If there are multiple sub interfaces and vlans are created with different security levels
Will the traffic flows from high security level interface to low security level interface?.
What is the case if we have the acls in place?
Thanks in advance
Depends on what you are trying to do with your acl.
There is an implicit deny at the end of an acl so anything not explicitly permitted or denied in your acl will be dropped.
The ASA always allows traffic from higher to lower by default. If you have ACLs in place, then you'll need to allow the traffic through.
For example, if you have an ACL applied to the inside interface and the inside interface has a security level of 100, then that ACL will need to allow what you want out. If you want users to be able to surf the web, but nothing else, your acl will allow port 80 out, but deny everything else.