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-   -   "Velocity.curl" in CFX-post (https://www.cfd-online.com/Forums/cfx/78235-velocity-curl-cfx-post.html)

 Jasmine July 15, 2010 16:30

"Velocity.curl" in CFX-post

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 !

 ghorrocks July 15, 2010 19:04

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)

 Jasmine September 13, 2010 19:44

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...

Quote:
 Originally Posted by ghorrocks (Post 267552) 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)

 ghorrocks September 14, 2010 03:22

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.

 Jasmine September 14, 2010 12:10

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.

Quote:
 Originally Posted by ghorrocks (Post 275088) 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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