Three dimensional visualization of simulations of liquids and solids

Visualization in three dimensions is invaluable for understanding the nature of condensed and fluid systems, but it is not always easy. In nature it is hard to view sample interiors, but on computers it is possible. We describe and contrast two opposite approaches - “smoke” visualization for viewing interiors of liquid samples and interactive WebGL for solids and molecules. Both are extensions of earlier Technion Computational Physics group projects and complement and are interoperable with the recent SimPhoNy Fp7 project. They require only desktop hardware and software accessible to students. Examples and standalone instructions for both are presented, starting with sample creation and concluding with image galleries.

Pressure and velocity measurements of air flow past a proposed generic Aircraft carrier geometry

Research on the air flow disturbances in the aircraft carrier environment has gained prominence in recent times. However, there is presently no representative carrier model analogous to the Simplified Frigate Shape (SFS) which is generic naval frigate for air flow investigation. In the present study, a Generic Aircraft Carrier (GAC) model is proposed, as a simplified, benchmark model for aerodynamic research. With the motivation to provide validation data for future CFD studies, baseline experimental data is generated in the wind tunnel, in terms of pressure distribution over the deck, for two variants, namely, a complete flat deck configuration with no island and secondly, with the island in the baseline position of the GAC. Effect of the island in modifying the flow is discussed by a comparison between the two variants. Particle Image Velocimetry (PIV) is employed to record velocity and turbulence levels in the GAC environment, highlighting regions of velocity deficits, and unsteady flow which may hinder the landing procedure of an approaching pilot. Comprehensive database of experimental data is presented as baseline data for future work and for validation of numerical models. Traditional tuft and smoke visualization studies are also conducted to provide corroboratory qualitative insights.

Experimental testing of exterior wall mounted mechanical ventilation exhaust air outlet devices

The purpose of the study was to experimentally test the performance of four types of wall-mounted mechanical ventilation exhaust air outlet devices. A full-scale mock-up of a segment of an external wall with an exhaust air outlet was constructed. The tested exhaust air devices include a gravity louver, fixed-blade louver, louver plate, and exhaust nozzle. The performance assessment included two types of experiments over the exhaust airflow rate range of 25–94 l/s at isothermal conditions with no influencing wind: (i) the particle tracer method with smoke to visualize the exhaust air jets from the outlets, and (ii) the tracer gas method to measure the dilution of CO2 concentration in the exhaust air jet. Furthermore, the aerodynamic performance was comparatively evaluated in terms of pressure drop and exhaust air face velocity at the outlet. The qualitative comparison of airflow patterns by smoke visualization showed notable differences between the tested device types. Concentration decrease evaluation indicated that the exhaust air pollutants are more efficiently transported away from the building wall by exhaust outlets that discharge at 0–45 degrees downwards from the horizontal plane. Discharge angles 60–90 degrees downwards produced a wall-attached jet and the pollutant tracer concentration remained relatively high in the vicinity of the wall.

Design of Fire Source for Railway Vehicles and Measurement of Critical Velocity in Reduced-Scale Tunnels

In this study, the authors designed a reduced-scale railway vehicle fire, which was necessary for evaluating the fire safety of railway tunnels using a reduced model. To overcome the shortcomings of the methods used in conventional reduced-scale railway tunnel tests, the authors simulated the fire source of a railway vehicle using a methanol fire source for fire buoyancy, and a smoke cartridge for smoke visualization. Therefore, the heat release mass consumption rates of various methane trays were measured using a cone calorimeter (ISO 5660). The critical ventilation velocity in the railway tunnels was obtained using the designed fire source of the railway vehicle, which was evaluated by the measured temperature at the top of the tunnel as well as laser visualization.

Application of projection method to speed-up a new algorithm for the measurement of instantaneous flow velocity field

Исследована возможность применения метода проекций для ускорения нового оптического метода измерения мгновенных полей скорости потока по результатам дымовой визуализации. Алгоритм основан на анализе интегральных проекций изображений на координатные оси. Исследовано изменение случайной и систематической ошибок измерения в зависимости от величины однородного смещения частиц с диаметрами 2.2 и 10 пикс. На примере синтезированных изображений размерами 16 × 16, 32 × 32 и 64 × 64 пикс показано, что применение алгоритма ускорения позволяет увеличить скорость обработки результатов измерений примерно в 16, 140 и 1060 раз соответственно, однако снижает точность полученных данных по отношению к новому методу Smoke Image Velocimetry при обработке изображений с крупными частицами (10 пикс), моделирующих дымовые структуры. Тем не менее результаты, полученные с применением алгоритма ускорения, не уступают по точности аналогичным данным, полученным с применением метода Particle Image Velocimetry. Отмечается, что областью применения алгоритма ускорения может быть предварительное определение начального значения смещения с последующим его уточнением при использовании более точных алгоритмов вычисления. Applicability of projection method has been investigated to speed-up a new optical method for the measurement of flow velocity fields using smoke visualization. The algorithm is based on the analysis of integral projections of images on coordinate axes. The variation of random and bias measurement errors while changing the magnitude of uniform displacement of particles has been studied for the particle diameters of 2.2 and 10 pix. Synthetic images with sizes 16×16, 32×32 and 64×64 pix have been used to show that the application of projection method to image processing speeds up the processing time of the measurements by approximately 16, 140 and 1060 times, respectively. However, if compared with a new method of Smoke Image Velocimetry, it reduces the accuracy of the obtained data when processing the images with large particles (10 pix) imitating smoke structures. Nevertheless, the results obtained by the proposed speedup algorithm are not inferior in accuracy to similar data obtained by Particle Image Velocimetry. It is noted that the proposed speed-up algorithm can be applied to preliminary evaluation of initial displacement field with its subsequent refinement using more accurate computational algorithms and methods.

Hawkmoth flight in the unsteady wakes of flowers

Flying animals maneuver and hover through environments where wind gusts and flower wakes produce unsteady flow. Although both flight maneuvers and aerodynamic mechanisms have been studied independently, little is known about how these interact in an environment where flow is already unsteady. Moths forage from flowers by hovering in the flower’s wake. We investigate hawkmoths tracking a 3D-printed robotic flower in a wind tunnel. We visualize the flow in the wake and around the wings and compare tracking performance to previous experiments in a still air flight chamber. Like in still air, moths flying in the flower wake exhibit near perfect tracking at low frequencies where natural flowers move. However, tracking in the flower wake results in a larger overshoot between 2-5 Hz. System identification of flower tracking reveals that moths also display reduced-order dynamics in wind, compared to still air. Smoke visualization of the flower wake shows that the dominant vortex shedding corresponds to the same frequency band as the increased overshoot. Despite these large effects on tracking dynamics in wind, the leading edge vortex (LEV) remains bound to the wing throughout the wingstroke and does not burst. The LEV also maintains the same qualitative structure seen in steady air. Persistence of a stable LEV during decreased flower tracking demonstrates the interplay between hovering and maneuvering.Summary statementWe examined how moths maneuver in the wake of flowers and discover that flower tracking dynamics are simplified compared to still air, while the leading edge vortex does not burst and extends continuously across the wings and thorax.