Hydraulic Turbine Blades Research Articles

Extrapolation of dynamic load behaviour on hydroelectric turbine blades with cyclostationary modelling

In this paper, we present the application of cyclostationary modelling for the extrapolation of short stationary load strain samples measured in situ on hydraulic turbine blades. Long periods of measurements allow for a wide range of fluctuations representative of long-term reality to be considered. However, sampling over short periods limits the dynamic strain fluctuations available for analysis. The purpose of the technique presented here is therefore to generate a representative signal containing proper long term characteristics and expected spectrum starting with a much shorter signal period. The final objective is to obtain a strain history that can be used to estimate long-term fatigue behaviour of hydroelectric turbine runners.

Inverse Kinematics and Model Calibration Optimization of a Five-D.O.F. Robot for Repairing the Surface Profiles of Hydraulic Turbine Blades

This paper presents and discusses the results of an ongoing R&D project aiming to design and build a fully automated prototype of a specialized spherical robotic welding system for repairing hydraulic turbine surfaces eroded by cavitation pitting and/or cracks produced by cyclic loading. The system has an embedded vision sensor built to acquire range images by laser scanning over the blade's surface and produce 3D models to locate the damaged spots to be registered in a 3D coordinate system into the robot controller, enabling the robot to repair the flaws automatically by welding in layers. The paper is focused on the robot kinematic model and describes an iterative algorithm to process the inverse kinematics with only five degrees-of-freedom. The algorithm makes use of data collected from a vision sensor to ensure that the welding gun axis is perpendicular to the blade's surface. Besides this, it proposes a modelling and optimization mathematical routine for more efficient robot calibration, which can be used with any type of robot. This robot calibration optimization scheme finds the optimal error parameter vector based on the condition number of the manipulator transformation composed from the partial derivatives of the error parameters. Experimental results proved both the iterative algorithm to perform the inverse kinematics and the technique to optimize robot calibration to be very efficient.

Quality Surface Modification for Refractory Stainless Steel by Tungsten Deposition, Using Electro-Spark Deposition Method

In this paper were analyzed Tungsten electrode depositions using electro-spark deposition method, on stainless steel, used for hydraulic turbine vanes and blades of mixing blades for chemical industry, in order to achieve an improved wear resistance. This deposition method was chosen due to its relatively low cost, easy to achieve, and leads to obtaining thin layers with good adherence to the substrate, and with different thicknesses, depending on the number of deposited layers. The chosen electrode is an alpha character element and generates an increase of the mechanical properties at low and high temperatures for austenitic stainless steels. Tungsten does not modify the corrosion resistance for the stainless steels. The samples were analyzed on scanning electrons microscope (SEM) and also the chemical analysis (EDX) for distinguish the layer-support structure and the elements repartition on the surface and in line.

Research on Splicing and Three-dimensional Measurement of Hydraulic Turbine Blades Surface

The splicing and three-dimensional measurement of the hydraulic turbine blade is achieved in this paper. The large size of hydraulic turbine blades makes it impossible to take a complete picture of the entire blade. Multiple images of various segments must be obtained and then spliced together at later stages. Landmarks are installed in public area of the adjacent segments of hydraulic turbine blades, which are used when splicing segmental images together using least squares method, to obtain three-dimensional surface information ofthe entire blade. Based on the principles of the structure light measurement, a three-dimensional measurement system is designed, its parameters are also defined, and mathematical models of the three-dimensional measurement are established. The hydraulic turbine blade is simulated by using software package “3ds max” to build a hydraulic turbine blade model. Simulation of splicing and threedimensional measurement of the hydraulic turbine blade shape is achieved. The reconstruction of the three-dimensional Hydraulic turbine blade is then obtained based on the measured data.

Estimation and prediction of the roughness function on realistic surfaces

Large-eddy simulations are carried out in turbulent open-channel flows to determine the roughness function and the equivalent sand-grain roughness height, ks, over sand-grain roughness and different types of realistic roughness replicated from hydraulic turbine blades. A range of Reynolds numbers and mean roughness heights is chosen, leading to both transitionally and fully rough regimes. The start of the fully rough regime is shown to depend on the roughness type, and ks depends strongly on the surface topography. We then examine several existing correlations that predict ks based on the information of the surface geometry. In the cases where the surface slope is an important parameter, the moments of surface height statistics do not predict the roughness function, while the existing forms of slope-based correlations perform well. The range of applicability of various correlations is shown to vary with the roughness topography, as the critical value of the effective slope, separating the waviness and roughness regimes, is shown to be higher for a realistic surface, compared to the value for the more regular types of roughness that were previously studied.

The Generation of Cracks in Hydraulic Turbine Blades and the Instances

Turbine blades crack problem is widespread. Combined with the characteristics of hydropower, analyzes the causes of cracks in the turbine, materials, design and manufacturing, operation and so on. Plant No. 6 in Little Bay machine as an example, were detected by macroscopic, chemical composition analysis, crack cross-section analysis, microstructure examination, crack source electron microscopy and spectroscopy to analyze the crack, the final cause of the crack is leaves the local area resonance, the resonance of the blade in the crater formed at the source of fatigue and fatigue development along at the source, the formation of fatigue cracks.

Experimental Study on Abrasive Waterjet Polishing of Hydraulic Turbine Blades

In this paper, an experimental investigation is implemented on the abrasive waterjet polishing technique to evaluate its capability in polishing of surfaces and edges of hydraulic turbine blades. For this, the properties of this method are studied and the main parameters affecting its performance are determined. Then, an experimental test-rig is designed, manufactured and tested to be used in this study. This test-rig can be used to polish linear and planar areas on the surface of the desired workpieces. Considering the number of parameters and their levels, the Taguchi method is used to design the preliminary experiments. All experiments are then implemented according to the Taguchi L18 orthogonal array. The signal-to-noise ratios obtained from the results of these experiments are used to determine the importance of the controlled polishing parameters on the final quality of the polished surface. The evaluations on these ratios reveal that the nozzle angle and the nozzle diameter have the most important impact on the results. The outcomes of these experiments can be used as a basis to design a more precise set of experiments in which the optimal values of each parameter can be estimated.

Part 1 – Experimental study of the pressure fluctuations on propeller turbine runner blades during steady-state operation

A good evaluation of the unsteady pressure field on hydraulic turbine blades is critical in evaluating the turbine lifespan and its maintenance schedule. Low-head turbines such as Kaplan and Propeller, using a relatively low number of blades supported only at the hub, may also undergo significant deflections at the blade tips which will lead to higher amplitude vibration compared to Francis turbines. Furthermore, the precise evaluation of the unsteady pressure distribution on low-head turbines is still a challenge for computational fluid dynamics (CFD). Within the framework of an international research consortium on low-head turbines, a research project was instigated at the Hydraulic Machines Laboratory in Laval University (LAMH) to perform experimental measurements of the unsteady pressure field on propeller turbine model runner blades. The main objective of the project was to measure the pressure fluctuations on a wide band of frequencies, both in a blade-to-blade channel and on the pressure and suction side of the same blade, to provide validation data for CFD computations. To do so, a 32 channels telemetric data transmission system was used to extract the signal of 31 pressure transducers and two strain gages from the rotating part at an acquisition frequency of 5 KHz. The miniature piezoelectric pressure transducers were placed on two adjacent runner blades according to an estimated pressure distribution coming from flow simulations. Two suction sides and one pressure side were instrumented. The strain gages were mounted in full-bridge on both pressure and suction sides to measure the blade span wise deflection. In order to provide boundary conditions for flow simulations, the test bench conditions during the measurements were acquired. The measurements were made in different operating conditions ranging from part load, where a cavitating vortex occurs, to full load under different heads. The results enabled the identification and the quantification of the major known sources of pressure fluctuation as well as some unexpected ones. The paper first presents the experimental methodology discussing relevant topics such as telemetric system setup, transducers calibration and errors analysis. The main results are then presented to illustrate the relative amplitude of the main source of pressure fluctuations under different operating conditions. The discussion and conclusion addresses the important observations stemming from the data analysis and illustrates that most of the results can be correlated with the known behavior of hydraulic turbines while some require further investigation.

Damping measurements in flowing water

Fluid-structure interaction (FSI), in the form of mass loading and damping, governs the dynamic response of water turbines, such as Francis turbines. Water added mass and damping are both critical quantities in evaluating the dynamic response of the turbine component. Although the effect of fluid added mass is well documented, fluid damping, a critical quantity to limit vibration amplitudes during service, and therefore to help avoiding possible failure of the turbines, has received much less attention in the literature. This paper presents an experimental investigation of damping due to FSI. The experimental setup, designed to create dynamic characteristics similar to the ones of Francis turbine blades is discussed, together with the experimental protocol and examples of measurements obtained. The paper concludes with the calculated damping values and a discussion on the impact of the observed damping behaviour on the response of hydraulic turbine blades to FSI.

Stress analysis and deformation prediction of a heavy hydraulic turbine blade casting during casting and heat treatment

Owing to their large and curved shape, blade castings, a key component for heavy hydro turbines, are susceptible to deformation during casting and heat treatment. In the present paper, the stress analysis of a blade casting during both casting and heat treatment is performed. The coupled thermo-stress and thermo-phase transformation stress models are used for casting and heat treatment respectively. Machining allowance distribution is used as the deformation criterion and an algorithm of inverse deformation determination is presented. The mechanical properties of the martensitic stainless steel ZG0Cr13Ni4Mo (13Cr–5Ni–1Mo) at different temperatures are measured under as cast and heat treated status. Finally, the inverse deformation of the blade during both casting and heat treatment processes is obtained, and a series of sections of the blade casting with inverse deformation design are given for pattern making. The calculated deformation results are compared to the measured one, and they are basically in agreement.

Hardfacing by plasma transfer arc process

The plasma powder transferred arc welding process which uses feed stock in a powder form has similarities with plasma wire transferred arc welding. This paper describes a comparative study of the two processes using a cobalt-based alloy commercially known as stellite 6. This Co-based alloy is recognized for its superior cavitation erosion resistance. The aim of this paper is to investigate the potential of plasma transferred arc coatings for the protection and refurbishment of hydraulic turbine blades. Coatings were evaluated for the influence of plasma gas flow rate on coating dilution, geometry, hardness and microstructure. Coatings processed with the atomized stellite 6 powder feedstock showed a superior surface quality, lower dilution, better wettability and wider tracks. This study provided new information about the refurbishing of worn hydraulic turbine blades, leading to a longer service working life.

Active and Passive Deformation of Large Thin-Walled Workpiece in Heat Treatment Process

Displacement is traditionally deemed to be equivalent to deformation. However, displacement is not exactly deformation, for example, the tip of a workpiece illustrates big displacement, but, it caused by the deformation of main body. In this paper, theory of active and passive deformation is proposed for the evaluation of the deformation of workpiece during heat treatment process and the corresponding algorithm was established. The deformation consists of active and passive deformation; the former is the actual deformation, while the latter is caused by the deformation of other areas. This algorithm was applied to the deformation analysis of a hydraulic turbine blade which is a large thin-walled workpiece. And the real deformation area of the blade is found.

Dynamic Measurement of Temperature Field and Deformation in Hydraulic Turbine Blade at Cooling Stage of Heat Treatment

The hydraulic turbine blade is a kind of large,complex and curved casting.It is susceptible to significant warping deformation in the heat treatment process because of no-uniform cooling and phase transformation,which is a serious problem for the dimension control of the blade.A non-contact temperature field and dynamic displacement measurement system is established with the infrared thermal imaging system used for temperature measurement and special devices for the deformation measurement.It is adopted to investigate the temperature distribution and deformation behavior of a blade at the cooling stages of normalizing and tempering in production.The results reveal the temperature evolutions and dynamic deformation of the blade in heat treatment.The deformations of the blade mainly occur at the cooling stage of normalizing owing to the effect of uneven cooling and phase transformation.While,it is small during tempering in which only uneven cooling effect exists.This research and the results are of great significance to the exploration and study of the deformation behavior of hydraulic turbine blades.And the established system is useful for temperature fields and deformation measurement for parts during heat treatment.

Research on Multi-axis CNC Programming in Machining Large Hydraulic Turbine's blades Based on UG

Researched on the multi-axis CNC Integrated machining method of blade on large Francis turbine based on UG to automatic programming software architecture. Discussed the way to enhance the quality and to promote efficiency of machining .The key technology of five-axis CNC programming to large sculptured surface in hydro turbine's blade was introduced, which establishing 3-D model and tool-path generation and cutting simulation with small force, high precision and low cost. we have introduce this machining method and hope it is helpful to machining of similar parts.

Feasibility analysis for monitoring fatigue crack in hydraulic turbine blades using acoustic emission technique

In order to investigate the feasibility of monitoring the fatigue cracks in turbine blades using acoustic emission (AE) technique, the AE characteristics of fatigue crack growth were studied in the laboratory. And the characteristics were compared with those of background noise received from a real hydraulic turbine unit. It is found that the AE parameters such as the energy and duration can qualitatively describe the fatigue state of the blades. The correlations of crack propagation rates and acoustic emission count rates vs stress intensity factor (SIF) range are also obtained. At the same time, for the specimens of 20SiMn under the given testing conditions, it is noted that the rise time and duration of events emitted from the fatigue process are lower than those from the background noise; amplitude range is 49-74 dB, which is lower than that of the noise (90-99 dB); frequency range of main energy of crack signals is higher than 60 kHz while that in the noise is lower than 55 kHz. Thus, it is possible to extract the useful crack signals from the noise through appropriate signal processing methods and to represent the crack status of blade materials by AE parameters. As a result, it is feasible to monitor the safety of runners using AE technique.

Digital manufacture of large-grade hydro turbine's blades

The blade is one of the vital components and the most difficulty in manufacturing of large hydro turbines. In order to cost-effectively and productively manufacture these kinds of blades, a series of innovative digital techniques have been developed. It includes the digital design of hydro turbine blades based on manufacturers’ requirements, computer-aided location and the machined error evaluation with three-dimensional digitized measure, tool path generation strategy for enhancing machining efficiency and controlling deviation in NC machining, tool path generation and NC machining simulation by means of a virtual NC machining environment for blades, and feasible strategy and the systematic scheme for manufacturing of large blades with 5-axis simultaneous CNC machining technology. The developed innovative digital manufacture techniques have been successfully applied in the manufacturing of both the large grade Kaplan and Francis hydraulic turbine blades. It has been shown that the higher efficiency and the better surfaces finish accuracy can be achieved in practical engineering.

Damage localization in hydraulic turbine blades using kernel-independent component analysis and support vector machines

A hydraulic turbine runner has a complex structure, and traditional source location methods do not have the higher accuracy to meet engineering requirements. The source location of crack acoustic emission (AE) signals in hydraulic turbine blades has been researched by combining it with kernel-independent component analysis (KICA) as feature extraction, with support vector machines (SVMs) as position recognition. This method is compared with those applied SVMs with feature extraction using kernel principal components analysis without feature extraction. The results show that the recognition rate in the crack region is 100 per cent by using both original AE parameters and feature parameters. Support vector regression by feature extraction using KICA can perform better than the other methods. As a result, it is a better method for source location of complex big size structures to combine KICA with SVM. It decreases the dimensionality of input signals and also improves the accuracy of location.

Flow stress model of stainless steel 0Cr13Ni5Mo at elevated temperature

For a more accurate forming calculation and numerical simulation of hydraulic turbine blade, experimental studies on the flow stress of stainless steel 0Cr13Ni5Mo were carried out upon Gleeble-1500 thermal simulator under different deformation conditions. The results then were analyzed and the effects of all influencing factors were summarized consequently. New mathematic models were conceived. Utilizing the software Matlab, regression coefficients were calculated by the least square method. The model has an eminent capability of curve-fitting performance with impact structure whose correlation coefficient is up to 0.908 0 and the cosine coefficient is 0.995 8. All mathematic models and process parameters can be used in engineering calculations or computer simulations.

Mobile platform for hydraulic turbine blade repair robot

The wall-climbing mobile platform (MP) of a robot for repairing a hydraulic turbine blade onsite is developed. The MP is equipped with ferromagnetic adhesive devices and can work on a spatial curved surface. The contradiction between mobility and load-bearing ability is analyzed, and the problem of self-adaptation to the curved face is solved using differential-driven wheeled locomotion with ferromagnetic adhesive devices. The platform adheres to the blade surface through the force provided by the ferromagnetic devices, and a certain gap exists between the magnetic devices and the blade’s surface. A mechanism of three revolution degrees of freedom, which connects the magnetic devices with the platform’s chassis, is developed to make the platform self-adapt to the complex curved surface of the turbine blade. A proof-of-principle prototype has been manufactured, and experiments prove the success of the MP. The payload of the zero-turn-radius MP with excellent maneuverability exceeds 80 kg. The platform can automatically adapt to complex spatial surfaces, which satisfy the requirements of a hydraulic turbine blade in-situ repair robot.

Phase transformation during cavitation erosion of a Co stainless steel

Cavitation erosion is a surface degradation mechanism that affects hydraulic turbine blades. Materials have been developed in order to minimise the detrimental effect. This work uses a Co stainless steel specially developed to exhibit improved cavitation resistance. The role of the γ austenite to ε-martensite phase transformation during cavitation erosion is assessed and the influence of surface finish on the cavitation erosion behaviour is evaluated as welded surfaces were ground and remelted before ultrasonic cavitation testing. Results reveal that structure refinement due to remelting contributes to a longer incubation period and that phase transformation is responsible for up to 25% of this erosion stage.