A Summary of the Cooled Turbine Blade Tip Heat Transfer and Film Effectiveness Investigations Performed by Dr. D. E. Metzger

The clearance gap between the stationary outer air seal and blade tips of an axial turbine allows a clearance gap leakage flow to be driven through the gap by the pressure-to-suction side pressure difference. The presence of strong secondary flows on the pressure side of the airfoil tends to deliver air from the hottest regions of the mainstream to the clearance gap. The blade tip region, particularly near the trailing edge, is very difficult to cool adequately with blade internal coolant flow. In this case, film cooling injection directly onto the blade tip region can be used in an attempt to directly reduce the heat transfer rates from the hot gases in the clearance gap to the blade tip. The present paper is intended as a memorial tribute to the late Professor Darryl E. Metzger who has made significant contributions in this particular area over the past decade. A summary of this work is made to present the results of his more recent experimental work that has been performed to investigate the effects of film coolant injection on convection heat transfer to the turbine blade tip for a variety of tip shapes and coolant injection configurations. Experiments are conducted with blade tip models that are stationary relative to the simulated outer air seal based on the result of earlier works that found the leakage flow to be mainly a pressure-driven flow which is related strongly to the airfoil pressure loading distribution and only weakly, if at all, to the relative motion between blade tip and shroud. Both heat transfer and film effectiveness are measured locally over the test surface using a transient thermal liquid crystal test technique with a computer vision data acquisition and reduction system for various combinations of clearance heights, clearance flow Reynolds numbers, and film flow rates with different coolant injection configurations. The present results reveal a strong dependency of film cooling performance on the choice of the coolant supply hole shapes and injection locations for a given tip geometry.

Uprated 501F Gas Turbine, 501FA

This paper introduces the engineering approach taken in developing the 501FA gas turbine, which is an uprated version of the existing 501F 150MW class gas turbine. The concepts and procedures which were utilized to uprate this gas turbine are also presented. To achieve better performance, new techniques were incorporated which reflected test results and operating experience. No advanced technologies were introduced. Instead, well experienced techniques are adopted so as not to deteriorate reliability. Improvement of the performance was mainly achieved mainly due to the reduction of cooling air. Tip clearances were also optimized based on shop test and field results.

Local Heat Transfer Coefficient and Adiabatic Wall Temperature Measurement Beneath Arrays of Staggered and Inline Impinging Jets

Recent work, Van Treuren et al. (1993), has shown the transient method of measuring heat transfer under an array of impinging jets allows the determination of local values of adiabatic wall temperature and heat transfer coefficient over the complete surface of the target plate. Using this technique, an inline array of impinging jets has been tested over a range of average jet Reynolds numbers (10,000–40,000) and for three channel height to jet hole diameter ratios (1, 2, and 4). The array is confined on three sides and spent flow is allowed to exit in one direction. Local values are averaged and compared with previously published data in related geometries. The current data for a staggered array is compared to those from an inline array with the same hole diameter and pitch for an average jet Reynolds number of 10,000 and channel height to diameter ratio of one. A comparison is made between intensity and hue techniques for measuring stagnation point and local distributions of heat transfer. The influence of the temperature of the impingement plate through which the coolant gas flows on the target plate heat transfer has been quantified.

Compressor Washing Maintains Plant Performance and Reduces Cost of Energy Production

This paper reports about the results of a field test conducted over a period of 8000 operating hours on the effect of combined on line and off line compressor washing on a 66 MW gas turbine operating in a combined cycle plant at UNA’s Lage Weide 5 power plant in Utrecht. Observations have shown a sustained high output level close to the nominal guaranteed rating, despite difficult atmospheric conditions. Investigations on the correlations between fouling gradients in the compressor and atmospheric conditions are also presented. The evaluation of the results demonstrate the importance of implementing an optimised regime of on line and off line washing in the preventive turbine maintenance program. It will improve the plant profitability by reducing the costs of energy production.

Leading Edge Film Cooling of a Turbine Blade Model Through Single and Double Row Injection: Effects of Coolant Density

Experiments have been conducted on a large model of a turbine blade. Attention has been focussed on the leading edge region, which has a semi-circular shape and four rows of film cooling holes positioned symmetrically about the stagnation line. The cooling holes were oriented in a spanwise direction with an inclination of 30° to the surface, and had streamwise locations of ±15° and ±44° from the stagnation line. Film cooling effectiveness was measured using a heat/mass analogy. Single row cooling from the holes at 15° and 44° showed similar patterns: spanwise averaged effectiveness which rises from zero at zero coolant mass flow to a maximum value η* at some value of mass flow ratio M*, then drops to low values of η at higher M. The trends can be quantitatively explained from simple momentum considerations for either air or CO2 as the coolant gas. Close to the holes, air provides higher η values for small M. At higher M, particularly farther downstream, the CO2 may be superior. The use of an appropriately defined momentum ratio G collapses the data from both holes using either CO2 or air as coolant onto a single curve. For η*, the value of G for all data is about 0.1. Double row cooling with air as coolant shows that the relative stagger of the two rows is an important parameter. Holes in line with each other in successive rows can provide improvements in spanwise averaged film cooling effectiveness of as much as 100% over the common staggered arrangement. This improvement is due to the interaction between coolant from rows one and two, which tends to provide complete coverage of the downstream surface when the rows are placed correctly with respect to each other.

Studies on Wake-Affected Heat Transfer Around the Circular Leading Edge of Blunt Body

Detailed measurements are performed about time-averaged beat transfer distributions around the leading edge of a blunt body which is affected by incoming periodic wakes from the upstream moving bars. The blunt body is a test model of a front portion of a turbine blade in gas turbines and consists of a semicircular cylindrical leading edge and a flat plate afterbody. A wide range of the steady and unsteady flow conditions are adopted as for the Reynolds number based on the diameter of the leading edge and the bar-passing Strouhal number. The measured heat transfer distributions indicate that the wakes passing over the leading edge cause significant increase in beat transfer before the separation and the higher Strouhal number results in higher heat transfer. From this experiment, a correlation for the heat transfer enhancement around the leading edge due to the periodic wakes is deduced as a function of the Stanton number and it is reviewed by comparison with the other experimental works.

Operating Experience and Economic Benefit of a 3-MW Gas Turbine in an Industrial Peak Shaving Application

In the late 1970’s, due to increasing electric energy costs and the potential for power interruption at Solar Turbines Incorporated’s Harbor Drive manufacturing facility, management evaluated several self-generating options available at the time. With large fluctuating loads and a very limited need for thermal energy, the appropriate solution was determined to be peak shaving. In 1980, a 2.5-MW dual fuel industrial gas turbine generator set was installed. Its intended operating cycle was during on-peak billing periods, 5 days a week throughout the year. Through August 31, 1993, the system has accumulated 22,743 hours of use and 3879 starts. Its overall start reliability has been 99.9% with an availability of 98.2%. Payback on the installation was in 4.2 years. It has continued to generate savings since installation, with net savings for 1992 alone exceeding $470,000. This paper highlights the key aspects of the economic methodology justifying installation of the peak shaving system, operating procedures, maintenance practices and system modifications put in place over the life of the installation.

Technical and Economic Evaluation of Nominal 280 MW Compressed Air Energy Storage Plant in Salt Dome

This paper summarizes the results of the technical and economic data of nominal 280 MW Compressed Air Energy Storage Plants (CAES) using caverns in salt domes located in southeastern parts of Mississippi for intermediate duty generation of 1,000 hours per year and peaking duty generation of 750 hours per year. The plants are assumed to operate 90% time on Natural Gas and 10% of the time on No. 2 distillate. A weekly cycle of 10 hours of generation and 12 hours of charging daily with 15 hours of weekend charging was the basis for the study. The study includes conceptual layout, optimization, detailed cost analyses, reliability and operation and maintenance of the Compressed Air Energy storage plant. The objective of the study is low capital cost of the CAES plant and optimum performance.

Advanced GT’s Call for Advanced CC’s (OR: the 4 S’s)

Four key parameters, the 4 S’s, determine the technoeconomical performance of the steam bottoming cycle to a given gasturbine: [S1], the temperature of the heat Source, [S2], the temperature of the heat Sink, [S3] cycle Structure and [S4] component Specifications. The first two are given by the gasturbine exhaust gas temperature (TEX) and ambient water/air temperatures respectively; the last two are designer’s choice but depend on economics: how much can you afford to pay for an extra kW? (parity factor or differential capital outlay). The paper analyses the effect of current trends in the first two S’s on the latter two: «S1», the higher TIT (turbine inlet temperature) of advanced GT’s generally leads to higher TEX, especially when coupled with Sequential Combustion; and [S2]«S2», the trend from fresh water cooling to cooling towers — and again from wet to dry types — due to environmental considerations and/or water shortages leads to higher condenser pressures. These trends change the economics of «S3», the structure (one-, two- or three-pressure, reheat, supercritical etc.); finally, macro-economical trends (fuel cost, cost of capital, more Independent Power Producers or IPP’s) determine «S4», equipment specifications (delta-T’s, delta-P’s, number of stages or exhaust flows etc.). In this written paper the authors report on their technoeconomical analysis; at the conference they will present hands-on solutions, optimized for ABB’s Type GT24 (60Hz, 165 MW) and GT26 (50 Hz, 240 MW) gasturbines. (Note that throughout the paper definite figures are only given for ABB gasturbines and steam turbines, as the authors cannot vouch for information published by other manufacturers or third parties).

Effect of Steam Injected Gas Turbines on the Unit Sizing of a Cogeneration Plant

The effect of installing steam injected gas turbines in a cogeneration plant is analyzed in the aspects of unit sizing and operational planning. An optimization method is used to determine the capacities of gas turbines and other auxiliary machinery in consideration of their operational strategies for variations of electricity and thermal energy demands. Through a numerical study on a plant for district hearing and cooling, it is clarified how the installation of steam injected gas turbines in place of simple cycle ones can improve the economic and energy saving properties. The influence of capital cost of steam injected gas turbines on the unit sizing and the above properties is also clarified.