To carry on with the demonstration of GBS applied to turbomachinery, we are pleased to present the CAD issued of a design process based on thermodynamics specifications and design rules. The impeller is now ready for 3d CFD computation or integration inside the final product!

GBS: https://github.com/ssg-aero/gbs

#turbomachinery #compressor #blade #stage #opensource #design #software #CAD #engineering #engineer #geometry #mechanical

We are pleased to announce the release of our  open source library geometrical GBS.

ssg-aero/gbs: gbs is a c++ header library to build and manage NURBS, some optional module are used for visualization and export. This library is compatible with OpenCASACADE and has a python biding. (github.com)

In a nutshell GBS is a powerful C++ header library to manage BSpline geometries.
​For now its capabilities range from basic geometry creation in a rational o  irrational fashion:

To more advanced geometrical creation algorithms:

Points approximation:

Surface creations from profiles:

More technical show case coming.

All the best for 2019 !!!

Keywords: Aerospace Valley, electric aircraft, hybrid propulsion, urban mobility

SSG-AERO was present during the seminar organized by AeroSpace Valley, one of the French Aero Clusters. 
During one complete day, a complete overview of all the current developments aimed at reducing the aero carbon footprint and to change local mobility were presented and discussed.
Airbus, Safran, Thales and Liebherr Aerospace shared their accomplishments and how they prepared and envisioned this major change in the Aero transportation world.
Presentations also focused on the numerous hurdles on the way towards the electrification and hybridization of flying machines allowing free discussions with small companies.

Time was also given to prospection and science-fiction, with some very interesting concepts :

• Neoptera: a new type of convertible
• Volta: the first ever electric helicopter
• Vahana: Airbus vision of a convertible

We are very grateful to the Aerospace Valley team, which allowed us to be in the pool of small companies with a 20min slot to present our services !
We introduced SSG-AERO, focusing especially on

• our proven records in optimizing propellers and wings for recreational drones,
• as well as our experience in designing electrically driven machines,
• and finally our homemade tools which allow the creation of ever more complex efficient geometries.

For those interested, our presentation is available for download by clicking on the icon under these words...

SSG-AERO is proud the be a member of Aerospace Valley, one of the french cluster focusing on aeronautics.

All the best to you all Internet people!

Our Demo Software is only available for Windows, for timing purposes only.
Our software shall be available on all the platforms.

To run our demo software,

1. Download it (see Download for this purpose)
2. Extract it in a directory
3. Install Visual Studio if you do not already have it on your machine. We have added an installer in the download package named vc_redist.x64 for this purpose.
4. run the executable called tst_demo_main

These elements can be used at the same time or not, and meshes are thus classified in two categories:

• Non structured: any agglomeration of elementary elements, organized or not. Most of the meshes in this category are hybrid meshes using hexahedrons and prisms. The cells in such meshes can have all their faces connected one to another, and are called conformal meshes. Otherwise they are called non conformal and fluxes will have to be distributed on exchange interface between the faces.
• Structured: an organized agglomeration of Hexahedrons. If all the faces of all the cubes are connected with another one or with a boundary condition, they are even called fully connected structured meshes. Most of the time, these elementary hexahedrons are part of bigger hexahedrons called blocks, and the assembly of all the blocks is called the meshing topology.

Here under are shown some of the possible configurations of meshes from a fully tetrahedra unstructured mesh to a fully connected multi-block structured mesh (in 2D to ease the understanding and the representation). 
​All the meshes discretize the same domain with two walls where the cells sizes have to be small in order to properly take into account the strong variations of speed from zero at the wall to any potential value farther from it - this refinement is called meshing the boundary layer.

It is always good to keep in mind the purpose of a mesh in CFD, which is to discretize a complex volume into small parts on which a flow simulation shall be run. This means that a very complex and heavy algorithm will use this discretization and travel through it hundreds of times to evaluate differences and solve Navier-Stokes equations using numerical schemes. 
As for the meshes, the most common CFD solvers using meshes are organized in 2 families:

• Unstructured solvers: simulations can be run on any type of small volumes whatever their organization,
• Structured solvers: as their name suggests, these solvers can only be run on structured meshes, with eventually exchange interfaces between some parts of the meshes.

 
Most of these solvers use the same type of resolution schemes and stabilization schemes which means that for a given type of flow (subsonic, supersonic, incompressible, …), the two solvers are comparable apart from how they manage the grid.
​Thinking about what makes a good mesh a really good mesh requires to understand the challenges put together in a CFD simulation. A good simulation needs to :

• be precise yet fast, 
• predict potential instabilities in the flow such as stall, surge, detachments, 
• capture violent phenomena such as shocks and viscous stresses,
• not corrupt the flow solution with numerical errors,
• probably all together…

​Looking at the mesh through this prism, the advantages of the structured meshes are straightforward :

• most of the time structured meshes require less cell to properly mesh a complex volume, hence they require less memory and lower iteration time during the CFD simulation,
• the boundary layer mesh is always well controlled and cells are almost everywhere normal the the walls in a structured mesh, which means that the viscous effects are potentially properly captured,
• the same goes for the compressibility effects, as the meshing process can impose refinements wherever a potential shock can occur,
• finally the hexahedrons in the mesh are in a huge majority very well proportioned and close the the shape of a cube, which means that the numerical dissipation used to stabilize most of the CFD common savers does not propagate much in all the directions corrupting results. This last factor is one of the main reason why simulations run on unstructured tetra-dominant meshes are not as accurate and also why they require more time to converge.