Location Of Transition Research Articles

Security Concerns at Hot-Spot Bus Stop Locations

Adequately addressing security concerns within public transportation will become a pressing issue over the next decade. These safety concerns frequently relate to terrorism, crime, and general disorder within public transportation with little systematic analysis directed toward transit locations. The given study geocoded 2 years of outdoor crime data within a midsized city and found the main bus terminal and three bus stop locations generated the highest levels of concentrated crime. Nonparticipatory windshield survey site observations were conducted at each location to qualitatively identify attributes that were possibly generating general disorder and crime incidents within these hot-spots. Implications for the criminology of place are discussed along with policing/security strategies for specific locations that facilitate an unusually high amount of official crime.

Constrained multi-objective aerofoil design using a multi-level optimisation strategy

AbstractA novel approach for the multi-objective design optimisation of aerofoil profiles is presented. The proposed method aims to exploit the relative strengths of global and local optimisation algorithms, whilst using surrogate models to limit the number of computationally expensive CFD simulations required. The local search stage utilises a re-parameterisation scheme that increases the flexibility of the geometry description by iteratively increasing the number of design variables, enabling superior designs to be generated with minimal user intervention. Capability of the algorithm is demonstrated via the conceptual design of aerofoil sections for use on a lightweight laminar flow business jet. The design case is formulated to account for take-off performance while reducing sensitivity to leading edge contamination. The algorithm successfully manipulates boundary layer transition location to provide a potential set of aerofoils that represent the trade-offs between drag at cruise and climb conditions in the presence of a challenging constraint set. Variations in the underlying flow physics between Pareto-optimal aerofoils are examined to aid understanding of the mechanisms that drive the trade-offs in objective functions.

Large Eddy Simulation of wind turbine wakes: detailed comparisons of two codes focusing on effects of numerics and subgrid modeling

In this work we report on results from a detailed comparative numerical study from two Large Eddy Simulation (LES) codes using the Actuator Line Model (ALM). The study focuses on prediction of wind turbine wakes and their breakdown when subject to uniform inflow. Previous studies have shown relative insensitivity to subgrid modeling in the context of a finite-volume code. The present study uses the low dissipation pseudo-spectral LES code from Johns Hopkins University (LESGO) and the second-order, finite-volume OpenFOAMcode (SOWFA) from the National Renewable Energy Laboratory. When subject to uniform inflow, the loads on the blades are found to be unaffected by subgrid models or numerics, as expected. The turbulence in the wake and the location of transition to a turbulent state are affected by the subgrid-scale model and the numerics.

Resistance Prediction on Submerged Axisymmetric Bodies Fitted with Turbulent Spot Inducers

A method to predict bare hull ship resistance is presented in this article. Hull resistance is assumed to consist of friction drag and residual drag. The friction drag coefficient is represented by an equivalent flat plate coefficient multiplied by a form factor to incorporate effects of body geometry and boundary layer (BL) characteristics on drag. Theories of form factors including the effect of BL transition locations have been successfully derived. Form factors are shown to have a noticeable effect on body drag at high Reynolds numbers (Re) and a significant effect at model Re. Residual drag coefficient is obtained from model tests with application of scaling formulae to relate model scale residual drag coefficient to full scale drag coefficient. To address the issue of laminar flow on models in residual drag measurements, a new device termed a "turbulent spot inducer" is introduced in model tests. Finally, a new scaling formula to relate model scale residual drag coefficient to full scale residual drag coefficient with the flow on body surface partly laminar and partly turbulent is derived. It is shown that a traditional 1þK scaling method used in the marine industry is a special case of the newly derived residual drag scaling formula.

An intermittency model for predicting roughness induced transition

An intermittency transport equation for RANS modeling, formulated in local variables, is extended for roughness-induced transition. To predict roughness effects in the fully turbulent boundary layer, published boundary conditions for k and ω are used. They depend on the equivalent sand-grain roughness height, and account for the effective displacement of wall distance origin. Similarly in our approach, wall distance in the transition model for smooth surfaces is modified by an effective origin, which depends on equivalent sand-grain roughness. Flat plate test cases are computed to show that the proposed model is able to predict transition onset in agreement with a data correlation of transition location versus roughness height, Reynolds number, and inlet turbulence intensity. Experimental data for turbine cascades are compared to the predicted results to validate the proposed model.

The effect of a low-viscosity near-wall film on bypass transition in boundary layers

Bypass transition in a two-fluid boundary layer is examined using direct numerical simulations (DNSs). A less-viscous wall film is considered and the impact on transition location is evaluated at two different viscosity ratios and free-stream turbulence intensities. The less-viscous wall film absorbs the mean shear from the outer stream, weakens the lift-up mechanism, and alters the disturbance field inside the boundary layer. These effects all favour a delay in the onset of bypass transition. However, the viscosity and mean-shear discontinuities across the two-fluid interface introduce a new mechanism for the generation of wall-normal vorticity in the boundary layer, and can therefore promote transition to turbulence. Conditionally averaged statistics and streak tracking techniques are adopted in order to examine the impact of the wall film on the bypass transition process. It is shown that the weaker amplification of the streaks in the outer fluid can delay breakdown to turbulence, despite the additional disturbance generation at the two-fluid interface. The efficacy of the wall film in delaying transition is demonstrated at moderate level of free-stream turbulence intensity, but is reduced as the turbulence intensity is increased.

Experimental and Numerical Methods for Transition and Drag Predictions of Laminar Airfoils

The friction component is responsible for more than 40% of typical civil aircraft drag. As a consequence, the issue of laminar flow has been of prime importance in aeronautics for many years now. This article is focused on Tollmien–Schlichting-induced transition and drag predictions of two-dimensional laminar airfoils obtained with experimental and numerical methods. In 2012, a test campaign in the ONERA-S2MA wind tunnel, including infrared acquisitions, pressure sensors, and wake analyses, allowed substantial data to be obtained on such airfoils in transonic conditions. To complete this study, two-dimensional fluid dynamics computations have been performed, either with a Reynolds-averaged Navier–Stokes solver using transition criteria or with a boundary-layer code combined with direct stability analysis. Furthermore, experimental (wake survey) and numerical (far-field theory) techniques allowing airfoil drag breakdown have been employed. Wind-tunnel and computational fluid dynamics transition predictions have been compared. Good agreement has been observed but the transition criteria may show some limitations in particular situations, such as long separation bubble development. The gains in lift and drag due to laminar flow have been quantified (natural vs triggered transition). Concerning drag reduction, the importance of the viscous pressure component has been highlighted. Finally, the effects of parameters such as angle of attack, Mach number, and Reynolds number on transition location and drag have been investigated.

Calibration of a [formula omitted] transition model and its validation in low-speed flows with high-order numerical method

Based on the Reynolds-averaged Navier–Stokes (RANS) equations and structured grid technology, the calibration and validation of γ-Reθ transition model is preformed with fifth-order weighted compact nonlinear scheme (WCNS), and the purpose of the present work is to improve the numerical accuracy for aerodynamic characteristics simulation of low-speed flow with transition model on the basis of high-order numerical method study. Firstly, the empirical correlation functions involved in the γ-Reθ transition model are modified and calibrated with experimental data of turbulent flat plates. Then, the grid convergence is studied on NLR-7301 two-element airfoil with the modified empirical correlation. At last, the modified empirical correlation is validated with NLR-7301 two-element airfoil and high-lift trapezoidal wing from transition location, velocity profile in boundary layer, surface pressure coefficient and aerodynamic characteristics. The numerical results illustrate that the numerical accuracy of transition length and skin friction behind transition location are improved with modified empirical correlation function, and obviously increases the numerical accuracy of aerodynamic characteristics prediction for typical transport configurations in low-speed range.

Nonadiabatic Surface Effects on Transition Measurements Using Temperature-Sensitive Paints

Tests were conducted at the Cryogenic Ludwieg-Tube Göttingen to investigate the influence on onset of boundary-layer transition of thermal gradients on the model surface, whereby the temperature-sensitive paint technique has been used to detect transition. The laminar airfoil under investigation was tested at high Reynolds and at both low and high subsonic Mach numbers. The influence on boundary-layer transition of the temperature difference between the flow and the model surface due to the temperature drop occurring during a test run at the Cryogenic Ludwieg-Tube Göttingen was examined. Various combinations of flow conditions and angles of attack were employed to investigate different stability situations. Linear-stability computations, based on the experimental data, were also carried out. The unfavorable impact of surface temperatures larger than the adiabatic-wall temperature was identified to be dependent on the considered boundary-layer-stability situation. For certain stability situations, it was shown that a nonadiabatic model surface can strongly influence the boundary-layer transition location.

Endogenous crisis waves: stochastic model with synchronized collective behavior.

We propose a simple framework to understand commonly observed crisis waves in macroeconomic agent-based models, which is also relevant to a variety of other physical or biological situations where synchronization occurs. We compute exactly the phase diagram of the model and the location of the synchronization transition in parameter space. Many modifications and extensions can be studied, confirming that the synchronization transition is extremely robust against various sources of noise or imperfections.

HIFiRE-5 Flight Test Results

The Hypersonic International Flight Research Experimentation (HIFiRE-5) is a hypersonic flight test vehicle designed to investigate the aerothermodynamics of a three-dimensional geometry. It is a 7-deg minor-axis half-angle elliptic cone with a aspect ratio and 2.5 mm nose radius. The flight test occurred in April 2012, but the upper stage of the sounding rocket failed to ignite, resulting in a peak Mach number of about 3 instead of the target of 7. The instrumentation (almost 300 thermocouples and 50 pressure transducers) performed well and provided a wealth of supersonic aeroheating and boundary-layer transition data. The pressure transducers indicated the expected dependence upon angle of attack and yaw and offer a check for the inertial measurement unit. Heat flux was calculated from paired thermocouples and boundary-layer transition locations were identified from the heating rates. Two boundary-layer transition mechanisms were encountered during the supersonic descent. One mode leads to transition over the acreage of the vehicle and correlates well with ; the other mechanism causes the leading-edge boundary-layer transition to advance rapidly over a small range of freestream and is suspected to be roughness-induced. The good performance of the instrumentation increases confidence in the success of a repeat flight.

Comparison of Robust Optimization Methods Applied to Hypersonic Vehicle Design

The use of various robust optimization methods to solve engineering problems with environmental parameter uncertainty was investigated. Comparisons were made between a novel multi-objective-based robust optimization formulation and conventional robust regularization-based and aggregation-based methods. The results, performance, and philosophies of each method are discussed. A hypersonic vehicle design problem was used as a test bed for the methods presented here. A focus was put on studying the effect of uncertain roughness-induced boundary-layer transition locations on vehicle controllability. The robust regularization results show that a flat wedgelike vehicle design is best for a worst-case scenario, whereas a pyramidal-shaped vehicle design minimizes the expected detrimental effects on vehicle controllability. The analysis proved that the multi-objective robust optimization method was able to identify these two types of results within an overall set of results while also capturing tradeoffs within the design space.

Differential infrared thermography for boundary layer transition detection on pitching rotor blade models

Differential infrared thermography (DIT) was investigated and applied for the detection of unsteady boundary layer transition locations on a pitching airfoil and on a rotating blade under cyclic pitch. DIT is based on image intensity differences between two successively recorded infrared images. The images were recorded with a high framing rate infrared camera. A pitching NACA0012 airfoil served as the first test object. The recorded images were used in order to investigate and to further improve evaluation strategies for periodically moving boundary layer transition lines. The measurement results are compared with the results of unsteady CFD simulations based on the DLR-TAU code. DIT was then used for the first time for the optical measurement of unsteady transition locations on helicopter rotor blade models under cyclic pitch and rotation. Image de-rotation for tracking the blade was employed using a rotating mirror to increase exposure time without causing motion blur. The paper describes the challenges that occurred during the recording and evaluation of the data in detail. However, the results were found to be encouraging to further improve the method toward the measurement of unsteady boundary layer transition lines on helicopter rotor models in forward flight.

30. Transitioning Adolescents With HIV to Adult Care: Examining Processes at Twelve Adolescent Medicine Clinics

The provision of uninterrupted care as youth with HIV transition from pediatric and adolescent to adult HIV care is essential as disengagement from care has implications for an individual's HIV-related and overall health and with the demonstration that treatment can serve as a means of prevention, the health of the broader community. Accordingly, this study examined the transition processes and protocols that exist across twelve clinics within the Adolescent Medicine Trials Network for HIV/AIDS Interventions (ATN). As part of a larger multi-method Care Initiative program evaluation, we completed three annual visits at each site from 2010-2012 and conducted 178 semi-structured interviews (Baseline n=64, Year 1 n=60, Year 2=54) with clinical and program staff (e.g., physicians, nurses, social workers, case managers). Interview data were analyzed using the constant comparative method with particular attention given to the alignment with the recent American Academy of Pediatrics transition recommendations that include: developing formal written protocols, timelines, and evaluation plans; introducing adolescents to transition early and providing individualized pre-transition preparation with youth; initiating transition between ages 18-25 that includes visits to adult clinics and data sharing (e.g., medical/health records) between adolescent and adult clinics; and the evaluation of transition outcomes for youth (e.g., care engagement and viral loads). Participants discussed the importance and challenges of transition from adolescent to adult care for both behaviorally and perinatally infected adolescents, highlighted by: “Adolescent care means that we are going to hold their hand a little longer than if they walk into an adult [clinic], the [adult providers] not going to have this patience”. The results correspond with AAP transition guidelines. Formal protocols: Sites had varying levels of formal transition protocols – 4 with formal written protocols and 6 with informal but detailed processes influenced by the location of transition (e.g., new physical space, same space with new provider). Transition preparation: Staff focused on life skills development (e.g., medication management, insurance documentation, budget) to prepare youth for transition, Adult clinic connection: Sites used a variety of strategies (e.g., site visits to adult clinics, adult provider working in adolescent clinic one day per week) to connect youth to adult clinics. Transition evaluation: Sites identified necessary components (e.g., inter-clinic data sharing) for evaluating transition outcomes (e.g., appointment adherence). Creating a seamless transition process for adolescents with HIV is especially important given the intersecting identities and stigmas often associated with the disease. Transitioning HIV-positive youth involves targeting behavioral and biological factors as well as provider and system-level issues. Addressing key factors is essential for developing streamlined, comprehensive, and context-specific transition protocols. Adolescent and adult HIV clinic collaboration is essential to reduce service fragmentation, provide coordinated care, and support individual and community level health.

Stimulated neutrino transformation through turbulence on a changing density profile and application to supernovae

We apply the model of stimulated neutrino transitions to neutrinos traveling through turbulence on a non-constant density profile. We describe a method to predict the location of large amplitude transitions and demonstrate the effectiveness of this method by comparing to numerical calculations using a model supernova (SN) profile. The important wavelength scales of turbulence, both those that stimulate neutrino transformations and those that suppress them, are presented and discussed. We then examine the effects of changing the parameters of the turbulent spectrum, specifically the root-mean-square amplitude and cutoff wavelength, and show how the stimulated transitions model offers an explanation for the increase in both the amplitude and number of transitions with large amplitude turbulence, as well as a suppression or absence of transitions for long cutoff wavelengths. The method can also be used to predict the location of transitions between antineutrino states which, in the normal hierarchy we are using, will not undergo Mikheev-Smirnov-Wolfenstein (MSW) transitions. Finally, the stimulated neutrino transitions method is applied to the turbulence derived found in a 2D supernova simulation and explains the minimal observed effect on neutrino oscillations in the simulation as as being due to excessive long wavelength modes suppressing transitions and the absence of modes that fulfill the parametric resonance condition.

Exact location of the phase transition for random (1,2)-QSAT

The QSAT problem is the quantified version of the SAT problem. We show the existence of a threshold effect for the phase transition associated with the satisfiability of random quantified boolean CNF formulas of the form ∀X∃Yϕ(X,Y), where X has m variables, Y has n variables and each clause in ϕ has one literal from X and two from Y. For such formulas, we show that the threshold phenomenon is controlled by the ratio between the number of clauses and the number n of existential variables. Then we give the exact location of the associated critical ratio c∗: it is a decreasing function of α, where α is the limiting value of m/ log (n) when n tends to infinity. Thus we give a precise location of the phase transition associated with a coNP-complete problem.

Experimental Investigation of the Effect of Forward-facing Steps on Boundary Layer Transition

The effect of geometric forward-facing steps on boundary layer transition was experimentally investigated at a high subsonic Mach number in a blow-down wind tunnel facility in Göttingen, Germany. Boundary layer transition was detected non- intrusively by means of the Temperature-Sensitive Paint (TSP) technique. Forward-facing steps of different height were installed on a spanwise invariant wind tunnel model. Streamwise pressure gradient and high chord Reynolds number were systematically varied and their effect on boundary layer transition was studied in the presence of forward-facing steps on the model surface. At all tested stability situations, the surface imperfections were shown to reduce the extent of the laminar region. Transition was observed to move gradually towards the step location with increasing step Reynolds numbers and increasing relative step height. For a given combination of step height and chord Reynolds number, more pronounced negative pressure gradients led to an increase in transition Reynolds number. The reduction in transition Reynolds number due to the effect of the surface imperfection was more marked at larger flow acceleration. The plots of the relative change in transition location as a function of the step Reynolds number and of the relative step height gave good correlation of the results. The correlations were found to be practically independent of the streamwise pressure gradient in the examined range. Criteria for the allowable tolerances on low- sweep Natural Laminar Flow surfaces can now be derived from the functional relations determined in this work.

Experimental Investigation of Leading Edge Bluntness Effects on Hypersonic Tow-dimensional Inlet

The leading edge bluntness effects on inlet boundary layer transition had been studied based on a typical hypersonic two-dimensional inlet. Four leading edge radii(R=0.05mm, R =0.1mm, R =0.2mm, R =0.25mm) had been experimented in FD-07 wind tunnel, including natural transition and artificial transition. The location of boundary layer transition was identified through the corner pressure distribution characteristics and inlet starting, by this method, we had obtained the regular of boundary layer transition location with the leading edge radii. Experimental results showed that, under the wind tunnel condition, the boundary layer transition location moved down stream with increasing the leading edge radius. The inlet would not start for leading edge radius R = 0.25mm and we had designed artificial transition strip based onlinear stability theory(LST) to make the inlet start successfully.

Methods used to parameterize the spatially-explicit components of a state-and-transition simulation model

Spatially-explicit state-and-transition simulation models of land use and land cover (LULC) increase our ability to assess regional landscape characteristics and associated carbon dynamics across multiple scenarios. By characterizing appropriate spatial attributes such as forest age and land-use distribution, a state-and-transition model can more effectively simulate the pattern and spread of LULC changes. This manuscript describes the methods and input parameters of the Land Use and Carbon Scenario Simulator (LUCAS), a customized state-and-transition simulation model utilized to assess the relative impacts of LULC on carbon stocks for the conterminous U.S. The methods and input parameters are spatially explicit and describe initial conditions (strata, state classes and forest age), spatial multipliers, and carbon stock density. Initial conditions were derived from harmonization of multi-temporal data characterizing changes in land use as well as land cover. Harmonization combines numerous national-level datasets through a cell-based data fusion process to generate maps of primary LULC categories. Forest age was parameterized using data from the North American Carbon Program and spatially-explicit maps showing the locations of past disturbances (i.e. wildfire and harvest). Spatial multipliers were developed to spatially constrain the location of future LULC transitions. Based on distance-decay theory, maps were generated to guide the placement of changes related to forest harvest, agricultural intensification/extensification, and urbanization. We analyze the spatially-explicit input parameters with a sensitivity analysis, by showing how LUCAS responds to variations in the model input. This manuscript uses Mediterranean California as a regional subset to highlight local to regional aspects of land change, which demonstrates the utility of LUCAS at many scales and applications.

Influence of Surface Roughness and Free-stream Turbulence on Crossflow-instability Transition

Surface-roughness and free-stream-turbulence effects on crossflow-instability transition are investigated experimentally and theoretically. A model baseflow is established and shown to be well predicted by boundary-layer analysis. Surface roughness is systematically introduced, with a factor-of-50 variation in r.m.s. levels. Free-stream turbulence levels are varied using grids across the test section, providing roughly a factor-of-10 variation in the turbulence intensity. For low turbulence levels, the transition is dominated by stationary crossflow instabilities. As the free-stream turbulence is increased, the traveling crossflow instabilities become increasingly relevant. For higher-turbulence and lower-roughness levels the transition appears to be dominated by the traveling crossflow instabilities. The results are linked to a variable N-factor method, which is shown to provide a good basis for estimating the transition location for low turbulence levels. The variable N-factor method is used to interpret the results and infer causality between roughness, turbulence and transition.