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Sof_70_Usthb June 26, 2011 18:00

Results of CFX Simulations
 
Helo,
I've done simulations, usin' CFX, on rotor passages. In the results i have noticed negative pressure values. I know that negative velocity values means that the fluid particule is movin' in the opposite direction, but i dont understand the meanin' of negative presuure values. Also, in papers reserchers show countours containin' regions of negative pressure.
NB: I'm speakin' about countour pressure values, not values of pressure difference witch can mean that the flow is in opposite direction.
I'll be gratefull if somebody explaine to me this.
Thanks.

Sof_70_Usthb June 26, 2011 18:35

turbomachinery velocity diagram in CFX
 
Hello,
Usin' CFX Simulations on compressor passages, I have difficulties understandin' the absolute velocity and the relative velocity knowin' that in my results i have countours of Cm; W; velocity; ...
I know that C=W+u; when C absolute velocity W relative velocity u speed of rotor, but in CFX documentation, i have found somewhere (with figures) the decompostion of V to streamwise velocity; spanwise velocity; circumferential velocity or to axial velocity; radial velocity, circumferencial velocity and also to Blade to blade velocity ...etc.
So is V absolute or relative velocity; or can we say that C= (that V)+u; and how can we obtain in resutls Cu velocity; Cr velocity; Wu velocity; Wm velocity; Wr velocity.
Can somebody help me understandin' this, or tell me in what part exactly of CFX documentation can i found the details of that (maybe i didn't searche well in it).

ghorrocks June 26, 2011 21:19

Pressure is measured relative to a reference pressure. A negative pressure simply means the pressure is less than the reference pressure. If the reference pressure is one atmosphere then a nagative pressure simply means a vacuum.

Sof_70_Usthb July 9, 2011 06:15

meanin' of Negative pressure values
 
Dear Ghorrocks,
Thank you so much for helpin' me understandin' negative pressure values.


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