Large Rotational Speed Research Articles

FSI simulation of a high-head pump-turbine during load rejection process

Abstract High-head pump-turbine suffers large centrifugal and hydraulic forces due to large rotational speed and severe pressure pulsations during transient processes, and the strong vibration may increase the risk of runner failure. Load rejection transient process is crucial for pumped-storage hydropower stations, and the evolution laws of the runner dynamic stress during this process need profound research. In this study, the evolution of the runner dynamic stress of a prototype pump-turbine during a load rejection transient process was simulated using the one-dimensional and three-dimensional coupling (1D-3D) method and the fluid-structure interaction (FSI) method. The results of this dynamic transient process were compared to the results of the static working points. It is shown that the rotational speed dominates the mean value of stress while the fluctuating amplitude of stress is dominated by pressure fluctuations, which are larger in the S-shaped region of characteristics. Compared with the static working point solutions, the transient process solutions can better reflect the stress fluctuations and should be used for safety assessment.

Grinding Force Model and Experimental Study on Ultrasonic Assisted Spiral Grinding of Silicon Carbide Ceramic Materials

In order to reveal the mechanical properties of silicon carbide ceramic materials during the drilling process, based on the indentation fracture mechanics theory, a grinding force model of ultrasonic assisted spiral grinding for hole making was established, and the experimental results of ultrasonic assisted spiral grinding for hole making verified the mechanical model. The results showed that the experimental results had the same change trend as the predicted results of the established mechanical model, and the values were close to each other, indicating the accuracy of the established prediction model. The influence of different process parameters on the size accuracy of the hole inlet and outlet aperture after machining is analyzed. It is found that it should be selected as large rotation speed, moderate axial feed speed and small feed pitch to ensure the accuracy of the aperture and effectively suppress the aperture defects during ultrasonic assisted spiral grinding.

High-altitude airship variable-pitch propeller performance analysis at multiple altitudes

To achieve better propulsion performance for high-altitude airships, this paper proposes a variable-pitch propeller design and performance analysis. Propeller surrogate models were constructed based on an in-house fluid–structure solver and validated by a wind tunnel experiment. Based on the surrogate model, this paper studied propeller performance under the common influence of propeller pitch variation and rotational speed, and proved the positive effect of the variable-pitch propeller on maintaining relatively high efficiency in large rotational speed range. This paper compared the performance of variable-pitch propellers and fixed-pitch propellers under the constraints of the motor. The results show that introducing variable-pitch propellers to high-altitude airships can significantly improve propeller performance at multiple altitudes and laminar wind speeds. And the potential of airship weight reduction brought by the variable-pitch technique is discussed as well.

A noncontact self-suction wheat shooting device for sustainable agriculture: A preliminary research

In this study, a noncontact self-suction wheat shooting device was developed through TRIZ theory to improve seed-filling performance and eliminate the contact between seed and device. A preliminary suction experiment was developed using FLUENT to simulate airflow velocity and evaluate the feasibility of self-suction performance of seeds. The DEM-CFD coupling simulation experiment was conducted to investigate the shooting performance. The simulation results showed the airflow velocity was over 6.5 m/s while rotational speed was more than 800 rpm, which could meet the seed-filling requirements. With the rotational speed increase, seed velocity and seed filling performance improves. On the contrary, a larger rotational speed and installation angle induced a higher CF (contact force). CF was significantly affected by rotational speed, window length and installation angle. The increasing window length resulted in the improvement of seed filling performance in a certain range. Meanwhile, the indicators of coefficient of variation for seeding uniformity (CVSU), coefficient of variation for seeding depth (CVSD) and seed damage rate (DR) were evaluated to investigate sowing performance of self-suction shooting device in validation experiment. Results from bench and field experiment showed the seed-filling and shooting performance of self-suction shooting device under optimized operation parameters could fully meet the sowing requirement of winter wheat in North China plain. The collision performance between seed and blades of optimized self-suction shooting device was superior to the mechanical one. In specific, CVSU, CVSD, ASD, ASS and seed germination rate of optimized self-suction shooting device were 11.3%, 8.7%, 31.0 m/s, 30.1 mm and 89.2%, respectively.

Internal Rotor Actuation and Magnetic Bearings for the Active Control of Rotating Machines

Passive rotors are often limited in rotational speed due to bearing constraints, stability and excessive vibration levels. To address the vibration issue, Active Magnetic Bearings (AMBs) levitating the rotor with a magnetic field can be used. They offer a clearance and variable stiffness and damping to the rotor support, which help to mitigate greatly the vibration issue. However, they are also limited at large rotational speed because of the high frequency control force required to levitate the rotor safely. To overcome the frequency limitation, a dual AMBs/internal bending control concept is investigated with associated modelling and control algorithms. This approach is examined in simulation with a 19 kg rotor running up to 10,000 RPM, where three resonance frequencies are present at 2700, 5300, and 9300 RPM, with the first resonant frequency being the most strongly excited. Using internal rotor bending control, a maximum radial displacement of 15 μm for the rotor mid-point is achieved, which gives a reduction in vibration amplitude of 45% compared to the case of no control. Variations of the algorithm are presented and discussed, showing the potential of the proposed approach.

Study on Dynamic Characteristics of Drill String Considering Rock-Breaking Process

Using various tools to obtain downhole data to reach a precise pore pressure model is an important means to predict overpressure. Most downhole tools are connected to the lower end of drill string and move with it. It is necessary to understand the motion state and dynamic characteristics of drill string, which will affect the use of downhole tools. In this paper, a drilling process considering rock-breaking process in vertical wells is simulated using finite element method. In the simulation, gravity is applied to the whole drill string. The contact force between PDC bit and formation is the weight on bit (WOB). And a rotation speed is applied to the upper end of drill string. Analysis of the results shows that the vibration amplitude of bottom hole WOB (contact force between PDC bit and formation, which is the real WOB in drilling process) is bigger than the amplitude of wellhead WOB (acquired through conversion using Hook load, which is on behalf of the WOB obtained on drilling site). Both wellhead WOB and bottom hole WOB decline with a fluctuation in drilling process. In small initial WOB and low rotation speed conditions, the fluctuation of wellhead WOB focuses on low frequency, the fluctuation of bottom hole WOB focus on high frequency, and the phase of them are not identical. In large initial WOB and high rotation speed conditions, the fluctuation of wellhead WOB and bottom hole WOB both become more irregular. As for wellhead torque and bottom hole torque, the fluctuation of them mainly focuses on low frequency. And in high rotation speed conditions, wellhead torque may become negative. The research results are beneficial to the usage of downhole tools.

Zero-point excitation of a circularly moving detector in an atomic condensate and phonon laser dynamical instabilities

We study a circularly moving impurity in an atomic condensate for the realisation of superradiance phenomena in tabletop experiments. The impurity is coupled to the density fluctuations of the condensate and, in a quantum field theory language, it serves as an analog of a detector for the quantum phonon field. For sufficiently large rotation speeds, the zero-point fluctuations of the phonon field induce a sizeable excitation rate of the detector even when the condensate is initially at rest in its ground state. For spatially confined condensates and harmonic detectors, such a superradiant emission of sound waves provides a dynamical instability mechanism leading to a new concept of phonon lasing. Following an analogy with the theory of rotating black holes, our results suggest a promising avenue to quantum simulate basic interaction processes involving fast moving detectors in curved space-times.

Extraction of repetitive transients with frequency domain multipoint kurtosis for bearing fault diagnosis

The appearance of repetitive transients in a vibration signal is one typical feature of faulty rolling element bearings. However, accurate extraction of these fault-related characteristic components has always been a challenging task, especially when there is interference from large amplitude impulsive noises. A frequency domain multipoint kurtosis (FDMK)-based fault diagnosis method is proposed in this paper. The multipoint kurtosis is redefined in the frequency domain and the computational accuracy is improved. An envelope autocorrelation function is also presented to estimate the fault characteristic frequency, which is used to set the frequency hunting zone of the FDMK. Then, the FDMK, instead of kurtosis, is utilized to generate a fast kurtogram and only the optimal band with maximum FDMK value is selected for envelope analysis. Negative interference from both large amplitude impulsive noise and shaft rotational speed related harmonic components are therefore greatly reduced. The analysis results of simulation and experimental data verify the capability and feasibility of this FDMK-based method

Rotating electroosmotic flow of viscoplastic material between two parallel plates

This study aims to investigate electroosmotic flow of a viscoplastic material, modeled as either Bingham plastic or Casson fluid, through a parallel-plate channel that rotates about an axis perpendicular to the plates. A relatively small yield stress, comparable to that of human blood, is considered in order to confine to the condition there is only one yield surface in the flow. An iterative finite-difference numerical scheme is developed to solve the Cauchy momentum equations and nonlinear constitutive equations. The location of the yield surface, and velocity and stress components in both the sheared and unsheared regions are found as functions of the yield stress, rotation speed and Debye parameter. Numerical results are presented to reveal that the system rotation and yield stress may counteract each other in controlling the resultant flow rate and flow direction. The effect of yield stress may even be reversed for a sufficiently large rotation speed.

Performance optimization of a U-Oscillating-Water-Column wave energy harvester

This paper deals with the problem of optimizing the performance of a U-Oscillating Water Column (U-OWC) wave energy converter equipped with a Wells turbine by controlling the turbine dynamics in a variety of incident wave conditions.The controller methodology is based on the identification of the reference turbine rotational speed providing the maximum average converted power. Two different approaches to the problem are proposed. The first relies on a sea-state based controller providing the optimum value of a reference rotational speed assumed constant during a sea state via a Maximum Power Point Tracking (MPPT) algorithm. In this context, it is shown that the significant wave height of the incident sea state is eligible as reference parameter for performing the tracking of the optimum conditions. The second solution is a wave-to-wave control algorithm relating the reference turbine rotational speed to the actual dynamic conditions of the plant. Numerical comparisons show that the assumption of a constant reference rotational speed within the sea state duration works better than a fast acting control. Finally, the consequences of the controller on the phase distribution of the dynamic system response is analysed. In this context, numerical results highlight the fact that the U-OWC responds differently in wind-dominated and swell-dominated sea states. Specifically, in wind-dominated sea states the maximum converted average wave energy occurs during the resonance condition; while, in swell-dominated sea states, the maximum converted average wave energy is obtained by adopting an adequately large turbine rotational speed, irrespective of the achievement of the resonance condition.

A Study on the Ignition System of a Pilot Flame in a Cannon-type-combustor of a Turbo-engine

We studied a stable pilot flame system for a cannon type combustor of turbo-engines by adding both a frontchamber and a pilot flame chamber with an electric ignition system to the conventional two-stage system with two-stage combustion domains: a primary zone and a secondary zone. The electric ignition period was about 1 second with 2760V(theoretical) generated by Kochcroft-Welton circuit, and the fuel was butane gas. The inlet was 25m/sec and the pressure was about 400Pascal at the inlet of combustor.We set two cases for the outlet configuration: a converging nozzle and a turbine. The outlet temperature was 280C at the outlet velocity of 25m/sec, and the temperature was 230C at the outlet velocity of 12m/sec. A sufficiently large rotational speed and torque was obtained to rotate the compressor and fan of the turbine. Weanalyzed the ignition mechanism by solving two dimensional compressible Navier-Stokes equations and found that the role of the front chamberwas to maintain the pilot flame after the ignition shock. We confirmed experimentally that this system can ignite and preserve a stable pilot flame with quite high probability.

Characterization and Dissolution Dynamics of Tricalcium Phosphates in Acidified Solution

Bioceramics used in biomedical applications must exhibit specific behaviors. In scaffolds, for instance, the degradability of bioceramics is important to allow the cell ingrowth. Therefore, the dissolution of calcium phosphates increases the ionic concentrations around the interface implant–bone, favoring a more rapid bone apposition to the graft surface. The dissolution takes place under static or dynamic conditions, but the latter is usually not performed under rigorous hydrodynamic control. In the present work, two bioceramics, β-tricalcium phosphate and β-tricalcium phosphate substituted by magnesium, were produced by pressing and sintering to form disks. They were characterized by XRD, Raman, ICP, SEM, AFM and photometric test. The influence of chemical composition in the dissolution test was conducted through strict control of the hydrodynamic conditions. The disks were rotating in a precise speed, in order to produce a dissolution under the well-controlled mass transfer. Subsequently, the calcium release was evaluated in a simulated infectious environment using pH equals to circa 4. Thus, it was possible to evaluate the fraction of dissolution related to mass transfer or surface reactions for a large rotation speed range. The magnesium added to the bioceramic inhibits the total dissolution when compared to pure tricalcium phosphate, probably related to more dense and less soluble ceramic. Moreover, the mass transfer affects relatively less the magnesium tricalcium phosphate than pure tricalcium phosphate.

A Magnetic-Assistance System as a Super Finishing Following Turning Machining

A design system using a magnetic force with high efficiency to assist discharging dregs out of the electrode gap during the electrochemical finishing on the surface finish process that follows turning machining process is investigated in the current study. Through the equipment attachment, magnetic-assistance during electrochemical finishing can follow the turning process on the same machine. This process can be used for various turning operations. Among the factors affecting electrochemical finishing, the magnetic-assistance is primarily discussed. The experimental parameters are magnetic strength, distance between the two magnets, current rating, on/off period of pulsed current, feed rate of workpiece, and rotational speed of workpiece. A higher current rating with magnetic-assistance reduces the finishing time and avoids the difficulty of dreg discharge. Providing a large magnetic field intensity or using a small distance between the two magnets produces a larger magnetic force and discharge ability and better finishing. A large rotational speed of the workpiece and electrode produces better finishing. Pulsed direct current can slightly promote the effect of electrochemical finishing, but the current rating needs to be increased. The magnetic-assistance during the electrochemical finishing process makes a great contribution in a short time by making the surface of the workpiece smooth and bright.

Three-dimensional coating and rimming flow: a ring of fluid on a rotating horizontal cylinder

AbstractThe steady three-dimensional flow of a thin, slowly varying ring of Newtonian fluid on either the outside or the inside of a uniformly rotating large horizontal cylinder is investigated. Specifically, we study ‘full-ring’ solutions, corresponding to a ring of continuous, finite and non-zero thickness that extends all of the way around the cylinder. In particular, it is found that there is a critical solution corresponding to either a critical load above which no full-ring solution exists (if the rotation speed is prescribed) or a critical rotation speed below which no full-ring solution exists (if the load is prescribed). We describe the behaviour of the critical solution and, in particular, show that the critical flux, the critical load, the critical semi-width and the critical ring profile are all increasing functions of the rotation speed. In the limit of small rotation speed, the critical flux is small and the critical ring is narrow and thin, leading to a small critical load. In the limit of large rotation speed, the critical flux is large and the critical ring is wide on the upper half of the cylinder and thick on the lower half of the cylinder, leading to a large critical load. We also describe the behaviour of the non-critical full-ring solution and, in particular, show that the semi-width and the ring profile are increasing functions of the load but, in general, non-monotonic functions of the rotation speed. In the limit of large rotation speed, the ring approaches a limiting non-uniform shape, whereas in the limit of small load, the ring is narrow and thin with a uniform parabolic profile. Finally, we show that, while for most values of the rotation speed and the load the azimuthal velocity is in the same direction as the rotation of the cylinder, there is a region of parameter space close to the critical solution for sufficiently small rotation speed in which backflow occurs in a small region on the upward-moving side of the cylinder.

Zonal jets and cyclone–anticyclone asymmetry in decaying rotating turbulence: laboratory experiments and numerical simulations

The problem of zonal jet formation and cyclone–anticyclone asymmetry in decaying rotating turbulence is addressed using both laboratory experiments and numerical simulations with a high-resolution shallow water model in a spherical geometry. Experiments are performed at different Rossby and Froude numbers and applying a rigid wall as meridional boundary in the numerical scheme to mimic the experimental apparatus. The formation of a zonally banded flow pattern, i.e. meridionally confined easterly/westerly jets, has observed; both experimental and numerical results confirmed that this tendency is favoured by high-planetary vorticity gradients. Also, in the experiments characterized by large rotation speeds and small Rossby deformation radius, an initial symmetric distribution of relative vorticity is found to evolve towards a dominance of anticyclonic structures, indicating a breaking of the cyclone–anticyclone symmetry. This aspect has deepened by numerically analysing the sensitivity of the temporal variations of the asymmetry index with respect to the position of the meridional confinement as well as the effect of relaxing the divergence of the fluid (i.e. non-divergent case) to zero. Results suggested that experiments characterized by the higher rotation speed and the lower fluid thickness are better reproduced by a divergent model with a high-latitude meridional boundary.

Flux Engineering To Control In-Plane Crystal and Morphological Orientation

We tailored nanostructured morphology and crystal texture of iron nanocolumns by engineering the inclination and azimuthal directions of the collimated flux characteristic of glancing angle deposition (GLAD). Under continuous substrate rotation, the flux is azimuthally isotropic within one rotation. With large substrate rotation speeds, we can deposit vertical nanocolumns with a faceted, tetrahedral apex, BCC crystal structure and ⟨111⟩ fiber texture. Designing the flux to have an azimuthal 3-fold symmetry, which reflects the symmetry of the tetrahedral apex, allows us to induce both an in-plane and out-of-plane texture (biaxial texture) by evolutionary selection. In-plane crystal orientation is accompanied by a preferential azimuthal nanocolumn orientation, where the sides of tetrahedral apex are directed toward the flux direction. This work demonstrates the flux engineering technique, which can orient in-plane crystal texture and morphology of crystalline nanocolumns on amorphous substrates. This control is a useful addition to vapor–solid, physical self-assembly with the potential to improve the performance of porous thin film architectures as biaxial buffer layers, and in a variety of device applications such as photovoltaics and energy storage.

Improving Safety and Performance of Small-Scale Vertical Axis Wind Turbines

Although horizontal axis wind turbines (HAWT) are considered more efficient in operation than their vertical axis wind turbine (VAWT) counterpart and are more commonly used in wind farms as large wind turbines, the VAWT may offer greater advantages in safety and operation when it comes to their application within the urban environment. Yaw control systems are an essential requirement for the safe operation of HAWT, which are costly and require high levels of maintenance, but are inherently unnecessary for VAWT. At low blade speed ratios, the performance of VAWT degrades owing to strong dynamic stall effects. This necessitates VAWT operation at high blade speed ratios to suppress them. However, the consequent large rotational speeds lead to hazardous operation especially in confined urban areas. Thus to improve the low blade speed performance, a preliminary experimental investigation has been carried out at the Aerodynamics Laboratory of the University of New South Wales on an H-type VAWT blade that employed zero-net mass flux actuation. This technique has traditionally been used for static stall delay and flow separation mitigation on aircraft wings. In the present study, large relative angles of incidence were simulated by sinusoidally oscillating the blade about its quarter-chord, and resulted in the formation of dynamic stall vortices. The application of zero-net mass flux actuation was found to have a beneficial effect on the blade aerodynamic performance by either suppressing dynamic stall or delaying its onset to higher angles of attack. This study, therefore, suggests that reduced oscillatory loads and more robust output power can be achieved with zero-net mass flux actuation on VAWT operating at low blade-speed ratios. Consequently, the findings have positive practical implications for the design of small-scale VAWT for widespread use in the urban environment.

Fracture and mechanical properties of friction stir spot welds in 6063-T6 aluminum alloy

The influence of the tool dimensions and of the welding parameters on the fracture and lap shear properties of friction stir spot welds is investigated. Interrupted lap shear tests allow to follow the mechanisms leading to weld fracture. A triangular cavity opens at the hook during lap shear testing. The distance between this triangular cavity and the hole left by the pin is the main parameter controlling the type of fracture. A too short distance favors a fracture through the weld nugget and hence should be avoided. In particular, this happens when the tool pin diameter is too small and when the plunge rate is too large. Fracture initiating at the triangular cavity and following the thermomechanically affected zone, i.e., by the pullout of the weld nugget, is preferred. This fracture type leads to significant plastic deformation and generally favors a large ultimate force during lap shear testing. Large ultimate forces are observed when the welds are cooler (large plunge rates and low rotation speeds), but the welding conditions should be chosen so as not to lead to fracture trough the weld nugget.

Fabrication and Characterization of Aluminum Fibers by Peripheral Milling

A novel peripheral milling process with an end milling cutter for manufacturing aluminum fibers is proposed. Most of the cutting is done by the peripheral teeth of the cutter and the chips removed by the teeth form aluminum fibers, while the cutter end has little effect on aluminum fibers. The machining principle and the formation mechanism of aluminum fiber cross-section are presented. The feasibility of this new fabrication process is experimentally investigated under different machining conditions. In addition, influences of cutting parameters on the equivalent diameter, the length, and surface morphology of aluminum fibers are analyzed. Experimental results indicate that aluminum fibers can be successfully manufactured by peripheral milling and the productivity can be improved by increasing the rotational speed n. Smaller radial depth of cut a e , larger rotational speed n, and smaller feed speedv f are in favor of obtaining slim aluminum fibers. The length of aluminum fibers is theoretically determined by the axial depth of cut a p and also actually affected by other cutting parameters. Of all the cutting parameters considered in these experiments, the optimum parameters of a e , n, and v f are 0.3 mm, 118 r/min, and 60 mm/min, respectively.

Spreading and fingering in a yield-stress fluid during spin coating

We study the deformation, spreading, and fingering of small droplets of a yield-stress fluid subjected to a centrifugal force on a rotating substrate. At low rotation rates and for small enough droplets, the droplets deform elastically but retain their essentially circular contact line. For large enough droplet volumes and rotation speeds, however, one or more fingers eventually form and grow at the edge of the drop. This fingering is qualitatively different from the contact line instability observed in other fluids, and appears to be a localized phenomenon that occurs when the stress at some point on the perimeter of the drop exceeds the yield stress.