Cooled Turbine Blade Research Articles

The industrialization of additive manufacturing

AbstractOur world is constantly facing a wide variety of social challenges — currently, issues such as climate change, security, demographic change, and resource conservation are of significant importance and show an acute need for action. Among other things, disruptive technologies are needed to tackle such problems. Additive manufacturing (AM) is regarded as the ‘game changer/paradigm shift’ technology for the digital, automated production of the future — as the key enabler of ‘Production 2.0’. This sustainable and resilient technology enables new paths to innovative solutions across all industries through a high degree of individualization (mass customization) and great design freedom (‘manufacture for design’ instead of ‘design for manufacture‘). For example, internally cooled turbine blades for H2‐capable gas turbines, lightweight structures for more efficient aircraft or patient‐specific implants are only made possible by AM. In this way, AM makes an important contribution to solving the social challenges mentioned above now it is necessary to transfer this technology to board industrial use.

Experimental Investigation of the Sensitivity of Forced Response to Cold Streaks in an Axial Turbine

In turbomachinery, geometric variances of the blades, due to manufacturing tolerances, deterioration over a lifetime, or blade repair, can influence overall aerodynamic performance as well as aeroelastic behaviour. In cooled turbine blades, such deviations may lead to streaks of high or low temperature. It has already been shown that hot streaks from the combustors lead to inhomogeneity in the flow path, resulting in increased blade dynamic stress. However, not only hot streaks but also cold streaks occur in modern aircraft engines due to deterioration-induced widening of cooling holes. This work investigates this effect in an experimental setup of a five-stage axial turbine. Cooling air is injected through the vane row of the fourth stage at midspan, and the vibration amplitudes of the blades in rotor stage five are measured with a tip-timing system. The highest injected mass flow rate is 2% of the total mass flow rate for a low-load operating point. The global turbine parameters change between the reference case without cooling air and the cold streak case. This change in operating conditions is compensated such that the corrected operating point is held constant throughout the measurements. It is shown that the cold streak is deflected in the direction of the hub and detected at 40% channel height behind the stator vane of the fifth stage. The averaged vibration amplitude over all blades increases by 20% for the cold streak case compared to the reference during low-load operating of the axial turbine. For operating points with higher loads, however, no increase in averaged vibration amplitude exceeding the measurement uncertainties is observed because the relative cooling mass flow rate is too low. It is shown that the cold streak only influences the pressure side and leads to a widening of the wake deficit. This is identified as the reason for the increased forcing on the blade. The conclusion is that an accurate prediction of the blade’s lifetime requires consideration of the cooling air within the design process and estimation of changes in cooling air mass flow rate throughout the blade’s lifetime.

Multidisciplinary Design Optimization of Cooling Turbine Blade: An Integrated Approach with R/ICSM

This paper presents an efficient integrated multidisciplinary design optimization method for shaping a high-pressure cooling turbine blade in aero engines. This approach utilizes a novel regression/interpolation combination surrogate model (R/ICSM), facilitating comprehensive design optimization through collaborative coupling feature parameterization modeling and numerical simulation analysis across various disciplines. The optimized blade adjusts the load distribution on its surface, effectively eliminating flow separation at the tip and trailing edge. Notably, the optimized blade achieves a 0.69% increase in isentropic efficiency while satisfying aerodynamic, strength, and structural constraints. This highlights the effectiveness and progressiveness of the multidisciplinary design optimization method for a cooling turbine blade based on the R/ICSM in enhancing overall performance. It offers a novel and feasible approach for turbine blade design optimization and provides valuable insights for future research and applications.

Effects of temperature gradients on thermomechanical fatigue of nickel-based superalloy

Temperature-gradient-mechanical fatigue (TGMF) is a significant concern in internal cooling turbine blades. In the present study, the through-thickness temperature gradient was determined by the inverse heat conduction method and investigated in TGMF. Using the continuum damage mechanics, the environmental impact was identified as the primary contributor to the in-phase TGMF damage. A damage accumulation model encompassing fatigue, creep and environmental impact was established and provided satisfactory accuracy in TGMF life assessments. The main conclusion is that temperature gradients do not change the fracture mode but significantly increase stress levels by at least 20%, accelerating oxidation damage and resulting in a TGMF life ca. 10 times shorter than that of TMF.

Heat and Flow Characteristics of Aerofoil-Shaped Fins on a Curved Target Surface in a Confined Channel for an Impinging Jet Array

The main purpose of this investigation was to explore the heat transfer and flow characteristics of aero-foil-shaped fins combined with extended jet holes, specifically focusing on their feasibility in cooling turbine blades. In this study, a comprehensive investigation was carried out by applying impinging jet array cooling (IJAC) on a semi-circular curved surface, which was roughened using aerofoil-shaped fins. Numerical computations were conducted under three different Reynolds numbers (Re) ranging from 5000 to 25,000, while nozzle-to-target surface spacings (S/d) ranged from 0.5 to 8.0. Furthermore, an assessment was made of the impact of different fin arrangements, single-row (L1), double-row (L2), and triple-row (L3), on convective heat transfer. Detailed examinations were performed on area-averaged and local Nusselt (Nu) numbers, flow properties, and the thermal performance criterion (TPC) on finned and smooth target surfaces. The study’s results revealed that the use of aerofoil-shaped fins and the reduction in S/d, along with surface roughening, led to significant increases in the local and area-averaged Nu numbers compared to the conventional IJAC scheme. The most notable heat transfer enhancement was observed at S/d = 0.5 utilizing extended jets and the surface design incorporating aerofoil-shaped fins. Under these specific conditions, the maximum heat transfer enhancement reached 52.81%. Moreover, the investigation also demonstrated that the highest TPC on the finned surface was achieved when S/d = 2.0 for L2 at Re = 25,000, resulting in a TPC value of 1.12. Furthermore, reducing S/d and mounting aerofoil-shaped fins on the surface yielded a more uniform heat transfer distribution on the relevant surface than IJAC with a smooth surface, ensuring a relatively more uniform heat transfer distribution to minimize the risk of localized overheating.

Aerothermal Optimization of Film Cooling Hole Locations on the Squealer Tip of an HP Turbine Blade

Abstract This article presents a time-efficient method to optimize the positions of film cooling holes on a gas turbine blade's squealer tip for cooling and aerodynamic performance. A computational approach is employed for the optimization, including validations against experiments. Five discrete film cooling holes are considered, and two different blowing ratios of 0.4 and 1.0 are studied. The positions of cooling holes on the tip along the tangential direction are varied as the input parameters of optimization. The multi-objective optimization uses an algorithm with an artificial neural network for fast fitness function predictions. The best cooling configuration found by the optimization achieves a 13.43% reduction in total heat flux and a 0.4% increase in aerodynamic loss when the blowing rate is 1.0. Including the casing relative motion in the computations results in a total pressure loss coefficient increase of about 8% for both blowing ratios. For M = 1.0, imposing the casing's motion results in a 10.2% reduction in total heat transfer to the tip compared to the stationary casing. For the lower blowing rate of 0.4, the total heat flux reduction to the tip is 12.0% because of the imposed casing motion. Hence, the cooling effectiveness can be improved by employing the particular position optimization method presented in this study. The results suggest that experimental and computational heat transfer studies on cooled turbine blade tips, especially in cascade arrangements, need to consider the relative motion of the blade tip.

Achieving Best Turbine Blade Cooling Efficiency from a Cylindrical Cooling Hole with Reverse-Vortex Generator Using Numerical Simulation

This investigation bargains mathematical investigation of the impact of kidney vortex generation (KVG) on the film cooling execution of a round cooling opening which has measurement (d = 20 mm) on a level plate. The collection between the stream cooling air and standard hot gases will result kidney vortex which will wipe out the film cooling adequacy. Two kind of reverse vortex generator (RVG) with various statures (H = 0.5 d and 0.25 d) are intended to eliminate the kidney vortex and examine best film cooling adequacy, where every one of them is mounted to the level plate upstream of the cooling opening by changing its parallel positions (A = 0.0 d, 0.25 d, 0.5 d and 0.75 d) concerning the opening community line and for each kind has diverse distance regard to opening focus line. The changing of blowing proportion (BP = 0.5-1.0) was considered in this investigation. The simulation model was used to simulate the formation of film cooling using a shear stress transfer (SST) model by Workbench 15 software. The outcomes have been introduced in terms of laterally averaged and maximum value of film cooling comparison diagrams, vorticy on x/d = 3.0 and film cooling distribution which clarified how the outcomes acquired. The Cases 04 and 07 gave the best situations for RVG where case 04 gave wide covered for laterally average film cooling efficiency (η = 0.35), while case 07 gave the highest expansion distribution and the maximum value for film cooling efficiency (η = 0.66). The best results are obtained when the blowing ratio (BP = 0.5) due to a lower velocity of cooling air which will made best interaction with the hot air (main stream)which will represent the hot gases in real case.

Computational Fluid Dynamics Analysis of Flow Characteristics and Heat Transfer Variabilities in Multiple Turbine Blade Cooling Channels

Abstract In the realm of gas turbine engine technology, turbine blades are persistently subjected to extreme thermal conditions due to prolonged exposure to high-temperature gases. Given this operating environment, devising effective cooling strategies is paramount for ensuring the turbine’s safety and longevity. Despite the critical nature of this issue, existing literature scarcely addresses cooling channels that incorporate factors like variable cross-sectional attributes and rotational effects. In this study, Computational Fluid Dynamics (CFD) and numerical methodologies were employed to analyze the flow mechanism and performance of three distinct cooling channels characterized by variable cross-sectional features. The results indicate a marginal thermal performance improvement of up to 3% for U-shaped cooling channels, specifically at a Reynolds number of 20,000, in comparison to Net cooling channels. Conversely, jet impingement channels outperform U-shaped channels by an impressive margin of over 11%. Additionally, at a Reynolds number of 60,000, jet impingement cooling channels manifest a significant upsurge of nearly 25% in the ratio between average Nusselt number, and the reference Nusselt number when compared with U-shaped and Net cooling channels.

Intelligent optimization method for real-time decision-making in laminated cooling configurations through reinforcement learning

Optimizing conjugate heat transfer in laminated configurations is pivotal for efficiently cooling turbine blades. The traditional approaches have limitations in achieving rapid optimization when design conditions change. The emergence of reinforcement learning offers an opportunity to address this issue. However, there is currently a notable scarcity of research on the application of reinforcement learning in the optimization of laminated cooling configurations. This paper presents a novel method using the Deep Q-Network (DQN) model for real-time optimization of laminated cooling configurations. A dataset comprising 246 sets of historical design data was generated through conjugate simulations and augmented with the incorporation of physical information. After undergoing off-policy reinforcement learning, the intelligent model was employed to address optimization problems associated with temperature levels and coolant usage. Results indicate that the intelligent model achieves accurate and real-time optimization for laminated cooling configuration, with an average time of 3 ms. The ability to identify the correct optimization direction is attributed to the formulation of reward and penalty mechanisms in reinforcement learning. Real-time optimization is enabled by establishing a forward computational path from design conditions to optimization results. The findings of this study are easily transferrable and contribute to cost savings in design.

A cooled turbine blade design and optimization method considering the cooling structure influence

This study introduces a multidisciplinary design methodology tailored for enhancing the performance of cooled turbine blades by amalgamating thermal and aerodynamic calculation modules. The approach is unique in terms of its integration of a multi-objective optimization platform, aimed at refining aerodynamic performance and gauging the heat transfer capabilities during the preliminary aerodynamic design phase. To accomplish this objective, a one-dimensional pipe-network calculation tool was incorporated into the thermal module to quickly evaluate the heat transfer performance of the blades under different conditions. This tool also provides more realistic film hole inlet boundary conditions essential for three-dimensional aerodynamic calculations. Implementing this platform in optimizing a high-pressure turbine blade revealed a Pareto-optimal front, comprising −η1 and η2 (representing optimization objectives for aerodynamic and heat transfer performance, respectively), showcasing a constrained relationship. Upon scrutinizing three optimization cases against the prototype, optimization case 1 demonstrates the most significant enhancements in aerodynamic performance, showing a 0.2015% improvement in aerodynamic efficiency relative to the prototype. Conversely, optimization case 3 displays a comparatively modest augmentation in aerodynamic performance but excels notably in heat transfer performance, showcasing a 7.61% reduction in the maximum temperature of the blade surface compared to the prototype. Through adept optimization strategies and meticulous variable selection, we maintained a relatively stable mainstream mass flow across the optimization cases (less than 0.05% variation). These findings underscore the efficacy of our multidisciplinary design approach for cooled turbine blades, promising efficiency improvements in current design practices and potential reductions in project duration.

CFD Analysis of Gas Turbine Blade Cooling with Staggered Holes

The role of turbine inlet temperature plays a pivotal role in determining overall turbine performance. As the temperature at the turbine inlet increases, it leads to an enhancement in the turbine's average efficiency. Gas turbines operate under extremely elevated temperatures, reaching levels of 1200°C to 1500°C. This extreme heat poses the risk of turbine blade melting and potential failure. Consequently, the need arises for a sophisticated cooling mechanism for the turbine blades. Optimally increasing the inlet temperature of the turbine blades can certainly elevate the turbine's overall efficiency. However, it's important to recognize that this increase in temperature directly impacts the durability of the turbine blades. To address this challenge, various innovative cooling technologies have been devised, including the implementation of distinct blade cooling hole configurations. These methodologies aim to ameliorate blade temperatures and consequently enhance turbine performance.Turbine blades are engineered using superalloys, renowned for their ability to withstand high thermal stress. Advanced software tools are harnessed to assess their performance under extreme temperatures. Computational Fluid Dynamics (CFD) software is commonly employed for analyzing turbine blades. A prevailing approach for blade temperature reduction entails employing diverse cooling systems, often utilizing air as a cooling agent. This directed airflow over the blades significantly curtails their temperatures. In this context, blade design featuring staggered hole layouts is applied, and both STATIC and CFD simulations, grounded in defined boundary conditions, are executed, yielding commensurate outcomes. Comparative analysis demonstrates that staggered hole configurations provide superior temperature distribution uniformity across blade surfaces, effectively reducing peak temperatures in contrast to blade configurations devoid of cooling holes..

Pulsed Impinging Jets for Heat Transfer: A Short Review

Abstract Because of their effectiveness and adaptability, impinging jets have found their way into a host of applications ranging from cooling turbine blades, to heat management of electronic systems. With constantly increasing demand for efficient and compact cooling systems in certain industries, such as the aerospace or electronics industries, variations on the textbook-setup of an impinging jet have been studied over the years. One such variation introduces a periodic disturbance into the jet that can have an effect on both the structure of flow and the thermal boundary layer at the target surface. In what follows is a short overview of studies having used pulsed jets, often in tandem with other modifications, to try and improve heat transfer. Special attention was also given to the methods by which the periodic disturbance can be produced since they involve setups of different levels of complexity and having different implementation costs.

Numerical Simulation of Heat Transfer and Flow Enhancement Through Multi-Row Film Holes for Gas Turbine Blade Cooling

Numerical Simulation of Heat Transfer and Flow Enhancement Through Multi-Row Film Holes for Gas Turbine Blade Cooling

Optimization Turbine Blade Cooling by Applying Jet Impingement Cooling Channels

Abstract The aim of this paper is to optimize turbine blade cooling channels by applying jet impingement Method. The selection of experiment data for NASA 3CX turbine blade, and 3D model using solidworks software and create computational fluid dynamics (CFD) simulations used to model the coolant flow and temperature distribution in the vane, while experimental testing can validate the CFD results and provide additional insights into the cooling system's performance., ANSYS FLUENT code was used as a CFD solver, and ANSYS ICEM-CFD was used for mesh generation. MATLAB code is used for calculation using experiment data and this was helpful for simulations. Heat transfer conjugation analysis bases SST shear stress analyses K-ω turbulent model. The results conclude that providing additional information about the cooling channels and how they differ in the studies being compared. The results demonstrate that the cooling channels' hydraulic diameter decreases by a significant percentage (up to 49.70%–69.55%) as they are drawn to the trailing edge of the blade. This can have a significant impact on the heat transfer coefficients and the performance of the cooling system. The pressure side of the turbine blade is observed to follow the Hylton Model, while the current study predicts a large over-anticipated heat transfer coefficient around the Turbine blade head and on the bulk of the suction side. In terms of average heat transfer coefficient, the two models differ by 23.36%. The authors found that the cooling effectiveness for the Optimized jet impingement model is 0.4892 for whole blade and compared it with the cooling effectiveness for the optimized jet impingement model, which is 0.6936, The results of the comparison between the base model and the optimized jet impingement model suggest that the optimized model has a significantly higher cooling effectiveness. The increase in cooling effectiveness of 29.46% for the whole blade and 28.823% for the trailing edge indicates that the optimized jet impingement design provides improved cooling performance. These results highlight the importance of considering optimized cooling designs for turbine blades to maintain efficient and safe operation.

DDES study on a pressure-side cutback cooling turbine blade with a whisker lip and a whisker trailing edge

In this study, the whisker structure of a harbor seal is applied to the lip and the trailing edge of a turbine cooling blade with a pressure-side cutback. Four cases are studied in this article, including a prototype, a whisker trailing edge, a PP (The lip’s peak and the trailing edge’s peak are designed at the same blade height) case, and a PV (The lip’s peak and the trailing edge’s valley are designed at the same blade height) case. The DDES method is used to simulate the flow and thermal mixing process in the cascade. The coolant mass flow ratios () of 0.5% and 1% at an outlet Mach number of 0.9 are simulated. The PP case can achieve the best aerodynamic performance, which reduces the thermodynamic energy loss coefficient of the prototype by 0.98% and 0.99% at = 0.5% and = 1%, respectively. The PP case and the PV case increase the lowest spanwise average adiabatic film cooling effectiveness on the cutback surface from 0.5 to 0.7 at = 0.5%. The film cooling effectiveness of the PP case and the PV case can remain close to 1 over the entire cutback surface at = 1%. The PP case transforms the trailing edge shedding vortices on the pressure side into hairpin vortices. The whisker lip suppresses the lip vortex and alters the closed separation bubble on the cutback surface, causing the coolant to converge toward Section 1. The convergence of coolant is more helpful for the PP case to control the pressure side shedding vortex, resulting in a lower thermodynamic energy loss.

EFFECTS OF ADDITIVELY MANUFACTURED SURFACE ROUGHNESS ON SMALL DIAMETER PLENUMS WITH MULTIPLE SIDE DISCHARGES FOR HIGH TEMPERATURE GAS TURBINE BLADE COOLING APPLICATIONS

Combined heat and power (CHP) applications have significant environmental and economic benefits that are consistent with the goals of the U.S. Department of Energy (DOE). One area that is currently being studied includes the potential benefits of CHP turbine operation at higher turbine inlet temperatures. Internal cooling concepts enabled by additive manufacturing (AM) are of primary interest. The effectiveness of internal cooling is hindered by many factors such as velocity distribution of the cooling air to the hot surface considering impingement cooling. To simulate cooling air exiting from a series of orifices for internal cooling in an airfoil, a straight smooth wall tubing with multiple side discharging orifices is used and compared to additively manufactured tubing (Ti6Al4V Grade 23) with orifice size and spacing as well as inner and outer diameters identical to the smooth wall tubing. Similar to flow discharging form perforated pipes, the flow discharged from individual orifices along the tubes in this study is found to be nonuniformly distributed, and the horizontal (axial direction) momentum can be observed from the experimental data. Discharge velocities have been measured with two-dimensional (2D) particle imaging velocimetry (PIV) and single element hot wire anemometry. Numerical analysis has also been conducted to predict the velocity distributions along the orifices in the smooth wall and additive manufacturing (AM) tubing, which are inherited with surface roughness. Numerical and measured results in this study are compared, presented, and discussed.

Applying Infrared Thermography as a Method for Online Monitoring of Turbine Blade Coolant Flow

Abstract As gas turbine engine manufacturers strive to implement condition-based operation and maintenance, there is a need for blade monitoring strategies capable of early fault detection and root-cause determination. Given the importance of blade cooling flows to turbine blade health and longevity, there is a distinct lack of methodologies for coolant flowrate monitoring. The present study addresses this identified opportunity by applying an infrared thermography system on an engine-representative research turbine to generate data-driven models for prediction of blade coolant flowrate. Thermal images were used as inputs to a linear regression and regularization algorithm to relate blade surface temperature distribution with blade coolant flowrate. Additionally, this study investigates how coolant flowrate prediction accuracy is influenced by the number and breadth of diagnostic measurements. The results of this study indicate that a source of high-fidelity training data can be used to predict blade coolant flowrate within about six percent error. Furthermore, identification of prioritized sensor placement supports application of this technique across multiple sensor technologies capable of measuring blade surface temperature in operating gas turbine engines, including spatially resolved and point-based measurement techniques.

The combined effect of coriolis and centrifugal buoyancy forces on internal cooling of turbine blades with modified ribs using Large Eddy Simulation (LES)

Cooling of turbine blades is necessary for longer durability and better thermal efficiency of the turbines. Turbine blade cooling is fulfilled by passing a coolant through the serpentine channel roughened with turbulators. In this work, the combined effect of the centrifugal buoyancy and the Coriolis force on heat transfer of a square duct roughened with ribs is studied using Large Eddy Simulation (LES). Simulations are carried for a Reynolds number based on bulk velocity of 20,000 with staggered square (SQ) rib, Backward step (BS) rib, and Forward step (FS) rib on the leading and trailing wall. The heat transfer performance of the square duct roughened with ribs is compared at rotation numbers Ro=0.35,0.67 and Richardson numbers Ri=0.0,12.0,28.0. The heat transfer augmentation for SQ-, BS-, and FS-ribs for Ro=0.67 and Ri=28 is 4.2%, 8.6% and 14.9%, respectively, higher than that without the effects of buoyancy. The friction coefficient for SQ-, BS-, and FS-ribs for Ro=0.67 and Ri=28 is 12.8%, 14.8% and 13.3% respectively higher than that without buoyancy.

Experimental Analysis of the Interaction of “Hot” and “Cold” Volume Elements during Thermal Fatigue of a Cooled Component Made from AISI 3161 Steel

Abstract Start-stop and load change procedures of combustion engines result in inhomogenous and instationary temperature fields, which induce cyclic mechanical loadings, e. g., in solid and cooled turbine blades and vanes. The present study shows results of so-called “complex thermal-mechanical fatigue” (CTMF) tests carried out with a two specimen testing system in order to simulate the interaction of the “hot” outer and the “cold” inner side of a cooled turbine blade. The test samples were made from the austenitic steel AISI 316 L. Specimen 1 represents the “hot” and specimen 2 the “cold” side of the blade, respectively. Both specimens were loaded by individual thermal cycles with closed loop control of the temperature. The mechanical interaction of the “hot” and the “cold” side was simulated by keeping the total strains of both specimes at identical values and keeping the sum of the forces at a value of zero at every moment throughout the tests. The results are discussed on the background of the microstructures resulting from the individual loadings of specimen 1 and 2.

A study on heat transfer characteristics by impinging jet within a few amounts of mist

• Heat transfer coefficient distribution. • Jet temperature distribution with and without mist. • Amount of heat evaporate in the main flow. • Temperature behavior on the heated plate. Jet impingement is used for cooling, drying purposes; typical applications include cooling turbine blades and electrical equipment, drying of textiles and other wetted surfaces and cooling of metal plates. The flow dynamics and heat and mass concentration in the turbulent boundary layer on the flat heated plate have been used to improve the heat transfer coefficient. Wide range of factors that have an effect on heat and mass concentration at several patterns which are X/D = 4, 7, 9 and velocity 15 m/ are analyzed. The experimental results indicate that, the heat transfer coefficient rate improved by 21% and 32% in case of M = 3 mg/s and 6 mg/s respectively, compared with the case without addition of mist. The amount of heat evaporates in the main air flow is almost twice, in case of M = 3 mg/s, ∆ Q = 8.81 W and when M = 6 mg/s, ∆ Q = 15.39 W at constant velocity distribution 6 m/s.