Gas Turbine Fogging Technology — A State-of-the-Art Review: Part II — Overspray Fogging, Analytical and Experimental Aspects

The strong influence of ambient temperature on the output and heat rate on a gas turbine has popularized the application of inlet fogging and overspray for power augmentation. One of the main advantages of overspray fogging is that it enhances power output as a result of decrease in compression work associated with the continuous evaporation of water within the compressor due to fog intercooling. A comprehensive review on the current understanding of the analytical and experimental aspects of overspray fogging technology as applied to gas turbines is presented in this paper.

An Investigation in Optimal Locations by Genetic Algorithm for Balancing Flexible Rotor-Bearing Systems

This study utilizes genetic algorithm to minimize the condition number of Hermitian matrix of influence coefficient (HMIC) to reduce the computation errors in balancing procedure. Then, the optimal locations of balancing planes and sensors would be obtained as fulfilling optimization. The finite element method is used to determine the steady-state response of flexible rotor-bearing systems. The optimization improves the balancing accuracy, which can be validated by the experiments of balancing a rotor kit.

Arrangement and Optimisation Turbocompressors in an Off-Shore Natural Gas Extraction Station

In this paper, a methodology for the optimization of a single off-shore gas compression station is developed. The station is composed of three gas turbines, each one driving a centrifugal compressor. The study concerns the feasibility of the most suitable arrangement to face the depletion of wells and the consequent reduction of the head top pressure. Once the arrangement is chosen, an optimization procedure is developed and carried out. The procedure, which is aimed at obtaining either high production rates or good station efficiency, is based on knowledge of the centrifugal compressor characteristics and on the availability of gas turbine thermodynamic cycle program, the latter allowing the definition of the machine actual operating state.

Mechanical Behavior of Anti-Symmetrically Laminated Composite Blades

Anti-symmetrically laminated composites have coupling effects between tensile stress and twisting deformation, and are very attractive as fan blade materials of aircraft engines. Blades fabricated by anti-symmetrically laminated composites can automatically adjust the stagger angle to better aerodynamic conditions with change of axial force or rotational speed owing to the coupling effects. Thus, the anti-symmetrically laminated composite blades are expected to improve aerodynamic efficiency and the stability of aircraft engines. In this paper, the mechanical behavior of anti-symmetrically laminated composite blades is evaluated by spin tests and finite element analyses. Three kinds of blades fabricated by carbon/epoxy laminated composites in different anti-symmetrical stacking sequences were tested. A non-contact measurement technique using a multi-channel optical fiber sensor was used for measurements of blade deformations at high-speed rotating conditions, up to 10,000 rpm. The twisted angle change at the blade tip could be successfully measured. The twisted angle change increased in proportion to the second power of rotational speed, and the maximum angle change was about 4 degree at 10,000 rpm. The finite element analysis results agreed well with the spin test results. Furthermore, the three-dimensional deformation of the test blades was evaluated based on finite element analyses.

Rotordynamic Coefficients of Labseals for Turbines: Comparing CFD Results With Experimental Data on a Comb-Grooved Labyrinth

The main goal of this paper is to improve identification methods for rotordynamic coefficients of labseals for turbines. This aim was achieved in joint effort of the Technische Universita¨t Mu¨nchen, working on experimental identification methods for rotordynamic coefficients, the University of Technology, Darmstadt, working on prediction methods, and Siemens AG, realizing the results. The paper focuses on a short comb-grooved labyrinth seal. Short labseals, amongst others the above mentioned comb-grooved labyrinth, were examined. by means of a very accurately measuring test rig. The rotor was brought into statically eccentric positions relative to the stator, in order to measure the circumferential pressure distribution as a function of pressure, rotating speed and entrance swirl. The data collected were used to validate results obtained with a numerical method. The theoretical approach is based on a commercial CFD tool, which solves the Navier Stokes equations using numerical methods. As a result, a detailed model of the flow within the test rig is produced. The efforts of computation here are greater than when compared with the likewise wide-spread Bulk flow models, however improved accuracy and flexibility is expected. As the validation of the model is successful, it could then be used to gain further insight in the flow within the seal, and to understand the results better. This showed that rotordynamic coefficients of labseals gained from different test rigs are not necessarily comparable.

A Test Rig for Air Bearings Rotordynamic Coeffcients Measurement

This paper describes the design and manufacturing of an experimental facility for measurement of equivalent stiffness and damping of air bearings. For these preliminary tests, the shaft moves only in two perpendicular directions, laying in the rotation plane, thus producing 2×2 characteristic matrices. However, the rig can be easily modified to measure rotordynamic characteristics related to angular motion of the journal and measuring 4×4 matrices. The testing facility uses an experimental magnetic bearing suspension system that allows imposing any given orbit to the shaft, during the testing experiments. All individual parts, as well as the assembly, were dynamically studied to determine their modal response and optimize it according to the test rig’s operating frequency range. The principle of operation is to produce a shaft orbit using the magnetic suspension system and measuring the forces generated on the test bearing housing. Then, the stiffness and damping coefficients are calculated using an iterative parameter identification algorithm (a modification of the IVF method). The force measurement is performed via three load cells placed in a triangle configuration around the test bearing housing. All data is gathered and processed using PC based data acquisition boards and software. The present design allows testing air bearings up to 44 mm in external diameter and a bandwidth of 0 Hz to 1.000 Hz. Preliminary testing was performed on this research that demonstrates the capability of the apparatus to measure the dynamic properties with ease and accuracy.

Artificial Intelligence for the Diagnostics of Gas Turbines: Part II — Neuro-Fuzzy Approach

In the paper, Neuro-Fuzzy Systems (NFSs) for gas turbine diagnostics are studied and developed. The same procedure used previously for the set up of Neural Network (NN) models was used. In particular, the same database of patterns was used for both training and testing the NFSs. This database was obtained by running a Cycle Program, calibrated on a 255 MW single shaft gas turbine working in the ENEL combined cycle power plant of La Spezia (Italy). The database contains the variations of the Health Indices (which are the characteristic parameters that are indices of gas turbine health state, such as efficiencies and characteristic flow passage areas of compressor and turbine) and the corresponding variations of the measured quantities with respect to the values in new and clean conditions. The analyses carried out are aimed at the selection of the most appropriate NFS structure for gas turbine diagnostics, in terms of computational time of the NFS training phase, accuracy and robustness towards measurement uncertainty during simulations. In particular, Adaptive Neuro-Fuzzy Inference System (ANFIS) architectures were considered and tested, and their performance was compared to that obtainable by using the NN models. An analysis was also performed in order to identify the most significant ANFIS inputs. The results obtained show that ANFISs are robust with respect to measurement uncertainty, and, in all the cases analyzed, the performance (in terms of accuracy during simulations and time spent for the training phase) proved to be better than that obtainable by MIMO and MISO Neural Networks trained and tested on the same data.

Advanced Services for Turbomachinery Asset Management

Operations have a key role to play in today’s highly competitive environment, as they must provide the utmost effectiveness in asset management practices to boost the Return on Capital Employed (ROCE) back to the asset Owners. Asset Management Effectiveness (AME) can be rooted in a certain number of Operator-controllable leverages, that this paper is aimed to show thru a simple model. The model ties the identified operational leverages to the ROCE, providing guidance for the Operators to communicate properly with the asset Owners for demonstrating the financial benefits of their operational practices. A certain number of advanced services available to the Operators are shown and described, that can support both Operations and asset Owners in their search for the highest financial returns from existing assets.

Thermodynamic Study of Humid Air Gas Turbine Cycle Power Plants

The major challenges before the design engineers of a gas turbine plant and its variants are the enhancement of power output, substantial reduction in NOx emission and improvement in plant thermal efficiency. There are various possibilities to achieve these objectives and humid air gas turbine cycle power plant is one of them. The present study deals with the thermodynamic study of humid air gas turbine cycle power plants based on first law. Using the modeling and governing equations, the parametric study has been carried out. The results obtained will be helpful in designing the humid air gas turbines, which are used as peaking units. The comparison of performance of humid air gas turbine cycle shows that it is superior to basic gas turbine cycle but inferior and more complex to steam injected cycle.

Modeling and Experimental Investigation of Micro-Hydrostatic Gas Thrust Bearings for Micro-Turbomachines

One of the major challenges for the successful operation of high-power-density micro-devices lies in the stable operation of the bearings supporting the high-speed rotating turbomachinery. Previous modeling efforts by Piekos [1], Liu et al. [2] and Spakovszky and Liu [3] have mainly focused on the operation and stability of journal bearings. However, since thrust bearings play the vital role of providing axial support and stiffness, there is a need to gain a fuller understanding of their behavior. In this work, a rigorous theory is presented to analyze the effects of compressibility in micro-flows (characterized by low Reynolds numbers and high Mach numbers) through hydrostatic thrust bearings for application to microturbomachines. The analytical model, which combines a 1-D compressible flow model with Finite-Element Analysis, serves as a useful tool for establishing operating protocols and assessing the stability characteristics of hydrostatic thrust bearings. The model is capable of predicting key steady-state performance indicators, such as bearing mass flow, axial stiffness and natural frequency as a function of the hydrostatic supply pressure and thrust bearing geometry. The model has been applied to investigate the static stability of hydrostatic thrust bearings in micro-turbine-generators, where the electrostatic attraction between the stator and rotor gives rise to a negative axial stiffness contribution and may lead to device failure. Thrust bearing operating protocols have been established for a micro-turbopump, where the bearings also serve as an annular seal preventing the leakage of pressurized liquid from the pump to the gaseous flow in the turbine. The dual role of the annular pad poses challenges in the operation of both the device and the thrust bearing. The operating protocols provide essential information for the required thrust bearing supply pressures and axial gaps required to prevent the leakage of water into the thrust bearings for various pump outlet pressures. Good agreement is observed between the model predictions and experimental results. In addition, a dynamic stability analysis is also performed, which indicates the occurrence of unstable axial oscillations due to flow choking effects in both forward and aft thrust bearings. These a-priori dynamic stability predictions were subsequently verified experimentally on a micro-turbocharger. The frequencies of unstable axial oscillations predicted using the model compare favorably to those determined experimentally, thus vindicating the validity of the model. A simple and useful dynamic stability criterion is established, where the occurrence of flow choking in both thrust bearings give rise to dynamic instability.