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Old   July 15, 2010, 16:30
Default "Velocity.curl" in CFX-post
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I am using Ansys 12. in CFX-post, there are variables "Velocity.curl", "Velocity.curl X", "Velocity.curl Y", and "Velocity.curl Z".

I thought "Velocity.curl" is a vector. But when I used "ave(Velocity.curl)@blade", it gave me a scalar, and this scalar is not the square root of "Velocity.curl X", "Velocity.curl Y", and "Velocity.curl Z".

What is "Velocity.curl" then? Thanks !
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Old   July 15, 2010, 19:04
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It is the magnitude of the Velocity.curl vector, so is just a scalar.

Also the average of the magnitude of a vector field does not equal the sqrt(sum of squares of vector field components). Do the maths and you will find they are not equal.

For instance, (sum(x))^2 does not equal sum(x^2)
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Old   September 13, 2010, 19:44
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Sorry. What is the magnitude of a vector field?
Here is what I got:
Velocity.Curl = 9102;
Velocity.Curl X= 132.4;
Velocity.Curl Y= 1289;
Verlocity.Curl Z= -9.074;

I still could not figure out how 9102 is related to other numbers...



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Originally Posted by ghorrocks View Post
It is the magnitude of the Velocity.curl vector, so is just a scalar.

Also the average of the magnitude of a vector field does not equal the sqrt(sum of squares of vector field components). Do the maths and you will find they are not equal.

For instance, (sum(x))^2 does not equal sum(x^2)
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Old   September 14, 2010, 03:22
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The magnitude is simply sqrt(X^2+Y^2+Z^2). This is basic vector maths, you won't get very far in CFD if you don't know things like that (sorry to be brutally honest).

Velocity.Curl is a vector field, made up of three scalar components Velocity.Curl X, Y and Z. At any point in the field the sqrt(X^2+Y^2+Z^2) will hold, but as I said previously this does not work if you average the variables over the field and expect sqrt(X^2+Y^2+Z^2) to hold on the averaged values.
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Old   September 14, 2010, 12:10
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Thank you, ghorrocks.

I got what you mean.

The values I got is the average value over the field instead of value for a signal point.


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Originally Posted by ghorrocks View Post
The magnitude is simply sqrt(X^2+Y^2+Z^2). This is basic vector maths, you won't get very far in CFD if you don't know things like that (sorry to be brutally honest).

Velocity.Curl is a vector field, made up of three scalar components Velocity.Curl X, Y and Z. At any point in the field the sqrt(X^2+Y^2+Z^2) will hold, but as I said previously this does not work if you average the variables over the field and expect sqrt(X^2+Y^2+Z^2) to hold on the averaged values.
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