first please upgrade to latest release 2020R1.
use 5 times infront, 10 times in rear, 5 to 7 times on sides. you can use symmetry to keep cell count low.
you can use body of influence for refinement. please check following.
https://forum.ansys.com/forums/topic/body-of-influence-for-sizing/
if you are using k-w sst, you need fine meshing near wall. you should aim for y+ ~ 1 to 5.
Regards,
Keyur
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