Location Of Transition Research Articles

Boundary Layer Transition Measurement Flight Test Based on Infrared Image Technique

According to the requirements of boundary layer transition detection measurement flight test, the study on the detection technique of infrared thermal image in real flight conditions was carried out. In this paper, the basic principle of infrared measurement technique was introduced firstly. Through the analysis of the main factors, such as emissivity, radiation incidence angle and temperature difference between the measured object and environment, the test means were determined, which includes surface treatment, infrared light path adjustment, solar radiation and internal heating of tested parts. Then the whole flight test method of boundary layer transition measurement was designed, including selecting test object and test instrument, determining test procedure and image processing procedure, and giving transition location criterion. Finally, the validity of this flight test method was demonstrated through testing results, the research of which would be helpful and meaningful in boundary layer transition measurement.

Influence of glow discharge on evolution of disturbance in a hypersonic boundary layer: The effect of second mode

This is the companion volume on the effects of artificial disturbance on the transition process of a boundary layer over a flat plate. The artificial disturbance with the frequency in the range of second-mode instability is introduced into the boundary layer by glowing discharge on the surface of the plate. Experiments are performed using Rayleigh-scattering visualization, wall pressure pulsations measurement, and high-frequency schlieren visualization in the Φ300 mm hypersonic quiet wind tunnel at Peking University. It is found that the second-mode instability waves are stimulated remarkably by the artificial disturbance, and the boundary layer transition is triggered effectively. The second-mode instability interacts with the first mode via a phase-lock mechanism, which leads to the rapid amplification of the first mode and the moving forward of transition location.

Enhancing SNR by Anisotropic Diffusion for Brillouin Distributed Optical Fiber Sensors

Anisotropic diffusion (AD) is employed to enhance the signal-to-noise ratio (SNR) of Brillouin distributed optical fiber sensor. A Brillouin optical time-domain analyzer (BOTDA) with 99-km-long fiber under test is set up, where a section of 2.3 m and another 182 m section at the end of the fiber are heated for experimental verification. The SNR of experimental data sets with different sampling point numbers are enhanced to several improvement levels by AD and three other methods for comparison. Results show that the 2.3 m section and the temperature transition region of the 182 m section are better preserved by AD than other methods for the same SNR improvement. Objective criteria analysis shows that AD achieves the best measured spatial resolution and temperature accuracy among the four methods, the location of temperature transition can be detected more accurately for data with low SPNs after AD denoising. In addition, the processing time of AD is 1/3 that of non-local means (NLM) and 6‰ that of block-matching and 3D filtering (BM3D). The edge-preserving quality and fast processing speed allow the proposed algorithm to be a competitive denoising alternative for sensors based on Brillouin scattering.

Analysis of the blade boundary-layer flow of a marine propeller using a RANS solver

In this paper a comparison between RANS simulations carried out with the k−ω SST turbulence model and γ−R̃eθt transition model, and experimental measurements for marine propeller P4119 is made. The experiments were conducted at the David Taylor Model Basin and comprehended three-dimensional velocity components measurements of the blade boundary-layer using a LDV system in uniform conditions. The present work includes an estimation of the numerical errors that occur in the simulations, analysis of the propeller blade flow, chordwise and radial components of the boundary-layer velocity profiles and boundary-layer characteristics. From this comparison and depending on the selected inlet turbulence quantities, we conclude that the transition model is able to predict the extent of laminar and turbulent regions observed in the experiments. Moreover, the predicted velocity profiles show good agreement with the experimental measurements and verified the location of transition.

Validation case for supersonic boundary layer and turbulent aero-optical investigation in high-Reynolds-number freestream by WCNS-E-5

Turbulent flat-plate boundary layer flows have been widely employed for numerical validation in the aero-optical field. In present study, the laminar-to-turbulent evolution induced by wavy roughness in high-Reynolds-number supersonic freestream is investigated using a numerical technique based on the fifth-order weighted compact nonlinear scheme (WCNS-E-5). The computational procedure and post-processing method are described in detail, and the acquired instantaneous flow structure and statistical data are compared with other theoretical, experimental, and numerical results to demonstrate the feasibility of predicting turbulence using WCNS-E-5. Further, to reduce the computational resources required to simulate turbulent flow, a velocity correlation function is introduced to decrease the computational domain in the spanwise direction. Additionally, the effects of different grid sizes on the simulation results are examined by reducing the number of cells in the streamwise, wall-normal, and spanwise directions. Finally, the authors conduct a tentative investigation into the aero-optical effects of the laminar-to-turbulent flowfield using a ray-tracing method, considering both the feasibility of aero-optical detection and the effect of grid scale on the time-averaged imaging quality, as well as a deeper probe into the characteristic structures reflected by aero-optical frequency spectrum. The results elucidated that the wall-normal grid number has the strongest influence on the transitional location, and undoubtedly affects wavefront aberrations. However, different gird scales lead to similar aero-optical spectrum, and revealed the Kolmogorov-type turbulence at small-scale regime. As a prelude to further aero-optical simulations of wall-bounded flows, the current study provides some reference for the code validation process and aero-optical interrogation.

Effect of mach number on high-subsonic and low-Reynolds-number flows around airfoils

High-subsonic and low-Reynolds-number flow is a special aerodynamic problem associated with near space propellers and Mars aircrafts. The flow around airfoils and the corresponding aerodynamic performance are different from the incompressible flow at low-Reynolds-number, due to complex shock wave-laminar separation bubble interaction. The objective of this paper is to figure out the effect of Mach number on aerodynamic performance and special flow structure of airfoil. An in-house Reynolds-averaged Navier–Stokes solver coupled with [Formula: see text] transition model is employed to simulate the flows around the E387 airfoil. The results show that the lift slope is larger than [Formula: see text] in the linear region. No stall occurs even at an attack angle of [Formula: see text]. With increase of Mach number, lift coefficient decreases when attack angle is below [Formula: see text]. However, once the angle of attack exceeds [Formula: see text], higher Mach number corresponds to higher lift coefficient. In addition, the strength and number of shock waves are very sensitive to Mach number. With increase of Mach number, the region of reverse flow vortex near transition location becomes smaller and finally disappears, while a new reverse flow vortex appears near the trailing edge and becomes larger.

Improving the k–ω–γ–Ar transition model by the field inversion and machine learning framework

Accurate simulation of transition from the laminar to the turbulent flow is of great importance in industrial applications. In the present work, the framework of field inversion and machine learning has been applied to improve the four-equation k–ω–γ–Ar transition model. The low-speed transitional flows past two airfoils were numerically simulated. Based on the experimental transition locations, the regularizing ensemble Kalman filtering (EnKF) was performed to obtain the distributions of space-varied correction terms for the first mode time scale in the transitional flows over a natural-laminar-flow (NLF) airfoil, NLF(1)-0416. Then, two machine learning methods, random forest (RF) and artificial neutral network (NN), were adopted to construct the mapping from the mean flow variables to the correction terms. Finally, the learned models were embedded into the original solver. The results show that the regularizing EnKF can efficiently obtain the posterior distribution of the correction terms only by the transition locations. Meanwhile, both the RF- and NN-augmented transition models can predict more accurate transition locations past NLF(1)-0416 at both interpolated and extrapolated angles of attack. Moreover, the RF-augmented model can predict more accurate transitional flows on both the windward and leeward sides of NACA0012 at the same angle of attack. It indicates that the discrepancies within the model are learned and reduced. The modified model has good applicability and generalization ability. Furthermore, by analyzing the relative importance of the features in the RF model, it is found that the streamwise pressure gradient plays the most important role in the physical information and interpretation of the learned model.

The influence of wavy wall on hypersonic boundary layer instability over a flared cone

The influence of wavy wall on the hypersonic boundary layer instability and the related aerodynamic heating are investigated over a flared cone. Experiments are conducted in a Mach 6 wind tunnel using Rayleigh-scattering flow visualization, fast-response pressure sensors and infrared thermography. Three sizes of wavy wall have been placed on the model in comparison with the smooth wall cone. The results show that compared to the smooth-wall cone, all the wavy-wall cones can suppress the second-mode instability to a certain degree and eliminate the local heating spot before transition is completed. Also, it is found that with the decrease of wavy wall wavelength, the transition location is shifted downstream.

Parameter uncertainty quantification for a four-equation transition model using a data assimilation approach

A majority of the simulation discrepancies for RANS models are due to parameter uncertainties. In this paper, a data assimilation approach called the ensemble Kalman filtering (EnKF), was used to investigate the parameter uncertainties of a four-equation k-ω-γ-A r transition/turbulence integrated model. The transitional flows past two wind-turbine airfoils were analyzed, while the transition onset and end locations, as well as the skin friction coefficients, were taken as the observation variables. The results show that the posterior distributions of the parameters can be efficiently obtained through the filtering process, while the estimated parameter variations are observed among different angles of attack (AoAs), as well as different sides at the same AoA. After the EnKF analysis, the most sensitive parameter, C 2 , is changed into an adaptive parameter, which demonstrates the pressure gradients effects through a modified shape factor. More accurate transition locations are calculated by the adaptive C 2 at different AoAs for NLF(1)-0416, and on both sides for NACA-0012 than the original model having constant C 2 . • The EnKF is used to investigate the parameter uncertainties of a transition model. • The estimated parameter variations are observed among different cases. • The most sensitive parameter is modified based on the boundary layer shape factor. • The modified model demonstrates more accurate transition prediction.

Nematic ordering of worm-like polymers near an interface.

The phase behavior of semi-flexible polymers is integral to various contexts, from materials science to biophysics, many of which utilize or require specific confinement geometries as well as the orientational behavior of the polymers. Inspired by collagen assembly, we study the orientational ordering of semi-flexible polymers, modeled as Maier-Saupe worm-like chains, using self-consistent field theory. We first examine the bulk behavior of these polymers, locating the isotropic-nematic transition and delineating the limit of stability of the isotropic and nematic phases. This effort explains how nematic ordering emerges from the isotropic phase and offers insight into how different (e.g., mono-domain vs multi-domain) nematic phases form. We then clarify the influence of planar confinement on the nematic ordering of the polymers. We find that while the presence of a single confining wall does not shift the location of nematic transition, it aligns the polymers in parallel to the wall; above the onset of nematic transition, this preference tends to propagate into the bulk phase. Introducing a second, perpendicular, wall leads to a nematic phase that is parallel to both walls, allowing the ordering direction to be uniquely set by the geometry of the experimental setup. The advantage of wall-confinement is that it can be used to propagate mono-domain nematic phases into the bulk phase.

Summertime Post-Cold-Frontal Marine Stratocumulus Transition Processes over the Eastern North Atlantic

Abstract Marine boundary layer (MBL) cloud morphology associated with two summertime cold fronts over the eastern North Atlantic (ENA) is investigated using high-resolution simulations from the Weather Research and Forecasting (WRF) Model and observations from the Atmospheric Radiation Measurement (ARM) ENA Climate Research Facility. Lagrangian trajectories are used to study the evolution of post-cold-frontal MBL clouds from solid stratocumulus to broken cumulus. Clouds within specified domains in the vicinity of transitions are classified according to their degree of decoupling, and cloud-base and cloud-top breakup processes are evaluated. The Lagrangian derivative of the surface latent heat flux is found to be strongly correlated with that of the cloud fraction at cloud base in the simulations. Cloud-top entrainment instability (CTEI) is shown to operate only in the decoupled MBL. A new indicator of inversion strength at cloud top that employs the vertical gradients of equivalent potential temperature and saturation equivalent potential temperature, which can be computed directly from soundings, is proposed as an alternative to CTEI. Overall, results suggest that the deepening–warming hypothesis suggested by Bretherton and Wyant explains many of the characteristics of the summertime postfrontal MBL evolution of cloud structure over the ENA, thereby widening the phase space over which the hypothesis may be applied. A subset of the deepening–warming hypothesis involving warming initially dominating over moistening is proposed. It is postulated that changes in climate change–induced modifications in cold-frontal structure over the ENA may be accompanied by coincident changes in the location and timing of MBL cloud transitions in the post-cold-frontal environment.

Environmental Predictors of a Drug Offender Crime Script: A Systematic Social Observation of Google Street View Images and CCTV Footage

The extent to which environmental context has been considered when developing crime scripts has been limited to descriptions of the locations offenders visit during the crime. This research contributes a description of the environmental characteristics of an open-air drug market and identifies environmental facilitators and inhibitors toward offender actions during a drug-selling crime script. Closed-circuit television (CCTV) camera footage is combined with Google Street View images to determine whether physical disorder, decay, and “crime generators” characterize the drug market under study. There is little evidence to suggest that the former two dimensions influence the crime sequence; however, crime generators such as retail facilities and bars and liquor stores are environmental facilitators toward a drug-selling crime script; and transit locations, corner stores, and public parks are environmental inhibitors toward the script.

Rapid Generation of Block Copolymer Libraries Using Automated Chromatographic Separation.

A versatile and scalable strategy is reported for the rapid generation of block copolymer libraries spanning a wide range of compositions starting from a single parent copolymer. This strategy employs automated and operationally simple chromatographic separation that is demonstrated to be applicable to a variety of block copolymer chemistries on multigram scales with excellent mass recovery. The corresponding phase diagrams exhibit increased compositional resolution compared to those traditionally constructed via multiple, individual block copolymer syntheses. Increased uniformity and lower dispersity of the chromatographic libraries lead to differences in the location of order-order transitions and observable morphologies, highlighting the influence of dispersity on the self-assembly of block copolymers. Significantly, this separation technique greatly simplifies the exploration of block copolymer phase space across a range of compositions, monomer pairs, and molecular weights (up to 50000 amu), producing materials with increased control and homogeneity when compared to conventional strategies.

High-Fidelity Simulations of Discrete Roughness Boundary-Layer Transition with Added Perturbations

High-fidelity numerical results have been obtained for low-disturbance wind-tunnel tests of transitional flow including isolated, discrete roughness elements on a 7 deg half-angle cone. Solutions for a range of roughness heights, two angles of attack, and several levels of introduced disturbances were calculated using a wall-resolved high-order, high-fidelity simulation methodology. It was found that the roughness elements did cause transition to turbulence in a manner similar to the experimental data. With no perturbations added, transition occurs downstream of the experimentally observed location. The addition of perturbations moves the transition location forward to more closely match the experimental data, in keeping with trends seen in the wind-tunnel campaign.

Assessment of drivers of forest changes using multi-temporal analysis and boosted regression trees model: a case study of Nyeri County, Central Region of Kenya

The Central Region of Kenya has undergone significant changes in land cover due to a broad range of drivers. These changes are more pronounced in forestland conversions. Past researches within the study area have identified drivers of land cover change without quantifying the influence of these drivers. Predictor variables include population density, precipitation, elevation, slope, forest fires, soil texture, proximity to roads, rives and towns. Land cover changes were analyzed using multi-temporal land cover maps between year 1990 and 2014. Boosted regression trees model was applied to determine the significant drivers and quantify their relative influence on key forestland transitions. The local and spatial influence of the drivers has further been analyzed by geographical weighted regression using coefficients determined at each sample point. Significant land cover changes continuously occurred over the study period. Forestland reduced from 38.90% in 1990 to 38.14% in 2014. Grassland reduced from 32.59 to 22.57%, cropland increased from 28.05 to 38.83% and wetland changed from 0.07 to 0.04%. Other land which constitutes of bare land and built up increased from 0.38 to 0.42%. The results show population density had the highest contribution to forestland changes throughout the study period, with a minimum contribution of 20.02% to a maximum of 26.04%. Other significant variables over the study period are precipitation, slope, elevation and the proximity variables. The results indicate that the relative influence of the drivers to forestland conversion varies with time, location and type of transition.

The cost of congestion and the benefits of congestion pricing: A general equilibrium analysis

The benefits of congestion pricing are examined with a spatially detailed computable general equilibrium model of the Greater LA region. The model treats choices of roads on a network, of driving or public transit, of residence and job location, of non-work trip patterns, of housing type and size; vacancies and new construction, production, interindustry trade and exports. The aggregate benefit of pricing LA County road congestion increases 2.7 fold when the toll revenue is recycled to cut the income tax of the poorer LA County workers while maintaining region-wide tax revenue neutrality. Consumers get 66% of the aggregate benefit and landlords 41%, while importers suffer losses equal to 7% of the aggregate benefit. Gross regional product increases by 1.34%. The aggregate benefit changes negligibly when the toll revenue is recycled to cut sales taxes instead of the income tax, but gross product still rises by 0.6%. Under the sales tax cut, consumers, importers and landlords benefit more evenly than under the income tax cut, but with the property tax cut nearly all of the cut is capitalized into property values.

Unsupervised Idealization of Nano-Electronic Sensors Recordings with Concept Drifts: An Information Theory Approach for Non-Stationary Single-Molecule Data Analysis

Unsupervised Idealization of Nano-Electronic Sensors Recordings with Concept Drifts: An Information Theory Approach for Non-Stationary Single-Molecule Data Analysis

Radius of convergence in lattice QCD at finite μB with rooted staggered fermions

In typical statistical mechanical systems the grand canonical partition function at finite volume is proportional to a polynomial of the fugacity $e^{\mu/T}$. The zero of this Lee-Yang polynomial closest to the origin determines the radius of convergence of the Taylor expansion of the pressure around $\mu=0$. The computationally cheapest formulation of lattice QCD, rooted staggered fermions, with the usual definition of the rooted determinant, does not admit such a Lee-Yang polynomial. We argue that the radius of convergence is then bounded by the spectral gap of the reduced matrix of the unrooted staggered operator. This is a cutoff effect that potentially affects all estimates of the radius of convergence with the standard staggered rooting. We suggest a new definition of the rooted staggered determinant at finite chemical potential that allows for a definition of a Lee-Yang polynomial, and, therefore of the numerical study of Lee-Yang zeros. We also describe an algorithm to determine the Lee-Yang zeros and apply it to configurations generated with the 2-stout improved staggered action at $N_t = 4$. We perform a finite-volume scaling study of the leading Lee-Yang zeros and estimate the radius of convergence of the Taylor expansion extrapolated to an infinite volume. We show that the limiting singularity is not on the real line, thus giving a lower bound on the location of any possible phase transitions at this lattice spacing. In the vicinity of the crossover temperature at zero chemical potential, the radius of convergence turns out to be $\mu_B/T \approx 2$ and roughly temperature independent. Our simulations are performed at strange quark chemical potential $\mu_s=0$, but the method can be straightforwardly extended to strangeness chemical potential $\mu_S=0$ or strangeness neutrality.

Los correos terrestres de Cartagena de Indias en tiempos de la renta (1768-1810): Itinerarios, cartografía, un «mapa en relación topográfica», GPS y un SIG

Este artículo ensaya una reconstrucción de la organización espacial del correo terrestre en el ámbito de la administración principal de correos de Cartagena, instalada en 1768. Se apoya esencialmente en dos informes manuscritos, uno de José Antonio de Pando de aproximadamen­te 1774 y otro anónimo (probablemente de Antonio de Miranda) de 1801. Ambos documentos contienen detallada información sobre la frecuencia de las carreras, los lugares de tránsito, las distancias entre ellos y la calidad de caminos. Usando información complementaria como ca­rreteras actuales, datos GPS y mapas de la época georreferenciados, se reconstruyen las rutas con un sistema de información geográfica (SIG) en un proceso que al mismo tiempo permite ponderar sobre las prácticas de medir y expresar distancias en ese tiempo.

Classical and Quantum Signatures of Quantum Phase Transitions in a (Pseudo) Relativistic Many-Body System

We identify a (pseudo) relativistic spin-dependent analogue of the celebrated quantum phase transition driven by the formation of a bright soliton in attractive one-dimensional bosonic gases. In this new scenario, due to the simultaneous existence of the linear dispersion and the bosonic nature of the system, special care must be taken with the choice of energy region where the transition takes place. Still, due to a crucial adiabatic separation of scales, and identified through extensive numerical diagonalization, a suitable effective model describing the transition is found. The corresponding mean-field analysis based on this effective model provides accurate predictions for the location of the quantum phase transition when compared against extensive numerical simulations. Furthermore, we numerically investigate the dynamical exponents characterizing the approach from its finite-size precursors to the sharp quantum phase transition in the thermodynamic limit.