Location Of Transition Research Articles

Video Shot Boundary Detection using the Scale Invariant Feature Transform and RGB Color Channels

<p>Segmentation of the video sequence by detecting shot changes is essential for video analysis, indexing and retrieval. In this context, a shot boundary detection algorithm is proposed in this paper based on the scale invariant feature transform (SIFT). The first step of our method consists on a top down search scheme to detect the locations of transitions by comparing the ratio of matched features extracted via SIFT for every RGB channel of video frames. The overview step provides the locations of boundaries. Secondly, a moving average calculation is performed to determine the type of transition. The proposed method can be used for detecting gradual transitions and abrupt changes without requiring any training of the video content in advance. Experiments have been conducted on a multi type video database and show that this algorithm achieves well performances.</p>

A simple method for estimating transition locations on blade surface of model propellers to be used for calculating viscous force

Effects of inflow Reynolds number (Re), turbulence intensity (I) and pressure gradient on the transition flow over a blade section were studied using the γ-Reθ transition model (STAR-CCM+). Results show that the ReT (transition Re) at the transition location (PT) varies strongly with Re, I and the magnitude of pressure gradient. The ReT increases significantly with the increase of the magnitude of favorable pressure gradient. It demonstrates that the ReT on different blade sections of a rotating propeller are different. More importantly, when there is strong adverse pressure gradient, the PT is always close to the minimum pressure point. Based on these conclusions, the PT on model propeller blade surface can be estimated. Numerical investigations of pressure distribution and transition flow on a propeller blade section prove these findings. Last, a simple method was proposed to estimate the PT only based on the propeller geometry and the advance coefficient.

Performance assessment on a variety of double side structure during collision interaction with other ship

Abstract The main goal of the present paper was to study the physical response of a double side skin (DSS) structure under impact load in a collision event between two ships. Collision energy and damage extent (size and location) during the collision process were observed together with damage patterns on side structure. The ships were modeled after a Ro-Ro passenger ship and cargo reefer which were involved in a ship collision on the Sunda Strait while the analyseswere performed using non-linear simulations FEMto produce virtual simulation data. Several caseswere proposed to be investigated in this work with involvement of parameters i.e. penetration location and ship materials which were embedded on the structure model. A series of material experiments and testing was conducted to obtain detailed material properties which were to be deployed in simulation. It was shown that, after penetration at the transition location, the striking ship was successfully deforming and forming tears to the inner skin. On the other hand, with identical structure and identical mass of construction, the use of high-strength low-alloy (HSLA) steel as the repair material offered considerably better capacity in absorbing the impact load than plain-carbon steel.

Transition due to Roughness on Blunt Capsule: Comparison with Transient Growth Correlation

The effect of uniformly distributed surface roughness on the onset of boundary-layer transition for a capsule geometry was experimentally investigated in a conventional hypersonic blowdown wind tunnel. The thin-walled scale model of the Orion Crew Exploration Vehicle used in this study was mounted at a 28 deg angle of attack in the Adjustable Contour Expansion wind tunnel. A test matrix of 24 runs was developed to experimentally estimate the location of transition and to relate the flow properties at this location and the roughness height to established transient growth scaling. Tests were conducted for four different Reynolds numbers at six quasi-uniform surface roughness height distributions. The tunnel was nominally set to Mach 6.0 and a total temperature of 430 K for each run. Infrared thermometry was used to measure the surface temperature distribution. Heat transfer rates generated through a series of surface temperature maps were processed into normalized Stanton number centerline plots. These plots directly indicated the boundary-layer transition location. Analysis of the results indicated that the experimental data matched the established transient growth scaling.

Wind-Tunnel and CFD Investigations Focused on Transition and Performance Predictions of Laminar Wings

This paper is a continuation of the paper recently published by Hue et al. (“Experimental and Numerical Methods for Transition and Drag Predictions of Laminar Airfoils,” AIAA Journal, Vol. 53, No. 9, Sept. 2015, pp. 2694–2712) that focused on transition and drag predictions of laminar airfoils. The extension of such studies to three-dimensional configurations representative of modern civil aircraft is a further step toward the implementation of natural laminar-flow technologies. The present work, therefore, focuses on validating the laminar design of a low-swept wing for business jet applications. In 2015, an experimental campaign was carried out in the European Transonic Windtunnel, and included laminar/turbulent transition measurements with temperature-sensitive paint at Mach and Reynolds numbers typical of cruise flight conditions. Subsequently, fluid dynamics computations were performed on this aircraft geometry either with a Reynolds-averaged Navier–Stokes solver using both Tollmien–Schlichting and crossflow transition criteria, or with a boundary-layer code using either database methods for transition location or exact stability analyses. In this paper, experimental and numerical transition predictions are compared for three representative cases corresponding to different angles of attack. The agreement that is achieved is satisfactory, and extended regions of laminar flow are observed on the wing at cruise lift levels. In these conditions, the drag reduction can account for 10–15% of the aircraft drag.

Modeling of Laminar-Turbulent Transition in Boundary Layers and Rough Turbine Blades

A local, intermittency-function-based transition model was developed for the prediction of laminar-turbulent transitional flows with freestream turbulence intensity Tu at low (Tu < 1%), moderate (1% < Tu < 3%), and high Tu > 3% levels, and roughness effects in a broad range of industrial applications such as turbine and helicopter rotor blades, and in nature. There are many mechanisms (natural or bypass) that lead to transition. Surface roughness due to harsh working conditions could have great influence on transition. Accurately predicting both the onset location and length of transition has been persistently difficult. The current model is coupled with the k–ω Reynolds-averaged Navier–Stokes (RANS) model, that can be used for general computational fluid dynamics (CFD) purpose. It was validated on the ERCOFTAC experimental zero-pressure-gradient smooth flat plate boundary layer with both low and high leading-edge freestream turbulence intensities. Skin friction profiles agree well with the experimental data. The model was then tested on ERCOFTAC experimental flat plate boundary layer with favorable/adverse pressure gradients cases, periodic wakes, and flows over Stripf's turbine blades with roughness from hydraulically smooth to fully rough. The predicted skin friction and heat transfer properties by the current model agree well with the published experimental and numerical data.

R134a condensation flow regime and pressure drop in horizontal microchannals cooled symmetrically and asymmetrically

An experimental investigation was conducted for two-phase flow regimes and friction pressure drop during condensation of refrigerant R134a in oval parallel microchannels with a hydraulic diameter of 301.6µm, an aspect ratio of 2.46 and a length of 50mm. The effects of microchannel cooling methods, including asymmetric cooling and symmetric cooling, were studied. The flow regimes and pressure drops were recorded for qualities of 0.1–0.9 and mass flux of 60–250kg/(m2s). The inlet saturation temperature of R134a is 31.3°C. Film wavy flow, corner wavy flow, slug flow and bubbly flow were observed. The flow regimes were mapped and compared with 8 flow regime maps in the literature. Two flow regime criteria were given using vapor Weber number. The wavy-intermittent flow transition locations were measured and compared with the correlations in the literature. The transition location moves downstream with increasing refrigerant mass flux and inlet quality. The transition locations were more upstream for the condensation flow cooled symmetrically then that cooled asymmetrically. The friction pressure drop increases with increasing mass flux and quality. The pressure drop for microchannels with symmetric cooling is lower than asymmetric cooling. The pressure drop data was compared with the correlations in the literature.

Hypersonic transition induced by three isolated roughness elements on a flat plate

Hypersonic boundary layer transition from laminar to turbulent induced by three isolated roughness elements (ramp, diamond, and cylinder) was investigated by direct numerical simulations based on finite volume formulation with high order MDCD scheme. The effects of roughness shape on the transition mechanism, aerodynamic and aero-thermodynamic performances were quantitatively compared. The transition is dominated by three-dimensional shear layer instability and the streamwise transition locations are almost the same for all three roughness elements. The width of turbulent wake, the drag increment and the heat flux are the largest for cylinder. At the same time, the turbulent wake is the narrowest and drag and heat flux are the lowest for the ramp.

THE EFFECT OF TRANSITON LOCATION ON AEROTHERMOELASTICITY OF A HYPERSONIC ALL-MOVABLE CENTROL SURFACE

The transition prediction of hypersonic boundary layer has been a difficulty in fluid dynamics. The friction coefficient and heat-transfer coefficient could be changed because of transition. The location of transition has an effect on thermal environment around the aircraft surface, which accounts for marked changes of Aeroelastic characteristics further. Considering the uncertainly of transition prediction of hypersonic boundary layer, this paper has analyzed the effects of transition location to aerothermodynamics of hypersonic all-movable control surface. First of all, the thermal environment around the control surface is obtained by solving the N-S (Navier-Stocks) equation using the model of laminar and turbulent flow respectively. In the next place, a parameterized model considering the given location of transition for temperature distribution is proposed. Base on this model, the structural thermal mode considering thermal stress and material inherent characteristics is analyzed. Finally the aeroelasticity is analyzed by the method of local flow piston theory based on CFD. This paper chooses an all-movable control surface as study subject with M=6, H=15 km and the calculation results show that:(1) As the transition location moving from leading edge to trailing edge, the structural frequencies increase and flutter velocity has an increased trend. Research indicates that maximum variation of flutter velocity is 6% brought by transition location; (2) When transition is located near the rudderpost, the flutter characteristics of the structure change violently. Decomposition and analysis of stiffness characteristic show that the major factor is the stiffness of rudderpost whose influence accounts for more than 80% of the whole structure.

Database Approach for Laminar-Turbulent Transition Prediction: Navier–Stokes Compatible Reformulation

This paper presents a transition prediction model that adds additional equations to the Reynolds-averaged Navier–Stokes set. It is based on the so-called -factor method, which is valid for natural transition on wings due to the hypothesis that it relies on (modal instabilities disturbing the boundary layer). It consists of an integration of the disturbance growth rates along the edge streamline. Herein, the disturbance growth rates are obtained via a database approach: ONERA—The French Aerospace Lab’s so-called parabolas method. Numerically, integration of the growth rates along the edge streamline is performed through additional transport equations, thus removing the need for any topology specification from the end user. Implementation caveats are illustrated on the ONERA-D airfoil in incompressible conditions. This method is then successfully applied for transition prediction on a two-dimensional industrial laminar airfoil at transonic conditions, with varying upstream conditions and angles of attack. Satisfactory agreements with both the experimental data and the conventional transition predictions (local, linear stability results) are obtained, which illustrate the accuracy of the predicted transition location.

The Maximum Skin Friction and Flow Field of a Planar Impinging Gas Jet

The maximum skin friction and flow field are experimentally measured on a planar impinging gas jet using oil film interferometry (OFI) and particle image velocimetry (PIV), respectively. A jet nozzle width of W = 15 mm, impingement ratios H/W = 4, 6, 8, 10, and a range of jet Reynolds numbers Rejet = 11,000–40,000 are tested to provide a parametric map of the maximum skin friction. The maximum skin friction predictions of Phares et al. (2000, “The Wall Shear Stress Produced by the Normal Impingement of a Jet on a Flat Surface,” J. Fluid Mech., 418, pp. 351–375) for plane jets agree within 5% of the current OFI results for H/W = 6, but deviates upward of 28% for other impingement ratios. The maximum skin friction is found to be less sensitive to changes in the impingement ratio when the jet standoff distance is roughly within the potential core length of the jet. PIV measurements show turbulence transition locations moving toward the nozzle exit with increasing Reynolds number, saturation in the downstream evolution of the maximum axial turbulence intensity before reaching a maximum peak upon impingement, followed by sudden damping at the plate surface. As the flow is redirected, there is an orthogonal redistribution of the fluctuating velocity components, and local peaks in both the axial and transverse turbulence intensity distributions at the plate locations of the maximum skin friction.

The Crystallographic and Electronic Phase Diagrams of Yttria-Stabilized Zirconia Model Electrolytes

Yttria-stabilized zirconia (YSZ) is known for its high ionic conductivity at elevated temperatures, which makes it ideal for usage as an oxygen ion conducting electrolyte. Thus, it is often utilized in chemical sensors or solid oxide fuel cells. In SOFCs, it is also employed as a component of the anode (a Ni/YSZ cermet). There, besides facilitating the transport of oxygen anions from the electrolyte to the three-phase boundary, it plays a role in the catalytic process involving the activation of various fuels fed to the SOFC. In both cases, the relevant properties – be it the ionic/electronic conductivity or the catalytic activity – are defined by the existence of oxygen vacancies and the electronic structure of the complex oxide. In order to investigate this systematically, thin film model systems with varying compositions, ranging from 3 mol% Y2O3 to 40 mol% Y2O3, were deposited by means of a home-built direct current ion beam sputter source.[1] This source allows for the preparation of thin films (approximately 25 nm) at a controlled growth rate, facilitating the epitaxial growth. As substrates, freshly-cleaved NaCl(001) single crystals were employed, which allowed the thin films to be used as unsupported transmission electron microscopy (TEM) specimens. Using selected area electron diffraction, the crystallography was investigated. However, since the tetragonal and cubic polymorphs contain lattice planes with the same spacings, a distinction is not trivial. Nevertheless, this can be circumvented by calculating the unit cell height, i.e. the lattice parameter c, which is equivalent for the tetragonal and cubic structures, and plotting it as a function of the yttria-content. There, a retention of the unit cell height between 8 and 20 mol% Y2O3 can be observed, which indicates that a phase transition from tetragonal to cubic is present between 8 and 20 mol% yttria as, due to the higher yttria concentration (with Y3+ being the larger ion than Zr4+), the unit cell volume must increase. Hence, the retention of the unit cell height can only be explained by an expansion in the lateral dimensions, i.e. the tetragonal cell becomes cubic.[1] In fact, using magnetron sputtering, the location of the phase transition could be narrowed down to be between 8 and 9.3(4) mol% Y2O3,[2] which is crucial knowledge if, for instance, the cubic structure for the electrolyte is desired. Very similar trends can be found for the direct (by means of valence EELS) and indirect band gaps (UPS), which show a decreasing trend as more Zr is substituted by Y – and, thus, as more oxygen vacancies are generated. However, at the phase transition, there is a discontinuity as the band gaps increase significantly. Furthermore, the electron affinity, i.e. the energy difference between the vacuum level and the conduction band minimum, is shown to follow the same function as well. This parameter exhibits another rare phenomenon: it is negative. Because of this, the vacuum level is within the band gap, which causes electrons that have been excited into the conduction band by, for instance, optical absorption, to be emitted with almost no barrier. This makes these materials also suitable as photocathodes, for example in spin-polarized electron microscopes. With Čerenkov emission spectroscopy, where the light emitted when an electron traverses the sample at a speed larger than the speed of light inside the medium is recorded, another electronic transition at slightly above 3 eV (also displaying the same trend as the lattice parameter as a function of the Y2O3content) was found. By comparison with densities of states from DFT calculations, this can be determined as being the excitation of electrons from the valence band maximum into the unoccupied oxygen vacancy-related gap states, i.e. these values depict the gap state level. With help of these investigations, not only can a crystallographic thin film phase diagram be constructed, but also an electronic structure phase diagram, which displays the relation of various electronic niveaus as a function of the Y2O3content in the YSZ thin films relevant for applications in SOFCs. [1] Götsch, T.; Wallisch, W.; Stöger-Pollach, M.; Klötzer, B.; Penner, S. AIP Adv. 2016, 6 (2),025119 [2] Götsch, T.; Schachinger, T.; Stöger-Pollach, M.; Kaindl, R.; Penner, S. Appl. Surf. Sci. 2017, 402,1–11 Figure 1: The unit cell height (top panel) as well as the band gaps (lower panel) show the same behavior as a function of the yttria content. Figure 1

Locating of normal transitions in a Bi2223 high temperature superconducting coil by using capacitor type voltage terminals and the active power method

It is important to locate positions of normal transitions in a high temperature superconducting (HTS) coil for identifying its design and fabrication weakness. In this paper, the authors propose a locating method by using capacitor type voltage terminals and the active power method. The former is a method to measure voltage in a HTS coil without electric contact and the latter is a method to detect the normal transitions by measuring active power dissipated in the coil. Combination of the two methods can achieve precise location of the normal transitions. The authors show usefulness of the method through experimental results for a Bi2223 HTS coil.

Aeroelastic tailoring of an NLF forward swept wing

This article introduces the application of a multidisciplinary analysis process chain based on high-fidelity simulation methods for the aeroelastic tailoring of an natural laminar flow (NLF) forward swept wing. With this approach the interactions between aerodynamics, loads and structural sizing are considered in the wing analysis. The resulting process enables an integrated aerostructural wing design including aeroelastic tailoring using carbon fiber reinforced plastics. The main feature of the process chain is the hierarchical decomposition of the problem into two levels. On the highest level, the orthotropy direction of the composite structure will be analyzed. The lower level includes the wing box sizing for essential load cases considering the static aeroelastic deformations. Thereby, the wing box sizing can be performed with a given ply share of the laminate or a ply share optimization. Additionally, the airfoil shapes are transferred from a given NLF wing design. The natural laminar flow is considered by prescribing laminar–turbulent transition locations. The process chain evaluates the wing mass, the lift-to-drag ratio under cruise flight conditions and the corresponding design mission fuel consumption. Results of aerostructural wing design studies and optimizations are presented for an NLF forward swept wing aircraft configuration. The aerostructural wing optimization with 3 orthotropy angles as design parameters shows a wing mass reduction in the order of 8% and a design mission fuel consumption reduction in the order of 4% in comparison to the aeroelastic tailored wing design of the reference aircraft.

The MEXICO rotor aerodynamic loads prediction: ZigZag tape effects and laminar-turbulent transition modeling in CFD

This paper aims to provide an explanation for the overprediction of aerodynamic loads by CFD compared to experiments for the MEXICO wind turbine rotor and improve the CFD prediction by considering laminar-turbulent transition modeling. Large deviations between CFD results and experimental measurements are observed in terms of sectional normal and tangential forces at the blade tip (r/R=0.82 and 0.92) of the MEXICO rotor operating in axial condition at the design tip speed ratio λ=6.7. The first part of this study identifies the effects of ZigZag tape, which is used in the experiment to trigger boundary layer transition, by analyzing the available experimental data of a single, non-rotating MEXICO rotor blade. The analysis indicates that ZigZag tape has a significant impact on sectional aerodynamic tip loads: it alters the boundary layer thickness and additionally reduces the effective airfoil camber besides the expected tripping. These additional effects most likely also occur in the rotating MEXICO experiment, reducing the sectional loads and hence lead to an overprediction by CFD. To eliminate the ZigZag tape interference, experimental data with an untripped blade is preferred to be used as validation case. In the second part of this study, a transitional flow simulation for the MEXICO rotor is performed by using RANS-based transition model k−kL−ω within OpenFOAM-2.1.1. The numerical results are compared against experimental data obtained from the untripped, new MEXICO experiments. The comparison gives that transitional simulation present a very good tip loads prediction for the untripped blade. The measured data also confirms that the ZigZag tape indeed has a significant influence on the blade tip loads in rotating conditions. The transition onset over 3D MEXICO blade is visualized and transition locations are identified. The results shown in the present study can explain the causes of the large differences between CFD and experiment observed in the MEXICO blind comparisons.

Numerical simulation of transitional flow on a wind turbine airfoil with RANS-based transition model

ABSTRACTThis paper presents a numerical investigation of transitional flow on the wind turbine airfoil DU91-W2-250 with chord-based Reynolds number Rec = 1.0 × 106. The Reynolds-averaged Navier–Stokes based transition model using laminar kinetic energy concept, namely the k − kL − ω model, is employed to resolve the boundary layer transition. Some ambiguities for this model are discussed and it is further implemented into OpenFOAM-2.1.1. The k − kL − ω model is first validated through the chosen wind turbine airfoil at the angle of attack (AoA) of 6.24° against wind tunnel measurement, where lift and drag coefficients, surface pressure distribution and transition location are compared. In order to reveal the transitional flow on the airfoil, the mean boundary layer profiles in three zones, namely the laminar, transitional and fully turbulent regimes, are investigated. Observation of flow at the transition location identifies the laminar separation bubble. The AoA effect on boundary layer transition over wind turbine airfoil is also studied. Increasing the AoA from −3° to 10°, the laminar separation bubble moves upstream and reduces in size, which is in close agreement with wind tunnel measurement.

Schizoid Fantasy: Refuge or Transitional Location?

The schizoid personality, a type increasingly representative of our times, lives in a detached individual world. But this retreat sometimes can offer a place of transition, serving as a creative bridge to everyday life. An extended case illustration describes a schizoid patient who was able to use a playful form of psychotherapy to move from make-believe to real relationship.

Excited-state quantum phase transitions in a two-fluid Lipkin model

Background: Composed systems have became of great interest in the framework of the ground state quantum phase transitions (QPTs) and many of their properties have been studied in detail. However, in these systems the study of the so called excited-state quantum phase transitions (ESQPTs) have not received so much attention. Purpose: A quantum analysis of the ESQPTs in the two-fluid Lipkin model is presented in this work. The study is performed through the Hamiltonian diagonalization for selected values of the control parameters in order to cover the most interesting regions of the system phase diagram. [Method:] A Hamiltonian that resembles the consistent-Q Hamiltonian of the interacting boson model (IBM) is diagonalized for selected values of the parameters and properties such as the density of states, the Peres lattices, the nearest-neighbor spacing distribution, and the participation ratio are analyzed. Results: An overview of the spectrum of the two-fluid Lipkin model for selected positions in the phase diagram has been obtained. The location of the excited-state quantum phase transition can be easily singled out with the Peres lattice, with the nearest-neighbor spacing distribution, with Poincar\'e sections or with the participation ratio. Conclusions: This study completes the analysis of QPTs for the two-fluid Lipkin model, extending the previous study to excited states. The ESQPT signatures in composed systems behave in the same way as in single ones, although the evidences of their presence can be sometimes blurred. The Peres lattice turns out to be a convenient tool to look into the position of the ESQPT and to define the concept of phase in the excited states realm.

An empirical model to predict temperature‐dependent thermal conductivity of amorphous polymers

ABSTRACTThermal conductivity in polymers has been theoretically and experimentally studied in good detail, but there is a need for more accurate models. Polymeric thermal conductivity exhibits a plateau‐like transition at temperatures around 10 K, which is not well accounted for by existing models. In this work, an empirical model that can predict temperature‐dependent thermal conductivity of amorphous polymers is developed. The model is based on kinetic theory and accounts for three sets of vibrational modes in polymers, and is developed using classical expressions, results of previous simulations, and experimental data. Fundamental material properties like density, monomer molecular weight, and speed of sound are the only input parameters. The model provides estimates for the locations of transitions between different sets of vibrational modes, an upper limit for the thermal conductivity, and temperature‐dependent thermal conductivity, which are in good agreement with experimental data. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1160–1170

Location-dependent Raman transition in gravity-gradient measurements using dual atom interferometers

The location-dependent Raman transition was investigated based on dual atom interferometers which were designed for gravity-gradient measurements. The cross talk between the Raman beam pairs generated by an electro-optical modulator make the Raman transition location dependent. Therefore, the fringe contrast also depends on the location where the Raman pulses interact with the atoms, so it is important to adjust the interaction location to optimize the precision of the gravity-gradient measurements. To further reduce the residual cross talk, the detuning of the Raman beams for $^{85}\mathrm{Rb}$ atoms was controlled using the saturated absorption spectra of the $^{87}\mathrm{Rb}$ atoms. The optimal location for the Raman transition was determined by theoretical analysis and modulation experiments, and the atomic trajectory was optimized and applied to the gravity-gradient measurements. The resolution of the differential gravity measurement evaluated by the Allan deviation was $4.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ m/${\mathrm{s}}^{2}$ @ 15 000 s, and the corresponding resolution of the gravity gradient measurement was 7.4 E @ 15 000 s.