Computational Aerodynamics Questions & Answers  
Question by Student 201427102
I wrote at terminal
./warp -r rarefaction.wrp -i out.01 -oi out.01i -q
But Terminal said
Data file has 20 grid lines along i but the control file specifies 40 grid lines.
How can I correct this problem?
05.23.17
Hm, this means that the file out.01 was created with a different mesh size than is now specified in your control file. I recommend not to use the interpolation file flags -oi or -ii if this gives you trouble (this saves on some computing time, but is a bit harder to operate). Simply create a new out.01 with the -o flag without reading in out.01i. That will work just as well but will be a bit slower.
Question by Student 201427564
Professor, I have a question about Question#2. Is it possible that ${P}_{i+1}$ increase while ${P}_{i-1}$ decrease?
I guess you mean an increase/decrease from one mesh level to the other? Yes, it's possible. This means the derivative is becoming larger. 1 point bonus.
Question by Student 201427564
Professor, I have a qeustion about calculating '$p$'. In your table, $r=\frac {{\Delta x}_{c}} {{\Delta x}_{f}} $. By this definition, is it correct that $r=\frac {1} {\sqrt{2}}$ ? Because the fine one is $\sqrt {2}$ times more fine than coarse one.
No, it's the opposite.. This was mentioned in class.
Question by Student 201238707
Professor, When I start "Assignment 7 - Question #2". I just use $(R_\Delta)_\max = 1E-3$ or find convergence value of $(R_\Delta)_\max$
05.24.17
You can keep xiverge set to 1E-3. 1 point bonus.
Question by Student 201527110
Professor, I don't understant what does 'Semi Disc. equation' exactly what we do last lecture. Usually, scalar equation can be denoted as $$\frac{\partial u} {\partial t} + a \frac{\partial u}{\partial x}=0$$, but I wonder why we didn't considered about wave speed 'a' in 'Semi Disc. equation'. (I think you noted semi disc eq as $\frac{u^{n+1}_i-u_i} {\delta t} + \frac{u_{i+1/2}-u_{i-1/2}}{\delta x}=0$)
05.25.17
That's a mistake: I should have added the sound speed of course. Please correct your notes. Because it is constant, an easy way to add the sound speed is to change $\Delta t$ to $a\Delta t$ everywhere $\Delta t$ appears. This will make more sense! 2 points bonus.
Question by Student 201427564
Professor, when you explain about 'Roe Average', you wrote like this. $ { A }_{i+ \frac {1} {2}} ({U}_{i+1} - {U}_{i}) = {F}_{i+1} - {F}_{i} $. I can not understand that how can it be possible that $ {A}_{i+ \frac {1} {2}} {U}_{i+1} = {F}_{i+1} $ and $ {A}_{i+ \frac {1} {2}} {U}_{i} = {F}_{i} $ . Because subscript of A and U are different each other.
05.29.17
Hm, I don't understand the question. You need to explain better what you don't understand..
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$\pi$