High Rotational Speed Research Articles

Behavior of an aerodynamic sliding bearing with textured surface under turbulent conditions

Abstract Recent advancements in turbomachinery development aim to reduce components while improving performance and minimizing environmental impact. Aerodynamic bearings, supporting high-speed rotors by dissipating significant energies, are key elements requiring thorough understanding. In order to better predict the behavior of aerodynamic bearings operating under severe conditions, numerical models using computational fluid dynamics have been employed to study the thermal effect on the tribological behavior of these air-lubricated bearings. An analysis of surface texturing of the bearings has also been conducted to evaluate its influence on operational performance compared to non-textured surfaces, considering the influence of rotation speed, radial load, and textures on the tribological performance of plain bearings. The main results observed are as follows. First, there is a noticeable change in geometric characteristics, such as the application of micro-textures, lubrication and friction, compared with conventional plain bearings. This textured surface appears to have a significant influence on the pressure and velocity distribution of the lubricating fluid, leading to significant changes in the bearing's tribological and operational performance. In addition, numerical analysis also reveals significant variations in shear stresses in the vicinity of the bearing walls. These variations can potentially affect the strength and durability of the bearing under severe operating conditions. Additionally, the results show a downward trend in system temperature, suggesting improved thermal management thanks to the textured surface. Another essential aspect revealed by this analysis is the decrease in the coefficient of friction with increasing shaft speed. This observation underlines the importance of operating speed and applied radial load in the bearing's tribological behavior and suggests further optimization possibilities for reducing energy losses and extending the life of the aerodynamic sliding bearing.

Investigation of cavitation characteristics in an aircraft centrifugal fuel pump

Cavitation is a classic gas–liquid two-phase flow phenomenon that needs to be restricted for the hydraulic performance enhancement of centrifugal pumps. However, due to the particularity of fuel mediums and rigorous aviation conditions, the characteristics of cavitation occurring in aircraft centrifugal fuel pumps have not been elaborated. In this research, cavitation characteristics in an aircraft centrifugal fuel pump with a high rotational speed of 14,000 rpm were investigated by considering the influence of the flow rate ranging from 0.2Qd to 1.2Qd and the fuel temperature ranging from 20 °C to 100 °C. An experiment for testing the hydraulic performance of an aircraft centrifugal fuel pump was built, and a corresponding numerical simulation of gas–liquid two-phase flow was employed. The distributions of the pressure, streamlines, and turbulence kinetic energy in the centrifugal pump for different flow rates and fuel temperatures were comparatively analyzed. The net positive suction head available (NPSHa) was defined to represent the cavitation degree, and the net positive suction head required (NPSHr) was introduced to characterize the critical cavitation occurrence. It was also found that a large area of cavitation bubbles was generated in the inducer and that this area grew to block the flow channel of the impeller when the NPSHa was close to or lower than the NPSHr, which was the cavitation mechanism of hydraulic performance degradation. Additionally, the developments of the NPSHr with the flow rate and fuel temperature were determined adequately using natural exponential curve fitting. It was deduced that the occurrence of cavitation was more sensitive to higher flow rates, especially when the flow rate was higher than the designed flow rate. The effect of fuel temperature variations should also be considered for the long-time high-speed operation of centrifugal fuel pumps in the aerospace industry.

Demonstration of a small‐scale power generator using supercritical CO2

AbstractThe supercritical CO2 (sCO2) power cycle could improve efficiencies for a wide range of thermal power plants. The sCO2 turbine generator plays an important role in the sCO2 power cycle by directly converting thermal energy into mechanical work and electric power. The operation of the generator encounters challenges, including high temperature, high pressure, high rotational speed, and other engineering problems, such as leakage. Experimental studies of sCO2 turbines are insufficient because of the significant difficulties in turbine manufacturing and system construction. Unlike most experimental investigations that primarily focus on 100 kW‐ or MW‐scale power generation systems, we consider, for the first time, a small‐scale power generator using sCO2. A partial admission axial turbine was designed and manufactured with a rated rotational speed of 40,000 rpm, and a CO2 transcritical power cycle test loop was constructed to validate the performance of our manufactured generator. A resistant gas was proposed in the constructed turbine expander to solve the leakage issue. Both dynamic and steady performances were investigated. The results indicated that a peak electric power of 11.55 kW was achieved at 29,369 rpm. The maximum total efficiency of the turbo‐generator was 58.98%, which was affected by both the turbine rotational speed and pressure ratio, according to the proposed performance map.

Interaction and superposition of creep damage and high-cycle fatigue of coarse-grained nickel-base alloy 247

ABSTRACT The cast coarse-grained polycrystalline Alloy 247 is investigated, which is typically used in the rear turbine blades of land-based gas turbines. High rotational speeds up to 10,000 rpm in combination with high temperatures induce creep deformation. Additionally, gas turbine blades are subjected to high-frequency cyclic stresses. This complex loading state requires the investigation of the interaction of creep damage and high-cycle fatigue (HCF). Therefore, HCF tests with a stress ratio of Rσ = −1 were carried out on as-received and pre-crept specimens. In comparison, an HCF test series with high mean stresses (Rσ = 0.5) was conducted to consider the superposition of creep and fatigue. Since nickel-base alloys exhibit a pronounced elastic anisotropy, the grain orientations were considered in the damage analysis. The results show that creep-induced grain boundary damage is a dominant structural parameter for the HCF behaviour of Alloy 247 in both, sequential and superpositioned creep-fatigue loading.

Ispitivanje i optimizacija površine zavara i mehaničkih performansi termoplastičnih delova proizvedenih aditivnom proizvodnjom i zavarenih zavarivanjem trenjem

This study presents an experimental investigation into the weldability of ABS M30 (acrylonitrile butadiene styrene) plates produced by Additive Manufacturing (AM) using Friction Stir Welding (FSW). The effects of FSW process parameters on the yield stress and their optimal levels were determined using the Taguchi method. The optimal welding parameters were found to be a 16 mm tool shoulder diameter, 800 rpm tool rotation speed, and 10 mm/min traverse speed. The weld area of each sample welded using FSW was examined at a macroscopic level. The direction of tool rotation significantly affects the quality and strength of the FSW. When the FSW was performed with a clockwise rotation of the welding tool, a perfect weld could not be achieved. The tunnel effect resulted in gaps in the weld area of the samples at high rotation speeds. Differences were observed in the density between the weld area of the samples and the main parts.

Mechanical Properties of FSW Joints Magnesium Alloy at Different Rotational Speeds

Magnesium (Mg) has become a focus in the transportation industry due to its potential in reducing fuel consumption and gas emissions while improving recyclability. Mg alloys are also known for their low neutron absorption, good resistant of carbon dioxide as well as thermal conductivity which makes them suitable for use in industrial equipment for nuclear energy. there has been an increasing interest in the research and development of Mg alloys. These are the lightest of all metallic structural materials and are approximately 33% lighter than aluminium (Al) and 75% lighter than ferrous (Fe) alloys and have excellent specific mechanical properties. In this work, FSW of AZ31B Alloy was examined at the various rotational speeds of 900 -1440 rpm, with fixed welding speed of 40mm/min and 2° tool tilt angle using an HSS tool. The mechanical properties were compared for the different rotational speeds. The quality of FSW joints is dependent on input value of heat and material flow rate, which are prejudiced by process parameters., higher rotation speeds may cause abnormal stirring, resulting in a tunnel defect at the weld nugget due to increased strain rate and turbulence.

Effects of a rotating partition on mixed convection of hybrid nanofluid in a lid-driven cavity under different magnetic fields

There are many thermal engineering applications that employ partitions, such as heat exchangers, cryogenics, electronic cooling, and mixture separation. In this study, a novel type rotating partition is proposed and its performance is numerically assessed by the consideration of mixed convection in a lid-driven cavity with an inner isothermal blockage under magnetic field. A number of numerical simulations are run for various values of the Richardson number (0≤Ri≤50), rotational Reynolds number (0≤Rew≤50), Hartmann number of the inner domain (0≤Ha≤50), and non-dimensional size of the rotating partition (between 0.2 and 0.35). The experimental validation of the mixed convection for a lid-driven cavity is performed. It is observed the effects of rotation of the partition become important when natural convection effects become dominant. At the highest rotational speed, heat transfer reduction of 15% is obtained with increasing the Ri from 0.5 to 50, while at Ri = 50, partition rotation considering highest speed results in average Nusselt number (Nu) reduction by about 5.5%. Streamlines and isotherms are significantly affected by the size of the partition, while slight changes are obtained by varying the magnetic field strength. The reduction of Nu is obtained in the range of 8.5% and 8.8% with a higher magnetic field strength. The increments in the heat transfer by using the highest partition size are obtained in the range of 22.6% and 27.3%. When comparisons are made with non-partitioned lid-driven cavity, average Nu is reduced between 41.6% and 50% by using rotating partition. In the natural convection dominated case, heat transfer reduction will be 4% higher when rotations become active as compared to stationary partition. Feed forward recurrent network model with 25 neurons is used for accurate prediction of the thermal system of lid-driven cavity with rotating partition under magnetic field.

Combined Impact of SiC/TiB2 Nanoparticles in Friction Stir Welding of Different Aluminium Alloys

In this work, Friction Stir Welding process was done on the dissimilar alloys AA8014 and AA2024, with focus on analysing mechanical properties such as tensile strength (UTS), hardness (BHN), and wear rate (WRT). The influence of SiC/TiB2 nanoparticles, with Wt% ranging from 2 to 8 wt%, was examined on the mechanical properties. The rotational speed (RS) was changed from 1200 rpm to 1400 rpm, while the welding speed was kept at a constant 150 mm/min throughout the process. The results specified that an increase in RS to 1400 rpm, combined with 8 wt% , improved the ultimate UTS to 239.4 MPa. SEM examination of the fractured surface revealed that micro dimples were produced at this higher rotational speed. This phenomenon is attributed to the more intense stirring action at 1400 rpm, which leads to turbulent material flow in the stir zone. The resulting turbulence could cause uneven particle distribution and entrap air or other voids, contributing to the formation of micro dimples in the weld nugget.

A vibrating capillary for ultrasound rotation manipulation of zebrafish larvae.

Multifunctional micromanipulation systems have garnered significant attention due to the growing interest in biological and medical research involving model organisms like zebrafish (Danio rerio). Here, we report a novel acoustofluidic rotational micromanipulation system that offers rapid trapping, high-speed rotation, multi-angle imaging, and 3D model reconstruction of zebrafish larvae. An ultrasound-activated oscillatory glass capillary is used to trap and rotate a zebrafish larva. Simulation and experimental results demonstrate that both the vibrating mode and geometric placement of the capillary contribute to the developed polarized vortices along the long axis of the capillary. Given its capacities for easy-to-operate, stable rotation, avoiding overheating, and high-throughput manipulation, our system poses the potential to accelerate zebrafish-directed biomedical research.

Fe-doped Cu-based bimetallic metal-organic frameworks as nanoscale microwave sensitizers for enhancing microwave thermal and dynamic therapy for hepatocellular carcinoma.

Microwave ablation (MWA) is recognized as a novel treatment modality that can kill tumor cells by heating the ions and polar molecules in these cells through high-speed rotation and friction. However, the size and location of the tumor affect the effective ablation range of microwave hyperthermia, resulting in residual tumor tissue and a high recurrence rate. Due to their tunable porous structure and high specific surface area, metal-organic frameworks (MOFs) can serve as microwave sensitizers, promoting microwave energy conversion owing to ion collisions in the porous structure of the MOFs. Moreover, iron-based compounds are known to possess peroxidase-like catalytic activity. Therefore, Fe-doped Cu bimetallic MOFs (FCMs) were prepared through a hydrothermal process. These FCM nanoparticles not only increased the efficiency of microwave-thermal energy conversion as microwave sensitizers but also promoted the generation of reactive oxygen species (ROS) by consuming glutathione (GSH) and promoted the Fenton reaction to enhance microwave dynamic therapy (MDT). The in vitro and in vivo results showed that the combination of MWA and MDT treatment effectively destroyed tumor tissues via microwave irradiation without inducing significant side effects on normal tissues. This study provides a new approach for the combined application of MOFs and microwave ablation, demonstrating excellent potential for future applications.

Mechanical and Vibration Analysis of a High-Speed Outer Rotor Electric Motor

Mechanical and Vibration Analysis of a High-Speed Outer Rotor Electric Motor

High-Speed Synchronous Reluctance Machine Rotor Using Multi-Material Additive Manufacturing

High-Speed Synchronous Reluctance Machine Rotor Using Multi-Material Additive Manufacturing

Vehicle greenhouse gas emission factors based on multi-dimensional Bin interval mode

The emission factors of greenhouse gases from motor vehicles are of significant importance for low-carbon and environmentally friendly initiatives. This paper focuses on greenhouse gas emission factors of heavy-duty vehicles. The multi-dimensional Bin interval mode are proposed, which considers multiple parameters such as vehicle speed, acceleration, torque, and rotational speed. Based on this, the emission characteristics of greenhouse gases from heavy-duty vehicles. are investigated under different parameter conditions. The results indicate that as the VSPA value or the engine torque increases, the CO2 emission factor also increases accordingly. The CO2 emission factor is lower at medium to high rotational speeds, while it tends to increase at low rotational speeds. The research findings provide support for monitoring and evaluating greenhouse gas emissions and offer scientific guidance for formulating specific carbon reduction policies, emission targets, and plans.

Research on Micro Gap Flow Field Characteristics of Cylindrical Gas Film Seals Based on Experimental and Numerical Simulation

Flexible support cylindrical gas film seals (CGFSs) adapt well to rotor whirling and have a good gas lubrication effect during thermal deformation. However, when a CGFS operates under the “three high” (high interface slip speed, high-pressure differential, and high ambient temperature) operating conditions, the complex deformation of the support structure is a crucial factor affecting the stability of the CGFS. A thorough and systematic analysis of the micro gap flow field characteristics of flexible support CGFSs is a fundamental problem when we study the deformation of the support structure under multiple physical field conditions. This study uses a cylindrical gas film high-speed rotor test rig to study and compare the sealing characteristics of experiments and numerical simulations and then optimizes and verifies the accuracy and effectiveness of the simulation model. A cross-scale gas film grid model is used to analyze the flow field characteristics and seal ability of different groove models and compare the mechanical characteristics and sealing performance. We also analyze the gas film pressure distribution in micro gaps and explore the impact of dynamic pressure groove microstructure on flow field characteristics. Results show that micro gaps are the primary conditions for generating hydrodynamic effects, and high rotational speed, high-pressure differential, and large eccentricity have a significant effect on improving hydrodynamic effects and enhancing gas film stability. However, an increase in these parameters can cause an increase in leakage rate. A single flow channel makes it easier to improve the hydrodynamic effect, gas film load-bearing ability, and gas film stability while reducing leakage rate. The analyses in this study supplement and improve the theory of the flow field characteristics of cylindrical annular micro gaps and provide a theoretical basis for exploring the relation between the support structural parameters of the CGFS and the mechanical characteristics of the micro gap flow field. This study provides important guidance to the establishment of a quantitative design theory of supporting structures.

Investigation on Secondary Flow of Turbodrill Stator Cascade with Variable Rotary Speed Conditions

There are various secondary flow types in turbodrill’s blade cascades, and all kinds of secondary flow have a significant effect on flow loss. In this paper, the stator cascade of φ160 mm turbodrill is taken as the research object, and the CFD method is used to analyze the secondary flow and its evolution. The origin and evolution mechanism of secondary flow is explained from the flow mechanism. The results show that when the working rotary speed is lower than the design rotary speed, the secondary flows are composed of suction surface separation vortex, horseshoe vortex, and passage vortex coexisting. The intensity of secondary flows increases with the decrease of rotary speed. When the working rotary speed is near the design rotary speed, the secondary flows include horseshoe vortex, passage vortex, and corner vortex. When the working rotary speed is higher than the design rotary speed, the secondary flows consist of pressure surface separation vortex and suction surface trailing edge separation vortex. Regardless of rotary speed, secondary flow intensity in the shroud region is greater than the hub region, which has a greater influence on the mainstream. In addition, compared with high rotary speeds, secondary flow intensity is greater at low rotary speeds, resulting in greater flow losses.

The study investigates the effects of tool pin length, rotation speed, and dwell time on the microstructure and tensile strength of dissimilar joints between low-carbon galvanized steel and aluminium T6-6061 through friction stir spot welding

Friction stir welding is an efficient method for joining steel and aluminum plates at a point of disturbance. In many studies, the tool is only introduced into the aluminum plate, avoiding penetration into the steel plate due to its high strength and the need for a robust tool. Under such conditions, the created connection usually possesses low mechanical properties. In this research, by increasing the strength of the H13 steel tool through thermal operations, the possibility of penetration and bonding of aluminum 6061 with galvanized low-carbon steel has been provided. Moreover, by penetrating the steel plate, the integration of galvanized layers in the disturbance region has been facilitated. The examined variable parameters include pin length, rotational speed, and tool dwell time. Mechanical properties such as tensile strength, fracture force, and Vickers hardness were investigated. Furthermore, the weld microstructure and intermetallic layers were examined using scanning electron microscopy (SEM) and EDS analysis. Tensile and shear strength increase with an increase in pin length, rotational speed, and tool dwell time. Shear fracture loading showed a decrease with increasing pin length, then reached its maximum value when using long pins, while continuously increased with higher rotational speed and longer tool dwell time. As we approach the center of the weld in both the steel and aluminum parts, smaller grain sizes are observed due to increased plastic deformation, more material mixing, and increased mechanical tool pressure, while in the heat-affected zone, a coarse grain structure forms. Hardness in the aluminum plate decreased in the heat-affected zone and reached its minimum value in the thermo-mechanical-affected zone, then increased to the maximum value in the nugget zone, while hardness changes in the steel plate were uncertain. The most influential parameter on mechanical and microstructural properties was pin length, followed by rotational speed and tool dwell time.

Dynamic Characteristics of an Automotive Air-Conditioning Electromagnetic Clutch

The automotive air conditioning (AC) electromagnetic clutch plays a crucial role in accurately controlling power transmission between the engine and the compressor, ensuring the proper operation of the AC system. The aim of this paper is to provide high-quality experimental data for researchers who are interested in simulating the dynamic process of an AC electromagnetic clutch and also to assess the adaptiveness of empirical equations to describe the AC electromagnetic clutch performance that is limited in discussion in existing studies. In this study, an automotive AC electromagnetic clutch characteristic test system was employed along with an infrared (IR) camera to conduct comprehensive experimental analyses. The test system enabled the evaluation of various parameters, including the clutch torque output, compressor exhaust pressure, and temperature of the friction surface. The results revealed that the torque and exhaust pressure were closely associated with the on/off time and rotational speed, with a peak value observed around 3000 rpm. Additionally, longer break-in time, higher rotational speeds, and shorter on/off time led to varying increases in the temperature of the friction surface. These findings provided a theoretical foundation for optimizing the design and control of automotive AC electromagnetic clutches. By enhancing design or adjusting control strategies, these clutches can better handle high-load and high-frequency working conditions.

Improving the reliability of the turbocharger seal assembly by optimizing the elements of the seal assembly

Currently, most power units using internal combustion engines are equipped with turbocharging and that is explained by the requirements for efficiency, environmental safety and specific power characteristics. At the same time, the turbocompressor (TCR) is one of the resource-determining elements of power units, which accounts for a significant number of failures. Studies conducted towards the analysis of turbocompressor failures have shown that the main reason for it lies in a malfunction of the seal assembly, which is a consequence of extremely unfavorable conditions for its operation, consisting in a high (up to 800 оС) exhaust temperature, aggressive environment, a high (up to 120.000 min-1) rotor speed, the sliding speeds of the mating parts, up to 150 m/s. Oil for lubrication and cooling of the TCR is supplied through floating plain bearings, while the cavities of the turbine and compressor are isolated by means of the seal assemblies. Violation of their operability leads to the ingress of oil in a cavity of the impellers, to the imbalance of a rotor and, ultimately, to a turbocompressor failure. The determining factor affecting the operability of the seal assembly is a heat density of its parts. This factor is especially manifested in operating under forced conditions and engine shutdown, when cooling of a turbine volute is stopped by blown air, and a bearing assembly is stopped by circulating oil. In this case, a large part of the thermal energy is transferred from a heated turbine volute to the seal assembly and to the bearing assembly. The focus is on the temperature influence on performance of the turbocompressors’ sealing rings.

Action mechanism of axial flow on windage loss in open shaft‐type gap with CO2

AbstractThe windage loss in rotor‐stator gap has an important effect on rotating machinery, especially with higher rotational speed and fluid density. However, the mechanism of axial flow on windage loss in open shaft‐type gap is hardly studied in most literature. To clarify it, the influences of axial Reynolds number Reu and rotational Reynolds number Reω on skin friction coefficient Cf are investigated, and flow characteristics are analyzed with different gap geometry, radius ratio η. First, the results reveal that the Cf remains constant when Reu is less than 2.8 × 104 and increases rapidly as Reu when Reu ≥ 2.8 × 104, which indicates that the effect of axial velocity u on Cf is negligible for low Reu. The positive relative deviation Δ suggests that the axial flow makes windage loss and Cf rise. Besides, a larger number of Taylor vortexes fill with gap when the effect of the centrifugal force is larger than that of the inertial force, but they gradually disappear as Reu. Subsequently, the Cf and Δ increase as η, highlighting that the effect of u on windage loss and Cf is more prominent for larger η. The fact that vorticity near walls is larger than that at the center of gap reveals that windage loss arises from the interaction between walls and fluid rather than the dissipation with fluid itself. Finally, the model of Cf in shaft‐type gap is proposed in different Reω ranges based on numerical results, and the maximum sum of squares error of 1.02 × 10−5 and minimal R2 of 0.969 satisfy the requirement of fitting accuracy and indicate that the fitting model can accurately predict Cf. The conclusions significantly help predict windage loss in open shaft‐type gap with axial flow, and further improve the design for generators of supercritical CO2 turbine‐alternator‐compressor unit.

Hydrodynamic design of the Separate Effect test facility for Flow-Accelerated Corrosion and Erosion (SEFACE) studies in liquid lead

Flow-accelerated corrosion and erosion (FACE) phenomena can be crucial for performance of structural elements in heavy liquid metal (HLM) cooled reactor systems. Existing experimental observations indicate that turbulent flow characteristic can affect FACE, but there is no quantitative data that can be used for model development and validation. Main recirculation pump impellers, which operate at high relative velocities and rotational flow conditions can be especially vulnerable to FACE. For comparison, the core internals operate at lower velocities and in axial flow conditions, but at higher temperatures and neutron fluence. Hence, systematic experimental data is needed to improve our knowledge on FACE phenomena. The Separate Effect Test Facility for Flow-Accelerated Corrosion and Erosion (SEFACE) is designed to obtain such experimental data including high relative velocities (up 20 ms−1) and high temperatures (400 to 550 °C) of liquid lead. This article focuses on the hydrodynamic design of SEFACE. The aim of the design is to achieve well defined flow conditions for experiments and ensure safe operation of the facility. First, we examine three design concepts (i.e., forced convection loop, rotating cylinder, and rotating disk) and motivate the choice of the rotating disk approach for SEFACE. Second, we discuss different design options, i.e., a confined rotor–stator test chamber and the unconfined rotating disk configuration. We used Reynolds-Averaged Navier Stokes (RANS) calculations to identify and solve the issues stemming from the high rotational speed. These include, for instance, lead free surface deformation, radial pressure buildup, and axial bending forces due to asymmetric test chamber. The CFD-derived torque and power predictions in rotor–stator and rotating disk systems are verified with selected empirical turbulent friction factor correlations or/and DNS calculations. We demonstrate that the developed hydrodynamic design of SEFACE solves identified issues and enables obtaining experimental data under well-defined flow conditions. The findings are deemed to also be applicable to the design of rotating disk-type FACE installations for other liquid mediums.