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OpenLB – Open Source Lattice Boltzmann Code Forums on OpenLB General Topics Lift and Drag Coefficient Calculation in OpenLB

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• #8898
gdhir
Participant

Hi,

I hope you are doing well. I am currently working on establishing grid convergence for the flow over a single circular cylinder in OpenLB at a Reynolds number of 100. The problem is time periodic. Grid convergence needs to be established for reasons related to a review.

The problem dimensions involve a domain of size 80D X 80D where D refers to the cylinder diameter. Grid convergence analysis is performed for resolution of size 10, 20, 30, 40 lu per diameter and so on. Since the flow is time periodic, the rms lift and the average drag coefficients can serve as global indicators of convergence.

I wanted to know what is the procedure utilized to calculate the lift and the drag coefficients so that I can take into account any accuracy issues/uncertainties while establishing convergence. For instance, lift coefficient could be calculated as Cd = integral of Cp sin(phi) where phi is the angle from the x axis (I am not sure if this is the procedure utilized). I just wanted to know a little bit more detail and if its possible to make it more accurate in terms of better quadrature and so on.

My main objective is to reproduce a second order accurate curve on log scale on error versus h plot.

I will be very thankful for some help on it.

#8899
mathias
Keymaster

The implementation is the momentum exchange by Ladd et al. and there is a second version which is based on Junk et al.. Both have been well validated, e.g. cf. the examples cylinder2d and cylinder3d in OpenLB.

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