Transient solution, variable does not change with time

JMOP · February 28, 2014, 05:37

I am attempting to determine the frequency of vortex shedding of a nozzle. The fluid is water. I have set up a steady state solver to provide the initial conditions for a transient solution. The solvers run concurrently and were set up following these instructions.

http://www.ansys-blog.com/multi-conf...te-simulation/

Both the steady state and transient cases are run using Shear Stress Transport as a turbulence model.

I set the time interval to give me a courant number of 5 and ran the transient case for 500 time steps. In the results window I inserted a point just downstream of the nozzle and created a chart of pressure against time. Apart from an initial fluctuation, pressure settles to a value and remains unchanged. I get the same result if I plot total pressure. The steady state solution shows eddy viscosity to be in the order of 0.38Pa S downstream of the nozzle, so I am minded to think that there would be some pressure fluctuation. Can anyone advise me as to what I might be doing wrong?

ghorrocks · February 28, 2014, 15:57

The basics are covered in an FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

February 28, 2014, 05:37	Transient solution, variable does not change with time	#1
JMOP New Member Jamie Join Date: Feb 2014 Posts: 1 Rep Power: 0	I am attempting to determine the frequency of vortex shedding of a nozzle. The fluid is water. I have set up a steady state solver to provide the initial conditions for a transient solution. The solvers run concurrently and were set up following these instructions. http://www.ansys-blog.com/multi-conf...te-simulation/ Both the steady state and transient cases are run using Shear Stress Transport as a turbulence model. I set the time interval to give me a courant number of 5 and ran the transient case for 500 time steps. In the results window I inserted a point just downstream of the nozzle and created a chart of pressure against time. Apart from an initial fluctuation, pressure settles to a value and remains unchanged. I get the same result if I plot total pressure. The steady state solution shows eddy viscosity to be in the order of 0.38Pa S downstream of the nozzle, so I am minded to think that there would be some pressure fluctuation. Can anyone advise me as to what I might be doing wrong?

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February 28, 2014, 15:57		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	The basics are covered in an FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F