Turbine Blade Surface Research Articles

Thermo-Structural Analysis of Carbon Fibre-Ni Based Super Alloy Composite Employed in Gas Turbines

A computational analysis was carried out on two different materials of turbine blades, namely Inconel MA754 and Nimonic 80A, in order to determine their structural and thermal properties at elevated temperatures. Long carbon fibers of uniform length were used and deposited at varying thicknesses ranging from 1 mm to 4 mm, on the top surface of turbine blades and then analyzed for its performance. It is seen that the carbon fibers (IM10) embedded in the super alloys drastically improve the load bearing parameters of the configurations being analyzed. The improvement in structural load carrying ability is a result of higher Young's modulus primarily. Subsequent analysis with higher volume fraction of the fibers indicated saturation of performance at about 70 % volume fraction for 4 mm fibers and significant improvement beyond it for the 1 mm fibers. With improvement in the load bearing characteristics the blade with fibers embedded into a tube like structure at 3 sections were configured and A thermal analysis of the same underscores the effectiveness of the 4 mm fibers in undergoing much reduced principal strains than other configurations. This is seen to be a result of insulation of the top surface from increase in temperature, which significantly reduces the thermal expansion, especially at the free end. This is in contrast to other configurations, where the low volume fraction of fibers resulted in high principal strain.

Uncertainty Quantification of the Effects of Blade Damage on the Actual Energy Production of Modern Wind Turbines

Wind turbine blade deterioration issues have come to the attention of researchers and manufacturers due to the relevant impact they can have on the actual annual energy production (AEP). Research has shown how after prolonged exposure to hail, rain, insects or other abrasive particles, the outer surface of wind turbine blades deteriorates. This leads to increased surface roughness and material loss. The trailing edge (TE) of the blade is also often damaged during assembly and transportation according to industry veterans. This study aims at investigating the loss of AEP and efficiency of modern multi-MW wind turbines due to such issues using uncertainty quantification. Such an approach is justified by the stochastic and widely different environmental conditions in which wind turbines are installed. These cause uncertainties regarding the blade’s conditions. To this end, the test case selected for the study is the DTU 10 MW reference wind turbine (RWT), a modern reference turbine with a rated power of 10 MW. Blade damage is modelled through shape modification of the turbine’s airfoils. This is done with a purposely developed numerical tool. Lift and drag coefficients for the damaged airfoils are calculated using computational fluid dynamics. The resulting lift and drag coefficients are used in an aero-servo-elastic model of the wind turbine using NREL’s code OpenFAST. An arbitrary polynomial chaos expansion method is used to estimate the probability distributions of AEP and power output of the model when blade damage is present. Average AEP losses of around 1% are predicted mainly due to leading-edge blade damage. Results show that the proposed method is able to account for the uncertainties and to give more meaningful information with respect to the simulation of a single test case.

Effects of Boot-Shaped Rib on Heat Transfer Characteristics of Internal Cooling Turbine Blades

Abstract Gas turbine engine has been widely applied to many heavy industries, such as marine propulsion and aerospace fields. Increasing turbine inlet temperature is one of the major ways to improve the thermal efficiency of gas turbines. Internal cooling for gas turbine cooling system is one of the most commonly used approaches to reduce the temperature of blades by casting various kinds of ribs in serpentine passages to enhance the heat transfer between the coolant and hot surface of gas turbine blades. This paper presents an investigation of the boot-shaped rib design to increase the heat transfer performances in the internal cooling turbine blades for gas turbine engines. By varying the design parameter configuration, the airflow is taken with higher momentum, and the minor vortex being at the front rib is relatively removed. The object of this investigation is increasing the reattachment airflow to the heated wall and reducing the vortex occurring near the rib for improving the performances of heat transfer using three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) with the SST model. A parametric study of the boot-shaped rib design was performed using various geometric parameters related to the heel-angle, toe-angle, slope-height, and rib-width to find their effect on the Nusselt number, temperature on the ribbed wall, friction factor ratio of the channel, and thermal performance factor. The numerical results showed that the heat transfer performances are significantly increased with the heel-angle, toe-angle, slope-height, while that remained relatively constant with the rib width.

Reynolds analogy and turbulent heat transfer on rotating curved surfaces

To evaluate turbulent heat transfer on rotating turbine blades, knowledge of the Reynolds stress and heat conduction moments on the blades is required. This involves solving the mean flow equations of momentum and thermal energy on the rotating blades. In this paper, the turbine blades are represented by rotating curved surfaces, and turbulent heat transfer calculations are carried out by invoking a valid Reynolds analogy because of its simplicity. The classic Reynolds analogy is defined as the ratio between the eddy and thermal diffusivity in a stationary plane flow; however, its counterpart for rotating curved flows is still not known. To derive a Reynolds analogy for rotating curved flows, appropriate turbulence models to close the Reynolds transport equations for momentum and thermal energy are required. Assuming that, in the constant flux region, advection and diffusion of Reynolds stress and heat conduction moments are negligible compared to the production of turbulent energy, the Reynolds shear stresses and heat conduction moments can be solved in terms of the mean flow gradients, a turbulent Prandtl number (Prt)rc and a gradient Richardson number for rotating curved flows Rirc. These dimensionless numbers are dependent on mean flow properties, surface curvature, and system rotational speed. Thus derived, the classic Reynolds analogy can be recovered only when Rirc << 1 and (Prt)rc = 1. For turbine blade heat transfer, Rirc is not necessary very small and (Prt)rc differs from unity in the whole flow field. Therefore, using the classic Reynolds analogy to estimate turbine blade heat transfer will lead to incorrect result. The new Reynolds analogy, formulated for turbulent thermal flows on rotating curved surfaces, takes all pertinent external body force effects into account; thus, turbulent heat transfer evaluation on turbine blade surfaces can be substantially improved.

Metamodeling-based parametric optimization of DBD plasma actuation to suppress flow separation over a wind turbine airfoil model

While dielectric-barrier-discharge (DBD) based plasma actuation systems have been successfully demonstrated to suppress massive flow separation over wind turbine blades to reduce the transient aerodynamic loadings acting on the turbine blades, it is still a non-trivial task to establish a best combination of various operating parameters for a DBD plasma actuation system to achieve the optimized flow control effectiveness. In the present study, a regression Kriging based metamodeling technique is developed to optimize the operating parameters of a DBD plasma actuation system for suppressing deep stall over the surface of a wind turbine blade section/airfoil model. The data points were experimentally obtained by embedding a nanosecond-pulsed DBD (NS-DBD) plasma actuator at the leading edge of the airfoil model. The applied voltage and frequency for the NS-DBD plasma actuation were used as the design variables to demonstrate the optimization procedure. The highest possible lift coefficient of the turbine airfoil model at deep stalled angles of attack (i.e., α = 22° and 24°) were selected as the objective function for the optimization. It was found that, while the metamodeling-based procedure could accurately predict the objective function within the bounds of the design variables with an uncertainty ~ 2%, a global accuracy level of ~ 97% was achieved within the whole design space.

Damage accumulation model of ice detach behavior in ultrasonic de-icing technology

Wind turbines that operate under cold climates sustain icing events. Ice accretion on the surfaces of wind turbine blades not only constitutes a severe threat to operation safety, but also reduces wind energy output. As a novel mechanical de-icing method, the ultrasonic de-icing technique has attracted high attention in both wind energy and aviation industry, due to its low energy consumption, light weight and low cost. According to the ultrasonic de-icing mechanism, a damage accumulation model was proposed to describe the ice detachment behavior under ultrasonic wave. This model that was constructed with damage mechanics provided an assessment method for the ultrasonic de-icing effect and predicted the time consumption of ice layer detachment. This method was numerically simulated with the finite element method. In addition, a set of experimental apparatus for ultrasonic de-icing method was designed. Following, a confirmatory experiment was carried out in laboratory environment. The parameters of the damage accumulation model were determined by the experimental data. The ice detachment behavior in the experiment was consistent with the prediction assessment proposed in this paper.

Outer Hinged Blades Vertical Shaft Kinetic Turbine Flow Pattern Visualization

The Micro hydro power plant (MHPP) development can be used to supply electricity to people living in remote areas. Because the electricity needed in this area is usually not too big. In remote areas and located far from the electricity transmission network, electricity supplies from small capacity power plants is needed, especially those that utilize renewable local energy potential. The energy utilization as electricity generation is by utilizing available kinetic energy (water potential and water flow speed). The research carried out experimentally and then optimized with Response Surface Methodology. The optimization results are then tested again so as to obtain verification results from the optimization value. Furthermore, based on the value of optimization, visual observations are made to see the flow behavior that occurs on the outside hinged blade and turbine chamber. From the visual observations, it was found that not all the water flow hit the turbine blade surface. On the blade back side, the water flow that hits the turbine blade will increase the turbine rotation. On the blade front side, the water flow that hits the outer blade will open the blade and the water flow will come out immediately from the turbine so that it will reduce the negative torque or back rotation.

Implications of biofouling on cross-flow turbine performance

While biofouling is known to degrade the performance of marine energy conversion systems, prior experimental work has not explored this topic for cross-flow turbines. Here, we present experiments that investigate the impact of biofouling on turbine power output and structural loads. Using additive manufacturing, a three-dimensional scan of a barnacle was patterned onto the surface of turbine blades at three sizes and number densities, representing the progression from initial colonization to maturity. The impact of barnacles on turbine power output was found to be substantial and, for the most severe cases of fouling, the turbine does not produce power at any rotation rate. Conversely, barnacle fouling was found to have minimal impact on structural loading. To maintain generation capacity over extended periods, these results highlight the importance of antifouling coatings and proactive blade cleaning.

Numerical Study of Lightning Protection of Wind Turbine Blade with De-Icing Electrical Heating System

In order to solve the problem of icing on the surface of wind turbine blade, a heating system that includes a carbon fiber net (CFN) and power cables is proposed recently. When lightning strikes at the blade with a de-icing heating system, the blade and its heating system are more easily damaged due to the overvoltage between the lightning protection system (LPS) of the blade and the heating system. In this paper, the models of a wind turbine blade with the de-icing heating system are established by Alternative Transients Program/Electromagnetic Transients Program (ATP–EMTP) and the accuracy of models is verified through an experiment. With these models, the influence of lightning current, surge protective devices (SPDs) and earthing resistance of wind turbine are analyzed by calculating the voltage between the down-conductor of the LPS and the heating system. The results show that the voltage is positively correlated with lightning current amplitude and negatively correlated with the front time of lightning current. SPDs are quite useful to reduce the voltage, and an optimal installation scheme of SPDs is obtained by simulation. It is noted that voltage decreases slightly with the increasing earthing resistance with the optimal installation scheme of SPDs.

Improvement of the Turbine Blade Surface Phase Structure Recovered by Plasma Spraying

This paper presents the results of research on the construction, technological parameters and criteria that control the process of formation of optimal phase structure of austenitic- and martensitic-class material for steam turbine blades. The hypothesis that the established correlation could increase the quality of blade recovery and its resistance against dynamic and vibrational loads was proved. The efficiency of the developed implantation method for the recovery of steam turbine blades was demonstrated. The optimal technological parameters of the process of laser plasma recovery were established empirically, allowing the development of the system for the fine tuning of the phase composition of austenitic- and martensitic-class steel.

Thermo-Structural Analysis of Carbon Fibre-Ni Based Super Alloy Composite Employed in Gas Turbines

A computational analysis was carried out on two different materials of turbine blades, namely Inconel MA754 and Nimonic 80A, in order to determine their structural and thermal properties at elevated temperatures. Long carbon fibers of uniform length were used and deposited at varying thicknesses ranging from 1 mm to 4 mm, on the top surface of turbine blades and then analyzed for its performance. It is seen that the carbon fibers (IM10) embedded in the super alloys drastically improve the load bearing parameters of the configurations being analyzed. The improvement in structural load carrying ability is a result of higher Young's modulus primarily. Subsequent analysis with higher volume fraction of the fibers indicated saturation of performance at about 70% volume fraction for 4 mm fibers and significant improvement beyond it for the 1 mm fibers. With improvement in the load bearing characteristics the blade with fibers embedded into a tube like structure at 3 sections were configured and A thermal analysis of the same underscores the effectiveness of the 4 mm fibers in undergoing much reduced principal strains than other configurations. This is seen to be a result of insulation of the top surface from increase in temperature, which significantly reduces the thermal expansion, especially at the free end. This is in contrast to other configurations, where the low volume fraction of fibers resulted in high principal strain.

Damage Evaluation of TBC by Rapid Thermal Cycling Test Utilizing a Laser Irradiation

Thermal barrier coating (TBC) is deposited onto the gas turbine blade surface in order to protect the substrate from high-temperature combustion gas. Cracks and delamination of the ceramic coating which come from high heat flux loading are serious problem in TBC. In this study, the rapid thermal cycling device utilizing laser irradiation was developed. It was then investigated how the damage progresses in the ceramic coating exposed to cyclic rapid thermal loading. As a result, a sintering layer was formed in the surface of the ceramic coating, although such phenomenon was not recognized in TBC sample tested by the conventional thermal cycling test using an electric furnace. It was also revealed from the cross-sectional observation that the vertical crack was initiated at the surface of TBC and propagated into sintering layer. Finally, mechanical factors of those damages from finite element analysis using the TBC model including sintering progress was discussed

Anti-icing epoxy resin surface modified by spray coating of PTFE Teflon particles for wind turbine blades

Epoxy resins are widely used for the outer surface of wind turbine blades and many other engineering applications. An anti-icing epoxy resin surface was generated by a spray coating of polytetrafluoroethylene (PTFE; commonly known as Teflon) nanoparticles. The Teflon particles with a mean diameter of 300 nm were dispersed in acetone to achieve 5 % weight fraction. The static contact angle and the roll-off angle for deionized water were measured at 154° and below 2° respectively. The ice detachment strength at the temperature of −10 °C and 16 % relative humidity was approximately 30 kPa on average, which was about 2.5 % of the ice detachment strength of an aluminum substrate and was about 20 % of the ice adhesion strength of plain epoxy. This spray coating method has no limit on the application coverage surface area. To demonstrate the scalability of this coating method, a 101.6 mm by 101.6 mm aluminum surface was successfully produced in the laboratory and demonstrated the same superhydrophobic and icephobic surface characteristics as the smaller test surfaces.

Electrical insulation improvements of ceramic coating for high temperature sensors embedded on aeroengine turbine blade

Intelligent aeroengine requires high temperature sensors, especially MEMS thin film sensors directly fabricated on the surface of turbine blade. For this purpose, an electrical insulation layer is needed on blade substrate metals. However, the electrical insulation of ceramic materials will degrade at high temperatures, thereby affecting the characteristics of the sensor. In this paper, ceramic material of YSZ thermal barrier coating (TBC) formulation was modified by adding a certain amount of Al2O3 to improve its insulation at high temperatures. Micro processing was carried out on the surface of the TBC, including the fabrication of platinum-point thermocouples and thermal resistor on TBC surface, and high temperature electrical insulation properties of the modified TBC were studied. Results show that electrical insulation can be improved several orders of magnitude with adding Al2O3 which meets the requirement to build reliable thin film sensors on the top of TBC surface coated on turbine blade metals. Several verification experiments were carried out to ensure the working ability of TBC layer, including robustness test, thermal shock test and high temperature retention test.

Separated boundary layer transition under pressure gradient in the presence of free-stream turbulence

Large-eddy simulation (LES) has been carried out to investigate the transition process of a separated boundary layer on a flat plate. A streamwise pressure distribution is imposed to mimic the suction surface of a low-pressure turbine blade, and the free-stream turbulence intensity at the plate leading edge is 2.9%. A dynamic subgrid scale model is employed in the study, and the current LES results compare well with available experimental data and previous LES results. The transition process has been thoroughly analyzed, and streamwise streaky structures, known as the Klebanoff streaks, have been observed much further upstream of the separation. However, transition occurs in the separated shear layer and is caused by two mechanisms: streamwise streaks and the inviscid K-H instability. Analysis suggests that streamwise streaks play a dominant role in the transition process as those streaks severely disrupt and break up the K-H rolls once they are formed, leading to significant three-dimensional (3D) motions very rapidly. It is also demonstrated in the present study that the usual secondary instability stage under low free-stream turbulence intensity where coherent two-dimensional (2D) spanwise rolls get distorted gradually and eventually broken up into 3D structures has been bypassed.

Influence of multiple laser impacts on thin leading edges of turbine blade

Laser shock peening is a mechanical surface improvement treatment used to enhance the fatigue life of critical components. This paper investigates the influence of multiple square laser impacts to study their special effect on the diverse mechanical behaviours of the thin leading edge surface of turbine blades. Most works existing in the literature have presented experimental investigations. The originality of our paper is to validate and numerically simulate the proposed model. Indeed, a 3D finite element method of a thin leading edge specimen, Ti–6Al–4V, of a turbine blade is numerically simulated using the ABAQUS software. The mechanical surface modifications (residual stresses, equivalent plastic strains and Johnson–Cook superficial damage) induced by the multiple square laser impact are examined in detail. The main purpose of this investigation is to determine the effects of single-sided and double-sided laser shock peening.

Wind turbine blade surface inspection based on deep learning and UAV-taken images

As a key component of wind turbines (WTs), the blade conditions are related to the WT normal operation and the WT blade inspection is a significant task. Most studies of WT blade inspection focus attention on acquired sensor signal processing; however, there exist problems of stability, sensor installation, and data storage and processing. Onsite visual surface inspection is still the most common inspection method, but it is inefficient and requires a long downtime. Aimed at solving the above issues, a novel blade inspection method based on deep learning and unmanned aerial vehicles is proposed. Since common defect types are visible, the inspection problem is regarded as an image recognition problem. Three convolutional neural networks are trained by using the constructed dataset for image recognition, and the F1-score is applied to evaluate the models. The VGG-11 model is chosen for the final model due to its best performance. Then, the alternating direction method of multipliers algorithm is employed to compress the model to reduce the requirements on hardware devices. The blind area of the WT can be reduced, the efficiency of subsequent maintenance can be improved, maintenance costs can be reduced, and the economic performance can be increased. Finally, a comparison experiment of different inspection methods is carried out to demonstrate the proposed advantages.

An analysis-oriented parameter extraction method for features on freeform surface

The features on freeform surface are common in products with complex curved surfaces, such as gas film holes attached on turbine blade surface or pressing head on the multi-spots bending press. The freeform surfaces generally have tiny geometric structure, the large number and regular arrangement, which makes it hard to extract analysis parameters from CAD structures and construct equivalent analysis features. Therefore, the analysis models generation will be accelerated if parameters for analysis could be extracted automatically rather than manually. In this paper, the analysis-oriented parameter extraction problem is proposed and analyzed. The geometry pattern parameter and physical attribute parameter are summarized and defined as the research kernel based on common analysis scenarios. Based on Hough transform and k-means clustering method, a geometry pattern parameter extraction method is proposed, which can convert analytic criterion of extraction requirements into clear pattern recognition problems. A physical attribute parameter extraction method based on rule reasoning is also put forward to extract numeric analysis parameters with physical meanings. Finally, two representative cases are taken to illustrate the implementation steps of the proposed method, and to verify the effectiveness and practicability in engineering. The instance demonstrates that the proposed method could significantly reduce the time consumption of analysis model generation and improve the integration degree of CAD/CAE.

A Two-Stage Data-Driven Approach for Image-Based Wind Turbine Blade Crack Inspections

A two-stage approach for precisely detecting wind turbine blade surface cracks via analyzing blade images captured by unmanned aerial vehicles (UAVs) is proposed in this paper. The proposed approach includes two main detection procedures, the crack location and crack contour detection. In locating cracks, a method for extracting crack windows based on extended Haar-like features is introduced. A parallel sliding window method is developed to scan images and the cascading classifier is developed to classify sliding windows into two classes, crack and noncrack. Based on detected windows containing cracks, a novel clustering algorithm, the parallel Jaya K -means algorithm, is developed to assign each pixel in crack windows into crack and noncrack segments. Crack contours are obtained based on boundaries of crack segments. The effectiveness and efficiency of the proposed crack detection approach are validated by executing it on a personal computer and an embedded device with UAV-taken images collected from a commercial wind farm. Computational results demonstrate that the proposed approach can successfully identify both the blade crack locations and crack contours in UAV-taken images.

Reduction of aerodynamic forces on turbine blading by asymmetric layout of struts based on flow interaction between rotor-strut-volute

The flows in the power turbine and nonaxisymmetric exhaust volute with struts are closely coupled and inherently unsteady for marine gas turbines, and the flow interactions between them have a significant influence on the rotor and strut blade aerodynamic force characteristics; however, the asymmetric flow interactions have not been taken into account properly in current turbine design approaches. This paper is a continuation of the previous work and aims to clarify effects of different symmetrical and asymmetric layouts of struts on the flow interactions between power turbine and exhaust volute, in an attempt to seek an optimal layout of struts with the objective of making use of the mentioned asymmetric flow interactions to reduce the rotor and strut blade aerodynamic forces. This work was carried out using coupled unsteady simulations with the full annulus computational domain including 76 rotor blades, 9 strut blades, and an exhaust volute. Results show that the level of aerodynamic force at specific frequencies on the power turbine blade surface can be reduced by applying a proper distribution of asymmetric layout of struts; using the asymmetric strut design, although the reduction of the rotor blade aerodynamic force is weak, the strut blade aerodynamic force has been reduced significantly; the asymmetric layout of struts does not improve the overall flow characteristics of turbines very much. The present results indicate that it is possible to reduce vibration and increase blade fatigue life by asymmetric strut designs.