Spinning Cylinder Research Articles

Convective mass transfer from a horizontal rotating cylinder in a slot air jet flow

The effects of air jet impinging on the mass transfer characteristics from a rotating spinning cylinder surface were experimentally investigated. The effects of rotational Reynolds numberRer, jet-exit Reynolds number Rej, the nozzle width-to-cylinder diameter ratio B/d, and the ratio of the distance between nozzle exit and the front of cylinder to nozzle width L/B on the mean \( \overline {Sh} \) were determined. The phenomena of the first and second critical point was analyzed and validated. On the basis of experimental data, the correlation equation was obtained.

FLEXURAL INSTABILITY OF VISCOELASTIC SPINNING CYLINDERS PARTIALLY FILLED WITH LIQUID

This paper deals with the determination of free vibration characteristics and instability conditions of flexible spinning cylinders partially filled with fluid. Using the linearized Navier–Stokes equations for the incompressible, inviscid flow, a 2D model is developed for fluid motion at each section of the cylinder. The forces exerted on the cylinder wall as a result of the fluid motion are calculated as functions of lateral acceleration of the cylinder axis in the Laplace domain. Applying the Hamilton principle, the governing equations of flexural motion of the cylinder are derived and then combined with the equations describing the fluid forces to obtain the coupled field equations of the structural motion and the liquid sloshing dynamics. Using the obtained model, the free vibration and the stability conditions of the cylinder as well as the effect of material viscoelasticity on the stability boundaries are examined. The results of the stability analysis are presented for a number of examples, and some conclusions are outlined.

VORTEX-GENERATED SOUND IN FLOW ABOUT SPINNING CYLINDERS

This study provides a computational insight into unsteady far-field and surface pressure developed by vortex interaction with multiple rigid bodies in lift conditions. Flows around a spinning cylinder and two cylinders in tandem were taken as simple but yet representative prototypes of flows around multi-element lifting devices. The unsteady Euler equations are solved in terms of propagating disturbances originating from deforming vortices in the mean flow developed in the neighborhood of cylinders. Numerical errors associated with the discretization and boundary conditions were kept small employing a high-order scheme with accurate nonreflecting boundary conditions. To model the interaction of vortices with rigid bodies using moderate amount of computational resources, we apply a single-grid approach and implement the bipolar coordinate transformation where applicable. We address here the amplification of sound by the mean flow with nonzero circulation, strong influence of vortex profile on the generated sound waves, and different degree of amplification of sound in lifting flows for localized and nonlocal vortices. We find that the flow about a cylinder not only amplifies the sound strength but it also shifts the sound directivity. Vortices deforming within the flow about cylinders placed in tandem and in the traverse layouts were examined.

Multinuclear MRI of Solids: from Structure to Transport

Direct multinuclear imaging of rigid solids has been performed using the conventional two-pulse spin-echo pulse sequence and liquids magnetic resonance imaging (MRI) hardware. Two-dimensional 27Al and 51V images of an Al2O3-V2O5-glass composite sample and 11B, 23Na, 27Al and 29Si images of glass have been detected, extending the range of nuclei and solid materials that can be studied by this approach. For a spinning cylinder packed with Al2O3 powder, quantitative velocity maps have been obtained by directly detecting the 27Al nuclear magnetic resonance signal of the solid phase. The two velocity components in the imaging plane transverse to the rotation axis have been mapped using the three-pulse stimulated echo sequence. Some possibilities to improve sensitivity in the MRI experiments on rigid solids have been considered. In particular, inversion of the satellite transitions by a double frequency sweep adiabatic passage has led to a signal enhancement by a factor of two in 27Al MRI of a glass sample despite a short repetition time (0.5 s) of the imaging pulse sequence.

Mm wavelengths complex Doppler analysis using dark field illumination

Experimental results that indicate that at least two fundamental modes of Doppler generation are present when a rotating steel cylinder is broadside illuminated by radar. Improvised bistatic measurements at 77GHz are discussed and second order Doppler effects studied. Complex Doppler returns, consisting of two or more Doppler contributions, are decomposed and studied using empirical methods. In particular, ground illumination techniques are used to study Doppler in the shadow region of a cylinder of circumference 81 wavelengths. It is concluded that the complex Doppler response from the spinning cylinder consists of both direct (first order) and delayed (second order) Doppler components. Further measurements are proposed to study the delayed Doppler effect further.

Three-Dimensional Instabilities in Flow Past a Rotating Cylinder

Flow past a spinning circular cylinder placed in a uniform stream is investigated via three-dimensional computations. A stabilized finite element method is utilized to solve the incompressible Navier-Stokes equations in the primitive variables formulation. The Reynolds number based on the cylinder diameter and freestream speed of the flow is 200. The nondimensional rotation rate, α, (ratio of the surface speed and freestream speed) is 5. It is found that although the two-dimensional flow for α=5 is stable, centrifugal instabilities exist along the entire span in a three-dimensional set-up. In addition, a “no-slip” side-wall can result in separation of flow near the cylinder ends. Both these effects lead to a loss in lift and increase in drag. The end conditions and aspect ratio of the cylinder play an important role in the flow past a spinning cylinder. It is shown that the Prandtl’s limit on the maximum lift generated by a spinning cylinder in a uniform flow does not hold.

Study of Aerodynamic Forces on a Rotating Wind Driven Ventilator

A wind driven ventilator is a simple, cost-effective and environmentally-friendly device that can improve comfort and the working environment. Unfortunately very little is known about the complex flow field associated with the operation of this device. A wind tunnel investigation of the flow associated with a rotating wind ventilator was, therefore, carried out at the aerodynamic laboratory of the University of New South Wales within the Reynolds number range of 1.1 times 105 to 5.5 times 105. An attempt was also made to study some of the important features associated with operation of a rotating wind ventilator using a simple model of a stationary and a spinning cylinder. The results were encouraging and several flow features were identified for future improvement in the performance of a wind ventilator.

Analysis of crack arrest event in NESC-1 spinning cylinder experiment

In the NESC-1 spinning cylinder test, a large surface-breaking flaw in a thick steel cylinder component was subjected to high primary and secondary stresses produced by combined rotation and thermal shock loading. The crack was arrested after relatively small amounts of ductile tearing and cleavage crack extension. Finite element analyses have been carried out to obtain static elastic stress intensity factors for the initial and arrested crack under constant load and constant displacement boundary conditions. Applied static elastic stress intensity factors for the arrested crack have been compared with the plane strain crack arrest toughness values measured using small-scale compact crack arrest (CCA) specimens. The present analyses of the crack arrest event in the NESC-1 spinning cylinder test have concluded: (1) Applied static elastic stress intensity factors are reduced significantly for the lobe-shaped arrested crack which developed from the initial semi-elliptical surface crack as a result of the localised cleavage crack propagation. This reduction in crack driving force is likely to be the main reason for crack arrest. (2) The analysis carried out and comparison with the full-scale experiment confirm the prevailing approach to the assessment of crack arrest that brittle propagation will stop if the applied crack driving force falls below the crack arrest toughness. (3) The results justify the use of the static elastic stress intensity factor as the crack propagation driving force parameter and the static plane strain crack arrest toughness as the resistance parameter for crack arrest evaluation for small relative crack jump dimensions. (4) The small-scale CCA tests can be employed to evaluate crack arrest in a large cylinder of the same material.

Dynamic Stability of a Flexible Spinning Cylinder Partially Filled With Liquid

Dynamic stability of a flexible spinning cavity cylinder partially filled with liquid is discussed in the paper. The cylinder is assumed to be slender. Choosing characteristic quantities and estimating the orders of magnitude of all terms in the governing equations and boundary conditions, the three-dimensional flow in the slender cylinder is reduced to a quasi-two-dimensional flow. Using the known formulas of a two-dimensional dynamic force acting on the rotor and regarding the slender cylinder as a Bernoulli-Euler beam, the perturbed equations of the liquid-filled beam-wise cylinder are derived. The analytical stability criteria as well as the stability boundaries are obtained. The results further the study of this problem.

Evaluating the NESC-I test and the integrated approach to structural integrity assessment

The NESC-I spinning cylinder test was designed to simulate selected conditions associated with an ageing reactor pressure vessel (RPV) subjected to severe pressurised thermal shock (PTS) loading and containing hypothetical flaws. It formed the focal point of the first project of the Network for Evaluation of Structural Components (NESC), with the objective of validating the combination of non-destructive inspection and structural mechanics assessment procedures for evaluating the integrity of such an aged structure containing postulated flaws. The huge amount of data generated over the seven-year project has been evaluated and is now available to the international community. The test demonstrated that, for the specific conditions considered, defects of up to 74 mm depth in material related to that of an ageing RPV would not propagate to cause catastrophic failure under a severe PTS-type thermal shock. This outcome was fully in line with the pre-test analysis forecasts, which combined the defect-size information supplied from blind inspections trials, a comprehensive materials data set, and a range of structural analysis tools.

Developments in Local Approach methodology with application to the analysis/re-analysis of the NESC-1 PTS benchmark experiment

Local Approach methods have received considerable attention in recent years as a complementary approach to structural integrity assessment. These approaches are based on the application of micro-mechanistic models of failure in which the stress, strain and ‘damage’ local to the crack-tip are related to the critical conditions required to initiate/propagate fracture. The models are calibrated in terms of material parameters that are deemed fully transferable and derived using a combination of reference test data and supporting stress analysis. Once calibrated, using small-scale test data, the models are assumed independent on geometry and loading configuration. For a given failure mechanism, the model parameters may be used in the assessment of a structure fabricated from the same material (for appropriate temperatures, loading rates, etc). The paper describes the work initially undertaken in relation to the NESC-1 (Network for Evaluating Steel Components) spinning cylinder test, in order to validate the application of Local Approach methods for the case of PTS loading. The predicted amount of pre-cleavage ductile tearing and the timing of the subsequent cleavage event are compared with the observed fracture behaviour of the defect. The paper then highlights several areas in which Local Approach methodology has been developed since the initial work on PTS. These include: • Calibration of the cleavage model across a range of temperatures and constraint states. • Treatment of 3D defects. • Reference to hydrostatic stress in cleavage fracture predictions. • Simplification and standardisation of analytical techniques for more routine use in integrity assessments. The paper concludes that results from large-scale structural experiments, such as the NESC-1 spinning cylinder test, will be of lasting value in validating developments in Local Approach methodology and other advanced methods of fracture assessment. This is particularly true in the authors’ current work that seeks to achieve an overall simplification in methodology, without sacrificing predictive accuracy.

Key features arising from structural analysis of the NESC-1 PTS benchmark experiment

Interpreting the results of the NESC spinning cylinder test represents a significant challenge for structural integrity specialists. The test was conceived to provide data on the behaviour of underclad defects and a large, through-clad defect under simulated PTS loading conditions. It contained the following structural features, the understanding of which is essential to obtaining a full interpretation of the test results: • cladding effects; • residual stresses; • constraint effect; • effective crack front width; • warm prestressing effect. The paper presents the results of the NESC-1 test with particular reference to the essential features listed above, and their relative importance. The paper notes that the most significant uncertainty factor that influenced the integrity assessment of the test is the variability of material toughness. This is in relation to both intrinsic variability (scatter) and that of the near-surface (clad/HAZ/base metal) region. There is some evidence to suggest that a loss of constraint influenced the near-surface behaviour of the largest underclad defect and the through-clad defect. However, the higher toughness of the HAZ, reduced crack front width (relative to that of a 25 mm CT specimen) and cladding effects are significant factors, too. The paper concludes by pointing out the need to provide (through continued international collaboration) validated procedures for relating fracture test data on specific specimen geometries to local constraint parameters estimated from 3D finite element simulations. Here, it is apparent that significant progress is to be gained from a formal unification of local approach methodology, the master curve description of cleavage toughness and ‘classical’ constraint-based fracture assessment methods.

Consistency of fracture assessment criteria for the NESC-1 thermal shock test

In this report, a best estimate analysis of the NESC Spinning Cylinder test is performed and the consistency of the state of the art application of the different fracture parameters and assessments criteria is examined. Direct fracture toughness measurements best describes the fracture behavior of the NESC Spinning Cylinder in the simulated pressurized thermal shock loading. The concept based on the ASME RT NDT reference temperature (either Pellini or Cv test) does not provide consistent description of the NESC1 fracture assessment. In general the fracture mode, i.e. ductile initiation and tearing followed by cleavage event, was successfully estimated by 3D FE based fracture assessment, combined with Master Curve description of fracture toughness.

Aerodynamics of a Spinning Cylinder in Rarefied Gas Flows

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Fracture Analysis of the Heat-Affected Zone in the NESC-1 Spinning Cylinder Experiment

This paper presents updated analyses of the cylinder specimen being used in the international Network for Evaluating Steel Components (NESC) large-scale spinning-cylinder project (NESC-1). The NESC was organized as an international forum to exchange information on procedures for structural integrity assessment, to collaborate on specific projects, and to promote the harmonization of international standards. The objective of the NESC-1 project is to focus on a complete procedure for assessing the structural integrity of aged reactor pressure vessels. A clad cylinder containing through-clad and subclad cracks will be tested under pressurized-thermal shock conditions at AEA Technology, Risley, U.K. Three-dimensional finite-element analyses were carried out to determine the effects of including the cladding heat-affected zone (HAZ) in the models. The cylinder was modeled with inner-surface through-clad cracks having a depth of 74 mm and aspect ratios of 2:1 and 6:1. The cylinder specimen was subjected to centrifugal loading followed by a thermal shock and analyzed with a thermoelastic-plastic material model. The peak KI values occurred at the clad/HAZ interface for the 6:1 crack and at the HAZ/base interface for the 2:1 crack. The analytical results indicate that cleavage initiation is likely to be achieved for the 6:1 crack, but questionable for the 2:1 crack.

NESC spinning cylinder experiment: pre-test structural analysis evaluation

This spinning cylinder experiment, organised under the auspices of the Network for the Evaluation of Steel Components (NESC), is designed to address the cleavage initiation behaviour of axial subclad and surface breaking flaws in end of life RPV material under pressurised thermal shock (PTS) transient conditions. Pre-test structural integrity assessments have been performed to assist in the detailed design of the experiment and in particular the specification of the initial defect sizes. The results presented offer an insight into the influences of experimental variables on the probability of realising a cleavage event during the transient.

Pretest fracture assessment of the NESC-1 spinning cylinder under a PTS transient

This report presents pretest fracture assessments of the NESC-1 spinning cylinder. The clad cylinder has an internal diameter of 1045 mm, a wall thickness of 175 mm and a length of 1296 mm. An internal surface breaking crack with a depth of 73 mm and a length of 205 mm subjected to a thermal shock is studied. Three-dimensional elastic-plastic finite element calculations, considering the crack-tip constraint, are employed in the assessments. Also performed are sensitivity studies to demonstrate how different affecting factors, especially the cladding residual stresses, impact the crack driving force. It is found that the crack front conditions in the cladding and at the deepest point of the crack are far from critical, but cleavage fracture events can be expected in the cladding HAZ. The results show substantial loss of crack-tip constraint in the cladding HAZ compared with the SSY solutions. From the sensitivity studies, it is observed that uncertainties due to different assumptions in the analysis influence the assessment results less than uncertainties in the fracture toughness data of the materials.

Diffusional spinning as a probe of DNA fragments conformation

The dependence of the spinning diffusion coefficient of a wormlike chain upon contour length L, persistence length P, and radius R is shown here to follow a ‘‘Lorentzian’’ law of width Γ vs σβL/R, where σ2β=l0/P is the variance of the bending angles distribution of Monte Carlo simulated chains with bond length l0. This description is equivalent to that of a spinning cylinder of length L and effective radius Reff=R(L,P), with Reff≥R. When considering experimental data it is found that fluorescence polarization anisotropy (FPA), a technique very sensitive to spinning, also yields apparent DNA radii depending upon fragment length. In order to derive DNA parameters which are independent of fragment length, we introduce a procedure for fitting FPA data which takes into account thermal distortions and employs the parametric expressions for rigid body rotations, spinning and tumbling, depending only upon L, P, and the actual DNA radius, R. Then the apparent persistence length P can be estimated once a value of R is assumed together with the value of the dynamic persistence length, the latter affecting the internal bending motions of the fragments. Fitting the FPA data is easily accomplished with the value of R=10 Å as suggested by a number of recent measurements.

First spinning cylinder test analysis using a local approach to fracture

In recent years, several experimental programmes on large-scale specimens have been organized to evaluate the capabilities of the fracture mechanics concepts employed in structural integrity assessment of pressurized water reactor pressure vessels. During the first spinning cylinder test, a geometry effect was revealed experimentally showing the difficulties of transferring toughness data from small-scale to large-scale specimens. An original analysis of this test, by means of a local approach to fracture, is presented in this paper. Both compact tension specimen and spinning cylinder fracture behaviour were computed using a continuum damage mechanics model developed at EDF. We confirmed by numerical analysis that the cylinder's resistance to ductile tearing was considerably larger than in small-scale fracture mechanics specimen tests, about 50%. The final crack growth predicted by the model was close to the experimental value. Discrepancies in J R curves seemed to be due to an effect of stress triaxiality and plastic zone evolution. The geometry effect inducing differences in resistance to ductile tearing of the material involved in the specimens can be investigated and explained using a local approach to fracture methodology.

Comparative assessment of project FALSIRE—results

The analysis results of the recently completed Phase I for the Project Fracture Analysis of Large Scale International Reference Experiments (FALSIRE) are summarized in a comparative manner. Thirty-nine analyses of the pressurized thermal shock experiments NKS-3 and NKS-4 from MPA-Stuttgart (FRG), PTSE-2 from ORNL (USA) and spinning cylinder SC-I and SC-II from AEA Technology (UK) were evaluated. Discussion of the results has focused on the discrepancies of the finite element results and on comparisons with the estimation scheme analyses. A set of quantities such as crack mouth opening (CMOD), strains, stresses, J-integral and constraint have been selected and compared for the different analyses to approximate the structural behaviour of the test specimens and the fracture behaviour of the cracks. A database of the results has been established. The influence of boundary conditions, approximation of material properties and calculational methods is shown in detail. The structure mechanics behaviour of the test specimens could be approximated well for the NKS experiments but not for PTSE-2. Most differences between the various analyses could be explained. In SC tests structural mechanics results could not be compared with experimental measures. The application of J R methodology to predict crack extension was partially successful in some cases (NKS experiments) but not in others (PTSE-2). The quality of fracture assessment is closely connected with the structural mechanics simulation. In all analyses with good structural mechanics approximation, the fracture prediction was reasonable. Fracture assessments based on CT-specimens overestimate stable crack growth in the case of NKS-4 and SC-I/II, because the crack resistance in the large-scale test specimens is greater than predicted by small specimens (e.g. CT-25). SC-I/II fracture results show that crack growth can be described quite well with the J-integral and the J R -curves of the large-scale test specimen. Therefore, future work has to be concentrated on extension of the J R methodology by a parameter which controls the geometry and load dependence of the crack resistance. This can only be achieved by close connection between numerical simulation and fracture mechanics testing.