Film cooling represents one of the few game-changing technologies that has allowed the achievement of today's high firing temperature, high-efficiency gas turbine engines. Over the last 30 years, only one major advancement has been realized in this technology, that being the incorporation of exit shaping to the film holes to result in lower momentum coolant injection jets with greater surface coverage. This review examines the origins of shaped film cooling and summarizes the extant literature knowledge concerning the performance of such film holes. A catalog of the current literature data is presented, showing the basic shaping geometries, parameter ranges, and types of data obtained. Specific discussions are provided for the flow field and aerodynamic losses of shaped film hole coolant injection. The major fundamental effects due to coolant-to-gas blowing ratio, compound angle injection, cooling hole entry flow character, and mainstream turbulence intensity are each reviewed with respect to the resulting adiabatic film effectiveness and heat transfer coefficients for shaped holes. A specific example of shaped film effectiveness is provided for a production turbine inlet vane with comparison to other data. Several recent unconventional forms of film hole shaping are also presented as a look to future potential improvements

A review of shaped hole turbine film-cooling technology

The durability of gas turbine engines is strongly dependent on the component temperatures. For the combustor and turbine airfoils and endwalls, film cooling is used extensively to reduce component temperatures. Film cooling is a cooling method used in virtually all of today's aircraft turbine engines and in many power-generation turbine engines and yet has very difficult phenomena to predict. The interaction of jets-in-crossflow, which is representative of film cooling, results in a shear layer that leads to mixing and a decay in the cooling performance along a surface. This interaction is highly dependent on the jet-to-crossflow mass and momentum flux ratios. Film-cooling performance is difficult to predict because of the inherent complex flowfields along the airfoil component surfaces in turbine engines. Film cooling is applied to nearly all of the external surfaces associated with the airfoils that are exposed to the hot combustion gasses such as the leading edges, main bodies, blade tips, and endwalls. In a review of the literature, it was found that there are strong effects of freestream turbulence, surface curvature, and hole shape on the performance of film cooling. Film cooling is reviewed through a discussion of the analyses methodologies, a physical description, and the various influences on film-cooling performance.

Gas Turbine Film Cooling

This study evaluates the impact of typical cooling hole shape variations on the thermal performance of fan-shaped film holes. A comprehensive set of experimental test cases featuring 16 different film-cooling configurations with different hole shapes have been investigated. The shape variations investigated include hole inlet-to-outlet area ratio, hole coverage ratio, hole pitch ratio, hole length, and hole orientation (compound) angle. Flow conditions applied cover a wide range of film blowing ratios M=0.5 to 2.5 at an engine-representative density ratio DR= 1.7. An infrared thermography data acquisition system is used for highly accurate and spatially resolved surface temperature mappings. Accurate local temperature data are achieved by an in situ calibration procedure with the help of thermocouples embedded in the test plate. Detailed film-cooling effectiveness distributions and discharge coefficients are used for evaluating the thermal performance of a row of fan-shaped film holes. An extensive variation of the main geometrical parameters describing a fan-shaped film-cooling hole is clone to cover a wide range of typical film-cooling applications in current gas turbine engines. Within the range investigated, laterally averaged film-cooling effectiveness was found to show only limited sensitivity from variations of the hole geometry parameters. This offers the potential to tailor the hole geometry according to needs beyond pure cooling performance, e.g., manufacturing facilitations.

Effect of Hole Geometry on the Thermal Performance of Fan-Shaped Film Cooling Holes

Methods and systems for low emission power generation in hydrocarbon recovery processes are provided. One system includes integrated pressure maintenance and miscible flood systems with low emission power generation. An alternative system provides for low emission power generation, carbon sequestration, enhanced oil recovery (EOR), or carbon dioxide sales using a hot gas expander and external combustor. Another alternative system provides for low emission power generation using a gas power turbine to compress air in the inlet compressor and generate power using hot carbon dioxide laden gas in the expander. Other efficiencies may be gained by incorporating heat cross-exchange, a desalination plant, co-generation, and other features.

Low emission power generation and hydrocarbon recovery systems and methods

Review on active thermal protection and its heat transfer for airbreathing hypersonic vehicles

A comprehensive set of generic experiments has been conducted to investigate the effect of elevated free-stream turbulence on film cooling performance of shaped holes. A row of three cylindrical holes as a reference case, and two rows of holes with expanded exits, a fanshaped (expanded in lateral direction), and a laidback fanshaped hole (expanded in lateral and streamwise direction) have been employed. With an external (hot gas) Mach number of Ma m =0.3 operating conditions are varied in terms of free-stream turbulence intensity (up to 11%), integral length scale at constant turbulence intensity (up to 3.5 hole inlet diameters), and blowing ratio. The temperature ratio is fixed at 0.59 leading to an enginelike density ratio of 1.7. The results indicate that shaped and cylindrical holes exhibit very different reactions to elevated free-stream turbulence levels. For cylindrical holes film cooling effectiveness is reduced with increased turbulence level at low blowing ratios whereas a small gain in effectiveness can be observed at high blowing ratios. For shaped holes, increased turbulence intensity is detrimental even for the largest blowing ratio (M=2.5). In comparison to the impact of turbulence intensity the effect of varying the integral length scale is found to be of minor importance. Finally, the effect of elevated free-stream turbulence in terms of heat transfer coefficients was found to be much more pronounced for the shaped holes.

Free-Stream Turbulence Effects on Film Cooling With Shaped Holes

The flow conditions at both, the cooling hole exit as well as the cooling hole entrance affect in a very different way the cooling performance downstream of cylindrical and fan-shaped holes. The consequences of a change in a flow parameter very obviously depend on the respective hole geometry. To gain an as complete as possible view of the specific effects of varying operating conditions and hence an enhanced understanding of the dominating mechanisms, a variation of the hole geometry is imperative. The expansion angle of the diffuser, the inclination angle of the hole, and the length of the cylindrical part at the hole entrance are considered to be the most important geometric parameters of diffuser holes. The effect of a change of exactly these parameters on the film cooling performance will be analyzed. For a better assessment of the characteristic effects associated with contouring of the hole, every dif-fuser hole is compared to an adequate cylindrical hole. The comparison will be performed by means of discharge coefficients and local and laterally averaged adiabatic film cooling effectiveness and heat transfer coefficients derived from experiments.Copyright © 2008 by ASME

Effect of Geometry Variations on the Cooling Performance of Fan-Shaped Cooling Holes

The invention relates to an arrangement for recirculating and cooling exhaust gas of an internal combustion engine (2), in particular of a diesel engine in a motor vehicle, wherein the internal combustion engine (2) has an exhaust line (3) with an exhaust gas turbine (6) and an intake line (4) with a charge air compressor (8) which is driven by the exhaust gas turbine (6), wherein an extraction point (1 1 ) for branching off an exhaust gas recirculation line (EGR line 5) is arranged downstream of the turbine (6) and a recirculation point (12) for recirculating the EGR line (5) is arranged upstream of the compressor (8), and wherein at least one exhaust gas heat exchanger (13) and an EGR valve (14) are arranged in the EGR line (5). It is proposed according to the invention that a charge air throttle element (17) is arranged in the intake line (4) and that the EGR valve (14), the recirculation point (12) and the throttle element (17) are formed as an integrated component (19).

Arrangement for recirculating and cooling exhaust gas of an internal combustion engine

From literature and our own studies it is known that the effects of hot gas cross-flow and in particular the turbulence of the hot gas flow highly influence the spreading of the coolant in the near hole vicinity. Moreover, the velocity of the hot gas flow expressed by a hot gas Mach number obviously plays a much more important role in case of diffuser holes than with simple cylindrical holes. To realize a certain blowing rate, a higher pressure ratio needs to be established in case of higher Mach numbers. This in turn may strongly affect the diffusion process in the expanded portion of a fan-shaped cooling hole. The said effects will be discussed in great detail. The effects of free-stream Mach number and free-stream turbulence, including turbulence intensity, integral length scale, and periodic unsteady wake flow will be considered. The comparative study is performed by means of discharge coefficients and by local and laterally averaged adiabatic film cooling effectiveness and heat transfer coefficients. Both cooling holes have a length-to-diameter ratio of 6 and an inclination angle of 30°. The fan-shaped hole has an expansion angle of 14°. The effect of the coolant cross-flow at the hole entrance is not considered in this study, i.e. plenum conditions exist at the hole entrance.Copyright © 2008 by ASME

Free-Stream Effects on the Cooling Performance of Cylindrical and Fan-Shaped Cooling Holes

Discharge coefficients of three film-cooling hole geometries are presented over a wide range of engine like conditions. The hole geometries comprise a cylindrical hole and two holes with a diffuser-shaped exit portion (a fanshaped and a laidback fanshaped hole). For all three hole geometries the hole axis was inclined 30 deg with respect to the direction of the external (hot gas) flow. The flow conditions considered were the hot gas crossflow Mach number (up to 0.6), the coolant crossflow Mach number (up to 0.6) and the pressure ratio across the hole (up to 2). The effect of internal crossflow approach direction, perpendicular or parallel to the main flow direction, is particularly addressed in the present study. Comparison is made of the results for a parallel and perpendicular orientation, showing that the coolant crossflow orientation has a strong impact on the discharge behavior of the different hole geometries. The discharge coefficients were found to strongly depend on both hole geometry and crossflow conditions. Furthermore, the effects of internal and external crossflow on the discharge coefficients were described by means of correlations used to derive a predicting scheme for discharge coefficients. A comparison between predictions and measurements reveals the capability of themore » method proposed.« less

Christian Saumweber

Papers

Free-Stream Turbulence Effects on Film Cooling With Shaped Holes

Effect of Geometry Variations on the Cooling Performance of Fan-Shaped Cooling Holes

Arrangement for recirculating and cooling exhaust gas of an internal combustion engine

Free-Stream Effects on the Cooling Performance of Cylindrical and Fan-Shaped Cooling Holes

Effect of Internal Coolant Crossflow Orientation on the Discharge Coefficient of Shaped Film-Cooling Holes