Introduction to CFD Questions & Answers
 Question by Student 201427564 Professor, I have a question about $\phi(r)$. In the table, $\phi(r)=max(0, min(1,r))$. But last class, you wrote like this. ${({\phi^{+}}_{i+ \frac {1} {2}})}_{1} = max(0,min(1, 2{r^{+}}_{i}))$ Why did you use $2{r^{+}}_{i}$ rather than ${r^{+}}_{i}$ ?
 06.01.17
Both $\phi=\max(0,\min(1,r))$ and $\phi=\max(0,\min(1,2r))$ respect the rule of the positive coefficients and reduce to first order at extrema and are hence valid. But $\phi=\max(0,\min(1,2r))$ is better because it is closer to the second-order stencil. 1.0 point bonus.
 Question by Student 201227147 Professor, I have a question about assignment 8 question #2-(b). Last class, you calculated $r _{i} ^{-}$ to find out $\phi _{i+1/2} ^{-}$ because you used this relationship I guess: $$\phi _{i+1/2} ^{-} = max(0, min(1,2r _{i} ^{-} ))$$ However, I think $r _{i} ^{-}$ should be $r _{i+1} ^{-}$ because $\phi _{i+1/2}$ is $\phi _{i+1/2} ^{-}$. Is it right? or is there some reasons you calculated $r _{i} ^{-}$?
Hm no, if we set $\phi _{i+1/2} ^{-} = \max(0, \min(1,2r _{i+1} ^{-} ))$ then we should define $r_{i+1}^-\equiv\frac{u_i-u_{i+1}}{u_{i+1}-u_{i+2}}$. However, because $r_i^-\equiv\frac{u_i-u_{i+1}}{u_{i+1}-u_{i+2}}$ then we have to set $\phi _{i+1/2} ^{-} = \max(0, \min(1,2r _{i} ^{-} ))$. 1 point bonus.
 Question by Student 201227147 I have another question about $r_{i+1}^-$. In the table, $r_{i} = \frac{u_{i+1}-u_{i}}{u_{i}-u_{i-1}}$. But you calculated $r_{i}^-$ with $r_{i+1}^-\equiv\frac{u_i-u_{i+1}}{u_{i+1}-u_{i+2}}$. Does it mean that the equation in the table is assumed positive upwind (from left($i-1$) to right($i+1$)) so that notations should be from right($i+2$) to left($i$) when I apply it in negative upwind case?(it means $i-1$->$i+2$, $i$->$i+1$, and $i+1$->$i$)By the way, Does your answer about previous question mean that there's just difference in notating $r$ and use same equation?
I guess your concerns are due to the fact you are using an older version of tables.pdf.. The tables have changed slightly in the last few days. After downloading the latest version, if you still have some concerns, ask the question again below.
 Question by Student 201238707 Professor, I have a question about subsonic inflow's velocity angle. Why those are same? $$\theta^{n+\frac {1} {2}}_1 = \theta^{n+1}_1$$ because we assumed steady-state?
 06.05.17
I don't recall this step. You need to put your question into context so I can recall why we did this.
 Question by Student 201238707 when we found velocity vector $u^{n+1}_1$ $\&$ $v^{n+1}_1$. we extrapolated $u^{n+\frac {1} {2}}_1$ $\&$ $v^{n+\frac {1} {2}}_1$. And we put $\theta^{n+\frac {1} {2}}_1 = \theta^{n+1}_1$ then used $$\theta^{n+1}_1 = atan(\frac{v^{n+1}_1}{u^{n+1}_1})= atan(\frac{\alpha*v^{n+\frac{1}{2}}_1}{\alpha*v^{n+\frac{1}{2}}_1})$$ but i wonder why those $\theta$ are same?
I don't understand. What other value would you give it?
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 $\pi$
The text passage contains a series of questions and answers from a CFD (Computational Fluid Dynamics) course, where students are asking for clarifications on specific concepts and equations, and the professor is providing detailed responses.
multiple_questions_with_answers
Given a text passage, determine:
    1. If it contains a mathematical question (including word problems or calculations)
    2. If an answer to that mathematical question is provided in the text

First, describe the content structure you found in 1-2 sentences.

Then provide your analysis in the following format:
TYPE: <one of the following values>
- NO_QUESTION
- SINGLE_QUESTION
- SINGLE_QUESTION_WITH_ANSWER
- MULTIPLE_QUESTIONS
- MULTIPLE_QUESTIONS_WITH_ANSWERS
system
Introduction to CFD Questions & Answers
 Question by Student 201427564 Professor, I have a question about $\phi(r)$. In the table, $\phi(r)=max(0, min(1,r))$. But last class, you wrote like this. ${({\phi^{+}}_{i+ \frac {1} {2}})}_{1} = max(0,min(1, 2{r^{+}}_{i}))$ Why did you use $2{r^{+}}_{i}$ rather than ${r^{+}}_{i}$ ?
 06.01.17
Both $\phi=\max(0,\min(1,r))$ and $\phi=\max(0,\min(1,2r))$ respect the rule of the positive coefficients and reduce to first order at extrema and are hence valid. But $\phi=\max(0,\min(1,2r))$ is better because it is closer to the second-order stencil. 1.0 point bonus.
 Question by Student 201227147 Professor, I have a question about assignment 8 question #2-(b). Last class, you calculated $r _{i} ^{-}$ to find out $\phi _{i+1/2} ^{-}$ because you used this relationship I guess: $$\phi _{i+1/2} ^{-} = max(0, min(1,2r _{i} ^{-} ))$$ However, I think $r _{i} ^{-}$ should be $r _{i+1} ^{-}$ because $\phi _{i+1/2}$ is $\phi _{i+1/2} ^{-}$. Is it right? or is there some reasons you calculated $r _{i} ^{-}$?
Hm no, if we set $\phi _{i+1/2} ^{-} = \max(0, \min(1,2r _{i+1} ^{-} ))$ then we should define $r_{i+1}^-\equiv\frac{u_i-u_{i+1}}{u_{i+1}-u_{i+2}}$. However, because $r_i^-\equiv\frac{u_i-u_{i+1}}{u_{i+1}-u_{i+2}}$ then we have to set $\phi _{i+1/2} ^{-} = \max(0, \min(1,2r _{i} ^{-} ))$. 1 point bonus.
 Question by Student 201227147 I have another question about $r_{i+1}^-$. In the table, $r_{i} = \frac{u_{i+1}-u_{i}}{u_{i}-u_{i-1}}$. But you calculated $r_{i}^-$ with $r_{i+1}^-\equiv\frac{u_i-u_{i+1}}{u_{i+1}-u_{i+2}}$. Does it mean that the equation in the table is assumed positive upwind (from left($i-1$) to right($i+1$)) so that notations should be from right($i+2$) to left($i$) when I apply it in negative upwind case?(it means $i-1$->$i+2$, $i$->$i+1$, and $i+1$->$i$)By the way, Does your answer about previous question mean that there's just difference in notating $r$ and use same equation?
I guess your concerns are due to the fact you are using an older version of tables.pdf.. The tables have changed slightly in the last few days. After downloading the latest version, if you still have some concerns, ask the question again below.
 Question by Student 201238707 Professor, I have a question about subsonic inflow's velocity angle. Why those are same? $$\theta^{n+\frac {1} {2}}_1 = \theta^{n+1}_1$$ because we assumed steady-state?
 06.05.17
I don't recall this step. You need to put your question into context so I can recall why we did this.
 Question by Student 201238707 when we found velocity vector $u^{n+1}_1$ $\&$ $v^{n+1}_1$. we extrapolated $u^{n+\frac {1} {2}}_1$ $\&$ $v^{n+\frac {1} {2}}_1$. And we put $\theta^{n+\frac {1} {2}}_1 = \theta^{n+1}_1$ then used $$\theta^{n+1}_1 = atan(\frac{v^{n+1}_1}{u^{n+1}_1})= atan(\frac{\alpha*v^{n+\frac{1}{2}}_1}{\alpha*v^{n+\frac{1}{2}}_1})$$ but i wonder why those $\theta$ are same?
I don't understand. What other value would you give it?
 Previous   1  ...  9 ,  10 ,  11 ,  12    Next  •  PDF 1✕1 2✕1 2✕2
 $\pi$
user
The text passage contains a series of questions and answers from a CFD (Computational Fluid Dynamics) course, where students are asking for clarifications on specific concepts and equations, and the professor is providing detailed responses.

TYPE: MULTIPLE_QUESTIONS_WITH_ANSWERS