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February 21, 2018, 09:45 
streamwise pressure gradient

#1 
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G Ionut
Join Date: Sep 2016
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Hello,
I need some help to calculate the streamwise pressure gradient for my UDF in Ansys Fluent. I have considered two 2D cases: Case A, a horizontal pipe and Case B, a tilted pipe (as in the figures below). The two cases have the same geometry, mesh and coordinate system, the difference is that the second pipe is tilted. For Case A the streamwise pressure gradient is found using the C_P_G(c,t)[0] function from fluent, the pressure gradient along the xaxis. For Case B the above function is not valid. How can the streamwise pressure gradient can be calculated for the considered case? 

February 21, 2018, 12:19 

#2 
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Join Date: Nov 2013
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Just use the definition of streamwise pressure gradient.
The streamwise pressure gradient is the inner product between the pressure gradient and the unit vector in the direction of the flow. How do you calculate the unit vector in the direction of the flow? Divide the velocity vector by its magnitude. Code:
real UVDF[ND_ND]; /*UVDF = unit vector in direction of Flow */ real flowmag; ... flowmag=sqrt(C_U(c,t)*C_U(c,t)+C_V(c,t)*C_V(c,t)+C_W(c,t)*C_W(c,t)); UVDF[0]=C_U(c,t)/flowmag; UVDF[1]=C_V(c,t)/flowmag; UVDF[2]=C_W(c,t)/flowmag; Code:
real SPG; /* SPG = streamwise pressure gradient */ ... SPG = UVDF[0]*C_P_G(c,t)[0]+UVDF[1]*C_P_G(c,t)[1]+UVDF[2]*C_P_G(c,t)[2]; 

February 21, 2018, 12:43 

#3  
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G Ionut
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fluent, pressure gradient, udf 
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