How to keep the velocity of a rigidbody2d while changing its direction according to rotation?

For the last few days I've been trying to have a rigidbody2d rotate while keeping its current velocity only changing where the velocity is directed. After some research, this is what I've come up with:

             var v:float;
             v = rigidbody2D.velocity.magnitude;
            
            var cos=Mathf.Cos(gameObject.rigidbody2D.rotation);
            var sin=Mathf.Sin(gameObject.rigidbody2D.rotation);
            
            var unitvector : Vector2;
            unitvector = Vector2(cos,sin);
            unitvector=unitvector.normalized;
            
            var x : float;
            var y : float;
            
            x=unitvector.x;
            y=unitvector.y;
            
            gameObject.rigidbody2D.velocity=Vector2(x*v,y*v);   

However, this only makes the object stand still in the air slighty wiggling back and forth when I press the key. What's wrong with my solution and how can I fix it?