A computational model is developed that predicts stresses in the blades of a centrifugal compressor. The blade vibrations are caused by the wakes coming off stationary inlet guide vanes upstream of the impeller, which create a periodic excitation on the impeller blades. When this excitation frequency matches the resonant frequency of the impeller blades, resonant vibration is experienced. This vibration leads to high cycle fatigue, which is a leading cause of blade failure in turbomachinery. Although much research has been performed on axial flow turbomachinery, little has been published for radial machines such as centrifugal compressors and radial inflow turbines. A time domain coupled fluid-structure computational model is developed. The model couples the codes unidirectionally, where pressures are transferred to the structural code during the transient solution, and the fluid mesh remains unaffected by the structural displacements. A Fourier analysis is performed of the resulting strains to predict both amplitude and frequency content. This modeling method was first applied to a compressor in a single stage centrifugal compressor test rig. The analysis results were then validated by experimental blade strain measurements from a rotating test. The model correlated very well with the experimental results. In this work, a model is developed for a liquefied natural gas (LNG) centrifugal compressor that experienced repeated blade failures. The model determined stress levels in the blades, which helped to predict the likely cause of failure. The method was also used to investigate design changes to improve the robustness of the impeller design.

In order to reduce the amount of carbon dioxide (CO2) released into the atmosphere, significant progress has been made into capturing and storing CO2 from power plants and other major producers of greenhouse gas emissions. The compression of the captured carbon dioxide stream requires significant amounts of power and can impact plant availability, and increase operational costs. Preliminary analysis has estimated that the CO2 compression process reduces plant efficiency by 8% to 12% for a typical power plant. This project supports the U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) objective of reducing energy requirements for carbon capture and storage in electrical power production. The primary objective of this study is to boost the pressure of CO2 to pipeline pressures with the minimal amount of energy required. Previous thermodynamic analysis identified optimum processes for pressure rise in both liquid and gaseous states. Isothermal compression is well known to reduce the power requirements by minimizing the temperature of the gas entering subsequent stages. Intercooling is typically accomplished using external gas coolers and integrally geared compressors. For large scale compression, use of straight through centrifugal compressors, similar to those used in oil and gas applications including LNG production, is preferred due to the robustness of the design. However, intercooling between each stage is not feasible. The current research develops an internally cooled compressor diaphragm that removes heat internal to the compressor. Results documenting the design process are presented including 3D conjugate heat transfer CFD studies. Experimental demonstration of the design is performed on a sub scale centrifugal compressor closed loop test facility for a range of suction pressures.

The use of gas bearings has increased over the last several decades to include microturbines, air cycle machines, and hermetically sealed compressors and turbines. Gas bearings have many advantages over traditional bearings, such as rolling element or oil lubricated fluid film bearings, including longer life, ability to use the process fluid, no contamination of the process with lubricants, accommodating high shaft speeds, and operation over a wide range of temperatures. Unlike fluid film bearings that utilize oil, gas lubricated bearings generate very little damping from the gas itself. Therefore, successful bearing designs such as foil bearings utilize damping features on the bearing to improve the damping generated. Similar to oil bearings, gas bearing designers strive to develop gas bearings with good rotordynamic stability. Gas bearings are challenging to design requiring a fully coupled thermo-elastic, hydrodynamic analysis including complex non-linear mechanisms such as Coulomb friction. There is a surprisingly low amount of rotordynamic force coefficient measurement in the literature despite the need to verify the model predictions and the stability of the bearing. This paper describes the development and testing of a 60,000 rpm gas bearing test rig and presents measured stiffness and damping coefficients for a 57 mm foil type bearing. The design of the rig overcomes many challenges in making this measurement by developing a patented, high-frequency, high-amplitude shaker system resulting in excitation over most of the subsynchronous range.

The use of gas bearings has increased over the past several decades to include microturbines, air cycle machines, and hermetically sealed compressors and turbines. Gas bearings have many advantages over traditional hearings, such as roiling element or oil lubricated fluid film bearings, including longer life, ability to use the process fiuid, no contamination of the process with lubricants, accommodating high shaft speeds, and operation over a wide range of temperatures. Unlike fluid fllm bearings that utilize oil, gas lubricated bearings generate very little damping from the gas itself. Therefore, .mccessful bearing designs such as foil bearings utilize damping features on the bearing to improve the damping generated. Similar to oil bearings, gas bearing designers strive to develop gas bearings with good rotordynamic stabiiity. Gas bearings are challenging to design, requiring a fully coupled thermo-eiastic, hydrodynamic analysis including complex nonlinear mechanisms such as Coulomb friction. There is a .•surprisingly low amount of rotordynamic force coefficient measurement in the literature despite the need to verify the model predictions and the stability of the bearing. This paper de.icribes the development and testing of a 60,000 rpm gas bearing test rig and presents measured stiffness and damping coefficients for a 57 mm foil type bearing. The design of the rig overcomes many challenges in making this measurement by developing a patented, high-frequency, highamplitude shaker system, resulting in excitation over most of the subsynchronous range.

Turbomachinery blade fatigue life estimation requires reliable knowledge of actual static and dynamic stresses occurring within the blades. A common method for predicting dynamic stresses is to construct a finite element model of the blade and simulate the dynamic response to aerodynamic loads. Although this method is powerful and very useful, modeling errors (geometry, boundary conditions, stress concentrations, damping, etc.) may result in inaccurate stress predictions. Furthermore, unavoidable variability in manufacturing results in blade mistuning, which significantly affects stress amplification at resonance. This paper presents two empirical methods for predicting dynamic stresses in turbomachinery blades that include the actual effects of structural damping and mistuning. Both methods use strain gauge measurements from a blade modal test to obtain load to strain transfer functions, which are applied to predict the blade strain or stress response to a simulated load. The advantages and disadvantages of each method are discussed. The predictions of each method are compared with dynamic blade strain data acquired during a rotating test of a centrifugal compressor impeller.