simple problem yet complex error: analysis of flow through diffuser

karthikn21590 · January 26, 2012, 14:59

Hello everyone,

I am new to both CFD and this forum. I tried to simulate turbulent flow through a diffuser. It is a 3D diffuser model. I used K-Eps model with a turbulence intensity of 1%. I used an inlet velocity boundary condition (45m/s)
and an outlet pressure condition (101325 pa). The diffuser exhausts to the atmosphere. The simulation runs fine and the pressure contours are fine. But I m unable to obtain a velocity contour. The velocity over the entire length is 0. Though the legend says that the max velocity is 46m/s, it doesnt reflect on the model. Please help. I m having a tough time with this. Do atmospheric exhausts create problems generally? My professor tried the problem in Star CCM+ and everything is fine. I m experiencing this problem in Fluent

swiftaircraft · January 26, 2012, 15:31

Have you tried to plot the velocities on the wall of the diffuser? If so they will be zero due to the no slip condition. Have you made a plane through the centre of the model and plotted the contours on that. The other way is to select the wall and turn off "Node value" in the contour block. Then it will show the value at the cell center.

karthikn21590 · January 27, 2012, 01:52

thanks a lot Swiftaircraft. I changed the wall condition to free slip and it works perfectly

January 26, 2012, 14:59	simple problem yet complex error: analysis of flow through diffuser	#1
karthikn21590 New Member karthiek Join Date: Jan 2012 Posts: 8 Rep Power: 14	Hello everyone, I am new to both CFD and this forum. I tried to simulate turbulent flow through a diffuser. It is a 3D diffuser model. I used K-Eps model with a turbulence intensity of 1%. I used an inlet velocity boundary condition (45m/s) and an outlet pressure condition (101325 pa). The diffuser exhausts to the atmosphere. The simulation runs fine and the pressure contours are fine. But I m unable to obtain a velocity contour. The velocity over the entire length is 0. Though the legend says that the max velocity is 46m/s, it doesnt reflect on the model. Please help. I m having a tough time with this. Do atmospheric exhausts create problems generally? My professor tried the problem in Star CCM+ and everything is fine. I m experiencing this problem in Fluent

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January 26, 2012, 15:31		#2
swiftaircraft Member David Stanbridge Join Date: Apr 2010 Location: Norwich, UK Posts: 59 Rep Power: 16	Have you tried to plot the velocities on the wall of the diffuser? If so they will be zero due to the no slip condition. Have you made a plane through the centre of the model and plotted the contours on that. The other way is to select the wall and turn off "Node value" in the contour block. Then it will show the value at the cell center.

January 27, 2012, 01:52		#3
karthikn21590 New Member karthiek Join Date: Jan 2012 Posts: 8 Rep Power: 14	thanks a lot Swiftaircraft. I changed the wall condition to free slip and it works perfectly