Energy Analysis to the Design of Rotor-Bearing Systems

In the design of rotating machinery, it is often desirable and necessary to change a subset of system parameters to meet the design requirements. The success in designing rotor bearing systems and/or in solving the vibration problems depends heavily upon the understanding of fundamental physical properties and insights of the systems. The modeling improvements and computational techniques have been extensively presented over the years. The design methodologies and fundamental properties have not been widely addressed to assist design engineers in solving their practical problems. The objective of this paper is to relate the various forms of energy and work and their contributions to the system dynamic characteristics. The design strategies and methodologies using the energy approach are also presented and illustrated in a turbine driven machine.

Nonlinear Analysis of a Rigid Rotor on Magnetic Bearings

A simple model of a rigid rotor supported on magnetic bearings is considered. A proportional control architecture is assumed, the nonlinear equations of motion are derived and some essential nondimensional parameters are identified. The free and forced response of the system is analyzed using techniques of nonlinear analysis. Both qualitative and quantitative results are obtained and stability criteria are derived for safe operation of the system.

Evaluation of High Pressure Turbine Blade Coatings on an LM2500 Rainbow Rotor

Two LM2500 rainbow rotors with repaired stage 1 and stage 2 high pressure turbine blades are being assembled for marine propulsion service evaluation by the US Navy. The blades have seen between 5,000 and 15,000 hours of service in the Navy’s Fleets. A number of corrosion resistant coatings including plasma sprayed CoCrAlHf (bill of material), composite plated CoCrAlHf, platinum aluminide, aluminum silicide, and physical vapor deposited yttria stabilized zirconia thermal barrier coating (PVD TBC) will be evaluated in the rainbow rotor. This paper will discuss the advantages and microstructures of the various coatings. Composite plated CoCrAlHf, and PVD TBCs were recently service evaluated in an industrial LM2500 rainbow rotor for 10,500 hours. Both these coatings performed well, although the PVD TBC had local spallation at the leading edge. This paper will review the details of performance of these two coatings in the industrial LM2500 application.

Optimization of Bearing Locations for Rotor Systems With Magnetic Bearings

This paper presents a method for quickly evaluating the effect of changes in bearing location on bearing design for stability of rotating machinery. This method is intended for use by rotating machinery designers to select the “best” bearing locations prior to the bearing design process. The purpose of the method is to improve the design process by separating the problem of determining the “best” bearing locations from that of determining the actual bearing design. The method is independent of the type of bearing employed. For each candidate bearing configuration, the method provides a scalar measure of the relative ability of bearings to meet stability specifications. Within certain limits, the stability specifications are defined by the designer. The scalar measure is used to rank the candidate bearing locations and thereby select the best one. The scalar measure is compared to a practical measure of magnetic bearing design such as the infinity norm of the controller for an example design of a multi-stage centrifugal compressor.

CT Multiscan: Using Small Area Detectors to Image Large Components

The small size and dynamic range of the best two-dimensional X-ray detectors are impediments to the use of three-dimensional X-ray computed tomography (3D-XRCT) for 100% inspection of large ceramic components. The most common industrial 3D-XRCT systems use a “rotate-only” geometry in which the X-ray source and the area detector remain stationary while the component placed between them is rotated through 360°. This configuration offers the highest inspection speed and the best utilization of X-ray dose, but requires that the component be small enough to fit within the X-ray/detector “cone.” Also, if the object is very dense, the ratio of an unattenuated X-ray signal to that through the longest path in the component may exceed the dynamic range of the detector. To some extent, both of these disadvantages can be overcome by using “Multiscan CT,” i.e., scanning small overlapping regions of a large component separately while maximizing the X-ray dose to each. The overlapping scans can then be combined seamlessly into a single scan with optimal contrast.

Probabilistic Assessment of Combustor Liner Design

A typical hot structural component within an engine such as composite combustor liner is computationally simulated and probabilistically evaluated in view of the numerous uncertainties associated with the structural, material, and thermo-mechanical load variables (primitive variables) that describe the combustor. The combustor is evaluated for buckling (eigenvalue) loads, vibration frequencies, and local stresses. Results show that the scatter in the combined stress is not uniform along the length of the combustor. Furthermore, coefficient of thermal expansion, hoop modulus of the liner material, and the thermal load profile dominate stresses near the support and the intermediate location of the combustor liner. However, the liner thickness, the liner material hoop modulus, and pressure load profile have significant impact on stresses near the free end of combustor.

Synchronous Rotor Vibration Driven by Fluid Forces From a Geometrically Imperfect Labyrinth Seal

The radial force acting on a rotor, due to an asymmetric pressure distribution inside the seal gland, generated from a slightly non-circular single gland labyrinth seal rotating inside a circular outer casing is investigated theoretically. A fluid mechanical lumped parameter model for the flow in and out of the seal as well as the flow around the gland in the seal is developed. The model includes first and second knife imperfections as well as rotating gland depth variations. Knife non-circularity on the rotor may be due to manufacturing tolerances or defects from in service wear damage. An appropriate solution technique for the coupled one-dimensional equations is presented. Results from this model are presented that indicate these fluid induced forces are comparable in magnitude to those generated by a rotating unbalance under some conditions. Considerations for design are given for avoiding synchronous vibration problems due to non-circular labyrinth seals.

Feasibility of Extending Current Allowable Weld Repairs for a Compressor Impeller

This research study was undertaken to evaluate whether gas tungsten arc welding (GTAW) could be utilised to extend the limits of an existing repair scheme. The compressor impeller of the GTC 85-71 suffers from such severe sand erosion to the leading edges, that the damage exceeds the manufacturers specification. The impeller is manufactured from Ti-6Al-4V. The study entailed performing a series of welding trials and post-weld heat treatments. After metallographic examination of the weld microstructure, mechanical property assessments (i.e. tensile and fatigue tests) were undertaken. The results demonstrated that the welds after the 550 °C/8 hr post-weld heat treatment had equivalent properties to those of the parent metal. The stress distribution determined by finite element analysis showed the weld to be in an area of low stress. The results achieved herein and the stress analysis showed that the GTAW process is feasible for extending the repair limits for restoration of the leading edges of the compressor impeller.

Dynamic Simulation of the FT8-2™ Gas Turbine

With the approach of the 1990 Clean Air Act compliance limits, the race is on to produce a functional, low-emission gas turbine. While most prototype Dry Low NOx (DLN) gas turbines are based on existing designs, the leap in technology required to meet NOx abatement levels is significant. To meet these goals, significant testing is required before low-emission turbines are ready for commercial production. This paper describes the test procedure that was used to verify control system and modulating valve technology for Turbo Power & Marine’s FT8-2™ Dry Low NOx prototype turbine. In particular, dynamic turbine simulation before the actual engine test will be discussed. The method and benefits of this test procedure will be presented.

Influence of Vaned Diffuser on Dangerous Blade Vibration due to Blade Flow Interactions in a Centrifugal Compressor

Influence of diffuser vane position on dangerous blade vibration due to blade flow interactions at part load operating condition was investigated in a centrifugal compressor. By means of some measurement and analysis techniques a mechanism of interaction between blade vibration and circumferential flow condition in the impeller with vaned diffuser was determined, which is a cause of dangerous blade vibration in resonance. Experiments for the compressor with different radial diffuser positions have been performed to reduce the effect of the blade flow interaction and the dangerous blade vibration A quantitative estimate of the influence of vaneless space length between diffuser and impeller on the blade flow interaction was made. An optimal diffuser position with lower blade vibration and higher compressor characteristics was determined.