Fluid Dynamics Technology Tips
Do Not Remesh. Morph Instead.
When you study and simulate variations of a given geometry, don’t spend time meshing each and every geometrical variation. Create only the initial mesh, then you can morph it to all geometrical variation thanks to RBF-Morph, a solution from an ANSYS partner.
- Mesh morphing is fast: Even a mesh with 10 million elements takes seconds to render.
- Mesh morphing recognizes parameters: You can use RBF-Morph with ANSYS DesignXplorer to automatically investigate a range of design parameters or perform design optimization studies.
- Mesh morphing is practical: With RBF-Morph, you can export any of the modified mesh geometry back to CAD.
These materials provide details about mesh morphing and RBF-Morph:
Previous Tech Tips
Imagine that you have to design a car and minimize its drag, or engineer a piping system and minimize pressure drop. In both cases, the actual shape of the design is the most important factor. When setting parameters for simulation, usually you define the shape and run parametric variations, often with the help of optimization tools. While this is a good approach, it has many limitations:
- Design shapes can be extremely complex, governed by hundreds of parameters (or more). It is impossible to consider all of them. How do you make sure that you select the relevant parameters?
- Even if you select one set of key design shape parameters, you still have a very large number of designs to evaluate. Simulating all these can be extremely time consuming.
For these reasons, you need a smart shape optimization tool — one that:
- Automatically identifies the section of the design (shape) that needs to be modified.
- Automatically guides shape optimization by determining how to modify the shape directly from simulation results, without the need for trial-and-error simulation run after run
- Quickly performs design shape optimization, requiring the minimum amount of simulations, and performing those simulations as fast as possible
What is the smart shape optimization tool?
The ANSYS smart shape optimization tool is called adjoint technology. The tool is actually a solver that uses CFD simulation results to find an optimal solution based on stated goals (reduce drag, maximize lift over draft ratioreduce pressure drop, etc.). But it doesn’t stop there: It also computes how to specifically modify the design. Because it is a solver, it has many advantages:
- It directly computes which section of the design needs to be modified and how. You do not need to define any parameters.
- It directly determines a better-performing shape as well as the associated performance improvement, all without needing another CFD simulation.
- It can, in a minimal number of simulations, determine the optimal shape. At each iteration, design performance increases until the optimal design is reached.
Why is this smart shape optimization tool so fast?
Because the adjoint solver directly determines what section of the shape to modify and how to do it, it reaches the optimal geometry faster. Because the adjoint solver works hand-in-hand with mesh morphing technologies, you do not need to redefine the geometry nor recreate the computational mesh; rather you simply morph the mesh to the new shape. In summary, this solution is fast because:
- The adjoint solver determines directly how to improve performance, so there is no time wasted by trials-end-error processes.
- A mesh morpher automatically adjusts the design shape and computational mesh following the adjoint solver recommendations, saving even more time.
The following materials provide details about the adjoint solver technology.
Turbulence is unarguably the most challenging area in fluid dynamics. It is the most limiting factor in accurate computer simulation of engineering flows. Turbulence flow constitutes a classic multiscale problem, one that is far beyond human intuitive understanding ― as well as beyond resolution capabilities of the most powerful modern parallel computers (for any foreseeable future).
Nobel-prize winning physicist Richard Feynman once described turbulence as the "most important unresolved problem in classical physics." An even more pronounced quote is associated to Werner Heisenberg: "When I meet God, I am going to ask him two questions: Why relativity? And why turbulence? I really believe he will have an answer for the first."
No single model or modeling approach can solve all types of turbulent flow, so different types of turbulence models have been developed in the past decades. So choosing the right turbulence model to match the application is critical to accuracy and computational resource optimization. ANSYS is a technology leader in this area, offering a wide range of the most advanced model formulations, including WMLES, ELES and transition models.
The following materials provide details about turbulence modeling.