Search

The flow structures and heat transfer within rotating cavities of aero-engine axial compressors influence the thermal expansion of the rotor disks, and consequently the blade-tip clearances. To investigate the flow field at the bore and lower cavity region, experimental measurements have been acquired in an engine-representative test facility. Axial, tangential, and radial velocities were measured using a miniature five-hole probe at a range of axial and radial positions. Time-averaged results from 28 tests carried out at nondimensional parameters comparable to engine conditions: 1.3 × 104 ≤ Rez ≤ 8.2 × 104, 3.0 × 105 ≤ Reθ ≤ 3.2 × 106, 0.11 ≤ Ro ≤ 3.24, 0.14 ≤ βΔT ≤ 0.36 are presented in this paper. The axial and tangential velocity measurements conform to previous work, while the radial velocity component provides quantitative evidence of an asymmetric toroidal vortex in the cavity gap, biased toward the downstream disk. The vortex is characterized by the local vorticity and grows in strength and size as Rossby number increases above Ro = 0.34 to 1.63. The effect of βΔT on the vortex formation is negligible compared to the influence of the tangential Reynolds number as the local circulation is suppressed by the Coriolis forces at high rotational speeds. Both the tangential and radial velocity results suggest that as Ro is increased, the proportion of air that is radially ingested and expelled from a cavity decreases. [ABSTRACT FROM AUTHOR]

The analysis of the structural dynamics of multistage cyclic structures as linked components is required to model the interstage coupling. In turbomachinery, this can result in a collaboration between different compressor or turbine stages. This paper investigates the coupling between two rear drum blade integrated disk stages of an axial compressor to support the mechanical design process. Considering the vibration modeshapes of a multistage system, different components may coparticipate in the dynamics. For this reason, criteria to identify the modes affected by the coupling and to quantify this coupling are defined. This allows to distinguish between modes with interstage coupling, requiring the multistage system for their description, and uncoupled modes, involving a single stage. In addition, it is of interest to research methods to reduce the impact of the coupling on the vibrating system without drastically altering the geometry of the components. The vibration analyses of a two-stage compressor generalized geometry, representative of a compressor rear drum blisk, are presented as a study case. The use of a reducing method allows to describe the behavior of the nominal multistage system with a computationally efficient technique, enabling a parametric analysis of the stages' coupling. The investigation considers the effect of a set of geometrical and mechanical parameters on the dynamics, identifying the driving parameters of the coupled vibration characteristics. [ABSTRACT FROM AUTHOR]

Intervertebral disc (IVD) degeneration and methods for repair and regeneration have commonly been studied in organ cultures with animal IVDs under compressive loading. With the recent establishment of a novel multi-axial organ culture system, accurate predictions of the global and local mechanical response of the IVD are needed for control system development and to aid in experiment planning. This study aimed to establish a finite element model of bovine IVD capable of predicting IVD behavior at physiological and detrimental load levels. A finite element model was created based on the dimensions and shape of a typical bovine IVD used in the organ culture. The nucleus pulposus (NP) was modeled as a neo-Hookean poroelastic material and the annulus fibrosus (AF) as a fiber-reinforced poroviscoelastic material. The AF consisted of 10 lamella layers and the material properties were distributed in the radial direction. The model outcome was compared to a bovine IVD in a compressive stress-relaxation experiment. A parametric study was conducted to investigate the effect of different material parameters on the overall IVD response. The model was able to capture the equilibrium response and the relaxation response at physiological and higher strain levels. Permeability and elastic stiffness of the AF fiber network affected the overall response most prominently. The established model can be used to evaluate the response of the bovine IVD at strain levels typical for organ culture experiments, to define relevant boundaries for such studies, and to aid in the development and use of new multi-axial organ culture systems. [ABSTRACT FROM AUTHOR]

The paper explores the distribution of matter in thick disks around black holes and wormholes both numerically and analytically. Kerr and Lame metrics are considered, and exact analytical solutions are derived. The influence of toroidal magnetic fields on the structure of the thick disk is taken into account. Images of thin disks are constructed depending on the values of metric parameters. [ABSTRACT FROM AUTHOR]

A chute rim seal cavity has been instrumented with time-resolved and time-averaged pressure transducers as well as a gas concentration measurement system at the Oxford Rotor Facility. The unsteady pressure transducers were unevenly distributed along the circumference generating 15 combinations of angular spacing to conduct a phase analysis. The test operating conditions were modified through different configurations of mainstream flow, a range of rotational speeds and several rates of purge flow to obtain test data in the regimes of rotationally-driven, pressure-driven, and combined ingestion. The rotating unsteady flow structures within the rim seal cavity were studied through a combination of phase analysis of dynamic pressure signals and inspection of the frequency domain. The introduction of mainstream flow (axial and swirled) increased the overall unsteadiness exciting an additional band of lower frequencies. The phase analysis revealed these were associated with acoustic waves, providing the first experimental evidence of the presence and coexistence of inertial and acoustic waves in the rim seal cavity. The interaction of the inertial and acoustic waves strongly depends on the operating conditions, and may be linked to changes in sealing effectiveness. [ABSTRACT FROM AUTHOR]

Fig fruits have recently received more attention by consumers for their quality as either fresh or dried fruits and, consequently, growers are becoming more interested in the cultivation of this species. Figs are mainly consumed as processed fruits (dried, marmalade, jam, etc.), but limited attention has been paid to new possible processing applications of several local cultivars grown in Mediterranean countries. This study aimed to investigate both the morpho-pomological characteristics and consumer sensory ratings (two groups: students and technicians) for four fig cultivars processed as a new type of product, 'dried fig disks'. The results showed that three out of the four cultivars (Processotto Nero, Natalese Nera, and Verde di Natale) had good pomological characteristics such as fruit weight and skin color, as well as easy peeling, yield, ripening time, and TSS. The same cultivars received positive hedonic scores for appearance (>5 on a 10-point hedonic scale), flavor (4–6 on a 10-point hedonic scale) and taste (6–7 on a 10-point hedonic scale). The overall score was positive for Processotto Nero, Natalese Nera, and Verde di Natale (>5 on a 10-point hedonic scale), whereas one cultivar, Comunione, was less appreciated (<5 on a 10-point hedonic scale). The flavor–sensory attributes most appreciated were black-red fruit, cooked, grassy, and floral; fig off-flavors were perceived as rancid only by students and to a limited extent. Consumer overall acceptance toward dried fig disks was mainly driven by the acceptability of appearance of the new product, together with pleasant flavor and taste. [ABSTRACT FROM AUTHOR]

In some circumstances, it is impossible to exploit resonance crossings to identify the modal properties of rotor disks. In these cases, the identification process must rely on nonsynchronous vibrations and becomes challenging for two reasons. First, the signals are weak (compared to the levels measured during resonance crossings) and random, thus an averaging procedure is necessary. Second, the dynamical system is time-variant due to the variation of the rotor speed. This paper presents a modal identification procedure formulated in the framework of the time-frequency analysis. A region of the time-frequency plane is stretched to map the system into a fictitious linear time-invariant (LTI) system. Then, the power spectral density function (PSD) of the response is computed by an averaging procedure. Finally, the modal properties are estimated through an output-only modal identification algorithm. The procedure is applied to simulated and experimental data regarding a bladed disk of a steam turbine. [ABSTRACT FROM AUTHOR]

The effect of differences in nominally equal sectors of a bladed disk (mistuning) is a well-known problem for designers since the forced response may show localized amplification of the blade response with respect to a cyclically symmetric (tuned) configuration. In order to perform a large number of simulations in a reasonable amount of time to characterize the highest blade response, corresponding to the worst mistuning pattern, reduction techniques have been developed, where the mistuning is introduced directly in a compact, reduced order model (ROM) obtained from very large finite element (FE) models. Typically, mistuning is introduced in the ROM in terms of natural frequency perturbations of the blade; nevertheless, a better insight is specifically required in order to correlate mistuning to a specific source (geometrical, material, contact mistuning). In this paper, a reduction technique is presented to take into account mistuning due to the contact uncertainties at the blade root joint, which can be caused by design tolerances, manufacturing process, assembly procedures, wear, etc. The technique takes its basis from the Craig-Bampton component mode synthesis (CB-CMS) applied to the uncoupled blade and disk sector, which is typically included in most of the FE software for easy implementation in standard industrial practice. The full set of master degrees-of-freedom (DOFs) at the random contacts are purposely reduced using an optimal local modal basis based on the Gram-Schmidt interface (GSI) technique developed by the authors. Experimental evidence of actual uncertain contact obtained during joint preloading is used to find an appropriate base to represent typical contact patterns. [ABSTRACT FROM AUTHOR]

The classical thermal network analogy is extended to plates bounded by two distinct states of convection, such as the walls of an enclosure. The full network is derived from an effective network representation, expressed in term of the average convection coefficient. The full network description allows the internal flow temperature of an enclosure to be treated as an unknown in analysis of convecting plates, which is an important class of problems in thermal packaging design. [ABSTRACT FROM AUTHOR]

High‐power laser sources are widely used in industrial precision processing and act as a new platform for strong‐field physics research using peak power over petawatt. This review focuses on realizing high‐energy solid‐state disk and slab systems and the nonlinear‐suppression strategies for high‐power fiber systems using the functional fibers. First, the implementations and enabling technologies of the solid‐state lasers for increasing peak power from gigawatt to petawatt are reviewed. Then the mechanisms and suppression strategies of the deterioration effects (including stimulated Raman scattering, stimulated Brillouin scattering, and transverse mode instability) in various fiber amplifiers are analyzed. At the same time, the mechanism and achievements of the current functional fibers are introduced. Finally, the challenges and perspectives of high‐power solid‐state and fiber amplifiers are summarized. [ABSTRACT FROM AUTHOR]

A coulter is one of the most important working elements of a grain seeder. Its operation affects not only the uniform distribution of the seeds but also the depth of their sowing. The manufacture of coulters without a seed covering device can be considered a disadvantage of the present coulters. This results in partial and uneven coverage of the seed furrow only caused by sloughing soil from the furrow walls, following the coulter disks. In this case, the partially and unevenly placed seeds can be distributed in the soil with different depths, etc. In turn, this can lead to the seeding quality and crop yields decrease. The research presented in this article is oriented towards improving the quality of sowing of grain crops by upgrading the coulter working process with furrow covering devices. These studies are relevant and of high economic importance to the agro-industrial complex of the Russian Federation. This article presents the design and operating principle of the developed coulter with furrow covering device. When using it, the seeding-down only by falling soil from the furrow walls is avoided; complete and uniform furrow covering without seed displacement together with the soil is provided; the most uniform seed distribution over the length of the furrow and the sowing depth is ensured.

The Jupiter–Saturn chaotic excitation (JSCE) scenario proposes that the protoplanetary disk was dynamically excited and depleted beyond ∼1–1.5 au in a few Myr, offering a new and plausible explanation for several observed properties of the inner solar system. Here, we expanded our previous work by conducting a comprehensive analysis of 37 optimal terrestrial planet systems obtained in the context of the JSCE scenario. Each optimal system harbored exactly four terrestrial planets analogs to Mercury, Venus, Earth, and Mars. We further investigated water delivery, feeding zones, and accretion history for the planet analogs, which allowed us to better constrain the water distribution in the disk. The main findings of this work are as follows: 1) the formation of four terrestrial planets with orbits and masses similar to those observed in our solar system in most of our sample, as evidenced by the dynamically colder and hotter orbits of Venus–Earth and Mercury–Mars analogs, and the high success rates of similar mutual orbital separations (∼40–85%) and mass ratios of the planets (∼70–90%) among the 37 systems; and 2) water was delivered to all terrestrial planets during their formation through the accretion of water-bearing disk objects from beyond ∼1–1.5 au. The achievement of Earth's estimated bulk water content required the disk to contain sufficient water mass distributed within those objects initially. This requirement implies that Mercury, Venus, and Mars acquired water similar to the amount on Earth during their formation. Several of our planet analogs also matched additional constraints, such as the timing of Moon formation by a giant impact, Earth's late accretion mass and composition, and Mars's formation timescale. • Our scenario yielded four terrestrial planets with similar orbits and masses to ours. • All terrestrial planets acquired comparable water abundances during their formation. • Terrestrial planets accreted their bulk water from objects beyond 1 au within ∼40 Myr. • Earth accreted most of its CC material from within 2 au during protracted accretion. • Mars analogs matched Mars' mass, eccentricity, inclination, and distance from Earth. [ABSTRACT FROM AUTHOR]

Mária Budai-Szűcs, 1 Attila Léber, 1 Lu Cui, 2, 3 Muriel Józó, 2, 3 Péter Vályi, 4 Katalin Burián, 5 Balázs Kirschweng, 2, 3 Erzsébet Csányi, 1 Béla Pukánszky 2, 3 1Institute of Pharmaceutical Technology and Regulatory Affairs, Faculty of Pharmacy, University of Szeged, Szeged, Hungary; 2Laboratory of Plastics and Rubber Technology, Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics, Budapest H-1521, Hungary; 3Institute of Materials and Environmental Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest H-1519, Hungary; 4Department of Periodontology, Faculty of Dentistry, University of Szeged, Szeged, Hungary; 5Institute of Clinical Microbiology, Faculty of Medicine, University of Szeged, Szeged, HungaryCorrespondence: Mária Budai-SzűcsInstitute of Pharmaceutical Technology and Regulatory Affairs, Faculty of Pharmacy, University of Szeged, Eötvös utca 6, Szeged 6720, HungaryTel +36 62 545-573Fax +36 62 545-571Email maria.szucs@pharm.u-szeged.huPurpose: Electrospun PLA fiber devices were investigated in the form of fiber mats and disks. Metronidazole was used as an active agent; its concentration was 12.2 and 25.7 wt% in the devices.Methods: The structure was studied by X-ray diffraction and scanning electron microscopy, drug release by dissolution measurements, while the antimicrobial efficiency was tested on five bacterial strains.Results: The XRD study showed that the polymer was partially crystalline in both devices, but a part of metronidazole precipitated and was in the form of crystals among and within the fibers. Liquid penetration and dissolution were different in the two devices, they were faster in disks and slower in fiber mats, due to the morphology of the device and the action of capillary forces. Disks released the drug much faster than fiber mats. Although the release study indicated fast drug dissolution, the concentration achieved a plateau value in 24 hrs for the disks; the inhibition effect lasted much longer, 13 days for bacteria sensitive to metronidazole. The longer inhibition period could be explained by the slower diffusion of metronidazole located inside the fibers of the device.Conclusion: The results suggest that the devices may be effective in the treatment of periodontitis.Keywords: drug release devices, fiber mats, disks, morphology, dissolution, capillary forces, diffusion, antimicrobial, inhibition

Validating simulation results of vibrating turbine blades relies on measurements of realistic or academic cyclic structures on special test rigs. In real operation the blades are excited mainly by aerodynamic forces. For measurements of blade vibration on special test rigs, the excitation should be well known. It is desirable to use excitation spectra that consist of only a few engine order excitations. Especially for nonlinear systems, unwanted excitation orders can possibly lead to nonlinear effects which may interfere with the measurement. To separate different engine orders, an innovative electromagnetic excitation device was developed at the institution to overcome the aforementioned problems. The excitation force spectrum is controlled by a variable air gap over the circumference between device and blade. Any desired engine order excitation can be realized. Additionally, by varying the devices coil current in a harmonic fashion, frequency sweeps at constant speed can be performed. In this manuscript, an extensive study of the excitation force spectrum of the device is conducted. Therefore, theoretical investigations of the expectable spectrum are given under simultaneous variation of air gap geometry and excitation current. These predictions are then validated by experiments featuring a small, academic bladed disk. The vibrations of the blades are measured. The device promises to create well predictable and controllable excitation force spectra which will improve the validation strategy in particular of nonlinear simulation tools for the prediction of turbine blade vibrations. [ABSTRACT FROM AUTHOR]

This contribution presents experimental investigations of friction torque in an open rotor-stator disk system by using two different measuring procedures. The first procedure is based on a thermo electrical wall shear stress sensor. The sensor is investigated in two different substrates and different measuring parameters. A thermal model consisting of the supplied heating power, the thermal resistance toward the fluid, and into the substrate as well as the over temperature is used to achieve the heat transfer coefficient on the sensor surface. This heat transfer coefficient is attributed by a functional relationship to the wall shear stress. This relationship is first calibrated in a rectangular channel and subsequently validated at a fully turbulent flat plat flow. The second measuring procedure based on the tangential displacement of the stator disk due the friction torque. The disk is attached at a torsion spring. The friction torque is achieved by the torsion spring constant and the tangential displacement of the stator disk. Both measuring procedures are compared and agree well with each other. The used test rig has the possibility of reaching rotational Reynolds numbers representative, for instance, of a modern gas turbine. The investigations were carried out by a 0.5 m diameter rotor disk rotating up to 8500 rpm with a gap ratio between 0.008 and 0.04. The friction torque is measured on the stator disk and can be converted into moment coefficient. Moment coefficient on stator and measured pressure distributions are presented for different gap ratios and rotational Reynolds number. [ABSTRACT FROM AUTHOR]

Heat transfer within the rotating compressor cavity of an aero-engine is predominantly governed by buoyancy, which can be characterized by the Grashof number. Unsteady and unstable buoyancy-induced flow structures influence the temperatures and stresses in the compressor rotors, and these affect the radial growth of the disks. In addition, the heat transfer from the disks and shroud increases the temperature of the throughflow of cooling air. This paper contains two connected parts. First, a heat transfer correlation for the shroud of a rotating cavity was determined from steady-state heat flux measurements collected in the bath compressor-cavity rig at engine-simulated conditions. The Nusselt numbers were based on the cavity air temperature adjacent to the shroud, which was predicted using the Owen-Tang buoyancy model. Heat transfer from the shroud was consistent with free convection from a horizontal plate in a gravitational field. Maximum likelihood estimation was used with a Rayleigh-Bénard equation to correlate the shroud Nusselt number with the local Grashof number. Second, an energy balance was used to calculate the enthalpy rise of the axial throughflow from the measured disk and shroud heat fluxes. Disk fluxes were derived from radial distributions of measured steady-state disk temperatures using a Bayesian model and the equations for a circular fin. The calculated throughflow temperature rise was consistent with direct thermocouple measurements. The complex, three-dimensional flow near the cavity entrance can result in enthalpy exchange penetrating upstream in the throughflow, and rotationally induced flow can create upstream axial flow in the outer part of the annulus. [ABSTRACT FROM AUTHOR]

This study presents, for the first time, distributions of local internal temperature and convective heat transfer in a rotating radial vane brake disk and explains mechanisms in conjunction with secondary flows and flow separation within its ventilated coolant passages. In particular, variations of radial, circumferential (vane-to-vane), and axial (inboard-to-outboard) heat transfer on internal end-wall surfaces, and their alteration due to varying number of radial vanes and rotating speed are experimentally detailed. It has been demonstrated that conventional ventilated radial brake disks where the air inflow is drawn from the inboard face are likely to suffer substantial axial variations of temperature and heat transfer between the inboard and outboard disks, which possibly exacerbates thermal distortion (i.e., coning). Further, for a typical number of vanes (i.e., 36 vanes) used on automobiles, internal thermal distributions are highly nonuniform. However, the thermal end-wall uniformity improves considerably as the number of vanes is increased to say 72 vanes. Specifically, as the number of vanes is increased, secondary flow mixing enhances overall convective heat transfer and improves thermal uniformity. In contrast, separation causes large end-wall thermal nonuniformities in radial and circumferential distributions between the pressure side and the suction side of radial vanes. This effect nonetheless also decreases as the number of vanes is increased. [ABSTRACT FROM AUTHOR]

Reduced order models (ROMs) are widely used to enable efficient simulation of mistuned bladed disks. ROMs based on projecting the system dynamics into a subspace spanned by the modes of the tuned structure work well for small amounts of mistuning. When presented with large mistuning, including changes of geometry and number of finite element mesh nodes, advanced methods such as the pristine-rogue-interface modal expansion (PRIME) are necessary. PRIME builds a reduced model from two full cyclic symmetric analyses, one for the nominal and one for the modified type of sector. In this paper, a new reduced order model suitable for large mistuning with arbitrary mesh modifications is presented. It achieves higher accuracy than PRIME, while saving approximately 25% computational effort during the reduction process, when using the same number of cyclic modes. The new method gains its efficiency by recognizing that large modifications from damage or repair are unlikely to be exactly the same for multiple blades. It works by building a partially reduced intermediate model: All nominal sectors are reduced using cyclic modes of the tuned structure. The single modified sector is kept as the full model. For this reason, the new reduction method is called partially reduced intermediate system model (PRISM) method. The accuracy of the PRISM method is demonstrated on an axial compressor blisk and an academic blisk geometry. [ABSTRACT FROM AUTHOR]

The flow and heat transfers inside high-pressure (HP) compressor rotating cavities are buoyancy driven and are known to be extremely difficult to predict. The experimental data of laser-Doppler anemometry (LDA) measurements inside an engine representative cavity rig are presented in this paper. Traverses using a two component LDA system have been carried out in the shaft bore and the cavity regions in order to map the axial and tangential velocity components. The velocity data are collected for a range of Rossby, Rotational, and Axial Reynolds numbers, Ro, Reθ, and Rez, 0.08

Large gas turbine design and service business are challenged with increased demands toward flexible operations, increasing number of start-stop cycles, and intermediate cycles. Probabilistic fracture mechanics simulation design tools have matured and became robust and reliable. We present a probabilistic reevaluation of Siemens E-class turbine disks by the combination of probabilistic two-dimensional axisymmetric part analysis of the disk and a novel probabilistic approach for the three-dimensional blade attachment. The first addresses the risk of inherent forging flaws, the latter combines the risk of surface crack initiation, growth, and failure. Both models consider the heterogeneous nature of material properties, flaw geometries, and detectability. These novel concepts developed at Siemens allow for an optimization of resource usage and safety, as well as the development of new service and inspection concepts for a variety of service frames and classes. [ABSTRACT FROM AUTHOR]

This paper presents large-eddy and direct numerical simulations of buoyancy-driven convection in sealed and open rapidly rotating cavities for Rayleigh numbers in the range 107-109, and axial throughflow Reynolds numbers 2000 and 5600. Viscous heating due to the Ekman layer scrubbing effect, which has previously been found responsible for the difference in sealed cavity shroud Nusselt number predictions between a compressible N-S solver and an incompressible counterpart using the Boussinesq approximation, is discussed and scaled up to engine conditions. For the open cavity with an axial throughflow, laminar Ekman layer behavior of the mean flow statistics is confirmed up to the highest condition in this paper. The Buoyancy number Bo is found useful to indicate the influence of an axial throughflow. For the conditions studied the mean velocities are subject to Ra, while the velocity fluctuations are affected by Bo. A correlation, Nu'=0.169(Ra')0.318, obtained with both the sealed and open cavity shroud heat transfer solutions, agrees with that for free gravitational convection between horizontal plates within 16% for the range of Ra' considered. [ABSTRACT FROM AUTHOR]

This contribution focuses on the combined analysis of mistuning and unilateral blade-tip/casing contacts. A two-dimensional (2D) phenomenological finite element (FE) model of an aircraft engine fan stage is considered. It is reduced by means of the Craig-Bampton component mode synthesis method and contact treatment relies on a Lagrange multiplier algorithm within an explicit time-integration scheme. Blade-tip/casing contacts are initiated through the deformed shape of a perfectly rigid casing. Mistuning is accounted for on the blades only. Monte Carlo simulations are carried out in both linear and nonlinear configurations, which allows to compare amplifications predicted in both context due to mistuning. Following a thorough convergence analysis of the proposed numerical strategy, the influence of mistuning level as well as the configuration of the external forcing are investigated. Presented results underline the detrimental consequences of mistuning in a nonlinear structural context, yielding even higher vibration amplifications than in a linear context. A cross-analysis between linear and nonlinear computations reveals that no correlation is found between linear and nonlinear amplifications which suggests that the effect of existing strategies to mitigate vibration amplifications within a linear context may not be suitable within a nonlinear context. [ABSTRACT FROM AUTHOR]

The change in compressor blade-tip clearance across the flight cycle depends on the expansion of the rotor, which in turn depends on the temperature and stress in the disks. The radial distribution of temperature is directly coupled to the buoyancy-driven flow and heat transfer in the rotating disk cavities. This paper describes a new test rig specifically designed to investigate this conjugate phenomenon. The rig test section includes four rotating disks enclosing three cavities. Two disks in the central cavity are instrumented with thermocouples to provide the radial distribution of temperature; the two outer cavities are thermally insulated to create appropriate boundary conditions for the heat transfer analysis. An axial throughflow of air is supplied between a stationary shaft and the bore of the disks. The temperature of the throughflow air is measured by thermocouples in rakes upstream and downstream of the central cavity. For a cold throughflow, the outer shroud of the central cavity is heated. Two independently controlled radiant heaters allow differential shroud temperatures for the upstream and downstream disks, as found in aero-engine compressors. Alternatively, the throughflow can be heated above the shroud temperature to simulate the transient conditions during engine operation where stratified flow can occur inside the cavity. The rig is designed to operate in conditions where both convective and radiative heat transfer dominate; all internal surfaces of the cavity are painted matt black to allow the accurate calculation of the radiant heat transfer. Separate attachments can be fitted to the cobs of both central disks; the attachments reduce the axial gap between the cobs--reducing the gap to zero creates a closed cavity, which can occur in some compressor designs. Other instrumentation includes heat-flux gages on the shroud and high-frequency pressure transducers embedded into the disk diaphragm to capture unsteady flow structures. Attention has been given to experimental uncertainty, including the computation of the thermal-disturbance errors, caused by thermocouples embedded in the rotating disks; a Bayesian statistical model is used to reduce the effect of uncertainties in temperature measurements on the calculation of the Nusselt number. The effect of relevant nondimensional parameters on the radial distribution of the disk and throughflow temperatures has been shown for some typical cases. [ABSTRACT FROM AUTHOR]

Across the open literature, there is no clear consensus on what the most suitable modeling fidelity is for rotating cavity flows. Although it is a widely held opinion that unsteady Reynolds-averaged-Navier-Stokes (URANS) approaches are unsuitable, many authors have succeeded in getting reasonable heat transfer results with them. There is also a lack of research into the validity of hybrid URANS/large eddy simulation (LES) type approaches such as detached eddy simulation (DES). This paper addresses these research challenges with a systematic investigation of a rotating cavity with axial throughflow at Grashof numbers of 3.03×109 and 3.03×1011. The disk near-wall layers remained laminar at both conditions, meaning that a turbulence model should not be active in these regions. The disk heat transfer was observed to affect the near-disk aerodynamics, which in turn affect the disk heat transfer: this feedback loop implies that conjugate heat transfer computations of rotating cavities may be worth investigating. On the shroud, additional eddy viscosity in URANS and DES was found to interfere with the formation of heat transfer enhancing streaks, whilst these were always captured by LES. DES exhibited a concerning behavior at the higher Grashof number. Locally generated eddy viscosity from the shroud was injected into the bulk fluid by the radial inflow. This contaminated the entire cavity with nonphysical modeled turbulence. As the radial inflow is a characteristic feature of rotating cavity flows, these results show that caution is necessary when applying hybrid URANS/LES approaches to this type of flow. [ABSTRACT FROM AUTHOR]

A method is proposed to analyze the modal damping in mistuned bladed-disk with root joints using large finite element models and the detailed description of frictional interactions at contact interfaces. The influence of mistuning on the dissipated energy for different blades on a bladed-disk and the modal damping factors for different vibration levels for any family of modes can be investigated. The dissipated energy and damping factors due to microslip are simulated by multitude of surface-to-surface elements modeling the friction contact interactions at root joints. The analysis is performed in the time domain, and an original reduction method is developed to obtain the results with acceptable computational times. The model reduction method allows the calculation of the modal damping of the mistuned assembly by evaluation of the energy dissipated at root joint of each individual blade using small parts of bladed disk sectors. The dependency of modal damping factor on blade mode shapes, engine-order excitation numbers, nodal diameter numbers, and vibration amplitudes is studied and the distributions of amplitude and dissipated energy on the mistuned bladed-disk are investigated using a realistic blade disk model. [ABSTRACT FROM AUTHOR]

This paper presents experimental and numerical investigation of mistuned forced responses of an integrally bladed disk with full set of underplatform dampers (UPDs). This research aims at providing: 1. An experimental benchmark for nonlinear dynamics of a mistuned bladed disks with UPDs. 2. A numerical model that can account for features of a mistuned forced response level. Accordingly, a detailed experimental campaign is conducted on a static test rig called Octopus. This rig is specifically designed to investigate the dynamics of a full-scale integrally bladed disk (blisk) with UPDs in a noncontact manner so that the dynamic response of the system is not modified. The effect of mistuning on experimental forced response levels is assessed and a linearized model is proposed to predict the modulation of frequency response functions (FRFs) due to the frequency splitting. In the development of the model, the mistuning pattern identified from the linear blisk without UPDs is used and it is assumed that adding the dampers does not change the structural mistuning of the blisk. In this study, the fundamental mistuning model identification (FMM ID) was employed to identify the mistuning pattern of the blisk. It is shown that the proposed model successfully predicts the modulation of linear mistuned FRFs. The linearized model is also able to predict the modulation of nonlinear mistuned FRFs in stick condition (when nonlinear friction damping is negligible) with a good accuracy validating this assumption that adding the dampers does not change the mistuning pattern. [ABSTRACT FROM AUTHOR]

The dynamic behavior of bladed disks in resonance crossing has been intensively investigated in the community of turbomachinery, addressing the attention to (1) the transient-type response that appear when the resonance is crossed with a finite sweep rate and (2) the localization of the vibration in the disk due to the blade mistuning. In real conditions, the two mentioned effects coexist and can interact in a complex manner. This paper investigates the problem by means of analytic solutions obtained through asymptotic expansions, as well as numerical simulations. The mechanical system is assumed as simple as possible: a 2DOF linear system defined through the three parameters: damping ratio ξ, frequency mistuning Δ, rotor acceleration Ω̇ ⁠. The analytic solutions are calculated through the multiple-scale method. [ABSTRACT FROM AUTHOR]

The paper presents a multidisciplinary approach for aero-thermal and heat transfer analysis for internal flows. The versatility and potential benefit offered by the approach are described through the application to a realistic low pressure turbine assembly. The computational method is based on a run time code-coupling architecture that allows mixed models and simulations to be integrated together for the prediction of the subsystem aero-thermal performance. In this specific application, the model is consisting of two rotor blades, the embedded vanes, the interstage cavity, and the solid parts. The geometry represents a real engine situation. The key element of the approach is the use of a fully modular coupling strategy that aims to combine (1) flexibility for design needs, (2) variable level of modeling for better accuracy, and (3) in memory code coupling for preserving computational efficiency in large system and subsystem simulations. For this particular example, Reynolds averaged Navier-Stokes (RANS) equations are solved for the fluid regions and thermal coupling is enforced with the metal (conjugate heat transfer, CHT). Fluid-fluid interfaces use mixing planes between the rotating parts while overlapping regions are exploited to link the cavity flow to the main annulus flow as well as in the cavity itself for mapping of the metal parts and leakages. Metal temperatures predicted by the simulation are compared to those retrieved from a thermal model of the engine, and the results are discussed with reference to the underlying flow physics. [ABSTRACT FROM AUTHOR]

The use of integrally blisk is becoming popular because of the advantages in aerodynamic efficiency and mass reduction. However, in an integrally blisk, the lack of the contact interface leads to a low structural damping compared to an assembled bladed disk. One emerging damping technique for the integrally blisk is based on the use of friction ring damper, which exploits the contact interfaces at the underneath of the disk. In this paper, three different geometries of the ring dampers are investigated for damping enhancement of a blisk. A full-scale compressor blisk is considered as a case study where a node-to-node contact model is used to compute the contact forces. The dynamic behavior of the blisk with the ring damper is investigated by using nonlinear modal analysis, which allows a direct estimation of the damping generated by the friction interface. The damping performance for the different ring dampers is evaluated and compared. It appears that the damping efficiency as well as the shift in the resonant frequency for the different geometries is highly related to the nodal diameter and contact pressure/gap distributed within contact interface. The geometry of the ring damper has significant impact on the damping performance. [ABSTRACT FROM AUTHOR]

Air plasma sprayed (APS) flash coatings on high velocity oxygen fuel (HVOF) bond coatings are well known to extend the lifetime of thermal barrier coatings (TBCs). Recent work compared flash coatings of NiCoCrAlY and NiCoCrAlYHfSi applied to both rods and disk substrates of alloy 247. For rod specimens, 100h cycles were used at 1100°C in wet air. Both flash coatings significantly improved the lifetime compared to HVOF-only and vacuum plasma spray (VPS)-only MCrAlY bond coatings with no statistical difference between the two flash coatings. For disk specimens tested in 1h cycles at 1100°C in wet air, the NiCoCrAlY flash coating significantly outperformed an HVOF-only NiCoCrAlYHfSi bond coating and a NiCoCrAlYHfSi flash coating. The flash coatings formed a mixed oxide-metal zone that appeared to inhibit crack formation and therefore extend lifetime. In addition to the flash coating increasing the bond coating roughness, the underlying HVOF layer acted as a source of Al for this intermixed zone and prevented the oxide from penetrating deeper into the bond coating. The lower Y+Hf content in the Y-only flash coating appeared to minimize oxidation in the flash layer, thereby increasing the benefit compared to a NiCoCrAlYHfSi flash coating. [ABSTRACT FROM AUTHOR]

Ferroliquids are an example of a colloidal suspension of magnetic nanomaterials and regular liquids. These fluids have numerous applications in medical science such as cell separation, targeting of drugs, magnetic resonance imaging, etc. The hybrid nanofluid is composed by scattering the magnetic nanomaterial of more than one type nanoparticles suspended into the base fluid. It has different scientific applications such as heat dissipation, dynamic sealing, damping, etc. Owing to the vast ferrofluid applications, the time-dependent squeezed flow of hybrid ferroliquids under the impact of non-linear radiation and mixed convection within two disks was explored for the first time in this analysis. Here, the cobalt and magnetite ferrofluids are considered and scattered in a 50%:50% mixture of water–EG (ethylene glycol). The similarity technique is used to reduce the leading PDEs into coupled non-linear ODEs. The transmuted equations together with recommended boundary restrictions are numerically solved via Matlab solver bvp4c. The opposing and assisting flows are considered. The impacts of an emerging parameter on fluid velocity and temperature field of hybrid ferroliquids are examined through the different graphical aids. The results showed that the opposite trend is scrutinized due to the magnetic influence on the temperature and velocity in the case of assisting and opposing flows. The velocity augments due to the volume fraction of nanoparticles in the assisting flow and declines in the opposing flow, while the opposite direction is noticed in the temperature field.

In this paper, we localize the zeros of the third derivatives of a complex polynomial in some sets. These sets are relevant to the first, second and third derivative of the polynomial, and they are respectively disks and cardioid interiors or generalized cardioid interiors. Here, for the first time we consider generalized cardioids, as the areas of zeros. [ABSTRACT FROM AUTHOR]

Estimates of the integrated (SFR) and specific (sSFR) rates of star formation are given for 181 galaxies of later Sc, Scd, and Sd types seen almost face-on. Their SFRs were determined from FUV fluxes in the GALEX survey. The median values of the sSFR are: -10.66 dex for Sc, -10.44 dex for Scd, and -10.40 dex for Sd types in units of yr-1. The average value of the sSFR for these galaxies falls off smoothly from low-mass to giant disks. After accounting for photometric errors, the specific star formation rate has a small cosmic variation of 0.16 dex. In order to reproduce the observed stellar mass on a cosmic time of 13.8 Gyr, the galaxies without bulges viewed face-on must have had an SFR two-three times higher in the past than observed now. [ABSTRACT FROM AUTHOR]

Given a finite range space Σ = (X , R) , with N = | X | + | R | , we present two simple algorithms, based on the multiplicative-weight method, for computing a small-size hitting set or set cover of Σ . The first algorithm is a simpler variant of the Brönnimann–Goodrich algorithm but more efficient to implement, and the second algorithm can be viewed as solving a two-player zero-sum game. These algorithms, in conjunction with some standard geometric data structures, lead to near-linear algorithms for computing a small-size hitting set or set cover for a number of geometric range spaces. For example, they lead to O (N polylog (N)) expected-time randomized O(1)-approximation algorithms for both hitting set and set cover if X is a set of points and R a set of disks in R 2 . [ABSTRACT FROM AUTHOR]

This paper presents experimental and computational results using a 1.5-stage test rig designed to investigate the effects of ingress through a double radial overlap rim-seal. The effect of the vanes and blades on ingress was investigated by a series of carefully controlled experiments: first, the position of the vane relative to the rim seal was varied; second, the effect of the rotor blades was isolated using a disk with and without blades. Measurements of steady pressure in the annulus show a strong influence of the vane position. The relationship between sealing effectiveness and purge flowrate exhibited a pronounced inflection for intermediate levels of purge; the inflection did not occur for experiments with a bladeless rotor. Shifting the vane closer to the rim-seal, and therefore the blade, caused a local increase in ingress in the inflection region; again, this effect was not observed for the bladeless experiments. Unsteady pressure measurements at the periphery of the wheel-space revealed the existence of large-scale pressure structures (or instabilities) which depended weakly on the vane position and sealing flowrate. These were measured with and without the blades on the rotor disk. In all cases, these structures rotated close to the disk speed. [ABSTRACT FROM AUTHOR]

The ingress of hot annulus gas into stator-rotor cavities is an important topic to engine designers. Rim-seals reduce the pressurized purge required to protect highly stressed components. This paper describes an experimental and computational study of flow through a turbine chute seal. The computations--which include a 360 deg domain--were undertaken using dlrtrace's time-marching solver. The experiments used a low Reynolds number turbine rig operating with an engine-representative flow structure. The simulations provide an excellent prediction of cavity pressure and swirl, and good overall agreement of sealing effectiveness when compared to experiment. Computation of flow within the chute seal showed strong shear gradients which influence the pressure distribution and secondary-flow field near the blade leading edge. High levels of shear across the rim-seal promote the formation of large-scale structures at the wheel-space periphery; the number and speed of which were measured experimentally and captured, qualitatively and quantitatively, by computations. A comparison of computational domains ranging from 30 deg to 360 deg indicates that steady features of the flow are largely unaffected by sector size. However, differences in large-scale flow structures were pronounced with a 60 deg sector and suggest that modeling an even number of blades in small sector simulations should be avoided. [ABSTRACT FROM AUTHOR]

Mistuning phenomena exist in the bladed disk due to the inevitable deviations among blades' properties, e.g., stiffness, mass, geometry, etc., leading to localization and response amplification. The dynamic performance of mistuned bladed disk is sensitive to the arrangement of blades. The blade arrangement optimization aims to obtain the optimal arrangement that minimizes the influence of mistuning. In this paper, a framework of high efficiency is raised to deal with the challenge of high computational cost this optimization. It comprehensively utilizes mixed-dimensional finite element model (MDFEM), Gaussian process (GP) regression, and genetic algorithm (GA). The MDFEM can perform mistuned modal analysis efficiently and provides the training set of GP regression rapidly. The GP model, as a surrogate model, predicts the desired dynamic performance directly without calculating the numerical model and can function as fitness function in optimization. GA has the capability to deal with combinatorial problems and is a good option for problems with large search domains and several local maxima/minima. The techniques and processes of three methods are illustrated in detail. Case studies, based on a real turbine, are concretely presented in a gradually progressive manner to test and verify the effectiveness, accuracy, and efficiency of methods and entire framework step by step. The results show the satisfactory optimal arrangement for a randomly chosen set of mistuned blades, and the influence of mistuning is reduced indeed. The time cost of the optimization has been reduced several orders of magnitude. This framework can be a promising approach for the blade arrangement optimization problem. [ABSTRACT FROM AUTHOR]

• Kaolin-doped ZnO disks and annealed under O 2 and N 2 ambientes were synthesised. • Microstructure and electrical properties of ZnO disks were studied. • The presence of the kaolin and annealing environment affected the electrical properties of ZnO disks. This study elucidates the effect of the annealing environment (oxygen and nitrogen) on the properties of kaolin-doped ZnO disks. The findings showed that, in comparison to the sample annealed in O 2 ambient, the sample annealed in N 2 has a greater average grain size. The tensile stress, lattice constants, and crystallite size of the (002) plane all indicate that annealing under N 2 enhanced the crystal quality of the ZnO disk. The bandgap energy shifted from 3.09 to 2.96 eV because of the doping and annealing processes. By annealing the kaolin-doped ZnO disk under N 2 atmosphere, the intrinsic defects were almost eliminated. The nonlinear coefficient of the disks varied from 3.6 to 2.0. It was proven in this study that kaolin can be used as an effective dopant/additive for ZnO varistors. [Display omitted] [ABSTRACT FROM AUTHOR]

The role of outflows in the formation of stars and the protostellar disks that generate them is a central question in astrophysics. Outflows are associated with star formation across the entire stellar mass spectrum. In this review, we describe the observational, theoretical, and computational advances on magnetized outflows, and their role in the formation of disks and stars of all masses in turbulent, magnetized clouds. The ability of torques exerted on disks by magnetized winds to efficiently extract and transport disk angular momentum was developed in early theoretical models and confirmed by a variety of numerical simulations. The recent high resolution Atacama Large Millimeter Array (ALMA) observations of disks and outflows now confirm several key aspects of these ideas, e.g., that jets rotate and originate from large regions of their underlying disks. New insights on accretion disk physics show that magneto-rotational instability (MRI) turbulence is strongly damped, leaving magnetized disk winds as the dominant mechanism for transporting disk angular momentum. This has major consequences for star formation, as well as planet formation. Outflows also play an important role in feedback processes particularly in the birth of low mass stars and cluster formation. Despite being almost certainly fundamental to their production and focusing, magnetic fields in outflows in protostellar systems, and even in the disks, are notoriously difficult to measure. Most methods are indirect and lack precision, as for example, when using optical/near-infrared line ratios. Moreover, in those rare cases where direct measurements are possible—where synchrotron radiation is observed, one has to be very careful in interpreting derived values. Here we also explore what is known about magnetic fields from observations, and take a forward look to the time when facilities such as SPIRou and the SKA are in routine operation.

A new method has been developed for the analysis of nonlinear forced response of bladed disks mistuned by blade anisotropy scatter and for the forced response sensitivity to blade material anisotropy orientations. The approach allows for the calculation of bladed disks with nonlinear friction contact interfaces using the multiharmonic balance method. The method uses efficient high-accuracy model reduction method for the minimization of the computational effort while providing required accuracy. The capabilities of the developed methods are validated and demonstrated using a two-blade model. A thorough study of the influence of the material anisotropy mistuning and its sensitivity on the characteristics of the forced response is carried out using finite element (FE) modes of anisotropy mistuned realistic bladed disk with nonlinear friction joints of blade roots and shroud contacts. The dependency of the nonlinear forced response on excitation level and contact pressure values has been carried out for anisotropy mistuned bladed disks. [ABSTRACT FROM AUTHOR]

Geometric uncertainties in the blade manufacturing process have important consequences in terms of dynamical properties of bladed disks. In this paper, we address the problem of modeling a full bladed disk composed by blades having uncertain geometry. The geometric imperfection of the blades is represented and analyzed according to a procedure previously presented by the authors, based on the principal component analysis (PCA) and the mesh morphing. The dynamical model of the full disk is constructed following the component mode synthesis (CMS) approach. The blade geometry is represented using a probabilistic model constructed from an experimental dataset. The effect of the geometric uncertainties is assessed using a linear uncertainty propagation approach, leading to a procedure that is fast enough to be embedded into a Monte Carlo simulation (MCS) loop. [ABSTRACT FROM AUTHOR]

Global warming is inducing sea ice retreat, which is opening new shipping routes and extending the accessible area for resource exploration. This encourages an increasing research interest in sea ice behavior. With the sea ice melting, level ice is broken up by waves propagated from the open ocean, resulting in an environment where both floating ice floes and waves exist. Such wave-ice interaction can bring significant influences on the potential human activities. This work presents a series of numerical simulations to predict the behavior of a circular ice floe forced by regular waves, with different wavelength and wave amplitude conditions being investigated. The numerical model was validated against experiments, and it revealed good accuracy in predicting the rigid body motion of an ice floe, including some extreme cases that are difficult to model by previous methods. Two specific behaviors were observed during the numerical simulations, namely overwash and scattering. Both behaviors are discussed in detail to analyze their linear/nonlinear effect on the ice floe motion. The applied model could be used to provide valuable estimations for arctic engineering purposes. [ABSTRACT FROM AUTHOR]