Hydraulic Turbine Blades Research Articles

Effects of spraying power on Fe-based amorphous coatings

To avoid the corrosion damage caused by cavitation and sediment erosion on the turbine blades, Fe-based amorphous coatings were deposited on steel of hydraulic turbine blades using plasma spraying with various spraying power. The effects of spraying power on the microstructure, electrochemical corrosion and wear resistance were systematically studied. Results show that the coatings have remarkable corrosion resistance and wear resistance compared with the substrate. Porosity is the most critical factor influencing the corrosion resistance of coatings. The anti-corrosion performance increases and the wear rate decreases as the spraying power increases. The coatings prepared at 25 kW has excellent corrosion resistance and wear resistance, with a corrosion rate of 0.011 mm·a−1, and a wear rate of only 5.91 mm3·N−1·m−1.

Updating singular value decomposition for modal analysis of slow-varying non-stationary vibration structures

This paper proposes a novel method for the modal analysis of slow-varying vibration structures based on vector autoregressive models. The basic idea of this method consists of using a short-time sliding window (STSW) to identify modal parameters for non-stationary vibrations. This method uses the recursive least-squares estimation for multivariable systems with the singular value decomposition (SVD) method to find the solutions within a segment of the data from each time window. Model identification is conducted by updating the SVD of the data matrix using the order and time from the previous computational window to monitor the modal parameters of a slow-varying system. Finally, this work was validated first by numerically simulating a system's gradual changes submitted to an exciting force and further by an experiment on a hydraulic turbine blade.

Numerical investigation on the blade load distribution in a pump as turbine

Pump as turbine plays an important role in modern industrial process. One of the major goals of turbine design and optimization is to maximize its efficiency. Therefore, it is of great importance to connect force with work in the analysis process. In the present study, the three-dimensional flow field of the pump as a hydraulic turbine has been investigated in the steady-state mode. The load distribution along three captured streamlines (i.e., the shroud, hub and middle streamline) on both the pressure and the suction surface is observed, and the relationship between the load distribution and the working capability is systematically analyzed. The results show that the load distribution on the pressure surface of the hydraulic turbine blade gradually transitions from the reverse “S” shape to the “S” shape in the process of increasing flow rate, while the load distribution on the suction surface keeps increasing with a concave trend. The main work area of the fluid medium on the hydraulic turbine impeller is in the middle section of the blade. As the flow rate increases, the loads on the blade depict a linear decreasing trend from the inlet to the outlet. The net load acting on the blade is distributed in a concave parabola profile along the radial position of the blade. Focusing on the inlet and middle section of the blade profile in the design or optimization process of the hydraulic turbines will be more useful. This study provides a new analysis method for the design or optimization of hydraulic turbine impellers.

Grain Refinement and Strengthening Mechanisms of In-situ Follow-up Hammering-Assisted Wire Arc Additive Manufacturing for Hydraulic Turbine Blade Repairing

Grain Refinement and Strengthening Mechanisms of In-situ Follow-up Hammering-Assisted Wire Arc Additive Manufacturing for Hydraulic Turbine Blade Repairing

Determined to the microstructural and mechanical properties of deposits made of high alloy steels used in the construction of environmentally friendly hydraulic turbines

Research on hydraulic turbines, regardless of type, has shown that all materials used in the manufacture of parts that are components of the flow path, working in the same conditions, are subject to hydro-abrasive wear, in different proportions. The most attacked components are the blades and the chambers of the hydraulic turbines. In this paper are studied materials used in the construction of hydraulic turbine blades that have been previously deposited by the method of the electro-spark deposition with tungsten carbide (WC) electrodes. These deposits were made in order to offer the turbine blades as high a reliability as possible but also to be able to use such hydraulic turbines in the harshest conditions and which could provide as much energy as possible. A high-alloy stainless steel containing Cr and Ni was used as the basic material for the study. The raw samples from a hydraulic turbine blade and those submitted were analyzed both structurally using the optical stereomicroscope and the SEM electron microscope and chemically using the EDX probe. High alloy steel based on Cr and Ni but also WC deposits will be subjected to mechanical tests to see how they resist wear.

Термічна обробка і властивості литої складнопрофільної лопаті гідротурбіни

The mode of heat treatment of massive castings of the blades of the impeller of the hydroturbine "Dniester HPSP" from steel of the martensitic class CA-6NM has been worked out. Based on the determination of mechanical properties, measurements of stiffness over the entire surface of the blades and metallographic studies, the expediency of the proposed heat treatment mode using intensive cooling and high tempering after high-temperature austenitizing heating is shown. It is shown that this mode provides the necessary level of mechanical properties of blade castings, eliminates the negative effect of internal stresses arising during crystallization and rapid cooling during subsequent heat treatment. Determination of the chemical composition of castings and its compliance with the requirements of ASTM A743 / A743M-98a ensures that the required level of product properties is obtained. Metallographically established the absence of unwanted segregation and the uniformity of the structure, the uniformity of mechanical properties over the body of the blade, which leads to an increase in resistance to destruction due to cavitation. As a result of the research, the expediency of using the following heat treatment mode for massive complex-profile castings of blades made of corrosion-resistant steel of martensitic class CA-6NM, consisting of heating to a temperature of 1030-1040°C and tempering at 580-590°C using rapid cooling, was confirmed. Keywords: hydraulic turbine blades, heat treatment, structure, mechanical properties.

Region-based path planning method with all horizontal welding position for robotic curved layer wire and arc additive manufacturing

For the curved layer deposition with wire and arc additive manufacturing on complex surface, the molten pool behavior and bead geometry are variant at different welding positions for the dragging effect of gravity, which lead to inconsistent layer appearance. A region-based path planning method for robotic curved layer wire and arc additive manufacturing (CL-WAAM) is developed, with which all horizontal welding position can be maintained at arbitrary region of the complex surface. The adverse effect of gravity is minimized and uniform bead appearance can be guaranteed. Firstly, with a two-stage clustering method , the complex surface was divided into a certain number of simple subregions . Then, the contour line across cluster centroid of each subregion was employed as initial path, and an adaptive bead overlapping model changed with local inclined angle was used to generate the offset curved path covering the subregion. Therefore, the overall welding paths were approximate to the contour line on the surface, and the horizontal welding position and consistent forming appearance can be achieved. Finally, three surface parts were designed to validate feasibility of the method, and the forming appearance was compared with traditional iso-parametric method and flat layer WAAM (FL-WAAM). The results suggested that the surface waviness and thickness were relatively consistent at arbitrary region of complex surface with the region-based method, and the stair-step effect appeared in FL-WAAM was significantly alleviated with the CL-WAAM. The proposed method helps achieve the uniform layer appearance deposited on complex surface, which could be widely used in the manufacturing or repairing of wear-resistant surface parts, such as the hot forging die and hydraulic turbine blade. • A framework of robotic curved layer wire and arc additive manufacturing (CL-WAAM) was proposed. • A region-based path planning method with all horizontal welding position for the CL-WAAM was implemented. • The complex surface was subdivided into simple patches with a two-stage clustering method. • The contour line across the cluster centroid was employed as the initial path, with which the all horizontal welding position could be ensured. • The uniform forming appearance was achieved through the proposed region-based path planning method.

Engineering design of the low-head Kaplan hydraulic turbine blades using the inverse problem method

Engineering design of the low-head Kaplan hydraulic turbine blades using the inverse problem method

Towards the Development of an Impeller with Splitters for a Radial-Axial Hydraulic Turbine

The question of the optimal shape of a hydraulic turbine blade is the chief issue in hydraulic turbine construction. It is necessary to design and create a sample of a turbine impeller with maximum efficiency and high cavitation properties. In order to achieve this objective, studies are conducted that are based on hydrodynamic analysis of the hydraulic turbine water path and selection of the best turbine blade geometry, by bringing in methods of genetic optimization. The author of this article proposes a different method of creating a turbine impeller: adding additional blade-splitters to the design.

A Calibration Method for a Laser Triangulation Scanner Mounted on a Robot Arm for Surface Mapping.

This paper presents and discusses a method to calibrate a specially built laser triangulation sensor to scan and map the surface of hydraulic turbine blades and to assign 3D coordinates to a dedicated robot to repair, by welding in layers, the damage on blades eroded by cavitation pitting and/or cracks produced by cyclic loading. Due to the large nonlinearities present in a camera and laser diodes, large range distances become difficult to measure with high precision. Aiming to improve the precision and accuracy of the range measurement sensor based on laser triangulation, a calibration model is proposed that involves the parameters of the camera, lens, laser positions, and sensor position on the robot arm related to the robot base to find the best accuracy in the distance range of the application. The developed sensor is composed of a CMOS camera and two laser diodes that project light lines onto the blade surface and needs image processing to find the 3D coordinates. The distances vary from 250 to 650 mm and the accuracy obtained within the distance range is below 1 mm. The calibration process needs a previous camera calibration and special calibration boards to calculate the correct distance between the laser diodes and the camera. The sensor position fixed on the robot arm is found by moving the robot to selected positions. The experimental procedures show the success of the calibration scheme.

Novel invariant feature descriptor and a pipeline for range image registration in robotic welding applications

This work proposes an invariant descriptor and a pipeline for the registration of surface range images based on segmentation/reconstruction making use of an edge detection technique combined with a clustering technique using mesh decimation. This novel descriptor is applied to contours and it is invariant to similarity transformations including rotation, translation, uniform scale and it is robust to noise. The proposed feature descriptor makes use of corresponding points extracted from two images and a signature label is assigned specifically to a point considering the geometrical distribution of its neighbourhood, reducing possible areas of overlapping and the ambiguity in the search process. The descriptor was evaluated through a series of tests with various object range images. To validate the candidate transformations, the fitting errors between the two range images are evaluated by the iterative closest point algorithm. This study also presents and discusses results from the application of the developed pipeline in a vision sensor mounted on a robot arm specially built as part of a R&D project to acquire range images by laser scanning over the surface of hydraulic turbine blades. The sensor generates 3D surface models to be registered in the 3D coordinate system of the robot controller.

A knowledge resources fusion method based on rough set theory for quality prediction

Quality prediction of the complex surface parts manufacturing process can be automated by designing a knowledge fusion model based on rough set algorithm. Such a model can be constructed by combining qualitative and quantitative knowledge resources modeling, and quality data mining. In this procedure, knowledge fusion model is used to merge knowledge resources in production process into data mining models, which could mine more abundant decision rules for various production conditions. This work exposes the correlation of knowledge resources that fuses in such indiscernibility correlation relation and the function relations. Quality prediction is shown for an operational evaluation processes and a set of prediction rules with varying precision and different structural forms. Results on quality prediction of multi axis milling for large hydraulic turbine blades show that knowledge fusion model alleviates the uncertainty of sample data and improves product quality conversely. Moreover, the prediction method is indeed beneficial to high quality and precision manufacture.

Cost-effective CFD for vortex shedding from a trailing edge of hydraulic turbine blade

This paper describes the method for analysing the vortex from a trailing edge of the blade with high accuracy using CFD. As for the analysis method, RANS and LES hybrid model, which is a combination of RANS with a low calculation load and LES with a high calculation load, was used on understanding the turbine-scale phenomenon with a relatively low calculation load. As for the first step its application as a turbine runner, we conducted the case study in which the blade model was fixed in a uniform and we confirmed that the present CFD could be predicted the vortex shedding phenomena, such as power spectra of velocity fluctuations, wake fluctuation, vortex shedding pattern and hydraulic force acting on the blade etc.

An FPGA-based controller design for a five degrees of freedom robot for repairing hydraulic turbine blades

This paper presents the design of a FPGA-based embedded system for controlling and monitoring a 5-D.O.F. spherical topology robot specialized in welding for repairing hydraulic turbine blade surfaces. The embedded controller has been developed using a hardware/software co-design approach in which a Nios II soft-processor is configured on a Terasic DE2-115 development kit, along with several support modules (timer, JTAG, I/O, memory and RS-232). Additionally, other dedicated hardware modules were designed to control the motors, encoders, the welding system and a joystick while daughter boards were designed to provide an opto-coupled connection from the FPGA kit to their respective external peripherals. Furthermore, the control system also provides a RS-232 interface to the pan-tilt, which provides the last two degrees-of-freedom to the manipulator. While the control algorithm runs on the FPGA it receives spatial coordinate points via a USB connection maintained with a PC where higher level software uses image processing techniques to map the turbine surface using a 3D LASER scanner and compute the welding trajectories. Finally, the validity of the system is verified with repeatability and welding tests.

A numerical method for the determination of flow-induced damping in hydroelectric turbines

To estimate structural fatigue, vibrational response to realistic spectrum of excitations and associated equivalent damping are of paramount importance. In this paper, an approach to quantify flow-induced damping of a relatively heavy fluid on a vibrating hydraulic turbine blade using numerical simulations is presented. First, mode shapes and frequencies of the immersed structure are obtained by modal analysis using the finite element method. Then, forced oscillatory modal motion is prescribed on the structural boundary of unsteady Reynolds-averaged Navier–Stokes flow simulations. Damping is finally computed as the normalized work done by the resulting fluid load on the structure. Validation is achieved by comparing the numerical results with available experimental data for a steel hydrofoil oscillating in flowing water. For this case, the linear increase in the damping ratio with the flow velocity is reproduced within 10% of the experimental values. Application of the method to an actual hydroelectric propeller turbine blade yields a fluid damping value of around 15% of critical damping for its first vibration mode.

State of the Art and Conceptual Design of Robotic Solutions for In Situ Hard Coating of Hydraulic Turbines

Hydropower turbine’s blades are constantly exposed to abrasion and cavitation phenomena, demanding regular maintenance for flow stability. Hard coating techniques by thermal aspersion are used to reduce the mechanical wear, thus increasing blade’s life cycle, and turbine efficiency. Currently, applying a new coating layer requires turbine disassembling and recalibration. EMMA is a robotic system to perform hard coating by thermal spray on hydraulic turbine blades within the turbine environment, i.e., hard coating application to an installed blade, significantly reducing the turbine downtime. This document is a study of the state of the art of in situ hydropower turbine robotic systems and describes the conceptual designs for EMMA. The results outlines the next steps for EMMA and future projects in the same area.

CFD evaluation of added damping due to fluid flow over a hydroelectric turbine blade

To estimate structural fatigue, vibrational response to realistic spectrum of excitations and associated equivalent damping are of paramount importance. In this paper, an approach to quantify flow-induced damping of a relatively heavy fluid on a vibrating hydraulic turbine blade using numerical simulations is presented. First, mode shapes and frequencies of the immersed structure are obtained by modal analysis using the finite element method. Then, forced oscillatory modal motion is prescribed on the structural boundary of unsteady Reynolds-averaged Navier-Stokes flow simulations. Damping is finally computed as the normalized work done by the resulting fluid load on the structure. Validation is achieved by comparing the numerical results with available experimental data for a steel hydrofoil oscillating in flowing water. For this case, the linear increase in the damping ratio with the flow velocity is reproduced within 10% of the experimental values. Application of the method to an actual hydroelectric propeller turbine blade yields a fluid damping value of around 15% of critical damping for its first vibration mode.

Non-probabilistic reliability research on multi-variable hydraulic turbine blade model

Based on the interval mathematics and possibility theory, the variables existing in hydraulic turbine blade are described. Considering the multi-failure mode in turbine blade, multi-variable model is established to meet the actual situation. Thus, non-probabilistic reliability index is presented by comparing with the output range and the given range.

Some aspects over the quality of thin films deposited on special steels used in hydraulic blades

The experimental research involved in this paper consists in the obtaining of superior physical, chemical and mechanical properties of stainless steels used in the construction of hydraulic turbine blades. These properties are obtained by deposition of hard thin films in order to improve the wear resistance, increasing the hardness but maintaining the tenacious core of the material. The chosen methods for deposition are electrospark deposition because it has relatively low costs, are easy to obtain, the layers have a good adherence to support and the thickness can be variable in function of the established conditions and the pulsed laser deposition because high quality films can be obtained at nanometric precision. The samples will be prepared for the analysis of the structure using optical method as well as for the obtaining of the optimal roughness for the deposition. The physical, chemical and mechanical properties will be determined after deposition using SEM and EDX, in order to emphasize the structure film-substrate and repartition of the deposition elements on the surface and in transversal section. The non-destructive testing has emphasized the good adherence between deposited layer and the metallic support, due to double deposition, spallation regions doesn't appear.

Quality Control of Thin Films Deposited on Special Steels Used in Hydraulic Blades

The hydraulic turbine blades are made from stainless steels having a hard layer for the improvement of the hydro abrasive wear, corrosion resistance, and resistance to mechanical impacts in order to increase the reliability of the turbine. The thin films from stellite and tungsten carbide were obtained by the method: electrospark deposition because it has relatively low costs, are easy to obtain, the layers have a good adherence to support and the thickness can be variable in function of the established conditions. In this paper, the physical, chemical and mechanical properties of the samples will be determined using Scanning Electron Microscope (SEM), in order to emphasize the structure film-substrate and repartition of the deposition elements on the surface and in transversal section. Also, the samples were nondestructively tested using the electromagnetic sensor with metamaterials in order to establish the adherence of the thin films to the steel, proving the potential of this NDT techniques. The complex signal delivered by the sensor has been stored while scanning a 6x6 mm area. The processing algorithm involve the use of the bidimensional Fourier transform after filtering the initial signal using Walsh-Hadamard numerical filter.