Prediction of Film Cooling Effectiveness and Heat Transfer due to Streamwise and Compound Angle Injection on Flat Surfaces

The distributed Yavuzkurt injection model is extended to predict the effectiveness and heat transfer coefficients for film cooling injection from a single row of holes, aligned both along the direction of the freestream and at an angle with it. The injection angles were 24° and 35°. The compound angles considered were 50.5° and 60°. The Yavuzkurt film cooling model is used in conjunction with a one-equation model to yield the effectiveness and heat transfer predictions. The density ratios considered were 1.6 and 0.95 for the effectiveness predictions and 1.0 and 0.95 for the heat transfer predictions. For the effectiveness predictions, the blowing ratios range from 0.5 to 2.5, and the momentum flux ratios from 0.16 until 3.9. The hole spacings were 3, 6, and 7.8 hole diameters. The Yavuzkurt model constants are seen to be definitely correlated with the momentum flux ratio. Correlations for the model constants are obtained in terms of the momentum flux ratio. For the heat transfer predictions, the blowing ratios ranged from 0.4 to 2.0, and the momentum flux ratios from 0.16 to 3.9. The spacing between the holes was 3, 6, and 7.8 hole diameters. The matching between the effectiveness correlations and the heat transfer predictions is done on the basis of the momentum flux ratio. Results indicate that the Yavuzkurt model predictions are best for the in-line round holes. Heat transfer predictions are close to the experimental results for lower blowing ratios, until the ratio exceeds 1. For higher blowing ratios, the predictions, though less accurate, follow the experimental trends.

Prediction of Unshrouded Rotor Blade Tip Heat Transfer

The rate of heat transfer on the tip of a turbine rotor blade and on the blade surface in the vicinity of the tip, was successfully predicted. The computations were performed with a multiblock computer code which solves the Reynolds Averaged Navier-Stokes equations using an efficient multigrid method. The case considered for the present calculations was the SSME (Space Shuttle Main Engine) high pressure fuel side turbine. The predictions of the blade tip heat transfer agreed reasonably well with the experimental measurements using the present level of grid refinement. On the tip surface, regions with high rate of heat transfer was found to exist close to the pressure side and suction side edges. Enhancement of the heat transfer was also observed on the blade surface near the tip. Further comparison of the predictions was performed with results obtained from correlations based on fully developed channel flow.

Qualifying Combustion Turbines for Inlet Air Cooling Capacity Enhancement

The relative potential of combustion turbines for capacity enhancement by inlet air cooling was examined. A new inlet air cooling effectiveness factor was developed for this purpose. It was found that combustion turbines vary significantly in terms of inlet air cooling effectiveness. Of the combustion turbines presented in this paper, the best-ranked combustion turbine had an effectiveness factor of 0.48 while the lowest-ranked turbine had a factor of 1.35. No strong correlation was found between the inlet air cooling effectiveness factor and the ISO turbine performance parameters of heat rate, pressure ratio, exhaust temperature, and the ratio of inlet air mass flow rate to power output.

Reheat and Regenerative Gas Turbines for Feed Water Repowering of Steam Power Plant

This study is concerned with the repowering of existing steam power plants (SPP) by gas turbine (GT) units. The energy integration between SPP and GT is analyzed taking into particular account the employment of simple and complex cycle gas turbines. With regard to this, three different gas turbine has been considered: simple Brayton cycle, regenerative cycle and reheat cycle. Each of these cycles has been considered for feed water repowering of three different existing steam power plants. Moreover, the energy integration between the above plants has been analyzed taking into account three different assumptions for the SPP off-design conditions. In particular it has been established to keep the nominal value for steam turbine power output or for steam flow-rate at the steam turbine inlet or, finally, for steam flow-rate in the condenser. The numerical analysis has been carried out by the employment of numerical models regarding SPP and GT, developed by the authors. These models have been here properly connected to evaluate the performance of the repowered plants. The results of the investigation have revealed the interest of considering the use of complex cycle gas turbines, especially reheat cycles, for the feed water repowering of steam power plants. It should be taken into account that these energy advantages are determined by a repowering solution, i.e. feed water repowering which, although it is attractive for its simplicity, do not generally allows, with Brayton cycle, a better exploitation of the energy system integration in comparison with other repowering solutions. Besides these energy considerations, an analysis on the effects induced by repowering in the working parameters of existing components is also explained.

Design, Part Load and Transient Operation of Combined Cycle Plants With Water Flashing

The last decade has seen remarkable improvement in gas turbine based power generation technologies, with the increasing use of natural gas-fuelled combined cycle units in various regions of the world. The struggle for efficiency has produced highly complex combined cycle schemes based on heat recovery steam generators with multiple pressure levels and possibly reheat. As ever, the evolution of these schemes is the result of a technico-economic balance between the improvement in performance and the increased costs resulting from a more complex system. This paper looks from the thermodynamic point of view at some simplified combined cycle schemes based on the concept of water flashing. In such systems, high pressure saturated water is taken off the high pressure drum and flashed into a tank. The vapour phase is expanded as low pressure saturated steam or returned to the heat recovery steam generator for superheating, whilst the liquid phase is recirculated through the economizer. With only one drum and three or four heat exchangers in the boiler as in single pressure level systems, the plant might have a performance similar to that of a more complex dual pressure level system. Various configurations with flash tanks are studied based on commercially available 150 MW-class E-technology gas turbines and compared with classical multiple pressure level combined cycles. Reheat units are covered, both with flash tanks and as genuine combined cycles for comparison purposes. The design implications for the heat recovery steam generator in terms of heat transfer surfaces are emphasized. Off-design considerations are also covered for the flash based schemes, as well as transient performances of these schemes, because the simplicity of the flash systems compared to normal combined cycles significantly affects the dynamic behaviour of the plant.

The Effect of a Constant Volume Recuperator on Brayton Cycle Efficiency and Equipment Cost

The purpose of this analysis is to predict the thermodynamic and design effects of a constant volume recuperator in a Brayton cycle. First Law and Second Law energy efficiencies were computed. Constant volume recuperators produce higher pressure, denser air for admission into the combustion chamber and turbine. Greater pressure and density in the combustion chamber results in higher fuel evaporation and combustion rates. The higher system pressure across the turbine also generates a slightly higher turbine efficiency. Furthermore, the increased density permits a smaller turbine in the first, hottest and most expensive stages. A novel constant volume, constant flow recuperator is described.

Energy Industry Changes: The Role of Advanced Combustion Turbine Technology

The Electric Power industry is in transition — where meeting the customer’s individual variable power needs will count more than just providing gross kilowatt hours production or some thoretical “generation mix” criteria. A number of advanced combustion turbine power plants are being developed for this market: the Intercooled Aeroderivative, the Humid Air Turbine/Cascaded Humidified Advanced Turbine, and the Compressed Air Storage with Humidification plants. Combustion turbines for the distributed generation application are also being emphasized. This success of all combustion turbine plants depend on meeting and maintaining the goals of high levels of durability, reliability, and availability. A number of technologies which EPRI has successfully applied that have materially assisted in meeting these goals are outlined.

Film Cooling From Spanwise Oriented Holes in Two Staggered Rows

Adiabatic effectiveness and iso-energetic heat transfer coefficients are presented from measurements downstream of film-cooling holes inclined at 30 degrees with respect to the test surface in spanwise/normal planes. With this configuration, holes are spaced 3d apart in the spanwise direction and 4d in the streamwise direction in two staggered rows. Results are presented for an injectant to freestream density ratio near 1.0, and injection blowing ratios from 0.5 to 1.5. Spanwise-averaged adiabatic effectiveness values downstream of the spanwise/normal plane holes are significantly higher than values measured downstream of simple angle holes for x/d<25–70 (depending on blowing ratio) when compared for the same normalized streamwise location, blowing ratio, and spanwise and streamwise hole spacings. Differences are principally due to different coalescence of injectant accumulations from the two different rows of holes, as well as significantly different lift-off dependence on momentum flux ratio. Spanwise-averaged iso-energetic Stanton number ratios are somewhat higher than ones measured downstream of other simple and compound angle configurations studied. Values range between 1.0 and 1.41, increase with blowing ratio at each streamwise station, and show little variation with streamwise location for each value of blowing ratio tested.

The Effect of Periodic Wake Passing on Film Effectiveness of Discrete Cooling Holes Around the Leading Edge of a Blunt Body

Detailed studies are conducted on film effectiveness of discrete cooling holes around the leading edge of a blunt body that is subjected to periodically incoming wakes as well as free-stream turbulence with various levels of intensity. The cooling holes have a configuration similar to that of typical turbine blades except for the spanwise inclination angle. Secondary air is heated so that the temperature difference between the mainstream and secondary air is about 20K. In this case, air density ratio of the mainstream and secondary air becomes less than unity, therefore the flow condition encountered in an actual aero-engine can not be simulated in terms of the density ratio. A spoke-wheel type wake generator is used in this study. In addition, three types of turbulence grids are used to elevate the free-stream turbulence intensity. We adopt three blowing ratios of the secondary air to the mainstream. For each of the blowing ratios, wall temperature around the surface of the test model are measured by thermocouples situated inside the model. The temperature is visualized using liquid crystals in order to obtain qualitative information of film effectiveness distribution.

Turbulent Transport Measurements in a Heated Boundary Layer: Combined Effects of Free-Stream Turbulence and Removal of Concave Curvature

Turbulence measurements for both momentum and heat transport are taken in a boundary layer over a flat, recovery wall downstream of a concave wall (R=0.97m). The boundary layer appears turbulent from the beginning of the concave wall and grows over the test wall with negligible streamwise acceleration. The strength of curvature at the bend exit, δ99.5/R, is 0.04. The free-stream turbulence intensity is ∼8% at the beginning of the curve and is nearly uniform at ∼4.5% throughout the recovery wall. Comparisons are made with data taken in an earlier study, in the same test facility, but with a low free-stream turbulence intensity (−0.6%). Results show that on the recovery wall, elevated free-stream turbulence intensity enhances turbulent transport quantities such as -uv¯ and vt¯ in most of the outer part of the boundary layer, but near-wall values of vt¯ remain unaffected. This is in contrast to near-wall vt¯ values within the curve which decrease when free-stream turbulence is increased. At the bend exit, decreases of -uv¯ and vt¯ due to removal of curvature become more profound when free-stream turbulence intensity is elevated, compared to low-TI behavior. Measurements in the core of the flow indicate that the high levels of cross transport of momentum over the upstream concave wall cease when curvature is removed. Other results show that turbulent Prandtl numbers over the recovery wall are reduced to −0.9 when free-stream turbulence intensity is elevated, consistent with the rise in Stanton numbers over the recovery wall.