Dear all, I am simulating flow past cylinder for Re = 11000 in StarCCM+, for validate the results I am finding mean drag, RMS lift coefficient, and strouhal number. My results and reference values are below. Mean Drag = 1.29 (1.15 s per Norberg(1993)) RMS lift coefficient = 0.84 (0.427 as per Norberg(1993)) Strouhal number = 0.209 ( 0.2 as per Mutlu summer) From the above results, I am getting cd and st is almost near the reference value, but the rms lift coefficient is double the reference value. pls, suggest to me where I have to correct calculation. Thank you.
Do you have already carried out a mesh refinement study (independence of your solution from the underlying mesh) and a time-step study, i.e. studying whether your determined shedding frequency is independent from the applied time resolution of your flow solution?
What about near-wall mesh resolution? What is your y+ of the iunderlying mesh for the given Re number? And with how many mesh cells the boundary layer around the cylinder is getting resolved?
Last but not least - are we talking here about a 2d or a 3d simulation? If 3d - have you studied on how your flow result might depend on the span width of the studied cut-out of the infinitely long cylinder?
Regards,
Dr. Th. Frank.
Dear Thomas,
Thanks for answer. I didnt do mesh and time step study.and its 3D simulation (L/D = 5).
The geometry of the computational domain, in terms of diameter (D),taken for this study is 40D×20D×5D in (X, Y, Z) directions respectively and its shown in Fig.1 with the boundary conditions. The cylinder placed at 10D from inlet, 30D from outlet and 10D from walls, to mitigate the wall effects on forces of cylinder. For all simulations, the length of cylinder is taken as one pitch of helical strakes(5D). The boundary conditions of upstream as velocity inlet, downstream as pressure outlet, side walls as wall with slip condition and top and bottom surfaces are symmetry condition. The wall y+ = 0.4. Near wall mesh size is 4x10e-3m.
So pls refer to some standard reference paper for flow past cylinder(3D) experimental study.
Thank you.
Sarvalogapathi .s : excuse me, but carrying out a literature study is IMHO a standard obligation of a good scientist. Maybe you want to use Google in order to find some standard reference paper for flow past cylinder? There should be many, because it is a frequently studied topic.
In the flow pattern which you posted it can clearly be seen, how your narrow mesh refinement around the von Karman vortex street is damping out the velocity oscillations on the non conformal mesh interfaces of your cut-cell mesh (hanging nodes). This has for sure the potential to limit to a certain extend the amplitude of oscillations in the vortex street to the width of this second finest mesh (since the flow cannot oscillate beyond this 2nd mesh interface).
And the vortex shedding is dampened out completely, if it reaches on the right hand side the interface between the second and third finest mesh. This will affect the pressure distribution on the outlet cross-section with unknown effects upstream (since flow is subsonic).
Regards,
Dr. Th. Frank.
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