Not getting vortex shedding

Donton · August 25, 2017, 08:03

Hello everyone,

I have started working in the area of CFD recently. Currently I am trying to write a C++ code to simulate 2D flow past a fixed circular cylinder using the immersed boundary method with finite volume and staggered grid, fractional step method as explained in http://www.sciencedirect.com/science...21999101967786 . Though in this paper the authors are using RK method for time advancement I am using Adams Basforth (convection term) and Crank Nicolson (diffusion) for time advancement. To evaluate the cell face values I have used central difference or liner interpolation. I am also using an uniformly distributed structurred rectangular mesh. With this at low Re number (Re<40) I am getting some what good result with the two recirculating zones behind the cylinder. But when I increased the Re number even at Re=100 I am not getting any shedding. Only the recirculating regions getting stretched along the direction of the flow.

Is it because of the linear interpolation for the cell face values?

For top and bottom wall I implemented the boundary condition as u=0,v=0, normal gradient of the pressure correction is zero and for the inlet and outlet boundary u=1,v=0, normal gradient of the pressure correction is zero.

Pleas help me stating what may be the possible reasons and solutions...

Thanks in advance.

FMDenaro · August 25, 2017, 10:38

Have you tried to run the code for enough long time? Do you monitor in time the velocity at some stations?

The code can introduce numerical viscosity by linear interpolation and a more refined grid could be required near the walls. Finally, the height of the domain should be enough large to allow the boundaries to be far from the cylinder. Similarily, the ourflow section must be far from the shedding.

Donton · August 28, 2017, 06:36

Thank you. When I run the code for a long time initially it is converging, the residual flux going 10^-2 order but after some 5000 iterations it started increasing resulting it to diverge. Any suggestion?
Instead of the central difference if I use upwind for the cell face values, Will that help?

August 25, 2017, 08:03	Not getting vortex shedding	#1
Donton New Member Donton Join Date: Aug 2017 Posts: 6 Rep Power: 8	Hello everyone, I have started working in the area of CFD recently. Currently I am trying to write a C++ code to simulate 2D flow past a fixed circular cylinder using the immersed boundary method with finite volume and staggered grid, fractional step method as explained in http://www.sciencedirect.com/science...21999101967786 . Though in this paper the authors are using RK method for time advancement I am using Adams Basforth (convection term) and Crank Nicolson (diffusion) for time advancement. To evaluate the cell face values I have used central difference or liner interpolation. I am also using an uniformly distributed structurred rectangular mesh. With this at low Re number (Re<40) I am getting some what good result with the two recirculating zones behind the cylinder. But when I increased the Re number even at Re=100 I am not getting any shedding. Only the recirculating regions getting stretched along the direction of the flow. Is it because of the linear interpolation for the cell face values? For top and bottom wall I implemented the boundary condition as u=0,v=0, normal gradient of the pressure correction is zero and for the inlet and outlet boundary u=1,v=0, normal gradient of the pressure correction is zero. Pleas help me stating what may be the possible reasons and solutions... Thanks in advance.

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August 25, 2017, 10:38		#2
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,768 Rep Power: 71	Have you tried to run the code for enough long time? Do you monitor in time the velocity at some stations? The code can introduce numerical viscosity by linear interpolation and a more refined grid could be required near the walls. Finally, the height of the domain should be enough large to allow the boundaries to be far from the cylinder. Similarily, the ourflow section must be far from the shedding.

August 28, 2017, 06:36		#3
Donton New Member Donton Join Date: Aug 2017 Posts: 6 Rep Power: 8	Thank you. When I run the code for a long time initially it is converging, the residual flux going 10^-2 order but after some 5000 iterations it started increasing resulting it to diverge. Any suggestion? Instead of the central difference if I use upwind for the cell face values, Will that help?