Common Research Model Research Articles

Development of flow structures in the near-field wake region of the Common Research Model

The flow in the near-field wake region of a generic transport aircraft configuration has been studied using both unsteady RANS and delayed detached-eddy simulations. The NASA Common Research Model has been used for this purpose, as experimental data obtained with this model in the cryogenic European Transonic Wind Tunnel during the ESWIRP test campaign were available for comparison and validation. Focusing on high angles of attack of \(\alpha = 16^\circ\) and \(\alpha = 18^\circ\), the results form the basis for the study of flow phenomena occurring at stall conditions. Such flight conditions are characterized by massive flow separation at the wing and highly unsteady flow in the wake. In a first step, the numerical results are compared with available test data using global force coefficients and pressure distributions on the wing. Both show a good agreement of numerical and experimental results, indicating slight deviations of the pressure variable at the inboard wing sections. In a second step, the turbulent structures of the near-field wake are examined using the proper orthogonal decomposition method based on snapshots (two-dimensional instantaneous flow fields). Frequencies of the first mode-pair match the dominant frequencies of the lift and velocity wake spectra very well.

Mouse Models for Campylobacter jejuni Colonization and Infection.

Relevant animal models for Campylobacter jejuni infection have been difficult to establish due to C. jejuni's inability to cause disease in many common animal research models. Fortunately, recent work has proven successful in developing several new and relevant mouse models of C. jejuni infection, including the SIGIRR-deficient mouse strain that develops acute enterocolitis in response to C. jejuni. Here we describe how to properly infect mice with C. jejuni, as well as a number of accompanying histological techniques to aid in studying C. jejuni colonization and infection in mice.

Transonic wing stall of a blended flying wing common research model based on DDES method

Numerical simulation of wing stall of a blended flying wing configuration at transonic speed was conducted using both delayed detached eddy simulation (DDES) and unsteady Reynolds-averaged Navier-Stokes (URANS) equations methods based on the shear stress transport (SST) turbulence model for a free-stream Mach number 0.9 and a Reynolds number 9.6×106. A joint time step/grid density study is performed based on power spectrum density (PSD) analysis of the frequency content of forces or moments, and medium mesh and the normalized time scale 0.010 were suggested for this simulation. The simulation results show that the DDES methods perform more precisely than the URANS method and the aerodynamic coefficient results from DDES method compare very well with the experiment data. The angle of attack of nonlinear vortex lift and abrupt wing stall of DDES results compare well with the experimental data. The flow structure of the DDES computation shows that the wing stall is caused mainly by the leeward vortex breakdown which occurred at x/xcr=0.6 at angle of attack of 14°. The DDES methods show advantage in the simulation problem with separation flow. The computed result shows that a shock/vortex interaction is responsible for the wing stall caused by the vortex breakdown. The balance of the vortex strength and axial flow, and the shock strength, is examined to provide an explanation of the sensitivity of the breakdown location. Wing body thickness has a great influence on shock and shock/vortex interactions, which can make a significant difference to the vortex breakdown behavior and stall characteristic of the blended flying wing configuration.

An automated multi-grid Chimera method based on the implicit hole technique

An automated multi-grid overset grid algorithm is presented for accurate simulation of viscous flows around complex configurations. The algorithm is based on the implicit hole cutting technique optimized with an overset grid construction strategy, a grid cutting criterion and a multi-level overset grid cutting method. The enhanced method is more general than the original method, while preserving the high degree of automation of the implicit hole cutting algorithm. Moreover, a mesh sequencing and multi-grid Chimera strategy is proposed to achieve convergence acceleration of the flow calculations. The present Chimera algorithm is demonstrated through the solution of the flows over the NASA Common Research Model configurations. The results show that the present mesh sequencing and multi-grid strategy in the overset grid framework are very effective in increasing convergence of solution in comparison with the standard three-level multi-grid. Wing pressure comparisons indicate the pressure distribution varies with grid solution at the shock, and a higher grid resolution improves shock definition. Abrupt reductions in lift and drag coefficients are correlated with the side-of-body separation bubble as angle of attack is increased. And various modeling and grid resolution have a strong impact on predicting the side-of-body separation. The side-of-body separation decreases with grid refinement. And the bubble size from spalart-allmaras (SA) modeling is larger than that from shear stress transport model.

Static and Dynamic Aeroelastic Tailoring with Variable-Camber Control

This paper examines the use of a variable-camber continuous trailing-edge flap system for aeroservoelastic optimization of a transport wing box, the Common Research Model. Along with patch-level structural wing-box design variables, the quasi-steady and unsteady motions of the flap system are used as design variables, for maneuver load alleviation, cruise fuel burn reduction, and active flutter suppression. The resulting system is able to minimize structural weight and/or fuel burn while satisfying constraints upon elastic stresses, panel buckling, actuator hinge moments, flutter margins, actuator work, and control cost metrics. Limitations to this success are imposed by including load cases where the actuation system is not active (open-loop) in the optimization process. Large open-loop safety factors, for either maneuver loads or flutter, dilute the importance of the closed-loop actuation mechanism, whereas small open-loop safety factors may produce an overly flexible wing, prone to failure. Similar tradeoffs between system performance and actuator work constraints are provided. A final theme of the paper explores aeroelastic performance penalties that may arise if the shapes available to the variable-camber actuation system are limited (i.e., if certain control segments are linked together).

Supercritical wing design based on airfoil optimization and 2.75D transformation

An optimization design method for a supercritical wing is developed in this paper based on a pressure distribution transformation between the airfoil and wing. This transformation takes the stream-wise variation of the local sweep angle and the local curvature of a tapered swept wing into account. With this method, the desired pressure distribution of the wing, which is critical to its supercritical characteristics, as well as the constraints and objectives, can be mapped onto a 2D airfoil. When the airfoil is optimized, the desired performances and the pressure distributions can be well realized on a 3D wing. Test cases based on the RAE2822 airfoil and on the common research model are used to validate the CFD tool and the transformation. A supercritical wing is then designed using this method. Comparisons between the results from the proposed method, an optimization based on the traditional transformation and a fully 3D wing optimization are conducted. These comparisons show that the proposed method, by essentially performing 2D optimization, greatly improves the design efficiency. Moreover, the more accurate transformation helps make the optimization more reliable and engineering applicable.

Global/Local Optimization of Aircraft Wing Using Parallel Processing

The structural optimization of a cantilever aircraft wing with stiffeners and curvilinear spars and ribs is described. The decomposition technique for the wing structure is widely used for the optimization of a complex wing. The optimization procedure is divided into two subsystems: the global wing optimization, which determines the geometry and location of spars and ribs, and local panel optimization to further reduce wing weight. Because the design variables that are changed in the global step have an impact on those changed in the local step and vice versa, an iterative process that iterates between the global and local optimizations is employed. Particle swarm optimization and gradient-based optimization are used to perform integrated global/local optimization. Parallel computing is used, implemented using Python, to reduce the central processing unit time. The license cycle-check method and memory self-adjustment method are developed and applied in the parallel processing framework to optimize the use of the resources. The integrated global/local optimization approach has been applied to the NASA Common Research Model wing, which proves the methodology’s application with finite element method analysis of appropriate fidelity. A 40% weight reduction of the Common Research Model wing has been achieved by the global/local optimization at an acceptable computational time.

Improved Convergence and Robustness of USM3D Solutions on Mixed-Element Grids

Several improvements to the mixed-element USM3D discretization and defect-correction schemes have been made. A new methodology for nonlinear iterations, called the Hierarchical Adaptive Nonlinear Iteration Method, has been developed and implemented. The Hierarchical Adaptive Nonlinear Iteration Method provides two additional hierarchies around a simple and approximate preconditioner of USM3D. The hierarchies are a matrix-free linear solver for the exact linearization of Reynolds-averaged Navier–Stokes equations and a nonlinear control of the solution update. Two variants of the Hierarchical Adaptive Nonlinear Iteration Method are assessed on four benchmark cases, namely, a zero-pressure-gradient flat plate, a bump-in-channel configuration, the NACA 0012 airfoil, and a NASA Common Research Model configuration. The new methodology provides a convergence acceleration factor of 1.4 to 13 over the preconditioner-alone method representing the baseline solver technology.

Effect of Vortex Generators on Transonic Swept Wings

This paper examines the effects of corotating blade-type vortex generators on transonic sweptback wings using computational fluid dynamics studies. Infinite-span (two-dimensional) swept wings are first considered to understand the basic physics of vortex generators. Sweep angles are given virtually to the wings by changing the freestream direction. Vortex generators are placed on the wings, and the visualized interactions of their tip vortices with the boundary layer reveal the relationship between the effect of the vortex generators and the wing sweep angle. The physics of vortex-generator tip vortices are then described to explain how vortex generators on swept wings efficiently suppress shock-induced separation by mixing boundary layers. It is also shown that the vortex-generator angle of incidence to the local flow can slightly improve the effect of the vortex generators but that wing sweep angle has a greater influence on their effect. Based on the discussion of infinite-span wings, the computational results of the NASA Common Research Model with and without vortex generators are finally examined and compared with the experiment. It is confirmed that toe-out vortex generators on the three-dimensional Common Research Model are as efficient as those on an infinite-span wing with a moderate sweep angle.

Collaborative Research on Academic History using Linked Open Data: A Proposal for the Heloise Common Research Model

Abstract: The paper presents a proposal for the Heloise Common Research Model (HCRM), to be implemented for the European research network on digital academic history – Heloise. The objective of Heloise is to interlink databases and other digital resources stemming from several research projects in the field of academic history, to provide an integrated database for federated research on the network databases. The HCRM defines three layers: the Repository Layer, the Application Layer and the Research Interface Layer, which are presented in detail. As part of the application and research interface layer, essential concepts are the symogih.org ontology and a Heloise network-specific thesaurus. The concepts have been tested on a sample of Heloise network’s datasets as a part of a prototype of the envisaged platform that the authors have started implementing. The paper concludes with future developments to be accomplished within the Heloise network.Keywords: academic history, domain ontologies, data interoperability, semantic web technologies, linked open data.Investigación colaborativa sobre la historia académica a través de los datos abiertos enlazados: una propuesta para el modelo de investigación común de HéloïseResumen: El artículo presenta una propuesta para el modelo de investigación común de Héloïse (HCRM en sus siglas en inglés) para su implementación por la red de investigación europea sobre la historia académica digital – Héloïse. El objetivo de Héloïse es interconectar las bases de datos y otros recursos digitales que pertenecen a varios proyectos de investigación en el campo de la historia académica con el fin de ofrecer una base de datos integrada para la investigación federada sobre las bases de datos de la Red. El HCRM define tres niveles: el nivel del repositorio, el nivel de la aplicación y el nivel de la interfaz de la investigación que se explican de forma detallada. Como parte del nivel de la interfaz de la investigación, la ontología symogih.org y un diccionario de sinónimos para la red Héloïse constituyen conceptos fundamentales. Los conceptos han sido probados sobre una muestra de datos de la red Héloïse como parte de un prototipo de la plataforma que los autores han empezado a desarrollar. El artículo concluye con propuestas de futuro desarrollo a realizar dentro del marco de la red Héloïse.Palabras clave: historia académica, ontologías de dominio, interoperabilidad de datos, tecnologías de web semántica, datos abiertos enlazados

Best practices for cardiac magnetic resonance imaging in common large animal research models.

Magnetic resonance imaging has proven to be useful for the study of cardiovascular physiology in health and disease; it provides important data and information about healthy and diseased states in humans and animals, and it facilitates the safe characterization and positioning of medical devices during cardiovascular applications. Looking to the future, magnetic resonance imaging will continue to play a formative role in biomedical research and applications. Here, we discuss how to avoid common pitfalls and provide safe transport, anesthetic support and physiologic support for animals that are used in dedicated or shared cardiovascular imaging facilities.

Multi-fidelity non-intrusive polynomial chaos based on regression

In this paper we present a multi-fidelity (MF) extension of non-intrusive polynomial chaos based on regression (point collocation) for uncertainty quantification purposes. The proposed method uses the principle of a global correction function from a previous similar method that uses spectral projection to estimate the coefficients. Due to its usage of regression to estimate the coefficients, the present method offers high flexibility in the sampling and generation of the polynomial basis. The method takes advantage of a nested sampling plan to create the samples for the low-fidelity (LF) and correction expansions where the high-fidelity (HF) samples are a subset of the LF ones. To build the polynomial basis, a total order or hyperbolic truncation strategy is used with a highly flexible combination of the LF and correction polynomial expansions. The method is demonstrated on some artificial test problems and aerodynamic problems of the Euler flow around an airfoil and common three-dimensional research models. In order to derive the strategies for successful MF approximation, the effect of the correlation and the errors between the LF and HF functions is also studied. The results show that high correlation and moderately low errors are important to improve the MF approximation’s accuracy. On a common research model problem, the MF approach with partially-converged simulations as the LF samples can successfully reduce the computational cost to about 40% for similar accuracy compared to an approach using a single HF expansion.

Values Education Research Trends in Turkey: A Content Analysis

The present study makes a situation analysis of graduate theses on values education published between 1999 and 2015 in Turkey. It has a qualitative research design, wherein data is collected through document analysis. The form developed for this purpose is comprised of nine sections, each of which focuses on a different aspect: universities, education levels, departments/programs, topics, research models, methodologies, sampling strategies, data collection instruments, and data analysis techniques. A total of 126 graduate theses were analyzed. The data was analyzed by means of content analysis. The study revealed that, of 126 theses, 106 were master’s theses, and 20 were doctoral theses; the highest number of theses on values education were submitted in 2013, and the most frequently studied topic was students’ values. It was also found that qualitative methods were the most common research methods, and survey was the most common research model. Finally, random sampling was found to be the most common sampling technique.

Multipoint Aerodynamic Shape Optimization Investigations of the Common Research Model Wing

The aerodynamic shape optimization of wings in transonic flow is an inherently challenging problem. In addition to the high computational cost of solving the Reynolds-averaged Navier–Stokes equations, there is a complex interdependence between the cross-sectional shape, wave drag, and viscous effects. Furthermore, it is necessary to perform multipoint optimizations to ensure good performance for a range of flight conditions. The choice of which flight conditions should be considered in a multipoint optimization and how many of these should be considered is still not well understood. This paper addresses this issue by solving a series of seven benchmark optimizations developed by the AIAA Aerodynamic Optimization Discussion Group. These optimization cases include a single-point optimization, four three-point optimizations, a nine-point optimization, and a five-point optimization. The optimizations consist in minimizing the weighted drag coefficient subject to lift, moment, thickness, and volume constraints. The optimizations were performed with respect to 768 shape design variables and an angle of attack for each flight condition. The single-point optimization was able to achieve an 8.1% drag reduction relative to the initial design, but it exhibited poor off-design performance. All the optimized designs were compared using a contour plot of to evaluate the wing performance over the complete transonic flight operating envelope. Each of the four three-point optimizations successfully mitigated the poor off-design performance of the single-point design. However, the three-point optimization with widely spaced Mach numbers yielded a much more complex contour with two distinct local maxima. Finally, the five- and nine-point optimizations yielded similar performance and the most robust off-design performance.

Unsteady Wake of the NASA Common Research Model in Low-Speed Stall

Following the completion of the European Strategic Wind Tunnel Improved Research Potential test campaign in the European Transonic Windtunnel, a large amount of data exists for comparison and validation of computational results at high Reynolds numbers. Unsteady simulations were performed using the NASA Common Research Model at a low-speed stall condition. The flowfield is characterized by large scale separation and a highly unsteady wake. An embedded high-resolution hexahedron block in the wake region of the grid has been used to improve resolution of the turbulence in unsteady Reynolds-Averaged Navier–Stokes and delayed detached eddy simulations. Model deformation occurring in the wind tunnel was incorporated into the computational setup. The computational fluid dynamics predictions match the force and wing pressure measurements from the wind tunnel very well. The mean and fluctuation data from the time-resolved particle image velocimetry measurements in the wake is matched by the delayed detached eddy simulations result, with the Reynolds-Averaged Navier–Stokes results showing stronger wake dissipation. Wake characteristics in delayed detached eddy simulations and Reynolds-Averaged Navier–Stokes have been compared using pressure spectra. The validity of the computational models has been evaluated as well.

Aerodynamic Shape Optimization of Common Research Model Wing–Body–Tail Configuration

Wing shape is one of the main drivers of aircraft aerodynamic performance, so most aerodynamic shape optimization efforts have focused solely on the wing. However, the performance of the full aircraft configuration must account for the fact that the aircraft needs to be trimmed. Thus, to realize the full benefit of aerodynamic shape optimization, one should optimize the wing shape while including the full configuration and a trim constraint. To evaluate the benefit of this approach, we perform the aerodynamic shape optimization of the Common Research Model wing–body–tail configuration using gradient-based optimization with a Reynolds-averaged Navier–Stokes model that includes a discrete adjoint implementation. We investigate the aerodynamic shape optimization of the wing with a trim constraint that is satisfied by rotating the horizontal tail. We then optimize the same wing–body configuration without the tail but with an added trim drag penalty based on a surrogate model we created before the optimization. The drag coefficient is minimized subject to lift and trim constraints. We found that considering the trim during optimization is a better approach than using a fixed-wing moment constraint. We also show that the trim drag surrogate model we created yields a minimum drag coefficient that is within 1.2 counts of the minimum drag coefficient obtained by rotating the tail to satisfy the trim constraint. However, we recommend rotating the tail within the optimization process to obtain the best possible performance.

Exergy-Based Performance Assessment of the NASA Common Research Model

Aircraft have evolved into extremely complex systems that require adapted methodologies and tools for efficient design processes. A theoretical formulation based on exergy management has been recently proposed by Arntz et al. for assessing the aerothermopropulsive performance of future aircraft configurations. The present article focuses on the validation of its numerical implementation in a FORTRAN code for the postprocessing of Reynolds-averaged Navier–Stokes flow solutions. The flow around the wing-body NASA Common Research Model is assessed in terms of anergy destruction. A 2 MW work potential associated with the lift-induced vortices is identified in the wake of the airplane. Subsequently, a six-level grid convergence study enables determining the robustness and accuracy of the exergy postprocessing code. The introduction and calibration of a numerical correction allows to account for the spurious numerical vortex dissipation and to obtain an accuracy similar to the traditional near-field drag method. Finally, the postprocessing code is validated for drag prediction against computational fluid dynamics and experimental wind-tunnel data.

Prediction and Measurement of the Common Research Model Wake at Stall Conditions

The development of the unsteady wake of transport aircraft under stall conditions and its impact on the empennage are challenging to predict, and the flow physics is far from being understood. In the European Strategic Wind Tunnels Improved Research Potential project, time-resolved particle image velocimetry measurements on the separated wake of the NASA Common Research Model were performed in the cryogenic European Transonic Windtunnel for flight Reynolds number conditions supplemented by aerodynamic measurements for a great variety of inflow conditions. In the time-resolved particle image velocimetry measurements, both low-speed stall (, ) and high-speed stall conditions (, ) were considered and the frequency resolution was as high as 1 kHz, enabling a sufficient characterization of the turbulent wake spectrum. For selected high- and low-speed stall conditions, hybrid Reynolds-averaged Navier–Stokes/large-eddy simulations were performed. In the present paper, the numerical results are discussed and compared to the experiments and first evaluations of the particle image velocimetry data are presented.

Identification of mouse gaits using a novel force-sensing exercise wheel.

The gaits that animals use can provide information on neurological and musculoskeletal disorders, as well as the biomechanics of locomotion. Mice are a common research model in many fields; however, there is no consensus in the literature on how (and if) mouse gaits vary with speed. One of the challenges in studying mouse gaits is that mice tend to run intermittently on treadmills or overground; this paper attempts to overcome this issue with a novel exercise wheel that measures vertical ground reaction forces. Unlike previous instrumented wheels, this wheel is able to measure forces continuously and can therefore record data from consecutive strides. By concatenating the maximum limb force at each time point, a force trace can be constructed to quantify and identify gaits. The wheel was three dimensionally printed, allowing the design to be shared with other researchers. The kinematic parameters measured by the wheel were evaluated using high-speed video. Gaits were classified using a metric called “3S” (stride signal symmetry), which quantifies the half wave symmetry of the force trace peaks. Although mice are capable of using both symmetric and asymmetric gaits throughout their speed range, the continuum of gaits can be divided into regions based on the frequency of symmetric and asymmetric gaits; these divisions are further supported by the fact that mice run less frequently at speeds near the boundaries between regions. The boundary speeds correspond to gait transition speeds predicted by the hypothesis that mice move in a dynamically similar fashion to other legged animals.

Numerical Analysis of Flow Over the NASA Common Research Model Using the Academic Computational Fluid Dynamics Code Galatea

A recently developed academic computational fluid dynamics (CFD) code, named Galatea, is used for the computational study of fully turbulent flow over the NASA common research model (CRM) in a wing-body configuration with and without horizontal tail. A brief description of code's methodology is included, while attention is mainly directed toward the accurate and efficient prediction of pressure distribution on wings' surfaces as well as of computation of lift and drag forces against different angles of attack, using an h-refinement approach and a parallel agglomeration multigrid scheme. The obtained numerical results compare close with both the experimental wind tunnel data and those of reference solvers.