing thermal equations of axisymmetric cylinders have been analyzed using a highly consistent and reliable developed mesh-free method. This numerical method predicts temperature fields via MLS shape functions and imposes essential boundary conditions with transformation approach. The effects of nanofiller content and distribution as well as thermal boundary conditions on the heat transfer responses of nanocomposite cylinders are studied. The results indicated that the use of nanofiller resulted in shorter stationary times and higher temperature gradients in FG nanocomposite cylinders. Moreover, the use of graphene in nanocomposites had stronger impact on thermal response than CNT.

Bump-Type Foil Bearings and Flexure Pivot Tilting Pad Bearings for Oil-Free Automotive Turbochargers: Highlights in Rotordynamic Performance

2015 ◽  
Author(s):  
Keun Ryu ◽  
Zachary Ashton
Keyword(s):  
High Performance ◽  
Load Capacity ◽  
Mechanical Efficiency ◽  
Outer Diameter ◽  
Gas Bearings ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Thermal Growth ◽  
Tilting Pad ◽  
Tilting Pad Bearings

Oil-free turbochargers require gas bearings in compact units of enhanced rotordynamic stability, mechanical efficiency, and improved reliability with reduced maintenance costs compared with oil-lubricated bearings. Implementation of gas bearings into automotive turbochargers requires careful thermal management with accurate measurements verifying model predictions. Foil bearings are customarily used in oil-free microturbomachinery because of their distinct advantages including tolerance to shaft misalignment and centrifugal/thermal growth, and large damping and load capacity compared with rigid surface gas bearings. Flexure pivot tilting pad bearings are widely used in high performance turbomachinery since they offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability. The paper details the rotordynamic performance and temperature characteristics of two prototype oil-free turbochargers; one supported on foil journal and thrust bearings and the other one is supported on flexure pivot tilting pad journal bearings and foil thrust bearings of identical sizes (OD and ID) with the same aerodynamic components. The tests of the oil-free turbochargers, each consisting of a hollow rotor (∼0.4 kg and ∼23 mm in outer diameter at the bearing locations), are performed for various imbalances in NVH (i.e, cold air driven rotordynamics rig) and gas stand test facilities up to 130 krpm. No forced cooling air flow streams are supplied to the test bearings and rotor. The measurements demonstrate the stable performance of the rotor-gas bearing systems in an ambient NVH test cell with cold forced air into the turbine inlet. Posttest inspection of the test flexure pivot tilting pad bearings after the hot gas stand tests evidences seizure of the hottest bearing, thereby revealing a notable reduction in bearing clearance as the rotor temperature increases. The compliant flexure pivot tilting pad bearings offer a sound solution for stable rotor support only at an ambient temperature condition while demonstrating less tolerance for shaft growth, centrifugal and thermal, beyond its clearance. The current measurements give confidence in the present gas foil bearing technology for ready application into automotive turbochargers for passenger car and commercial vehicle applications with increased reliability.

Thermal Mixing Points: A Comparison Using CFD

2006 ◽  
Author(s):  
Trevor G. Seipp
Keyword(s):  
Boundary Conditions ◽  
Temperature Fields ◽  
Analysis Tool ◽  
Element Analysis ◽  
Thermal Mixing ◽  
Thermal Boundary Conditions ◽  
Commercial Code ◽  
Calculated Stress ◽  
Computational Fluid Dynamics Cfd ◽  
Made In

In a previous paper, the author presented a procedure for evaluating piping thermal mixing points using finite element analysis. However, several assumptions had to be made with respect to the thermal boundary conditions. While, at the time, those were thought to be conservative assumptions, there was no comparison with alternate methods of determining the thermal boundary conditions. With recent advances in computational fluid dynamics (CFD), particularly the availability of high-quality commercial code, such a comparison can now be made. In this paper, the author reviews the piping thermal mixing point cases evaluated in the previous paper using CFD as the comparative analysis tool. The temperature fields in the piping thermal mixing points are compared. The calculated stress fields are also examined to determine if the original thermal boundary conditions were reasonable.

Bump-Type Foil Bearings and Flexure Pivot Tilting Pad Bearings for Oil-Free Automotive Turbochargers: Highlights in Rotordynamic Performance

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Keun Ryu ◽  
Zachary Ashton
Keyword(s):  
High Performance ◽  
Load Capacity ◽  
Mechanical Efficiency ◽  
Outer Diameter ◽  
Gas Bearings ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Thermal Growth ◽  
Tilting Pad ◽  
Tilting Pad Bearings

Oil-free turbochargers (TCs) require gas bearings in compact units of enhanced rotordynamic stability, mechanical efficiency, and improved reliability with reduced maintenance costs compared with oil-lubricated bearings. Implementation of gas bearings into automotive TCs requires careful thermal management with accurate measurements verifying model predictions. Gas foil bearings (GFBs) are customarily used in oil-free microturbomachinery because of their distinct advantages including tolerance to shaft misalignment and centrifugal/thermal growth, and large damping and load capacity compared with rigid surface gas bearings. Flexure pivot tilting pad bearings (FPTPBs) are widely used in high-performance turbomachinery since they offer little or no cross-coupled stiffnesses with enhanced rotordynamic stability. The paper details the rotordynamic performance and temperature characteristics of two prototype oil-free TCs; one supported on foil journal and thrust bearings and the other one is supported on FPTP journal bearings and foil thrust bearings of identical sizes (outer diameter (OD) and inner diameter (ID)) with the same aerodynamic components. The tests of the oil-free TCs, each consisting of a hollow rotor (∼0.4 kg and ∼23 mm in OD at the bearing locations), are performed for various imbalances in noise, vibration, and harshness (NVH; i.e., cold air driven rotordynamics rig) and gas stand test facilities up to 130 krpm. No forced cooling air flow streams are supplied to the test bearings and rotor. The measurements demonstrate the stable performance of the rotor–gas bearing systems in an ambient NVH test cell with cold forced air into the turbine inlet. Post-test inspection of the test FPTPGBs after the hot gas stand tests evidences seizure of the hottest bearing, thereby revealing a notable reduction in bearing clearance as the rotor temperature increases. The compliant FPTPGBs offer a sound solution for stable rotor support only at an ambient temperature condition while demonstrating less tolerance for shaft growth, centrifugal, and thermal, beyond its clearance. The current measurements give confidence in the present GFB technology for ready application into automotive TCs for passenger car and commercial vehicle applications with increased reliability.

A numerical investigation of heat transfer in a smooth bend part of a U-duct

2013 ◽  
Vol 24 (1) ◽  
pp. 137-147 ◽  
Author(s):  
Tareq Salameh ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Boundary Conditions ◽  
Turbine Blades ◽  
Turbulence Models ◽  
Numerical Results ◽  
Temperature Fields ◽  
Heat Transfer Analysis ◽  
Content Type ◽  
Thermal Boundary Conditions ◽  
Wall Boundary Conditions

Purpose – The aim of this paper is to study two-dimensional numerical simulations of the flow and temperature fields inside the bend (turn) part of a U-duct. Design/methodology/approach – Several turbulence models based on two and five equations were used to solve the momentum and energy equations inside the bend (turn) part of the U-duct. For two-equation models, both the renormalization group and realizable k-ɛ turbulence models were implemented. The five-equation model used is a Reynolds stress model with different wall boundary conditions. Standard, non-equilibrium and enhanced wall functions were used in parallel with the two- and five-equation models to treat the turbulent flow near the duct walls. Findings – Several turbulence models were used to simulate the flow and temperature fields along the bend part of a U-duct with different inlet and thermal boundary conditions. The numerical results indicate that the renormalization and realizable k-ɛ turbulence models with standard wall function treatment gave the best results when compared with experimental data obtained for similar conditions. Research limitations/implications – For heat transfer analysis, two different thermal boundary conditions, i.e. constant wall temperature and constant heat flux at the wall are implemented. The results are calculated for Reynolds number equal 20,000. Practical implications – The results can be used in designing heat exchangers, piping and duct systems, and internal passage cooling of gas turbine blades. Originality/value – The numerical results obtained here concentrate on the detailed investigation of flow and temperature field at the outer wall of the bend part. Different boundary conditions at the inlet and the outer bend walls of the U-duct were applied to study how these boundary conditions affect the flow and temperature fields.

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