Centrifugal Stress Research Articles

Centrifugal atomization of stainless-steel rotating rods melted by a high-power LASER beam

316L grade stainless steel powders were produced by centrifugal atomization during the melting of a rotating rod heated by a high-power LASER beam. The feasibility has been demonstrated by atomizing a range of stainless steel rods. The atomization process has been observed via high-speed imaging and fragmentation regimes have been identified according to a literature review on the rotating electrode process (REP). Results were compared with literature data and an existing prediction model for such a process. High-speed observation can monitor the present process and it is shown that a solidified layer of metal is formed at the edge of the rod during the process inducing metal flake ejection due to the centrifugal stresses. Effects of incident LASER beam power density, ejection speed and oxygen content of the surrounding atmosphere on the particle size distribution and the sample surface have been studied and compared with literature data on classical REP atomizers. The study focuses on the production of irregular particles during the atomization process and highlights the influence of the oxygen content in the surrounding atmosphere on the fragmentation regime and the resulting particle size distribution.

Comparative Study of Non-Rare-Earth and Rare-Earth PM Motors for EV Applications

Recently, non-rare-earth motors are attracting more and more attention due to the booming of the electric vehicle (EV) market and, more importantly, the increasing price of the rare-earth magnet material. This paper focuses on the performance comparison among a commercial interior permanent magnet (IPM) motor and two non-rare-earth motors, including a synchronous reluctance motor (SynRM) and a permanent-magnet-assisted synchronous reluctance motor (PMaSynRM). The design procedure to develop a high-torque-density, low-torque-ripple and high-efficiency SynRM is presented. Combined with a developed automatic modeling and simulation procedure, the finite element analysis (FEA)-based differential evolution (DE) algorithm is introduced for the SynRM rotor optimization. In order to fully inspire the potential of the SynRM, a novel method to optimize the motor split ratio is proposed under the constraint of the copper loss. In addition, different slot–pole combinations are investigated to maximize the motor torque, and the rotor structure is also dealt with towards the centrifugal stress at the maximum operating speed. Finally, the motor performance comparison is carried out, and the results show that although the SynRM achieves almost 61% cost savings, its poor torque capability, power factor and flux weakening (FW) capability are non-negligible defects. On the contrary, the PMaSynRM exhibits excellent features for the EV applications in terms of cost, torque density, efficiency and FW capability. This paper presents a novel split ratio optimization method for the optimal SynRM/PMaSynRM design and demonstrates the characteristics of the IPM motors, SynRMs and PMaSynRMs for EV applications.

Stress Analysis of Thin Film Thermocouple Sensor Based on Finite Element Simulation

As a new type of micro device, the reliability of thin film thermocouple sensor is very important in actual work. Aiming at a thin-film thermocouple sensor with NiCr as the functional layer, three main stresses of the thin-film sensor in actual work are analyzed: thermal stress, vibration stress and centrifugal stress. Various stress analyses have been verified through theoretical calculations or finite element simulations. The results show that thermal stress is the main influence stress, and the critical areas of reliability have been obtained. The prepared thin film sensor samples were tested through high temperature experiments, and the analysis results were verified. When a thermal load of 700 degrees Celsius is applied, the stress environment of the protective layer, the functional layer and the insulating layer of the structure is severe, and it is vulnerable to severe damage, and cracks are found in the insulating layer, which becomes a weak area of reliability.

高速回転斜流ブロワの遠心応力変形が及ぼす効率への影響

The target mixed flow blowers are required to have high efficiency, low noise, compact size and light weight. The target mixed-flow opentype impeller under consideration deforms due to centrifugal stress, and the blade tip clearance changes. This study investigated the effect of centrifugal stress deformation on fan efficiency using fluid structure interaction analysis. Using the results of fluid analysis, the authors compared the static pressure change in the flow direction inside the impeller with and without centrifugal stress deformation. The centrifugal stress deformation of the impeller has the effect of reducing the loss at the impeller outletside by increasing the impeller outer diameter and decreasing the blade tip clearance. However, deformation due to centrifugal stress increases the tip leakage vortex loss due to the enlarged tip clearance near the leading edge.

The Flattening and Stiffening Effect of Centrifugal Stress on Circular Saw Blades in Different States

Abstract Circular saw blades have many states, before and during the sawing process, depending on the different residual stresses and flatness of the circular saw blades. Based on the different states of circular saw blades, the effect of rotating centrifugal stress on the dynamic stability of circular saw blades is different, mainly reflected in flattening and stiffening effects. In this article, three representative states of circular saw blades were chosen and studied. The finite element method was chosen to simulate the deformation behavior of circular saw blades in the three states. The flattening and stiffening effects of centrifugal stress on circular saw blades in the three states were systematically studied. The axial stiffness of the outer edge of circular saw blades is increased with rotating speed. The rotating speed has a flattening effect on the circular saw blade, as a result of a centrifugal stress field. When the circular saw blade is in a different state, there are some differences in the flattening and stiffening effect of centrifugal stress.

Efficient Encapsulation and Controlled Release of N,N-Diethyl-3-methylbenzamide (DEET) from Oil-in-Water Emulsions Stabilized by Cationic Nanocellulose and Silica Nanoparticles

Oil-in-water emulsions containing N,N-diethyl-3-methylbenzamide (DEET) were developed aiming to extend the sustained release of the active compound, by using two oppositely charged nanomaterials, namely silica nanoparticles (SiNP) and cationic cellulose nanofibrils (CCNF), as stabilizers, and a mixture of food-grade nonionic surfactants to avoid precipitation by electrostatic aggregation. The formulations were stable for more than four months at room temperature, and strongly resistant to destabilization upon centrifugal and thermal stress. The results were correlated with the effect of SiNP on strengthening the network formation of CCNF in the aqueous phase by electrostatic interactions, which increased the viscosity of the external phase and, hence, emulsion stability. There was a significant size reduction of the internal oil phase containing DEET in the presence of CCNF, which was attributed to the increased viscosity in the external aqueous phase, as well as to interfacial stabilization. The combined action of CCNF and unmodified SiNP in the stabilization of the DEET-containing oil phase significantly decreased the release rate of the active compound, compared to non-emulsified DEET. Moreover, in the emulsions containing the CCNF/SiNP mixture there was a more sustained release for the period of 6 h, demonstrating the potential of these formulations for extended protection.

A unified quasi-three-dimensional solution for vibration analysis of rotating pre-twisted laminated composite shell panels

This study presents a unified quasi-three-dimensional (quasi-3D) solution for the free vibration analysis of rotating pre-twisted laminated composite shell panels. Based on the 3D elasticity shell theory, Carrera unified formulation is employed to reduce the complete 3D dynamic model to a hierarchical 2D dynamic model with a capacity for 3D solving accuracy. A separate quasi-static analysis is conducted to precisely acquire the centrifugal stresses that occur in the rotating laminated composite shell panels. The present quasi-3D dynamic model considers the Coriolis forces, rotational softening effect as well as prestress stiffening effect. Several case studies are presented including the rotating pre-twisted plates, pre-twisted cylindrical shell panels and untwisted conical shell panels with different lamination schemes and geometric parameters. In each case study, the vibration characteristics predicted from the present theoretical model are compared with the reported studies and those from the commercial finite element software. It indicates that the quasi-3D dynamic model has good accuracy and is appropriate for different types of rotating laminated composite shell panels. The influences of the rotating speed, pre-twisted angle, fiber orientation and subtended angle on the vibration behaviors of the rotating pre-twisted laminated composite shell panels are studied as well.

Three-dimensional vibration analysis of rotating pre-twisted cylindrical isotropic and functionally graded shell panels

A weak-form formulation for three-dimensional vibration analysis of rotating pre-twisted cylindrical isotropic and functionally graded (FG) shell panels is first developed. The present formulation is established with the three-dimensional (3-D) elasticity shell theory and Carrera unified formulation, which enables the expression of the traditional and high-order shell theories into a unified form. The potential energy stored in the boundary is transformed into a quantification form by using the penalty method. The 3-D coupled displacement fields are constructed by a modified version of the Fourier series with several additional boundary smoothed functions to ensure the exact description of displacement and stress fields. The complete second-order nonlinear strain terms in the frame of the curvilinear coordinate system are presented to take into consideration the initial centrifugal stresses that are exactly determined with a separate static deflection analysis. Numerical verifications and comparisons of the vibration results with the 3-D finite element method (FEM) show the capabilities of the developed high-order hierarchical model to accurately predict the frequency results and mode shapes of rotating pre-twisted cylindrical isotropic and FG shell panels. Parametric studies are then carried out to investigate the effect of the rotating speed, presetting angle, pre-twisted angle, subtended angle and power-law exponent on the dynamic characteristics of the pre-twisted cylindrical shell panels. It is expected that the present formulation for the rotating pre-twisted cylindrical shell panels will serve as benchmarks to assess the accuracy of other numerical and analytical models.

Analysis of aerodynamic performance of high‐speed rotational components for MEMS based turbomachinery considering effects of tip clearance and diabatic heat transfer

AbstractThis paper addresses a fundamental design guideline for rotational components of a micro‐scale gas turbine engine considering an interaction between geometrical structure and aerodynamics. The rotational components of the micro‐scale gas turbine engine may be subjected to the centrifugal stress due to high‐speed rotation. The efficiency of each component is strongly controlled by geometrical clearance between rotational and stationary components, and heat transfer from the turbine to the compressor. Therefore, the elastic deformations due to the centrifugal stress and heat transfer have important role to determine the practical aerodynamic performance of the rotational components. A new sophisticated geometrical structure was introduced to the rotational components to control the elastic deformation and maintain the compressor efficiency that is necessary to hold the minimum requirement for the thermodynamic cycle.

Thermal and centrifugal stresses in curved double wall transpiration cooled components with temperature dependent thermoelastic properties

The integration of double wall transpiration cooling (DWTC) into gas turbines and hypersonic vehicles is key for addressing future needs in aerospace and power generation. This paper identifies the roles of geometric curvature and temperature dependence of thermoelastic properties on stresses in DWTC systems under combined thermal and centrifugal loading. An increase of thermal expansion coefficient, α, with temperature as exhibited by Ni alloys is shown to dominate over the decrease of Young’s modulus, E, in double walls, such that the thermal stresses are significantly higher than the case of temperature independent E and α. The effect is generally promoted by the thermal mismatch between the walls; in highly curved systems, the difference in wall circumferences also comes into play. The critical stresses at film holes, impingement holes and pedestals are affected differently for systems with convex and concave hot outer surfaces while the optimal wall thickness ratio is suggested to depend on the severity of thermal loading with respect to centrifugal loading. Our elastic solutions provide the essential information for evaluating the structural integrity of DWTC systems and can be generalised to multiwall systems.

Laboratory experiments with self-cohesive powders: Application to the morphology of regolith on small asteroids

A series of experiments have been conducted to study the failure behavior of columns and piles comprised of cohesive fine powders in 1 ​g as a proxy for those which might occur in the agglomerated asteroid structure composed of cm-m size pebbles and boulders in a microgravity environment. Initially symmetrical piles of fine powders, under gravitation or centrifugal stress, develop features similar to those observed on asteroids, such as slide planes and finer cohesive structures. Failure of cohesive columns of fine powders occurs by the nucleation and propagation of fracture planes. In some cases, forming steep cliffs, also reminiscent of features observed on asteroids. Correlation between observed column failure and numerical simulations has been demonstrated based on preliminary results. Microstructure and particle size distribution are shown to substantially determine the extent of cohesiveness. Enhanced cohesion was observed for specific ratios of larger particle intermixed with fine powders. We propose that the wide range of qualitative features and behaviors may reasonably represent those observed on asteroid features as the surface ages. This work has important implications for our understanding and preparation for future missions to NEOs.

Multiscale analysis of thermomechanical stresses in double wall transpiration cooling systems for gas turbine blades

Double wall transpiration cooling (DWTC) is a new technology that allows the gas turbine inlet temperatures to be increased beyond current levels to promote higher engine efficiency. DWTC systems consist of outer hot and inner cooler walls, connected by pedestals, which contain film cooling and impingement holes, respectively. In order to employ these new systems, an evaluation of the stresses that drive fatigue and ratchetting at critical stress raisers is essential. We present a modelling framework which combines Computational Fluid Dynamics (CFD)-heat transfer solutions for the temperature field in DWTC systems, with theoretical and Finite Element (FE) elastic solutions for the thermal (T) stress and centrifugal (CF) stress fields. We demonstrate that uniaxial tensile CF loading causes much higher stress concentration factors (SCF) at cooling holes and wall-connecting pedestals than the thermally induced biaxial stresses. A theoretical framework is developed, supported by FE studies, that captures the dependence of the SCF on important geometric parameters, such as wall thicknesses, pedestal height and hole size, spacing and inclination angle, which provides important information for the optimisation of these systems. A key observation of relevance to both conventional and non-conventional turbine blade designs, is that the superposition of tensile CF stresses to compressive T stresses is beneficial for the performance at the critical film hole features; for double wall blades, however, the superposition degrades the performance at impingement holes and pedestals, as in these locations the T stresses are also tensile. These stresses can be balanced by using an optimal wall thickness ratio. Our elastic solutions can be readily used in analyses for predicting structural ratchet boundaries based on shakedown theory and the local cyclic strain range that drives thermomechanical fatigue in DWTC systems.

An improved analytical dynamic model for rotating blade crack: With application to crack detection indicator analysis

Rotating blade is one of the most important components for turbomachinery. Blade crack is one of the most common and dangerous failure modes for rotating blade. Therefore, the fault mechanism and feature extraction of blade crack are vital for the safety assurance of turbomachinery. This study is aimed at the nonlinear dynamic model of rotating blade with transverse crack and the prior feature extraction of blade crack faults based on the vibration responses. First and foremost, a high-fidelity breathing crack model (HFBCM) for rotating blade is proposed on the basis of criterion for stress states at crack section. Since HFBCM is physically deduced from the perspective of energy dissipation and the coupling between centrifugal stress and bending stress is considered, the physical interpretability and the accuracy of the crack model are enhanced comparing with conventional models. The validity of the proposed HFBCM is verified through the comparison study among HFBCM, conventional crack models, and finite element-based contact crack model (FECCM). It is suggested that HFBCM behaves best among the analytical models and matches well with FECCM. With the proposed HFBCM, the nonlinear vibration responses are investigated, and four types of blade crack detection indicators for rotating blade and their quantification method are presented. The numerical study manifests that all these indicators can well characterize the occurrence and severity of crack faults for rotating blade. It is indicated that these indicators can serve as the crack-monitoring indexes.

A Study of the Thermo-Mechanical Behavior of a Gas Turbine Blade in Composite Materials Reinforced with Mast

The turbine blades are subjected to high operating temperatures and high centrifugal tensile stress due to rotational speeds. The maximum temperature at the inlet of the turbine is currently limited by the resistance of the materials used for the blades. The present paper is focused on the thermo-mechanical behavior of the blade in composite materials with reinforced mast under two different types of loading. The material studied in this work is a composite material, the selected matrix is a technical ceramic which is alumina (aluminum oxide Al2O3) and the reinforcement is carried out by short fibers of high modulus carbon to optimize a percentage of 40% carbon and 60% of ceramics. The simulation was performed numerically by Ansys (Workbench 16.0) software. The comparative analysis was conducted to determine displacements, strains and Von Mises stress of composite material and then compared to other materials such as Titanium Alloy, Stainless Steel Alloy, and Aluminum 2024 Alloy. The results were compared in order to select the material with the best performance in terms of rigidity under thermo-mechanical stresses. While comparing these materials, it is found that composite material is better suited for high temperature applications. On evaluating the graphs drawn for, strains and displacements, the blade in composite materials reinforced with mast is considered as optimum.

Determination of Optimal Start-up Curve for Steam Turbine Unit Considering Centrifugal Stress

This paper concerns the optimal start-up schedule problem of steam turbine unit. Modelling of start-up process synthesizes the energy balance in turbine unit, depiction of control system, calculation of stress and damage. Quantitative analysis is made in the view of model feature, centrifugal stress’s effect, correction to the theoretical schedule and feasible space. Based on the synthetic model of turbine start-up schedule, a nonlinear unitary quadratic function is proposed and solved as the trajectory to improve start-up efficiency. Finally, the cold start-up of a domestic 300MW steam turbine unit is taken as a simulation example to prove the capability of this nonlinear start-up curve. Without violating the stress limit strictly, although the desired time improvement is only 6.35%, it still has important significance in practical thermal engineering, especially in the aspect of energy saving.

Aerodynamic optimization of the last stage turbine blade for an industrial gas turbine

A multi-objective, aerodynamic optimization of the last stage turbine blade of an 100Hz industrial gas turbine is presented. We aim at maximizing the stage’s efficiency, while at the same time meeting mechanical integrity. The optimization procedure was build, during the optimization process the mass flow rate and stage meridian were kept constant to obtain the required stage loading without changing the operating point. The optimized geometry are chosen taking into account aerodynamic constraints as well as mechanical constrains, such as centrifugal stress and bending stress. The SST turbulence model was used to calculate the flow field of the original and optimized stage, respectively. The geometry of the original and optimized blade was compared. The stage efficiency of the design point and under different operate conditions were compared. Stage and blade efficiency along span was analyzed in details. The blade loading at root mid top span of the original and optimized blade were discussed. Detailed flow field analysis shows that, after optimization, the peak Mach number of the root span profile was decreased from 1.22 to 1.09, which improves the flow field. Profile loss and end wall loss were also reduced. After optimization, maximum centrifugal stress and the maximum air bending stress were decreased which leads to improved blade life and safety. The number of blades and b/h were suggested for the last stage blade.

The Status Quo of Aerospace Engine Vibration Fatigue

In the working environment of aero engine blades, it is necessary to withstand the influence of factors such as aerodynamic stress, vibration stress, centrifugal stress, thermal stress, high temperature oxidation, thermal corrosion, etc. The blades often exhibit vibration fatigue fracture, foreign object damage, corrosion, material defects, and sports damage. This article summarizes the fatigue fracture problems of aero-engine blades, provides a systematic basic theory for the design, innovation and development of aero-engine blades, and has certain reference value.

Observational Evidence for Rotational Desorption of Complex Molecules by Radiative Torques from Orion BN/KL

Abstract Complex organic molecules (COMs) are believed to form in the ice mantle of dust grains and are released to the gas by thermal sublimation when grain mantles are heated to temperatures of T d ≳ 100 K . However, some COMs are detected in regions with temperatures below 100 K. Recently, a new mechanism of rotational desorption due to centrifugal stress induced by radiative torques (RATs) was proposed by Hoang & Tram (2020) that can desorb COMs at low temperatures. In this paper, we report observational evidence for rotational desorption of COMs toward the nearest massive star-forming region, Orion BN/KL. We compare the abundance of three representative COMs that have very high binding energy computed by the rotational desorption mechanism with observations by ALMA, and demonstrate that the rotational desorption mechanism can explain the existence of such COMs. We also analyze the polarization data from SOFIA/HAWC+ and JCMT/SCUBA-2 and find that the polarization degree at far-infrared/submillimeter decreases with increasing the grain temperature for T d ≳ 71 K . This is consistent with the theoretical prediction using the RAT alignment theory and Radiative Torque Disruption mechanism. Such an anticorrelation between dust polarization and dust temperature supports the rotational disruption as well as rotational desorption mechanism of COMs induced by RATs.

A quasi-3D dynamic model for free vibration analysis of rotating pre-twisted functionally graded blades

This study provides a quasi-three-dimensional (quasi-3D) dynamic model for rotating pre-twisted functionally graded (FG) blades based on the three-dimensional elasticity shell theory and Carrera unified formulation. The material properties of the pre-twisted FG blades alter continuously in the direction of the thickness. The boundary conditions (clamped-end and free-edge) are realized by utilizing the well-known penalty method. Initial centrifugal stress field due to the high rotating speed is determined by two centrifugal stress solving methods, direct integration of centrifugal forces (DICF) and static analysis under centrifugal forces (SACF). The modified Fourier spectral approach is utilized to construct the displacement variables of the higher-order configurations. Eigenvalue problems are obtained by using the Hamilton's principle on the base of the kinetic, strain, centrifugal potential and boundary potential energy. The results of the theoretical model display a good agreement with the reference data and FEM results. Parametric studies are then performed to assess the applicability of the centrifugal stress solving methods and investigate the effects of the centrifugal shear stress, rotating speed, pre-twisted angle, penalty factors as well as the volume fraction index on the vibration characteristics of the pre-twisted FG blades. It is expected that the quasi-3D solutions for the rotating pre-twisted FG blades will serve as benchmarks in future researches.

Dynamic Characteristic Analysis of Rotating Blade With Transverse Crack—Part I: Modeling, Modification, and Validation

Abstract This study aims at the systematical improvement and comparative analysis of analytical crack models for the rotating blade. Part I of this study focuses on analytical modeling, model modification, and model validation of transverse crack for the rotating blade. The most widely applied analytical crack models for the rotating blade are reviewed and compared, and then their limitations are discussed. It is indicated that the conventional analytical crack models suffer from low physical interpretability and vibration prediction accuracy. By considering these limitations of conventional analytical crack models, model modification is performed to enhance the physical meaning and improve the accuracy. First, the stress-based breathing crack model is modified by direct calculation of the breathing function based on the theory of linear elastic fracture mechanics and resetting the correction factor of centrifugal stiffening stiffness. Second, the vibration-based breathing crack models, including bilinear breathing crack model and cosine breathing crack model, are modified by introducing the coupling effect between bending stress and centrifugal stress based on the stress state at the blade crack section. The additional bending moment induced by the blade part outside the crack section is considered in all analytical models. The modified crack models’ validity is verified by comparing vibration responses obtained by the modified crack models, the finite element contact crack model, and the conventional crack models. The comparative results suggest that the modified models promote the physical interpretability and improve the vibration prediction accuracy of analytical crack models.