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Use this search facility to find out more about the profile of our HPC-Europa2 visitors, the type of work they have been doing, and their project achievements.
In the present work, a numerical study is conducted in order to investigate the unsteady aerodynamics of finite-span flapping rigid wings. The non-dimensional incompressible Navier-Stokes equations are solved in their velocity-pressure formulation using a second-order accurate in space and time finite-difference scheme. To tackle the problem of moving boundaries, the governing equations are solved on overlapping structured grids. The main goal is to investigate the wake topology and aerodynamic performance of low aspect-ratio flapping wings and their dependence on the flapping parameters (such as flapping frequency, flapping amplitude and Reynolds number). Specifically, the root-flapping motion characteristic of flying animals is studied. The numerical simulations are performed at a Reynolds number of Re = 1000 (a Reynolds number value often found in nature) and at different values of Strouhal number St.
In the present work, we have studied the root-flapping motion characteristic of flying animals, a subject virtually unexplored. It was found that, indeed, root-flapping motion produces wake structures similar to those of heaving or coupled heaving-and-pitching motions, but with the difference that the latter motions generate larger vortices and forces than root-flapping motion, presumably because the average velocity is higher across the span; aside from this, similar wake regimes occurs at similar St. In general, it was found that for values less than St < 0.25 we are in the drag production regime, for values approximately equal to St = 0.25 we produce little or no drag (or thrust), whereas for values higher that St > 0.25 we are in the thrust production regime.
The simulations also show that the wake of thrust producing, rigid finite-span wings is formed by vortex loops close to the wing surface, that slowly convert into vortex rings as they are convected downstream. It was also observed that the vortex rings are themselves inclined with respect to the free-stream; the angle of inclination of the vortex rings is found to be in the direction of their travel and in the streamwise direction for thrust producing configurations, whereas for drag producing configurations the angle of inclination is opposite to the direction of travel.
Additionally, the effect of aspec- ratio AR on the aerodynamic forces of finite-span wings was also assessed. It was observed that as we increase the wing AR, the aerodynamic forces also increase and this is chiefly attributed to the large area of high aspect ratio wings and to the decrease of three-dimensional effects in long wings. This observation leads us to think that the assumption of two-dimensionality has some validity for birds and insects, where the wings of many species tend to have relatively large aspect ratio.
All the qualitative and quantitative results found during this research support the hypothesis that: “flying and swimming animals cruise at a Strouhal number tuned for high power efficiency”
Our pourpose with this project was to conitnue the work we have been doing until now by extending the current implementation of llCoMP with a set of new tasks:
There is no doubt that making connections with other researchers, and the possibillity to attend to courses and practising English has been also my objective.
By gaining access to the high performance computing resources at EPCC, I've been granted with an invaluable opportunity to learn working with different tools and environments and also to compare different parallel computing models.
During my visit, the first goal, hybridation code, happened to be a quite interesting topic, which allowed us to writte some papers, so, we've changed the objectives of my visit to center our work on the hybridation of generated code. Using the EPCC machines for profiling and debugging of parallel applications, not only was a quite efficient and easy way to enhance the performance of llCoMP, but also was a good way to learn about this kind of tools (paraver, valgrind, etc), which otherwise I've never been able to use.
We have been able to implement most of the hybrid code generation inside llCoMP, and we've tested several codes (around seven different algorithms) on a wide range of machines (EPCC machines, like NESS and HPCx, and also another machines from other parts of Europe).
Due to the short time of my visit there (only six weeks), I haven't been able to implement the OpenMP 3.0 constructs to the compiler, which happened to be a quite complicated task, more than we thought in advance. However, we've been able to desing the way to do that, and we plan to work on that issue in the following months.
For the first application to HPC-Europa2, we had defined the topic of the project as investigation of aerodynamics of a heavy truck. But, at the start of the project, together with my home and host advisors we have decided to make the analysis over a dolphin body. It’s better to see the turbulent model with transition (SST) over a streamlined geometry for the first time. So, the dolphin geometry is a complex geometry and it needs too much mesh size and this requires high performance computers for both meshing and solution. And we have planned that after the simulations by means of these results we can apply this method to the heavy truck body. In recent days, a few commercial vehicle companies study on dolphin shape to adapt this to the trucks. They want to decrease the exhaust emissions and the fuel costs by benefiting from animals’ aerodynamic shapes. However, there are some other vehicles like vessels just like dolphin shape. We have used high performance computers quite much for the calculations and generally the simulations needed 24 GB memory and more. However, with 16 processors, 1 simulation needed for converging at least 2 weeks and more. Some of the simulations have been continuing for about 1 months and still running. Also, we can say that, due to the dolphin body is a streamlined body and needs the boundary layer mesh, it needs much more mesh and solution load than a conventional truck body by using the SST transition model.
Dolphins have already a good streamlined geometry and a lot of ability to reduce the drag which had been shaped by the nature. At this point, we search the flow regime whether it’s laminar or turbulent. However, we hope that there may be a laminar – turbulent transition over the dolphin body. With the new turbulent model “SST Transition Model” in the new version of “Fluent-12.1” package CFD code, we hope to capture a transition region over the dolphin body.
In this study, laminar – turbulent transition over the dolphin body has been numerically investigated by using Menter’s SST transition model. The model is integrated in the new version of Fluent 12.1 software which was employed for the simulations. In order to confirm the transition model, the flat plate transition is investigated and compared with the literature. In addition, the “Lotte” geometry (IAG-airship) is simulated with this new model and the pressure distribution is compared with the available experiments carried out at IAG Wind Tunnel. The onset of the transition was captured correctly for the flat plate and 2D axi-symmetrical airship geometry. The effect of the boundary layer mesh size and various flow parameters (such as free stream turbulent intensity) were investigated.
Next the dolphin simulations were made for only the dolphin head due to the meshing requirements, and then the complete dolphin geometry without fins was simulated for various free stream velocities. The complete model simulations are underway by meshing the full dolphin geometry with a special meshing strategy. In order to justify the accuracy of this approach, the 2D axi-symmetrical simulations for airship were also performed and the effect of this meshing approach was investigated.