The development of the supercritical Carbon Dioxide power cycle has relied on parallel tracks along which theoretical and experimental works have successfully complemented each other in the last few years. Following this approach, intensive work on the development of critical components has enabled the demonstration of the technology in small-scale test loops. The next step in the roadmap is scaling-up the technology in order to bridge the gap to commercialisation. To this aim, not only is it necessary to demonstrate that the cycle works, but it is also mandatory to rise component (and system) efficiencies to levels comparable with competing technologies. In this process, assessing the impact of the main design parameters on the efficiency of turbomachinery is deemed crucial. The present work is a follow-up to others presented by the authors in previous years where preliminary analysis on centrifugal compressor design combining tools of different levels of fidelity were used. Nevertheless, whilst these presented guidelines to design the main compressor successfully, this new piece of research presents how the design space of the unit is affected by the characteristics of the working fluid. A review of past research is first presented to evidence that the design space is largely influenced by the particular behaviour of the working fluid close to the critical point. Then, design maps are presented for different operating conditions (cycle heat balance), showing that their shapes change substantially depending on compressor inlet pressure and temperature. Also, a comparison of these maps confirms that the design regions enabling high efficiency can be substantially reduced depending on the inlet/outlet thermodynamic states. Finally, conclusions are drawn regarding optimal intervals for the main design parameters involved in the process.

Clearances of compressor and turbine blade tips and seals alter during and following speed transients. These changes affect the performance of the components and hence of the engine. This paper describes models for the prediction of blade tip clearance changes and seal clearance changes. These models have been applied to the H.P. Compressor and H.P. Turbine and to two seals controlling air flows in a Two-spool Bypass Engine. The predicted acceleration rates appear to be more influenced by the changes in the seal clearances than by the tip clearance changes. The increases in computing time in the engine transient program which result from inclusion of the model are acceptable.

This paper describes how allowance for the thermal effects of non-adiabatic flow, altered boundary layer development, changes in tip clearances and changes in seal clearances have been incorporated into a general gas turbine transient program. These non-adiabatic effects have been investigated, modelling a two-spool bypass engine. The model has predicted events that occur in practice and also indicates which of the parameters are the most influential in the alteration of transient performance.

Most current fuel schedules for accelerating or decelerating gas turbines use a limiting non-dimensional fuel flow expressed as a function of some engine parameter such as compressor pressure ratio. Usually the same schedule is used for, for example, accelerating ‘cold’ and ‘hot’ engines. This results in differing acceleration rates and differing usage of surge margins. The paper describes two methods of compensating the fuel schedules to account for the engine’s immediately preceding temperature history. One method uses the temperature response of the aerofoil of blades in the H.P. Compressor. The second method, which appears to be an improvement, uses a ‘delayed’ H.P. Shaft speed signal.

The paper describes a general program which has been developed for the prediction of the transient performance of gas turbines. The program is based on the method of continuity of mass flow. It has been applied successfully to a wide range of aero gas turbines, ranging from single to three-spool and from simple jet to bypass types with or without mixed exhausts. The results for three of these engine types are illustrated. Computing times are reasonable, increasing with the complexity of the engine. A parallel paper describes the inclusion of thermal effects in the prediction program.

This paper describes how allowance for the thermal effects of non-adiabatic flow, altered boundary layer development, changes in tip clearances and changes in seal clearances have been incorporated into a general gas turbine transient program. This program has been applied to a two-spool bypass engine. Revised predictions of surge margins in three common transients have been obtained. When the engine undergoes a “cold” acceleration, the thermal effects on the trajectory and on the surge line give a much increased proportion of unused surge margin in the H.P. Compressor, as compared to adiabatic predictions. In a “hot” acceleration this improvement is considerably reduced.

The international scientific community researching the supercritical carbon dioxide power cycle has already developed the first turbomachinery designs, which are currently operating in reference laboratories worldwide. Nevertheless, the performance of this equipment is still quite far from the target values yielding fairly disappointing system efficiencies (65% vs. 80% total to total efficiency for radial compressors). In the light of these past results, the thermal Power Group (GMTS) at the University of Seville, Spain, has been researching the SCO 2 cycle during the last few years. Hence, after researching elementary diffusion processes and some basic features of the system, the authors are now in the process of developing guidelines for compressor design based on one-dimensional codes developed in-house and CFD analysis. The results stemming from both approaches are presented in this paper showing that the rather simple 1D model is able to produce a fairly good model which can then be tuned with a more complex and computationally expensive 3D CFD code. The entire approach is presented in this paper, from the initial reference value for the key design parameters through the 1D code and to the multi-dimensional tool. The results of the two latter approaches are compared in detail in this paper.

Maintenance cost is one of the major life cycle costs of gas turbine engines. To reduce the maintenance costs, the maintenance should be changed from preventive (or scheduled) maintenance to predictive (or condition-based) maintenance where condition monitoring and diagnostics become crucially important. This paper represents the application of a gas path diagnostic technique, Gas Path Analysis, to the diagnostic analysis of an aero-derivative gas turbine (GE LM2500+) operated by Manx Electricity Authority in the Isle of Man, UK. In the application, an engine thermodynamic model is created and adapted to the performance of the engine using field data obtained at different operating conditions. Different data pre-processing methods are presented and compared in the diagnostic analysis. The uncertainty of measurement data is analysed and the most suitable measurements are identified in the prediction of key gas path component degradation. A non-linear GPA diagnostic analysis provides promising results for the prediction of compressor degradation and the performance improvement due to a compressor water washing. Such diagnostic information would be very useful for maintenance engineers to optimise their maintenance activities including overhauls and compressor washing.

The transient performance of the Selective Bleed Variable Cycle Engine (VCE) has been optimized during the transition from subsonic to supersonic mode. The Selective Bleed VCE concept has been developed with a Short Take-Off Vertical Landing (STOVL) aircraft in mind and the engine is characterized by its twin mode VCE feature. The transition optimization is constrained by the requirement of maintaining thrust and compressor surge margins. The engine variable geometry component schedules and the fuel flow are used as optimization variables. A differential algebraic formulation of an inter-component volume model is used to model the transient behavior of the engine. Sequential Quadratic Programming (SQP) is applied to the non-linear transient engine model directly, in order to solve the multivariable control problem. It is predicted that the mode switch can be carried out safely without violating the constraints and that the time required is limited by the actuator time of the hydraulic system.

This paper describes the effects of degradation of the main gas path components of the gas turbine topping cycle on the Combined Cycle Gas Turbine (CCGT) plant performance. Firstly the component degradation effects on the gas turbine performance as an independent unit are examined. It is then shown how this degradation is reflected on a steam turbine plant of the CCGT and on the complete Combined Cycle plant. TURBOMATCH, the gas turbine performance code of Cranfield University was used to predict the effects of degraded gas path components of the gas turbine have on its performance as a whole plant. To simulate the steam (Bottoming) cycle, another Fortran code was developed. Both codes were used together to form a complete software system that can predict the CCGT plant design point, off-design, and deteriorated (due to component degradation) performances. The results show that the overall output is very sensitive to many types of degradation, specially in the turbine of the gas turbine. Also shown is the effect on gas turbine exhaust conditions and how this affects the steam cycle.

This is the second paper exploring the effects of the degradation of different components on Combined Cycle Gas Turbine (CCGT) plant performance. This paper investigates the effects of degraded steam path components of steam turbine (bottoming) cycle have on CCGT power plant performance. Areas looked at were, steam turbine fouling, steam turbine erosion, heat recovery steam generator degradation (scaling and/or ashes deposition), and condenser degradation. The effect of gas turbine back-pressure on plant performance due to HRSG degradation is also discussed. A general simulation Fortran code was developed for the purpose of this study. This program can calculate the CCGT plant design point performance, off-design plant performance, and plant deterioration performance. The results obtained are presented in a graphical form and discussed.

This paper describes the steady state performance analysis of a 3-shaft closed cycle helium turbine using nuclear heat source. The analysis is carried out using a computer program, which is specifically made for this cycle. The computer model was tested for various Turbine Entry Temperatures (TET) and absolute pressures. The analysis of the change was focused on the compressors, as these are relatively more critical than the rest of the equipments. The change in TET triggered changes in shaft speed, mass flow rate, power output, absolute pressure etc. Adjustable guide vanes were used to study the operation with constant surge margin. The closed cycle was tested for various absolute pressures and it was established that the efficiency will not be affected in using the inventory control for the load variation.

Operating gas turbines at higher firing temperatures has been shown to be more thermally efficient with more power obtained from relatively less fuel. There is, however, an associated slight increase in operating and maintenance costs at higher power settings. This paper studies the relationship between gas turbine power setting, the hot gas-path components’ life consumption, operating and maintenance cost and how these parameters can affect the cost of electricity. A 165 MW gas turbine power plant is modelled and investigated with a comparative turbine blade lifing model that performs stress and thermal analysis, and creep life estimation using the parametric Larson Miller method. The outcomes of this analysis are then linked to an economic model to calculate the cost of generating electricity. The results shows that the optimum cost of electricity does not coincide with the lowest TET or power setting as would be expected when taking into account the creep life of the blade. This is because although lower TET results in improved component life, it will also result in lower thermal efficiency which is found to have a more significant impact on the overall electricity cost. In other words, the cost of electricity will increase at low TETs due to reduced thermal efficiency. On the other hand the cost of electricity will also increase at high TETs due to reduced turbine blade life that leads to increase in maintenance cost.