Dear Jijo,
the DKT case is a very dynamic case and minimal changes can cause a huge deviation, as has been seen in the literature several times. For example, Koblitz et al [1] pointed out that a different contact model caused the difference to the results of Uhlmann [2].
As far as I know, there was no contact model in 1.5, which could lead to an incorrect representation. One has been added in 1.6, but differences in the model, particle properties, use of a ε boundary, and other differences from the literature could lead to different results.
In conclusion, it is likely that the results don’t exactly match other results in the literature, since the contact model has not been used before.
Best regards,
Jan
[1]: Koblitz, Arndt Ryo, et al. “Direct numerical simulation of particulate flows with an overset grid method.” Journal of computational physics 343 (2017): 414-431.
[2]: Uhlmann, Markus. “An immersed boundary method with direct forcing for the simulation of particulate flows.” Journal of computational physics 209.2 (2005): 448-476.