After thinking about this and performing some tests, I am concluding that the source of this numerical instability is the discreteness of the FEM method.
I have now tried to stabilize the algorithm by taking the mean value between the last and former radiative heat vectors, and as far as I have...
Yest, it is a divergence problem. But it does not happen always. It commonly appears when one of the material properties (C or K) has an important discontinuity.
What do you mean with "block-oriented solver"?
I have also linearized all T4 terms, so that should not be an issue. Or do?
I only wanted to add that induced drag is not only a consequence of the tip vortices. It is a consequence of the span-wise variation of circulation, which is indeed the result of a finite aspect ratio. The induced drag is distributed all over the wingspan, although it does jump in regions of...
When the flow stops separating from the trailing edge of a wing, it does not only produces more drag, but it also decreases the production of lift. That is the most important reason why that situation needs to be avoided.
Wings produce lift because the sharp trailing edge gives continuity to the...
Thanks for your replay!
While I do know where the problem is, I don't really see how I can damp this effect without introducing artificial things that might pollute the solution.
Reducing the time step is something I don't really want to do, because I have to keep an eye in performance.
I am...
Hi everyone. I have here a problem understanding the stability of heat transfer through radiation. I'll give you some background, and later on I'll describe the physical problem.
Background
I am simulating the unsteady radiative heat transfer between mutually visible surfaces of objects through...
I can certainly recommend this publication here:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19960015887.pdf
This gives an idea of how hard it can be to compute the induced drag without much error.
Pressure integration along the surface doesn't seem to be a good idea, since it is...
I don't really like to get into messy discussions, but...
a. Any glider can stay in the air for a long time if it glides over a region where the wind goes upwards. So that doesn't say much about the performance of albatrosses.
b. I wouldn't compare the overall performance of birds with...
Well but that is just the point, the energy is not lost. The birds flap their wings, which certainly requires work, and it gets forward thrust in return. I totally agree that the mechanism is quite extraordinary. They actually invert the induced drag, but that requires energy. And that doesn't...
This occurs because the micro structure doesn't change immediately after the cooling. The micro structure remains the same: just one phase. Through a natural process called "aging", which is a sort of diffusion, the micro structure begins to change gradually. Several phases appear in the form of...
A different affair
The way birds get thrust is a different affair, which involves unsteady aerodynamics. Behind the aerodynamics, for a bird to get thrust it needs to release an amount of energy. The bird does that by putting its own structure into motion (flapping the wings), what requires...
Yes, that is another point. We use theories that neglect viscosity to calculate the induced drag. If our model was still perfect, viscosity would even affect that solution. An example of that is what happens on the wing tip: the separation point depends on the boundary layer and therefore on the...
I have been wondering this for a long time as well. After running many test with the vortex lattice method and reading books and papers, my conclusion was that, as the lifting line theory has been formulated under simple assumption (wake flatness in the direction of the stream and a a single...