Air-cooled Blades Research Articles

Stress intensity factors analysis for crack around film cooling holes in Ni-based single crystal with contour integral method

PurposeThis paper aims to provide SIF calculation method for engineering application.Design/methodology/approachIn this paper, the stress intensity factors (SIFs) calculation method is applied to the anisotropic Ni-based single crystal film cooling holes (FCHs) structure.FindingsBased on contour integral, the anisotropic SIFs analysis finite element method (FEM) in Ni-based single crystal is proposed. The applicability and mesh independence of the method is assessed by comparing the calculated SIFs using mode of plate with an edge crack. Anisotropic SIFs can be calculated with excellent accuracy using the finite element contour integral approach. Then, the effect of crystal orientation and FCHs interference on the anisotropic SIFs is clarified. The SIFs of FCH edge crack in the [011] orientated Ni-based single crystal increases faster than the other two orientations. And the SIF of horizontal interference FCHs edge crack is also larger than that of the inclined interference one.Originality/valueThe SIFs of the FCH edge crack in the turbine air-cooled blade are innovatively computed using the sub-model method. Both the Mode I and II SIFs of FCHs edge crack in blade increase with crack growing.

Numerical Study on Cooling Performance of a Steam-Cooled Blade Based on Response Surface Method

In order to investigate the cooling mechanism of the turbine blade and to enrich and supplement the experimental study of the blade, a numerical study of a steam-cooled blade with five cooling channels was carried out based on the response surface model. The surface cooling efficiency and dimensionless temperature distribution of the steam-cooled blade were obtained with different mainstream inlet temperature, outlet pressure, pressure ratio of inlet to outlet, temperature ratio and flow ratio of steam to mainstream by using the flow-solid coupling numerical method. The influence of the working parameters on the cooling performance of air-cooled blade and steam-cooled blade, including the average cooling efficiency, temperature non-uniformity, and average dimensionless temperature, was comparatively investigated; the correlation equation of the working parameters on the cooling performance of the steam-cooled blade was obtained. The results show that the influence of mainstream inlet temperature and outlet pressure on the cooling performance of the steam-cooled blade is not significant; the cooling efficiency of the steam-cooled blade increases by 5.92%, 7.35% and 26.51% respectively as the mainstream inlet to outlet pressure ratio, the temperature ratio and the flow ratio of steam to mainstream increase; the dimensionless temperature increases by 3.74% as the temperature ratio increases and decreases by 0.93% and 4.09% as mainstream inlet to outlet pressure ratio and flow ratio increase; the temperature non-uniformity decreases by 4.09% and 30.08% respectively, as the mainstream inlet to outlet pressure ratio and temperature ratio increase and increases by 37.99% as the flow ratio increases; the effect of working parameters on air-cooled blade and steam-cooled blade is the same, but the steam-cooled blade has 14.06–17.81% higher cooling efficiency, 18.47–29.01% higher temperature non-uniformity and 1.86–2.58% lower dimensionless temperature compared to the air-cooled blade under the same working parameters; the correlation equation obtained by fitting the response surface model has higher accuracy.

Fast prediction and sensitivity analysis of gas turbine cooling performance using supervised learning approaches

Fast prediction tools for turbine cooling performance have been demanded by industry for decades to support the iterative design process and the comprehensive response analysis and sensitivity analysis. This study aimed at establishing a comprehensively evaluated deep learning-based data modeling tool for the design of gas turbine blades. The geometry focused on was an air-cooled blade with ribbed channels and film cooling holes, which deformed globally within a wide range of geometrical parameters. A Conditional Generative Adversarial Network was constructed to model the distribution of the internal heat transfer coefficient and the external adiabatic film cooling effectiveness under any in-range geometry and boundary conditions. A series of single-point tests, response analysis, and sensitivity analysis were conducted using the trained model and compared with the Computational Fluid Dynamics results to comprehensively evaluate the model performance. The results showed that the model provided accurate predictions for cooling performance distributions, and also possessed the ability to obtain reasonable response and sensitivity. This study was a successful case of using deep learning approaches to model complex heat transfer problems. For practical applications, the proposed model could serve as an aid to designers to reduce the design burden.

Thermal Analysis of a Cooled Turbine Blade

Using Computational Fluid Dynamic (CFD), a gas turbine with an air-cooled blade was analyzed thermally. In terms of design, the domain was divided into three regions. The first region is the blade to blade passage (external flow) governed by a quasi-3-D Euler equation in a conservative form. Mac-Cormack’s technique algorithm based on the finite differences, was used for this region. The second region involves the coolant passage (internal flow). This region involved the use of 2-D axi-symmetric Navier Stokes equations (Finite volume with staggered grids). A 3-D Laplace heat transfer equation was applied for the third region which involves a blade metal, where the solution algorithm was based on the finite difference technique. Consequently, to achieve temperature distribution through blade metal, the three regions have been coupled via the external and internal boundaries. Six different cases were examined in same blade geometry. The effect of gas heat transfer coefficient was analyzed in cases 1 and 2. With regards to cases 3, 4, 5, and 6, gas and coolant temperatures were changed. The computational results showed that the blade surface (metal) temperature is cooler than the surrounding gases (external hot gases) by about 100-500 °C, depending on boundary condition. An increase in gas temperature by 100 °C resulted in 50-100 °C increase in metal temperature, while, an increase in coolant temperature by 100 °C resulted in an average 50 °C increase in blade temperature. The results also show a temperature difference in blade metal of 250 - 450 °C between the leading and trailing edges.

Thermodynamic simulation of two-shaft gas turbine to study invasive weeds optimization and Min-Max controller strategies considering air-cooled blades

Proper estimation of dynamic behavior of gas turbines is essential to control of these systems. This paper investigates a thermodynamic model of two-shaft gas turbines based on thermodynamic principles, component maps and matching equations considering the blade air cooling effects. An iterative method is applied to analyze design point condition and also to evaluate steady states and transient modes. An open loop control procedure is applied to regulate inlet guide vane position. An industrial min-max control strategy is also adopted to adjust proper fuel flow rate value considering physical limits. Moreover, an invasive weed optimization (IWO) algorithm as a proper optimization method is used to find out the optimal gain values of control structure. Finally, the results are analyzed and performance of control structure has been studied in part load conditions.

Aluminide Coating Formation on Internal Passages of GTD-111 Superalloy by Slurry Technique

The diffusion aluminide coatings are widely used in the air-cooling passages to protect their surfaces against high temperature corrosion. In this study plain and Si-modified aluminide coatings were applied by slurry technique on internal surfaces of Ni-base GTD-111 superalloy cylindrical specimens derived from a gas turbine air-cooled blade. The slurries containing Al or Al plus Si powders were applied on internal surfaces by injection method. Then, the samples were heated to high temperature (800-1000°C) to form the coatings. Optical, SEM-EDS, and XRD were utilized for characterizing microstructures and phase compositions of the coatings. The thicknesses of applied coatings on internal surfaces were in the range of 30-50 μm that meets specifications for diffusion coatings in such application (i.e. 25-756m). The examinations demonstrated that both coating types were contained β-NiAl phase as the matrix. The uniformities of coatings applied on different surface positions of passageway were determined. In addition, the effects of time and temperature of coating process as well as mass of dried slurry on the coating thickness were also discussed.

Creep damage evolution in a modeling specimen of nickel-based single crystal superalloys air-cooled blades

Plate specimens both with holes and without holes were used to model air-cooled turbine blades. Experimental study on the creep behavior of a second generation nickel-based single crystal has been performed at 980 °C with these modeling specimens in two crystallographic orientations [0 0 1] and [1 1 1]. The results of creep tests show that crystallographic orientations and cooling holes have remarkable influence on the stress rupture behavior. The scanning electron microscopy (SEM) observation on the fractured surface shows that the cavitation-controlled damage is the main mechanism inducing fracture. So the finite element analysis (FEA) with a modified form of Kachanov–Rabotnov damage law was carried out to simulate the damage evolution in modeling specimen with cooling holes in crystallographic orientation [0 0 1]. The FEM results reveal that the existence of cooling holes causes the stress and strain concentrations near the holes. The creep damage is localized in the cooling holes region, where the fracture will happen easily. The numerical result is coincident with the fracture appearance of the specimen.

Analytical Blade Row Cooling Model for Innovative Gas Turbine Cycle Evaluations Supported by Semi-Empirical Air-Cooled Blade Data

With the objective of performing reliable innovative gas turbine cycle calculations, a new procedure aimed at evaluating blade cooling performance is presented. This complete analytical (convective and film) blade cooling modeling provides the coolant mass flow and pressure loss estimation, and is a useful tool in the field of innovative gas turbine cycle analysis, mainly when alternative fluids are considered. In this case, in fact, the conventional semi-empirical data based on the use of air as traditional coolant and working media are no longer suitable. So the analytical approach represents a way of properly investigating alternative cooling methods and fluids. In the presented analysis the effects of internal blade geometry on cooling performance are summarized by the Z parameter, which also highly affects the coolant flow pressure losses. Since existing technology represents a natural starting point for the assessment of Z, the model is able to automatically estimate a proper value relying only on available semi-empirical data which were established for air-cooled gas turbine blades. When alternative fluids are considered, the same estimated value of Z is still maintained for the calculation, with the result of investigating the performance of existing blade technology for novel operational conditions. This represents an example of how the analytical approach, supported by conventional air-cooled blade semi-empirical data, appears as an innovative tool in the analysis of novel gas turbine cycles. In fact, the simulation results for the cooled blade were easily employed on the whole system level (gas turbine).

Heat transfer technology for internal passages of air-cooled blades for heavy-duty gas turbines.

The present review paper, although far from being complete, aims to give an overview about the present state of the art in the field of heat transfer technology for internal cooling of gas turbine blades. After showing some typical modern cooled blades, the different methods to enhance heat transfer in the internal passages of air-cooled blades are discussed. The complicated flows occurring in bends are described in detail, because of their increasing importance for modern cooling designs. A short review about testing of cooling design elements is given, showing the interaction of the different cooling features as well. The special focus of the present review has been put on the cooling of blades for heavy-duty gas turbines, which show several differences compared to aero-engine blades.

The Advanced Cooling Technology for the 1500°C Class Gas Turbines: Steam-Cooled Vanes and Air-Cooled Blades

It is very essential to raise the thermal efficiency of combined cycle plants from the viewpoint of energy saving and environmental protection. Tohoku Electric Power Co., Inc., and Toshiba Corporation in Japan have jointly studied the next generation of combined cycle systems using 1500°C class gas turbine. A promising cooling technology for the vanes using steam was developed. The blades are cooled by air, adopting the impingement cooling, film cooling, and so on. The cooling effectiveness was confirmed both for the vanes and the blades using a hot wind tunnel. This paper describes the design features of the vanes and the blades, and the results of the verification tests using the hot wind tunnel.

Analytical and experimental investigations of the vibrations of a hollow blade model of turbines

The practice of using air-cooled blades for the increased efficiency of turbine stage is a recent feature with advanced aero-engines. The objective of the present paper is to describe the results of numerical and experimental investigation of the dynamical behaviour of hollow cross-sectioned blades. The analytical method consists in modelling the blades by means of a finite-element method to determine the natural frequencies and normal modes of a hollow cross-sectioned blade model. Numerical results are compared with experimental values obtained from holographic tests.

Environmental Effects on the High-Temperature Corrosion of Superalloys in Present and Future Gas Turbines

Effects of temperature and contaminant levels on the high-temperature corrosion of superalloys used in gas turbines were investigated using pressurized passages which simulate the operating conditions of present-day gas turbines. The alloys were tested in a cooled configuration realistically simulating the air-cooled vanes and blades of a gas turbine. Conclusions are drawn as to the permissible level of contaminants and the effect of metal cooling on high-temperature corrosion. It is shown that the surface temperature of a blade or vane rather than the gas-stream temperature is the critical factor in determining the amount of attack to be expected at a given contaminant level and the amount of attack is an exponential function of this temperature. Furthermore, in a dynamic-type test no decrease in corrosion rate is noted at higher temperatures. It was concluded that the use of a 5 ppm Na/2 ppm V fuel would result in an excessive amount of attack with a metal surface temperature of 1500 deg F.

Paper 21: Some Aspects of Research at the National Gas Turbine Establishment on Internally Air-Cooled Turbine Blades

This paper describes some of the results obtained from a series of experiments on internally air-cooled turbine nozzle and rotor blades. These were formed by an extrusion process and had, respectively, sixteen and thirteen cooling passages of approximately elliptical cross-section. The cooling characteristics of both types of blade were measured in an experimental high-temperature turbine and further experiments were conducted in cascade tunnels. Some of the cascade experiments on the rotor blade were conducted at comparatively high Reynolds numbers and showed, in accordance with predictions, the extent to which chordwise non-uniformities in blade temperature become larger as Reynolds number is increased.Other experiments were conducted with the turbine to determine the effects on aerodynamic performance of discharging spent cooling air into the main gas stream. The results showed good agreement with predictions based on a simple flow model, and in particular indicated that flow separation, with its associated losses, did not occur. Finally the results of an endurance test are presented, together with a brief description of the way in which thermal plus centrifugal stress patterns can be redistributed by creep in non-uniformly cooled blades.Brief mention is made of those fields of research which require further attention, namely an investigation of the factors governing the local values of heat-transfer coefficient on the external surface of turbine blades and the testing of the assumptions used in calculating stresses in cooled blades.

An Experimental Single-stage Air-cooled Turbine: Part I. Design of the Turbine and Manufacture of Some Experimental Internally Cooled Nozzles and Blades

To facilitate future development of the cooled gas-turbine more test information is needed on the effectiveness of cooling in an actual turbine operating at high gas-temperatures. Part I of this paper deals with some design aspects of a single-stage experimental turbine built to enable an experimental investigation to be carried out on the air cooling of nozzles and blades. The turbine, built for operation at high gas-temperatures, was fitted with internally air-cooled blades having a large number of small cooling passages running the whole length of the blades. A description is given of the pressed powder technique used to introduce the small passages in blocks of heat resisting material from which the blades could be machined. Mention is made of some of the difficulties encountered in this method of manufacture and also of the need for careful consideration of suitable methods of disposal of the cooling air when internally cooled nozzles and blades of this form are used.

Heat Flow in the Gas Turbine

In this lecture experimental data are presented on turbine-blade heat transfer, which is an important factor in the design of high-temperature turbines. Blade stagger has a considerable effect on blade Nusselt number and on the rate of variation of Nusselt number with Reynolds number. For nozzleblades, theoretical and experimental values of the Nusselt number agree fairly well. A method is proposed for the approximate estimation of Nusselt number by Keynolds analogy. The experimental data are used in the calculation of heat flow in blades cooled at the root, and in internally air-cooled blades. Other methods of cooling have been proposed, including partial admission of cold air or liquid through the nozzle ring; the theoretically advantageous “sweat” cooling by exuding coolant air through a porous skin, or the injection of coolant air through slits; root cooling might include modifications, such as effective increase of blade conductivity by tubes of liquid embedded in the blade or reduction, by an insulating layer, of the amount of heat conducted to the blades; internal liquid cooling by forced or convective circulation is a possible alternative to internal air-cooling. Some of these methods have been successfully used-for example, internal air-cooling of hollow blades in German jet engines; internal liquid-cooling in an experimental German turbine; and a certain degree of “root” cooling in British aircraft turbines. Theoretical analysis of the problem of turbine cooling has been rendered difficult, in the past, by absence of data on blade heat-transfer coefficients. For root-cooled blades of heat-resisting alloy the cooled region is small, but it would be satisfactorily large for nozzle blades of high-conductivity material. Internal air-cooling needs only small quantities of coolant, provided a high internal blade conductance is achieved by subdividing the internal flow passage. The effectiveness of root-cooling diminishes with increase of scale; on the other hand, the relative cooling air quantity necessary to cool a blade internally diminishes with increase of scale. The heat exchanger is a bulky and expensive component of most “plant” gas-turbine systems, and with the aim of size reduction “regenerative” type exchangers have been investigated for some time as an alternative to the bulky recuperative type. The lecture deals with the advantage in bulk of the regenerator, and gives some relevant data on heat-transfer in laminar flow