Multi-Step Level-Set Ice Accretion Simulation with the NSMB solver

Icing effects can reduce the flight safety under certain weather conditions. According to the US National Transport Safety Board, icing is one of the major causes of flight accidents. Supercooled water droplets present in clouds impinge on the surface of aircraft structures. They either solidify totally on impact or partially then creating a thin liquid film runback depending on the flow temperature and speed hence, creating dry rime ice or glaze wet ice respectively. Designing an adequate de-icing mechanisms requires full knowledge of the icing phenomenon itself. Icing experimental study cannot exceed the scope of a handful of simple cases due to complexity and cost. Consequently the use of computational fluid dynamics is justified. The icing process is assumed broken up into four steps: 1) single phase air flows around the wing 2) transporting water suspended droplets; droplets impinge into the surface 3) generating a liquid or dry film exchanging energy with the surface 4) accreated to shape the final form during a certain exposure time. This process is usually assumed to occur on a single step considering that the time scale of the icing process is very long compared with that of the air flow. Current Icing simulation codes used by industries are based on over-simplified models. 1) A 2D inviscid panel methods with an empirical boundary layer method is used for the air flow. Which is usually followed by 2) a Lagrangian transport of droplets. And finally 3,4) an iterative thermodynamic model for the liquid film to compute the ice thickness. To generate the final geometry however, a Lagrangian node displacement is needed. A multi-step icing approach repeats this process for portions of the required exposure time but still with decoupled time scales. Maintaining a good grid quality requires a tedious amount of work, since strange irregularities in iced shapes are difficult to be fully accounted for. The Level-Set method introduced by Osher and Fedkiw could alleviate such a task. A passive scalar function is introduced and is put equal to zero at the interface, positively defined outside and negatively inside; the zero level represents the time evolution of the air/ice interface. To complete the model, a PDE type thermodynamic model is used for the film, coupled with an external flow solver. In the present study a new method of icing simulation is developed. To get the most out of such model, it is developed in the three-dimensional structured multiblock Navier-Stokes solver NSMB. For a multi-step icing procedure, the geometry is defined by a passive scalar called the level-set. This level-set function is set equal to the distance, negative on the inside and positive outside. A penalized Navier-Stokes equation is solved on the external flow using a simple non-body fitted mesh, wherein the solid is represented by the negative level-set valued cells. The droplets are transported using an Eulerian approach using a TVD and a local time stepping schemes. The impingement rate or what's called the collection efficiency is then fed to a Shallow-Water Icing Model that evaluates the ice accretion, its height and velocity. The convective heat transfer coefficient is obtained from the Navier-Stokes solver. Following that the Level-set function is advected with the icing velocity to predict the new deformed geometry. The process is then repeated for as many portions of the exposure time as needed

The search for freedom in extreme sports: A phenomenological exploration

Participation in extreme sports is continuing to grow, yet there is still little understanding of participant motivations in such sports. The purpose of this paper is to report on one aspect of motivation in extreme sports, the search for freedom. The study utilized a hermeneutic phenomenological methodology. Fifteen international extreme sport participants who participated in sports such as BASE jumping, big wave surfing, extreme mountaineering, extreme skiing, rope free climbing and waterfall kayaking were interviewed about their experience of participating in an extreme sport. Results reveal six elements of freedom: freedom from constraints, freedom as movement, freedom as letting go of the need for control, freedom as the release of fear, freedom as being at one, and finally freedom as choice and responsibility. The findings reveal that motivations in extreme sport do not simply mirror traditional images of risk taking and adrenaline and that motivations in extreme sports also include an exploration of the ways in which humans seek fundamental human values. © 2013 Elsevier Ltd

Adventurous Physical Activity Environments: A Mainstream Intervention for Mental Health

Adventurous physical activity has traditionally been considered the pastime of a small minority of people with deviant personalities or characteristics that compel them to voluntarily take great risks purely for the sake of thrills and excitement. An unintended consequence of these traditional narratives is the relative absence of adventure activities in mainstream health and well-being discourses and in large-scale governmental health initiatives. However, recent research has demonstrated that even the most extreme adventurous physical activities are linked to enhanced psychological health and well-being outcomes. These benefits go beyond traditional ‘character building’ concepts and emphasize more positive frameworks that rely on the development of effective environmental design. Based on emerging research, this paper demonstrates why adventurous physical activity should be considered a mainstream intervention for positive mental health. Furthermore, the authors argue that understanding how to design environments that effectively encourage appropriate adventure should be considered a serious addition to mainstream health and well-being discourse

Parametrization Effects of the Non-Linear Unsteady Vortex Method with Vortex Particle Method for Small Rotor Aerodynamics

International audienceThe aim of this article is to investigate the parameter sensitivity of the (Non-Linear) Unsteady Vortex Lattice Method-Vortex Particle Method [(NL-)UVLM-VPM] with Particle Strength Exchange-Large Eddy Simulations (PSE-LES) method on a lower Reynolds number rotor. The previous work detailed the method, but introduced parameters whose influence were not investigated. Most importantly, the Vreman model coefficient was chosen arbitrarily and was not suitable to ensure stability for this lower Reynolds number rotor simulation. In addition, the previous work presented a consistency study where geometry and time discretization were refined simultaneously. The present article starts with a comparative literature review of potential methods used to solve the aerodynamics of an isolated hovering rotor. This review highlights the differences in modeling, discretizations, sensitivity analysis, validation cases, and the results chosen by the different studies. Then, a transparent and thorough parametric study of the method is presented alongside discussions of the observed results and their physical interpretation regarding the flow. The sensitivity analysis is performed for the three free parameters of UVLM, namely Vatistas core size, the geometry and the temporal discretizations, and then for the three additional parameters introduced by UVLM-VPM, which are the Vreman model coefficient, the particle spacing, and the conversion time. The effect of different databases in the non-linear coupling is also shown. The method is shown to be consistent with both geometry and temporal refinements. It is also consistent with the expected behavior of the different parameters change, including the numerical stability that depends on the strength of the LES diffusion controlled by the Vreman model coefficient. The effect of discretization refinement presented here not only shows the integrated coefficients where different errors can cancel each other, but also looks at their convergence and where relevant, the distributed loads and tip singularity position. Finally, the aerodynamics results of the method are compared for different databases and with higher fidelity Unsteady Reynolds Averaged Navier–Stokes (URANS) 3D results on a lower Reynolds number rotor

Comparison of thermodynamic models for ice accretion on airfoils

International audiencePurpose This paper aims to assess the strengths and weaknesses of four thermodynamic models used in aircraft icing simulations to orient the development or the choice of an improved thermodynamic model. Design/methodology/approach Four models are compared to assess their capabilities: Messinger, iterative Messinger, extended Messinger and shallow water icing models. They have been implemented in the aero-icing framework, NSCODE-ICE, under development at Polytechnique Montreal since 2012. Comparison is performed over typical rime and glaze ice cases. Furthermore, a manufactured geometry with multiple recirculation zones is proposed as a benchmark test to assess the efficiency in runback water modeling and geometry evolution. Findings The comparison shows that one of the main differences is the runback water modeling. Runback modeling based on the location of the stagnation point fails to capture the water film behavior in the presence of recirculation zones on airfoils. However, runback modeling based on air shear stress is more suitable in this situation and can also handle water accumulation while the other models cannot. Also, accounting for the conduction through the ice layer is found to have a great impact on the final ice shape as it increases the overall freezing fraction. Originality/value This paper helps visualize the effect of different thermodynamic models implemented in the same aero-icing framework. Also, the use of a complex manufactured geometry highlights weaknesses not normally noticeable with classic ice accretion simulations. To help with the visualization, the ice shape is presented with the water layer, which is not shown on typical icing results

Integration of a high-speed cross correlator for microwave radiometry

Dr. Jeffrey Piepmeier has developed a high-speed digital cross correlator chip for use in microwave radiometry. Our project was to integrate the cross correlator integrated circuit in a PC-104 form factor compliant printed circuit board with an ISA bus microprocessor interface. Designs were necessary for analog to digital converters, logic translation circuits, adjustable voltage threshold circuits, and all related driver and control software. An additional printed circuit board meeting the PC-104 form factor was developed to supply power to a complete correlation system

WPI -- London Borough of Merton local nature reserves

Leisure Services of Merton Council wish to promote the thirteen Local Nature Reserves of Merton and to provide residents with helpful information about them to increase attendance. A user profile was created by gathering data from the residents of Merton through mail surveys, interviews at the reserves, and surveys from the local schools. Our findings showed a lack of awareness, which led us to create a teacher manual and a public transportation guide. The results also included information useful to the process of applying for future grant funding and a number of suggested improvements to enhance the thirteen nature reserves