Blade Stress Research Articles

Investigation of the Influence of Sublayer Thickness on Pairing of Metallic MEMS Shutter Blades

For the 3D self-assembly of microstructures, the net intrinsic stress within a hybrid metal layer stack is utilised to study the dynamics of the pairing of metallic MEMS shutter blades with dimensions of 150 × 400 µm2, representing a highly nonlinear Casimir system. The study focuses on two main geometries: (i) unpaired (freestanding) and (ii) paired metallic Micro-Electro-Mechanical Systems (MEMS) shutter blades. The hybrid metal stack comprises three metal layers that are under intrinsic stress, which enables the curling of the freestanding shutter blades. The top aluminum layer thickness is varied systematically, creating tailored stress in the shutter blades, resulting in the freestanding blades curling differently, as well as geometrical changes in the paired shutter blades. Concerning the thickness variations, a large technological processing window has been identified, during which the pairing of the neighbouring shutter blades occurs (the top aluminum layer thickness ranges between 70 and 88 nm). Circles and ellipses have been fitted to micrographs obtained by scanning electron microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). We observed a trend of the reduction of the radius of curvature RoC (ranging between 17 and 79 µm) for the unpaired shutters, and eccentricity (0.36 < ε < 0.67) occurs throughout the system for the paired shutters. Concerning the specific shape of the overlapping region of the two blades of the paired shutters, three pairing scenarios (I, II, and III) have been identified, classified, evaluated, and reported. The overlapping length lo between the paired shutter blades ranges between 31 and 8 µm. These scenarios also reveal nonlinearities in the pairing process.

A novel approach to reduce fan rotor blades stress in case of resonance due to inlet flow distortion by means of piezoelectric actuators

Resonant vibration condition involves a drop in the life-cycle of the components and is one of the main causes of high cycle fatigue failure (HCF) in turbomachinery blades. As a consequence vibration damping techniques play a key role for turbomachinery designers. Even though resonant vibration conditions can be identified by means of the Singh’s Advanced Frequency Evaluation (SAFE) diagram at the design level, not all resonant conditions can be avoided. Among these methods, systems of piezoelectric (PZT) actuators can be tuned to actively damp the vibrations caused by resonant excitations. In this work, an analytical model was developed to identify the optimal voltage distribution that maximises the reduction in blade stress. The model considers the flexural–torsional–extensional deformations coupling due to the pre-twisting, non-constant cross-section and inertial loads of the rotating blades. A typical case was examined to demonstrate the effectiveness of the proposed method, which involved vibration induced by inlet flow distortion in an axial fan stage coupled with a three-strut front frame. A decoupled approach based on Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) simulations was used to evaluate the aerodynamic loads and to numerically validate the optimal voltage distribution on the PZT actuator pairs. The results show that the proposed method alleviates the effects of the resonant response to an inlet flow distortion on a fan integrally bladed disc (blisk) and the optimal voltage distribution predicted by the model is the one that achieves the highest blade stress mitigation.

Stress and deflection analysis of trench back-filling dozer blades using FEM

The objective of this paper is to improve the dozer's sharp edges in soil refilling applications based on limited component technique. The re-enactment strategy is achieved by involving computer-aided design programming for the pressure and redirection examination. The different terminology of dozer edges is mathematically obliged with the readiness of the model and the execution is successfully achieved from the real-time experimental conditions with given boundary conditions. The energy obliged for the dozer cutting edge applications with 35Hp power inlaying machine and assessed powers acting at the soil-instrument interface. The proposed work brings about recognizing adequate resilience in changing the elements of dozer edge segments and improving the overabundance of machine weight in a strong area. Furthermore, to raise the heaviness of the sharp edge for a solid strength different material such as EN24, Grey Cast Iron, Carbon Steel, and NIMONIC 80a were considered in this research. Based on the outcomes a recommendation is suggested as a suitable material.

Surrogate models for predicting transient change in temperature, stress and strain in gas turbine blade

Surrogate models for predicting transient change in temperature, stress and strain in gas turbine blade

Fabrication, Testing, and 3D Comprehensive Analysis of Swept-Tip Tiltrotor Blades

This paper covers the design, fabrication, testing, and modeling of a family of Froude-scale tiltrotor blades. They are designed with the objective of gaining a fundamental understanding of the impact of a swept tip on tiltrotor whirl flutter. The goal of this paper is to describe the development of the blades needed for this purpose. The rotor is three bladed with a diameter of 4.75 ft. The blades have a VR-7 profile, chord of 3.15 inches, and linear twist of –37° per span. The swept-tip blades have a sweep of 20° starting at 80% R. The blade properties are loosely based on the XV-15 design. A CATIA and Cubit-based high-fidelity three-dimensional (3D) finite element model is developed. It accurately represents the fabricated blade and is analyzed with X3D. Experiments in a vacuum chamber were carried out to demonstrate the structural integrity of the blades. Measured frequencies and strains were validated with X3D predictions proving the fidelity of the 3D model. Thus, even though the wind tunnel facilities were closed due to COVID-19, hover and forward flight calculations for the blade stress could be performed using the high-fidelity 3D structural model. The results prove the blades have sufficient structural integrity and stress margins to allow for wind tunnel testing.

Dynamic stress characteristics and fatigue life analysis of a slanted axial-flow pump

The shaft of the slanted axial-flow pump device is inclined, so, the stress on the impeller is complex, which leads to the prominent problem of structural reliability. In order to study the mechanical characteristics and fatigue life of the slanted axial-flow pump, the stress-strain characteristics and variation law of impeller under different flow rate conditions are analyzed by fluid-structure interaction method, at the same time, the stress-strain characteristics of impellers with geometrically similar and five different structural sizes when nD value is equal are solved, finally, the fatigue analysis of blades is carried out based on Miner’s linear fatigue cumulative damage theory to predict the fatigue life of impellers. The results show that under different flow rate conditions, the maximum equivalent stress of the impeller blade is concentrated at the blade root and gradually attenuates to the blade flange. The maximum deformation of the blade is located at the blade rim and moves from the inlet side to the outlet side with the increase of flow rate. When the nD value is constant, the maximum equivalent stress and maximum deformation displacement of the blade increase with the increase of the impeller size. Under various flow rate conditions, the service life of the impeller reaches 108, and the safety factor of each part of the blade is greater than 15, when operating within the working condition range of 0.8 Qbep∼1.2 Qbep, the impeller can operate continuously for 14 years without fatigue damage.

Non-contact full-field dynamic strain reconstruction of rotating blades under multi-mode vibration

Dynamic strain measurements of rotating blades have attracted significant attention in the turbomachinery design, testing, and service stages. Measuring the blade full-field strain using traditional strain gauges (SGs) is difficult. Too many SGs may add damping to the measured blades, thereby lowering the peak strain that should have been experienced. The strain level was then underestimated for the blades without SGs. A non-contact displacement measurement technique, called blade tip timing (BTT), is promising for replacing SGs but requires effective displacement-to-strain transformation. The transformation under blade single-mode vibration has been studied in recent years. Although the multi-mode vibration of rotating blades is increasingly common, it is usually ignored. In contrast to single-mode vibration, when the blade is subjected to multi-mode vibration, the peak stress changes in both the temporal and spatial domains. This causes difficulties in predicting the blade stress limit and fatigue life. This study proposes a full-field dynamic strain reconstruction method for rotating blades under multi-mode vibration. Based on the BTT-measured displacement, the proposed method enables the full-field dynamic strain reconstruction of the blade in the time domain. First, the multi-mode displacement response of the rotating blades was measured using the BTT system. Second, a least-squares decoupling model for the multi-mode response was established. The blade tip displacement response was decoupled, and the multi-mode vibration parameters were identified, including the frequency, amplitude, and phase. Third, an analytical transform relationship between the tip displacement and full-field strain was derived based on the blade mode shapes. The blade full-field dynamic strain was reconstructed in the time domain using the decoupled displacement response and a displacement-to-strain transmissibility matrix. Finally, the full-field strain at different instants was visualised using a blade finite element model. The proposed method is validated on a rotor with five blades through both numerical simulations and spinning experiments. The reconstructed strain was compared with the result measured by the SG. The average strain relative errors of the five blades were within 7.1%. The peak stress is predicted, and the critical positions on the blade under multi-mode vibration are marked, which can provide valuable knowledge for blade fatigue life prediction and health monitoring.

Understanding Upward Scalability of Cycloidal Rotors for Large-Scale UAS Applications

This paper investigates the upward scalability of a cycloidal rotor (also known as a cyclorotor) from an aeromechanics standpoint while utilizing a two-dimensional computational fluid dynamics (CFD) solver and a lower order aeroelastic model. The CFD results show that the nondimensional thrust remains almost unchanged with increasing Reynolds number, while the nondimensional torque and power decrease significantly from Re= 104 to 105, which clearly shows that the cycloidal rotor scales up favorably from thrust production and aerodynamic efficiency standpoints. The structural scalability study shows that as the cyclorotor size is increased, the blade weight per unit thrust remains constant; however, the blade stress increases monotonically if the rotor geometry is kept similar. This monotonic increase in the blade stress is found to be independent of the blade structural design. To bound the blade stress with increasing size, the diameter of the cyclorotor needs to be increased at a faster rate compared to the blade span, which reduces the rotor aspect ratio (blade-span/rotordiameter). Proper scaling laws necessary to bound the blade stress are formulated. Utilizing these insights, an optimization framework based on a genetic algorithm is developed to determine optimal cyclorotor configurations for a thrust range from 1 to 1000 lb.

Integrated Aerodynamic and Structural Blade Shape Optimization of Axial Turbines Operating With Supercritical Carbon Dioxide Blended With Dopants

Abstract Within this study, the blade shape of a large-scale axial turbine operating with sCO2 blended with dopants is optimized using an integrated aerodynamic-structural three-dimensional (3D) numerical model, whereby the optimization aims at maximizing the aerodynamic efficiency whilst meeting a set of stress constraints to ensure safe operation. Specifically, three candidate mixtures are considered, namely, CO2 blended with titanium tetrachloride (TiCl4), hexafluorobenzene (C6F6), or sulfur dioxide (SO2), where the selected blends and boundary conditions are defined by the EU project, SCARABEUS. A single passage axial turbine numerical model is setup and applied to the first stage of a large-scale multistage axial turbine design. The aerodynamic performance is simulated using a 3D steady-state viscous computational fluid dynamic (CFD) model while the blade stress distribution is obtained from a static structural finite element analysis simulation (FEA). A genetic algorithm is used to optimize parameters defining the blade angle and thickness distributions along the chord line while a surrogate model is used to provide fast and reliable model predictions during optimization using a genetic aggregation response surface. The uncertainty of the surrogate model, represented by the difference between the surrogate model results and the CFD/FEA model results, is evaluated using a set of verification points and is found to be less than 0.3% for aerodynamic efficiency and 1% for both the mass-flow rate and the maximum equivalent stresses. The comparison between the final optimized blade cross section has shown some common trends in optimizing the blade design by decreasing the stator and rotor trailing edge thickness, increasing the stator thickness near the trailing edge, and decreasing the rotor thickness near the trailing edge and decreasing the rotor outlet angle. Further investigations of the loss breakdown of the optimized and reference blade designs are presented to highlight the role of the optimization process in reducing aerodynamic losses. It has been noted that the performance improvement achieved through shape optimization is mainly due to decreasing the endwall losses with both the stator and rotor passages.

Research on infrared nondestructive detection of small wind turbine blades

To obtain the optimal light conditions for field infrared nondestructive detection of wind turbine blades, this paper used a 2kw small wind turbine blade with different damage types and degrees of damage as the research object. Using the passive infrared thermal imaging detection method, the damage of the wind turbine blade was naturally stimulated under outdoor conditions with enough light in summer to collect infrared thermal images, and the numerical simulation of the damage was performed. The experimental and simulation results show that light intensity has a large influence on damage detection, and the three typical damage of the best detection conditions are obtained. Among them, the light intensity of a foreign body attached reaches 950 W/m2 or higher for the best detection effect, while facial wear and crack damage were best detected at a light intensity of around 1000 W/m2 in the sunny noon. The simulation results agree well with the experimental results when using COMSOL multiple physical field coupling software for wear and crack damage scene reconstruction of finite element simulation, proving that the use of solar radiation as a source of passive infrared thermal imaging detection technology to detect wind turbine blade damage within a certain range of light intensity is feasible. Meanwhile, the numerical model was used to thermodynamically couple the wear-damaged blade, yielding a positive linear relationship between light intensity and the blade's highest temperature, stress, and strain. Furthermore, the degree of wear damage and the stress-strain corresponding to the highest temperature of the blade are both positively linear.

Numerical Analysis of Conjugated Heat Transfer and Thermal Stress Distributions in a High-Temperature Ni-Based Superalloy Turbine Rotor Blade

This paper establishes a multidisciplinary method combining conjugate heat transfer (CHT) and thermal stress for a high-temperature Ni-based superalloy turbine rotor blade with integrated cooling structures. A conjugate calculation is performed to investigate the coolant flow characteristics, heat transfer, and thermal stress of the rotor blade under rotating and stationary conditions to understand the effects of rotation on the multidisciplinary design of the blade. Furthermore, the maximum resolved shear stress among the 30-slip systems and the corresponding dominant slip system are obtained to predict the deformation tendency of the blade by employing the crystal plasticity finite element method (CPFEM) and considering the specified anisotropic blade material (GTD-111). The results show that the forces of rotation, including centrifugal and Coriolis forces, and their induced buoyancy force, alter the coolant flow field and thus affect the rotor blade’s heat transfer distribution compared with the stationary condition. The maximum temperature and thermal stress of the rotor blade under rotating conditions are reduced by 5% and 21% compared with that under the stationary condition, respectively. Compared with the stationary condition, the temperature and thermal stress distribution on the blade under the rotating condition are more uniform, especially on the suction side. In addition, the blade root connecting with the hub, the film holes near the leading-edge region at the blade root, the mid-chord of the suction surface, and the grooved blade tip are easily damaged by the enormous resolved shear stress and the interface effect of different types of dominant slip system under the two conditions. In this work, it was feasible to use the cascade cooling effect test to analyze the dynamic test results for the rotor blade. Furthermore, the thermal stress analysis based on the CPFEM can provide a superior level of blade cooling design than CHT by considering the anisotropic material characteristics of a turbine blade.

Vibration Stress of the Last-Stage Blades of a Steam Turbine After Repair of a Single Blade

Vibration Stress of the Last-Stage Blades of a Steam Turbine After Repair of a Single Blade

Numerical investigation into fluid-solid coupling characteristics of blade leading edge vortex cooling under different rotation numbers

In this paper, the fluid-solid coupling analysis is carried out on the vortex cooling. Under rotation conditions, the process of high-temperature gas scouring the blade and the vortex coolant cooling the blade is numerically calculated. At the same time, five rotation numbers of 0, 0.183, 0.339, 0.457 and 0.512 are selected. In addition, this paper proposes a method to improve vortex cooling performance under rotation conditions. The results show that at high rotation numbers, the centrifugal force drives coolant to flow downstream of vortex chamber. The downstream chamber accumulates a large amount of coolant to derive centrifugal buoyancy, which causes the back flow of coolant and makes the upstream heat transfer effect poor. As the rotation number increased from 0 to 0.512, the average Nusselt number on the target wall decreased by 35.49%. For the blade solid region, the effect of thermal load plays a major role on blade stress and displacement characteristics. Insufficient cooling performance in the chamber upstream leads to a higher temperature of the blade root, and a higher thermal stress concentration is generated because the blade root is constrained. In addition, by improving the intake chamber into a convergent structure, the coolant flow into the vortex chamber can be promoted, and the effect of back flow can be reduced, thereby obtaining a better vortex cooling performance. The target wall average Nusselt number of the convergent intake chamber structure is 977.17, which is 23.63% higher than that of the original rectangular intake chamber structure.

Strength and vibration analysis of transonic compressor under multiple field loads

The transonic axial flow compressor Rotor 37 is subjected to the combined action of thermal load, centrifugal load, and aerodynamic load in real work. The difference in load will cause the blade deformation and the size and distribution of stress to change. And it will cause the vibration frequency of the blade to change compared with the static state at room temperature. This paper studies the compressor blades based on the fluid-thermal-structure coupling method, and comprehensively considers the combined effects of thermal load, centrifugal load and aerodynamic load on the compressor blades. The results of the study show: that when the thermal load acts on the blade alone, it will have less impact on the blade deformation and greater impact on the stress, but when coupled with other loads, it will have a greater impact on the blade deformation and stress. In the case of fluid-thermal-structure coupling, the deformation of the compressor blade will first increase and then decrease with the increase of mass flow, and the change of stress will not decrease with the increase of mass flow. Rotation speed will affect the change trend of blade stress with mass flow. Compared with the static state at room temperature, the natural frequency of the blade under fluid-thermal-structure coupling has undergone a huge change. The first-order vibration frequency has increased by 25.77 %. It can be seen from the Campbell diagram that the compressor blade has a resonance at about 63 % and 98 % Point, in this case, the blade is prone to resonance, and more attention should be paid.

Experimental validation of FEM-computed stress to tip deflection ratios of aero-engine compressor blade vibration modes and quantification of associated uncertainties

Blade Tip Timing (BTT) technology is concerned with the estimation of turbomachinery blade stresses. The stresses are determined from BTT data by relating the measured tip deflection to the stresses via Finite Element (FE) models. The correlation of BTT measurements with FE predictions involves a number of uncertainties. This paper presents the process for validating the FE stress and deflection predictions of aero-engine compressor blades under non-rotation conditions as a critical preliminary step towards the complete understanding of their dynamic behaviour under rotating conditions when using BTT measurements. The process steps are described in detail, including the FE modelling and analysis of the blades and the blade-disk assembly, and the measurements of the blade tip deflection and blade stress. Furthermore, the uncertainties associated with the FE modelling and the measurement processes are quantified. The results show that the FE model is valid considering the control of most uncertainties. The experimental validation of the FE-computed stress-to-tip deflection calibration factors in the present study provides the basis for the determination of the calibration factors under rotational conditions using a previously presented BTT data simulator, and for the design of corresponding rotating experiments using BTT.

Measurement of dynamic stress and optimized start-up method for prototype Francis turbine

Abstract This paper describes the measurement method and results of dynamic stress for a prototype high head Francis turbine runner, blades of which had fatigue cracks near the root of the blade outlet band side within one-year operation. In order to specify the cause of the cracks, first of all, dynamic stress of the runner blade was measured throughout complete one cycle operation including start-up, no load operation, increase/decrease of load and stopping. Excessive variable strain at the portion near the crack occurred at very low rotational speed during start-up. The large strains occurring during start-up are not due to Rotor-Stator Interaction, other definite cyclic forced vibration or resonance, but the stochastic vibration. Consequently, start-up mode survey was conducted with dynamic stress measurement. As a conclusion, maintaining a small guide vane opening below a certain rotational speed is an effective indicator to reduce the strain during start-up and to minimize the damage caused by this phenomenon.

A prediction model of residual stress for belt‐grinding blade based on geometrical characteristic and progressive wear of abrasive grains

AbstractThe formation mechanism of residual stress on the machined surface of belt grinding is sophisticated, and residual stress is an important factor affecting the fatigue life of aero‐engine blades. In this study, a prediction model of residual stress in a belt grinding blade is proposed with the geometrical characteristics and progressive wear of the grains as the research topic. By extracting the morphological features of abrasive belt, the residual stress based on different geometrical characteristics of grains (pyramidal, hexahedral, spherical, and conical belts) were investigated, and the optimal grain geometry was determined to be a uniformly arranged positive quadrilateral cone. Accordingly, a grinding experiment with a pyramidal belt was conducted to obtain an experienced model of the grain wear height. A numerical simulation model of the grain wear evolution under four wear states (no abrasion, early abrasion, middle abrasion, and late abrasion) was developed. Additionally, more detailed progressive wear of the abrasive grains was also applied to grind the entire profile of the complex curved blade. The residual stress on the blade surface was mainly compressive, and the surface stress values were distributed between −385 and −117 MPa with the service life of the pyramidal abrasive belt.

Surface micro-morphology and residual stress formation mechanisms of near-net-shaped blade produced by low-plasticity ultrasonic rolling strengthening process

Low surface integrity of near-net–shaped (NNS) blades is the primary problem associated with aero engine performance improvements. This paper proposes a low-plasticity ultrasonic rolling strengthening process (URSP) to improve the surface micro-morphology and residual stress of NNS blades. The surface micro-morphology and residual stress formation mechanisms produced by the low-plasticity URSP were introduced first. Then, the influences of the low-plasticity URSP parameters on the surface micro-morphology and residual stress were analyzed. Furthermore, the feasibility of low-plasticity URSP was analyzed through comparative experiments. Finally, the mechanism of low-plasticity URSP was further demonstrated from two aspects of surface micro-morphology and the residual stress. The results showed that increases in the extrusion depth improved the blade surface micro-morphology and residual stress level. The blade had a surface roughness of Ra 0.2 µm after low-plasticity URSP. A residual compressive stress layer of about 70 µm was formed on the blade surface, and the residual stress first increased and then decreased with the increase in depth. The maximum residual stress was 800 MPa when the residual stress layer depth was 30 µm, and the residual stress was close to that of the base material until the depth reached 70 µm.

Stress Coupling Analysis and Failure Damage Evaluation of Wind Turbine Blades during Strong Winds

Blades in strong wind conditions are prone to various failures and damage that is due to the action of random variable amplitude loads. In this study, we analyze the failure of 1.5 MW horizontal axis wind turbine blades. The computational fluid dynamics unsteady calculation method is used to simulate the aerodynamic load distribution on the blade. Fluid–structure coupling methods are applied to calculate the blade stress. The results show that the equivalent stress of the blade is the largest when the azimuth angle is 30°, and the maximum equivalent stress is 20.60 MPa. There are obvious stress peaks in six sections, such as r/R = 0.10 (the span length of blade/the full length of the blade = 0.10). The frequency of damage that is caused by the stress in each area of the blade is determined based on the blade damage. The frequency of gel coat cracking in the blade tips and leaves is 77.78% and 22.22%, respectively, and the frequency of crack occurrence is 87.75%, 10.20% and 2.05%, respectively. By combining the stress concentration area and the damage results, the cause of blade damage is determined, which can replace the traditional inspection methods and improve the inspection efficiency.

The effect of yaw speed and delay time on power generation and stress of a wind turbine

ABSTRACT Through the self-researched and manufactured dynamic rotating platform and model wind turbine, experiments were carried out at the open end of the wind tunnel, and the wind direction angle change and the yaw versus wind process were simulated. The influence of two variables (yaw speed and yaw delay time) on wind turbine power and blade stress is studied. The results are: During the dynamic yaw process, blade stress decreases from the root to the tip. Among the 4 yaw speeds (0.5°/s, 1.0°/s, 1.5°/s, 2.0°/s), the stress and power increase the fastest at 0.5°/s yaw speed, and the slowest increase at 2.0°/s. The rate of increase is inversely proportional to the yaw speed. It is found that in the dynamic yaw process, the yaw angle range of 20° to 0° is the main area of stress increase and power increase. In addition, the yaw delay time is investigated. It is found that if there is a delay time of 30S, when the yaw angle is 30°, the stress value decreases by 0.73711MPa, when the yaw angle is 60°, it decreases by 0.02965MPa, and when the yaw angle is 90°, it decreases by 0.0065MPa. It can be known that as the yaw angle increases, the effect of the delay time gradually decreases, so the delay time can be controlled in stages, that is, when the yaw angle is larger, a smaller delay time is used. We also introduce a dimensionless coefficient, which represents the ratio of power to blade stress. It is pointed out that a yaw speed of 0.5°/s is used at a yaw angle of 30°, a yaw speed of 1.0°/s at 60°, and a yaw speed of 2.0°/s at 90°. The results show that the staged control of the yaw speed can avoid power loss and improve the reliability of the wind turbine during operation.