[pallabi]

Why k-epsilon model is used most commonly?

[Arjun_kalkur]

Because it gives you the realistic approach of freestream subsonic air. Although k-epsilon behaves very bad in adverse pressure gradients.

[lcarasik]

Originally Posted by Arjun_kalkur

Because it gives you the realistic approach of freestream subsonic air. Although k-epsilon behaves very bad in adverse pressure gradients.

Also, it's reasonable cheap (computationally) to utilize and gives a sufficient answer for a lot of problems in an industrial setting.

[sbaffini]

Probably, being among the firsts 2 eq models developed, there is a relatively large body of experience on using it vs using more recent models. To the point that, in some fields, despite it being close to useless, it has been included in regulations.