Unsteady flow over 2d rectangular box.

techctrl · February 14, 2015, 14:52

Hi. I'm trying to simulate an unsteady flow over a 1x1 rectangular box, but the Cd & Cl plots don't reach steady oscillations even after 30000 iterations.

My time step is 0.05 seconds, iterations per time step 50, SIMPLE scheme, second order transient formulation. Residuals are set at 1e-06 and reference values for area and length are 1 m2 and 1 m. Fluid is air.

Boundary Conditions are:
velocity-inlet (u = 1 m/s, v=0)
pressure outlet (gauge pressure = 0)
Symmetry
Wall (no-slip, u = 1 m/s, v = 0)

Velocity has been defined for the bottom wall because I'm trying to model a moving object in a fluid domain.

Any advice? Does the solution require more time steps to be passed in order to reach the desired results?

techctrl · February 16, 2015, 00:40

Anyone.....?

flotus1 · February 16, 2015, 05:26

Estimate the Reynolds number of the flow you are simulating.
Think again if you really expect the vortex shedding to be periodic with only one frequency although you are using no turbulence model.

techctrl · February 16, 2015, 06:03

I did manage to obtain a steady solution with a reynolds number of 40, anything higher than 45 causes the flow to become unsteady and vortex shedding to occur.

I did not know that about turbulence modeling, thank you for stating it.

February 14, 2015, 14:52	Unsteady flow over 2d rectangular box.	#1
techctrl New Member Join Date: May 2014 Posts: 16 Rep Power: 12	Hi. I'm trying to simulate an unsteady flow over a 1x1 rectangular box, but the Cd & Cl plots don't reach steady oscillations even after 30000 iterations. My time step is 0.05 seconds, iterations per time step 50, SIMPLE scheme, second order transient formulation. Residuals are set at 1e-06 and reference values for area and length are 1 m2 and 1 m. Fluid is air. Boundary Conditions are: velocity-inlet (u = 1 m/s, v=0) pressure outlet (gauge pressure = 0) Symmetry Wall (no-slip, u = 1 m/s, v = 0) Velocity has been defined for the bottom wall because I'm trying to model a moving object in a fluid domain. Any advice? Does the solution require more time steps to be passed in order to reach the desired results? Last edited by techctrl; February 15, 2015 at 05:44.

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February 16, 2015, 00:40		#2
techctrl New Member Join Date: May 2014 Posts: 16 Rep Power: 12	Anyone.....?

February 16, 2015, 05:26		#3
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,400 Rep Power: 47	Estimate the Reynolds number of the flow you are simulating. Think again if you really expect the vortex shedding to be periodic with only one frequency although you are using no turbulence model.

February 16, 2015, 06:03		#4
techctrl New Member Join Date: May 2014 Posts: 16 Rep Power: 12	I did manage to obtain a steady solution with a reynolds number of 40, anything higher than 45 causes the flow to become unsteady and vortex shedding to occur. I did not know that about turbulence modeling, thank you for stating it.