How to connect to a named SQL Server instance without specifying its name?
If there is no default instance, then you could force the named instance to listen on port 1433.  SQL Server Configuration Manager, then navigate to the networking bit and turn off dynamic ports.  

This article goes into details on how you can do that for multiple instances running on the same server, but it gets complicated fast.  How to Add a Hostname alias for a SQL Server Instance.  

So there are the methods, but why do you want to do it that way?