A Method for the Calculation of the Tip Clearance Flow Effects in Axial Flow Compressors: Part II — Calculation Procedure

An algorithm was set up for the implementation of the tip clearance models, described in Part I, in a secondary flow calculation method. A complete theoretical procedure was, thus, developed, which calculates the circumferentially averaged flow quantities and their radial variation due to the tip clearance effects. The calculation takes place in successive planes, where a Poisson equation is solved in order to provide the kinematic field. The self induced velocity is used for the positioning of the leakage vortex and a diffusion model is adopted for the vorticity distribution. The calculated pressure deficit due to the vortex presence is used, through an iterative procedure, in order to modify the pressure difference in the tip region. The method of implementation and the corresponding algorithm are described in this part of the paper and calculation results are compared to experimental ones for cascades and single rotors. The agreement between theory and experiment is good.

The Investigation of the Travelling Wave Resonance of Driven Helical Gear

The main vibration type gearing in modern aeroengine transmission is the travelling wave vibration which is divided into two kinds: the forward travelling wave vibration and the backward travelling wave vibration. If the frequency of vibration exciting force, which comes from the meshing of a set of helical gears, is the same as the frequency of travelling wave resonance, the dangerous resonant vibration will take place. However both of forward and backward travelling wave resonance can not be excited as easily. The results of an aeroengine transmission test indicate that forward travelling wave resonant vibrations are more easily excited to the driven helical gear and more dangerous. The work done by the component force, which is generated because of the angle of travelling wave vibration, on the driven helical gear, work done on the forward travelling wave vibration is positive and the backward travelling wave vibration is negative. In other words, for backward travelling wave vibration the induced force acts as a damping force, but for forward travelling wave vibration the induced force acts as a self–exciting force. Therefore it is more dangerous to driven helical gear when forward travelling wave vibration appears.

Structural and Aerodynamic Influences to Airfoil Forced Response: Does a Thicker Airfoil Have Reduced Vibratory Response?

The influence of airfoil geometric and aerodynamic parameters on the vibratory response of low frequency modes subjected to low order excitations was investigated. The predicted vibratory response of a thicker airfoil was compared to the response of a baseline thickness design. Two types of forcing mechanisms were analyzed. It was found that force-controlled response, that may originate from mechanical input or surge, can be managed by increasing the airfoil thickness and providing sufficient margin below the endurance limit of the material. Velocity-controlled response, mainly from aerodynamic interactions, depend on the airfoil excitation placement. The aerodynamic forcing function and damping were determined using flat plate unsteady aerodynamic solutions integrated with an MSC/NASTRAN structural finite element model of the airfoil. Thickening appears to reduce blade response in a velocity-controlled situation provided the modal stress has been reduced by the thickening. However, the response reduction is greater for the force-controlled situation. The modal parameter model provides a quick assessment of either possibility.

Evolution of Gas Turbines Auxiliary Systems Designed for Reliability

Gas turbine design evolution and practice is driven by industry demand for increased output and improved operating efficiencies. New aerothermal design characteristics require a focus on improved materials and coatings, and cooling techniques. As environmental issues continue to confront the industry, Dry Low NOx combustion system designs represent a significant opportunity for meeting new emissions requirements. These issues represent opportunity for significant technology improvements and industry driven advances. However, just as important is the design evolution of the Control and Auxiliary systems which support the gas turbine. Historically, these support systems, as demonstrated by the Operational Reliability Analysis Program (ORAP), are typically the primary drivers of plant Availability and Reliability. Following a rigorous “Design for Reliability” approach provides opportunities for ensuring that the design meets three critical requirements: starting reliability, a minimum of unit shutdowns during operating demand periods and ease of maintenance. The design approach for the Control and Auxiliary systems for new turbine design (product improvement) therefore provides an opportunity for developing a uniform and standardized approach which continues to focus on Reliability, Availability, and Maintainability. This design approach also provides opportunities for improved field installation and reduced cycle time, a major benefit for the end user. This paper will describe the “Design for Reliability” approach followed by ABB Power Generation, Inc., and supported by Strategic Power Systems, Inc.® (SPS) for the GT11N2 auxiliary systems. The extension of the ORAP system for auxiliary systems will be discussed as the approach for monitoring unit Availability and Reliability, maintaining configuration control, and for promoting continuous improvement.

Numerical Simulation of Fluid Flow and Combustion in Gas Turbine Combustors

The finite-volume approach together with body-fitted curvilinear non-orthogonal coordinates and a non-staggered grid arrangement is used for investigating turbulent reacting flows inside gas turbine combustion chambers. The computational grids are generated by solving elliptic differential equations, permitting an accurate description of the complex geometry of commercial gas turbine combustors. Different combustion models are briefly discussed with a view to their suitability for practical combustor predictions. The k-ε model and the Eddy Dissipation Concept are selected to account for the turbulent combustion in the present study. The governing equations and coordinate transformations needed to derive the discretized equations are reviewed. One isothermal and two combusting flow fields are calculated. The calculations are in reasonable agreement with measurements, but the results should be improved by grid refinement and by using a better turbulence model.

Design and Performance Evaluation of a CBC Solar Space Power System: The Influence of Orbital and Solar Conditions

Design and performance evaluation of solar space Closed Brayton Cycle (CBC) is described in this paper taking into account the influence of orbital and solar conditions. With fixed external conditions (insolation, Tsink, power) overall performance and area of the plant are obtained and optimized (plant area minimization), while to evaluate plant mass a detailed and complete design of the plant components is carried out. Utilizing as the input the results obtained with fixed external conditions, plant transient orbital analysis (TOA) is performed taking into account modification of insolation, Tsink, and power to be generated versus orbit time, (quasi steady transient analysis). All these methods have been fully integrated — the common inputs are interchanged and the output of one code is directly input to the other codes — in a complete design procedure, named CBC-SPACE, suited for Low Earth Orbit (LEO) station power plant design. The most important results are presented and discussed, while the importance of this study is pointed out taking also into account the possibility to extend this analysis to SDCC (solar dynamic combined cycle) plant proposed by the author (Massardo, 1991).

The Effects of Scale Factor on the Aero-Thermodynamic and Infrared Radiation Performance of Naval Gas Turbine Exhaust System With Infrared Signature Suppression Device

On the basis of scale model tests in two different dimensions of marine gas turbine exhaust system with infrared signature suppression device, and in the light of similarity analysis and simplified numerical calculation, this paper discusses the effects of scale factor on the flow (flow resistance), temperature (of air-flow and tube wall), and infrared radiant (of exhaust plumes and exhaust uptake inner wall) fields of the exhaust system, and accordingly estimates the corresponding parameters of real ship exhaust systems as well as presents the magnitude of scale factor impacts and the recommended values for selecting the scale factor.

Impeller Rotating Stall as a Trigger for the Transition From Mild to Deep Surge in a Subsonic Centrifugal Compressor

The present paper concerns the transition from mild to deep surge in a single stage centrifugal compressor using a vaned diffuser. Time-resolved measurements of the mass flow rate and the static pressures at various locations of the compressor were analyzed for different diffuser geometries and different operating points in the compressor map. When the throttle valve was gradually closed at an impeller tip Mach number (Mu) above 0.4, the compressor showed first mild and then deep surge whereas at Mu=0.4 rotating stall was the dominant instability. This single-cell rotating stall was identified to be caused by the impeller. During mild surge at higher Mach numbers the instantaneous flow and pressure traces showed that the overall flow at the stage inlet intermittently dropped below the critical value associated with the occurence of impeller rotating stall. Rotating stall appeared for a while but vanished as soon as the flow increased again. With further throttling, however, a threshold was reached at which rotating stall triggered deep surge. The results show that triggering only occurred if the flow deficiency causing rotating stall persisted long enough to permit the stall cell to make at least one or two revolutions.

Swirl Generation and Recirculation Using Radial Swirl Vanes

The concept of the Swirl Number and its effect on recirculation is reviewed and problems with it are identified. Swirl generation through the use of radial inlet swirl vanes is then studied. The effect of vane and swirl cup design on recirculation is then evaluated using finite element computer modeling and verified using tufting tests. Vane geometry, combustor dome geometry, co- vs. counter-rotation and mass flow effects are all evaluated. It is shown that co- and counter-rotation generate very similar flow fields and recirculated mass flows. An approach for calculating swirl numbers in multiple swirler designs is proposed.

Large Combined Cycle HRSG Units Impact of Operating Considerations

Combustion turbine combined cycle plants continue to increase their role in worldwide power generation. Advanced combined cycle plants provide: • high efficiency, often in excess of 50% • short project schedules • reasonable cost with minimum environmental considerations For reliable operation of these facilities, it is essential the Heat Recovery Steam Generator (HRSG) design adequately address issues to include: • required load rangeability • transient operation, particularly start-up and shutdown • low life cycle costs through high availability This paper will address the more detailed aspects of the design configuration of large HRSG units.