Fluid structure interaction in ANSYS-CFX

Amol · February 12, 2011, 16:00

Hello everybody,
i am doing flutter analysis with two way FSI, coupling ANSYS(transient analysis system) and CFX. structural domain is panel of 5 mm thickness and fluid has supersonic flow above it. now problem is that when i am keeping large deflection ON in mechanical part of the ANSYS (i.e. by doing this i am considering geometric non linearity in panel) panel shows nice limit cycle oscillations in it (of amplitude 0.004 m without giving any initial disturbance to panel). but when i am doing same simulation with keeping large deflection OFF (i.e. geometric nonlinearity removed) it should show large deflections in panel instead of limit cycle oscillations. but don't know why i am getting very small deflections in panel (amplitude of just some nanometer). what might be going wrong?? please help................

peiji1984 · February 22, 2011, 12:52

I have the same question! I did a FSI calculation for a water pump impeller, and it seems to be linear problem(0.1-0.5mm deflection according to the test). So I have tried to keep large deflection off, the values are small, like 100 times less than experiment. One way coupling seems right. When I keep large deflection on, the deflection curve is not quite right. It is confusing! So I want to know, what has happened in software when large deflection is off.

va-ta-cfd · April 4, 2011, 02:08

Hello
I have the same problem and the structure (a long plate behind a rigid cylinder) has very little cross flow oscillation due to the vortex shedding.
it would be very helpful if any body has got the reason .

thanks
V.T

singer1812 · April 4, 2011, 10:49

Large deflections must be on for 2way FSI. Loads will be always applied to non-deformed body (within Mechanical Ansys) if large deflections are not on.

Amol · April 4, 2011, 13:18

Quote:

Originally Posted by singer1812

Large deflections must be on for 2way FSI. Loads will be always applied to non-deformed body (within Mechanical Ansys) if large deflections are not on.

even though the load is applied on non deformed bodies when we keep geometric nonlinearity OFF, what is the reason to get small deformations in structures as compared to the case when we keep geometric nonlinearity ON.
Is there any other option available in mechanical ANSYS while doing 2 way FSI using ANSYS-CFX????

February 12, 2011, 16:00	Fluid structure interaction in ANSYS-CFX	#1
Amol New Member Amol Join Date: Feb 2011 Posts: 4 Rep Power: 15	Hello everybody, i am doing flutter analysis with two way FSI, coupling ANSYS(transient analysis system) and CFX. structural domain is panel of 5 mm thickness and fluid has supersonic flow above it. now problem is that when i am keeping large deflection ON in mechanical part of the ANSYS (i.e. by doing this i am considering geometric non linearity in panel) panel shows nice limit cycle oscillations in it (of amplitude 0.004 m without giving any initial disturbance to panel). but when i am doing same simulation with keeping large deflection OFF (i.e. geometric nonlinearity removed) it should show large deflections in panel instead of limit cycle oscillations. but don't know why i am getting very small deflections in panel (amplitude of just some nanometer). what might be going wrong?? please help................

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February 22, 2011, 12:52		#2
peiji1984 New Member Ji Pei Join Date: Nov 2010 Posts: 8 Rep Power: 16	I have the same question! I did a FSI calculation for a water pump impeller, and it seems to be linear problem(0.1-0.5mm deflection according to the test). So I have tried to keep large deflection off, the values are small, like 100 times less than experiment. One way coupling seems right. When I keep large deflection on, the deflection curve is not quite right. It is confusing! So I want to know, what has happened in software when large deflection is off.

April 4, 2011, 02:08		#3
va-ta-cfd New Member Vahid Join Date: Jan 2011 Posts: 23 Rep Power: 15	Hello I have the same problem and the structure (a long plate behind a rigid cylinder) has very little cross flow oscillation due to the vortex shedding. it would be very helpful if any body has got the reason . thanks V.T

April 4, 2011, 10:49		#4
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 21	Large deflections must be on for 2way FSI. Loads will be always applied to non-deformed body (within Mechanical Ansys) if large deflections are not on.