Effect of Operating Conditions on the Elasto-Hydrodynamic Performance of Foil Thrust Bearings for Supercritical CO2 Cycles

2016 ◽  
Author(s):  
Kan Qin ◽  
Ingo H. Jahn ◽  
Peter A. Jacobs
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Supercritical Co2 ◽  
Operating Conditions ◽  
Hydrodynamic Performance ◽  
Working Fluid ◽  
Inertia Force ◽  
Fluid Structure ◽  
Thrust Bearings ◽  
Foil Bearings

In order to efficiently utilize the abundant solar resources in Australia, the supercritical CO2 cycle is proposed as an alternative to conventional steam power cycles due to high thermal efficiency and compact system layout. To mature the technology readiness of the supercritical CO2 cycle, each part, including turbine, compressor, seals and bearings, needs to be evaluated and possibly re-designed under consideration of the high density working fluid. One key technology is the foil thrust bearing, which is an enabler for high speed operation and oil-free systems. Bearings are at the core of the turbomachinery system and have a significant influence on the performance of the whole system. In this paper, a quasi three-dimensional fluid-structure model, using computational fluid dynamics for the fluid phase is presented to study the elasto-hydrodynamic performance of foil thrust bearings. For the simulation of the gas flows within the thin gap, the computational fluid dynamics solver Eilmer is extended and a new solver is developed to simulate the bump and top foil within foil thrust bearings. These two solvers are linked using a coupling algorithm that maps pressure and deflection at the fluid structure interface. Results are presented for ambient CO2 conditions varying between 0.1 to 4.0MPa and 300 to 400K. It is found that the centrifugal inertia force can play a significant impact on the performance of foil thrust bearings with the highly dense CO2 and that the centrifugal inertia forces create unusual radial velocity profiles. In the ramp region of the foil thrust bearings, they generate an additional inflow close to the rotor inner edge, resulting in a higher peak pressure. Contrary in the flat region, the inertia force creates a rapid mass loss through the bearing outer edge, which reduces pressure in this region. This different flow field alters bearing performance compared to conventional air foil bearings. In addition, the effect of turbulence in load capacity and bearing torque is investigated. This study provides new insight into the flow physics within foil bearings operating with dense gases and for the selection of optimal operating condition to suit foil thrust bearings in supercritical CO2 cycles.

Effect of Operating Conditions on the Elastohydrodynamic Performance of Foil Thrust Bearings for Supercritical CO2 Cycles

2016 ◽  
Vol 139 (4) ◽  
Author(s):  
Kan Qin ◽  
Ingo H. Jahn ◽  
Peter A. Jacobs
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Supercritical Co2 ◽  
Load Capacity ◽  
Fluid Phase ◽  
Operating Conditions ◽  
Inertia Force ◽  
Fluid Structure ◽  
Thrust Bearings ◽  
Foil Bearings

In this paper, a quasi-three-dimensional fluid–structure model using computational fluid dynamics for the fluid phase is presented to study the elastohydrodynamic performance of foil thrust bearings for supercritical CO2 cycles. For the simulation of the gas flows within the thin gap, the computational fluid dynamics solver Eilmer is extended, and a new solver is developed to simulate the bump and top foil within foil thrust bearings. These two solvers are linked using a coupling algorithm that maps pressure and deflection at the fluid structure interface. Results are presented for ambient CO2 conditions varying between 0.1 and 4.0 MPa and 300 and 400 K. It is found that the centrifugal inertia force can play a significant impact on the performance of foil thrust bearings with the highly dense CO2 and that the centrifugal inertia forces create unusual radial velocity profiles. In the ramp region of the foil thrust bearings, they generate an additional inflow close to the rotor inner edge, resulting in a higher peak pressure. Contrary to the flat region, the inertia force creates a rapid mass loss through the bearing outer edge, which reduces pressure in this region. This different flow fields alter bearing performance compared to conventional air foil bearings. In addition, the effect of turbulence in load capacity and torque is investigated. This study provides new insight into the flow physics within foil bearings operating with dense gases and for the selection of optimal operating condition to suit CO2 foil bearings.

Computational Fluid Dynamics Thermohydrodynamic Analysis of Three-Dimensional Sector-Pad Thrust Bearings With Rectangular Dimples

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
C. I. Papadopoulos ◽  
L. Kaiktsis ◽  
M. Fillon
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Carrying Capacity ◽  
Thermal Effects ◽  
Operating Conditions ◽  
Load Carrying Capacity ◽  
Performance Indices ◽  
Thrust Bearings ◽  
Load Carrying ◽  
Texture Design

The paper presents a detailed computational study of flow patterns and performance indices in a dimpled parallel thrust bearing. The bearing consists of eight pads; the stator surface of each pad is partially textured with rectangular dimples, aiming at maximizing the load carrying capacity. The bearing tribological performance is characterized by means of computational fluid dynamics (CFD) simulations, based on the numerical solution of the Navier–Stokes and energy equations for incompressible flow. Realistic boundary conditions are implemented. The effects of operating conditions and texture design are studied for the case of isothermal flow. First, for a reference texture pattern, the effects of varying operating conditions, in particular minimum film thickness (thrust load), rotational speed and feeding oil pressure are investigated. Next, the effects of varying texture geometry characteristics, in particular texture zone circumferential/radial extent, dimple depth, and texture density on the bearing performance indices (load carrying capacity, friction torque, and friction coefficient) are studied, for a representative operating point. For the reference texture design, the effects of varying operating conditions are further investigated, by also taking into account thermal effects. In particular, adiabatic conditions and conjugate heat transfer at the bearing pad are considered. The results of the present study indicate that parallel thrust bearings textured by proper rectangular dimples are characterized by substantial load carrying capacity levels. Thermal effects may significantly reduce load capacity, especially in the range of high speeds and high loads. Based on the present results, favorable texture designs can be assessed.

Fluid-Structure Interaction Model of a Synthetic Jet Using Coupled Computational Fluid Dynamics and Finite Elements

2012 ◽  
Author(s):  
Charles E. Seeley ◽  
Stan Weaver ◽  
Brian Rush
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Fluid Structure Interaction ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Working Fluid ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Active Cooling ◽  
Compact Size

Synthetic jets offer new capabilities for localized active cooling of electronics due to their compact size, low cost and substantial cooling effectiveness. The design of devices to create synthetic jets and optimize active cooling performance is challenging due to the strong, two way, fluid-structure interaction (FSI) between the working fluid and the flexible structure that moves the fluid driven with piezoelectric actuators. Previous modeling efforts relied on lumped parameter approaches or electrical analogs. Although computationally less intensive, these approaches may not be accurate in all regions of the design space of interest and trade off fidelity for ease of use. In this effort, a 3D finite element model of the structure is coupled with a 3D computational fluid dynamics model of the fluid to explore the viability of such an approach. The motion of the structure moves the fluid grid, and the fluid feeds back pressure forces onto the structure that are required to converge at each iteration. Transient response of the deflection, pressure and exit velocity will be presented. Validation of the FSI model with experimental data for the frequency response of these quantities will also be presented.

scholarly journals A Simulation Study on Temperature Uniformity of Photovoltaic Thermal Using Computational Fluid Dynamics

2021 ◽  
Vol 82 (1) ◽  
pp. 21-38
Author(s):  
Mohd Afzanizam Mohd Rosli ◽  
Irfan Alias Farhan Latif ◽  
Muhammad Zaid Nawam ◽  
Mohd Noor Asril Saadun ◽  
Hasila Jarimi ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Temperature Distribution ◽  
Thermal Stresses ◽  
High Efficiency ◽  
Cfd Simulation ◽  
Operating Conditions ◽  
Working Fluid ◽  
Percentage Error ◽  
Pv Module

The temperature distribution across the photovoltaic (PV) module in most cases is not uniform, leading to regions of hotspots. The cells in these regions perform less efficiently, leading to an overall lower PV module efficiency. They can also be permanently damaged due to high thermal stresses. To enable the high-efficiency operation and a longer lifetime of the PV module, the temperatures must not fluctuate wildly across the PV module. In this study, a custom absorber is designed based on literature to provide a more even temperature distribution across the PV module. This design is two standard sets of spiral absorbers connected. This design is relatively less complicated for this reason and it allows room for adjusting the pipe spacing without much complication. The absorber design is tested via computational fluid dynamics (CFD) simulation using ANSYS Fluent 19.2, and the simulation model is validated by an experimental study with the highest percentage error of 9.44%. The custom and the serpentine absorber utilized in the experiment are simulated under the same operating conditions having water as the working fluid. The custom absorber design is found to have a more uniform temperature distribution on more areas of the PV module as compared to the absorber design utilized in the experiment, which leads to a lower average surface temperature of the PV module. This results in an increase in thermal and electrical efficiency of the PV module by 3.21% and 0.65%, respectively.

Computational Fluid Dynamics of a Radial Compressor Operating With Supercritical CO2

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Rene Pecnik ◽  
Enrico Rinaldi ◽  
Piero Colonna
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Critical Point ◽  
Gas Turbine ◽  
Supercritical Co2 ◽  
Power Plants ◽  
Compressible Flows ◽  
High Efficiency ◽  
Working Fluid ◽  
Maximum Pressure

The merit of using supercritical CO2(scCO2) as the working fluid of a closed Brayton cycle gas turbine is now widely recognized, and the development of this technology is now actively pursued. scCO2 gas turbine power plants are an attractive option for solar, geothermal, and nuclear energy conversion. Among the challenges that must be overcome in order to successfully bring the technology to the market is that the efficiency of the compressor and turbine operating with the supercritical fluid should be increased as much as possible. High efficiency can be reached by means of sophisticated aerodynamic design, which, compared to other overall efficiency improvements, like cycle maximum pressure and temperature increase, or increase of recuperator effectiveness, does not require an increase in equipment cost, but only an additional effort in research and development. This paper reports a three-dimensional computational fluid dynamics (CFD) study of a high-speed centrifugal compressor operating with CO2 in the thermodynamic region slightly above the vapor–liquid critical point. The investigated geometry is the compressor impeller tested in the Sandia scCO2 compression loop facility. The fluid dynamic simulations are performed with a fully implicit parallel Reynolds-averaged Navier–Stokes code based on a finite volume formulation on arbitrary polyhedral mesh elements. In order to account for the strongly nonlinear variation of the thermophysical properties of supercritical CO2, the CFD code is coupled with an extensive library for the computation of properties of fluids and mixtures. A specialized look-up table approach and a meshing technique suited for turbomachinery geometries are also among the novelties introduced in the developed methodology. A detailed evaluation of the CFD results highlights the challenges of numerical studies aimed at the simulation of technically relevant compressible flows occurring close to the liquid–vapor critical point. The data of the obtained flow field are used for a comparison with experiments performed at the Sandia scCO2 compression-loop facility.

Development of a Computational Tool to Simulate Foil Bearings for Supercritical CO2 Cycles

2016 ◽  
Vol 138 (9) ◽  
Author(s):  
Kan Qin ◽  
Ingo Jahn ◽  
Rowan Gollan ◽  
Peter Jacobs
Keyword(s):  
Turbulent Flow ◽  
Supercritical Co2 ◽  
Three Dimensional ◽  
Structural Deformation ◽  
Working Fluid ◽  
Computational Tool ◽  
Element Analysis ◽  
Thrust Bearings ◽  
Foil Bearings ◽  
Foil Bearing

The foil bearing is an enabling technology for turbomachinery systems, which has the potential to enable cost efficient supercritical CO2 cycles. The direct use of the cycle's working fluid within the bearings results in an oil-free and compact turbomachinery system; however, these bearings will significantly influence the performance of the whole cycle and must be carefully studied. Moreover, using CO2 as the operating fluid for a foil bearing creates new modeling challenges. These include highly turbulent flow within the film, non-negligible inertia forces, high windage losses, and nonideal gas behavior. Since the flow phenomena within foil bearings is complex, involving coupled fluid flow and structural deformation, use of the conventional Reynolds equation to predict the performance of foil bearings might not be adequate. To address these modeling issues, a three-dimensional flow and structure simulation tool has been developed to better predict the performance of foil bearings for the supercritical CO2 cycle. In this study, the gas dynamics code, eilmer, has been extended for multiphysics simulation by implementing a moving grid framework, in order to study the elastohydrodynamic performance of foil bearings. The code was then validated for representative laminar and turbulent flow cases, and good agreement was found between the new code and analytical solutions or experiment results. A separate finite difference code based on the Kirchoff plate equation for the circular thin plate was developed in Python to solve the structural deformation within foil thrust bearings, and verified with the finite element analysis from ansys. The fluid-structure coupling algorithm was then proposed and validated against experimental results of a foil thrust bearing that used air as operating fluid. Finally, the new computational tool set is applied to the modeling of foil thrust bearings with CO2 as the operating fluid.

Computational fluid dynamics simulation of the supersonic steam ejector. Part 2. Optimal design of geometry and the effect of operating conditions on the ejector

2011 ◽  
Vol 226 (3) ◽  
pp. 715-723 ◽  
Author(s):  
L Cai ◽  
H T Zheng ◽  
Y J Li ◽  
Z M Li
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Optimal Design ◽  
Critical Pressure ◽  
Operating Conditions ◽  
Dynamics Simulation ◽  
Working Fluid ◽  
Entrainment Ratio ◽  
Steam Ejector ◽  
Mixing Chamber

The aim of this study is to investigate the use of computational fluid dynamics in predicting the performance and optimal design of the geometry of a steam ejector used in a steam turbine. In the current part, the real gas model was considered using IAPWS IF97 model, and the influences of working fluid pressure and backpressure were investigated. The results illustrate that working critical pressure and backflow critical pressure exist in the flow. Moreover, the entrainment ratio reaches its peak at the working critical pressure. The performance of the ejector was nearly the same when the outlet pressure was lower than the critical backpressure. Effects of ejector geometries were also investigated. The distance between the primary nozzle and the mixing chamber was at optimum, the length of the mixing chamber and the diameter of the throat had an optimal value according to the entrainment ratio. When the length of the diffuser or throat was decreased within a range, the entrainment ratio did not change significantly.

Preliminarily Design of Supercritical CO2 Compression Test System

2021 ◽  
Author(s):  
Geng Teng ◽  
Laijie Chen ◽  
Xin Shen ◽  
Hua Ouyang ◽  
Yubo Zhu ◽  
...  
Keyword(s):  
Simulation Model ◽  
Compression Test ◽  
Thermodynamic Model ◽  
Supercritical Co2 ◽  
Operating Performance ◽  
Test System ◽  
Operating Conditions ◽  
Working Fluid ◽  
Stable Operation ◽  
Test Loop

Abstract The centrifugal compressor is the core component of the supercritical carbon dioxide (SCO2) power cycle. It is essential to carry out component-level experimental research on it and test the working characteristics of the compressor and its auxiliary equipment. Building an accurate closed-loop simulation model of closed SCO2 compression loop is a necessary preparation for selecting loop key parameters and establishing system control strategy, which is also an important prerequisite for the stable operation of compressor under test parameters. In this paper, the thermodynamic model of compressor, pre-cooler, orifice plate and other components in supercritical CO2 compression test system is studied, and the simulation model of compression test system is established. Moreover, based on the system enthalpy equations and physical property model of real gas, the compressor, pre-cooler and other components in the test loop are preliminarily designed by using the thermodynamic model of components. Since the operating conditions are in the vicinity of the critical point, when the operating conditions change slightly, the physical properties of the working fluid will change significantly, which might have a greater impact on the operating performance of the system. So the operating performance and the parameter changes of key nodes in the test loop under different operating conditions are calculated, which will provide theoretical guidance for the construction of subsequent experimental loops.

Metal Temperature Prediction of a Dry Low NOx Class Flame Tube by Computational Fluid Dynamics Conjugate Heat Transfer Approach

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Antonio Andreini ◽  
Lorenzo Mazzei ◽  
Giovanni Riccio ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Operating Conditions ◽  
Metal Temperature ◽  
Thermal Loads ◽  
Flame Tube ◽  
Numerical Predictions ◽  
Partial Load ◽  
Critical Components

Combustor liner of present gas turbine engines is subjected to high thermal loads as it surrounds high temperature combustion reactants and is hence facing the related radiative load. This generally produces high thermal stress levels on the liner, strongly limiting its life expectations and making it one of the most critical components of the entire engine. The reliable prediction of such thermal loads is hence a crucial aspect to increase the flame tube life span and to ensure safe operations. The present study aims at investigating the aerothermal behavior of a GE Dry Low NOx (DLN1) class flame tube and in particular at evaluating working metal temperatures of the liner in relation to the flow and heat transfer state inside and outside the combustion chamber. Three different operating conditions have been accounted for (i.e., lean–lean partial load, premixed full load, and primary load) to determine the amount of heat transfer from the gas to the liner by means of computational fluid dynamics (CFD). The numerical predictions have been compared to experimental measurements of metal temperature showing a good agreement between CFD and experiments.

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