Results of CFX Simulations

Sof_70_Usthb · June 26, 2011, 18:00

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

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

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

June 26, 2011, 18:00	Results of CFX Simulations	#1
Sof_70_Usthb New Member AyAhSof Join Date: Jun 2009 Posts: 8 Rep Power: 16	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.

June 26, 2011, 18:35	turbomachinery velocity diagram in CFX	#2
Sof_70_Usthb New Member AyAhSof Join Date: Jun 2009 Posts: 8 Rep Power: 16	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).

July 9, 2011, 06:15	meanin' of Negative pressure values	#4
Sof_70_Usthb New Member AyAhSof Join Date: Jun 2009 Posts: 8 Rep Power: 16	Dear Ghorrocks, Thank you so much for helpin' me understandin' negative pressure values.

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June 26, 2011, 21:19		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	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.