The params can be passed to controller method variables in two methods 1. Through apexpages.currentpage().getparameter method as explained in this post http://salesforce.stackexchange.com/questions/24175/passing-method-parameters-with-apexactionfunction 2. Though a normal get set method as explained in this article http://www.salesforce.com/us/developer/docs/pages/Content/pages_compref_actionFunction.htm
1. Through apexpages.currentpage().getparameter method as explained in this post http://salesforce.stackexchange.com/questions/24175/passing-method-parameters-with-apexactionfunction
2. Though a normal get set method as explained in this article http://www.salesforce.com/us/developer/docs/pages/Content/pages_compref_actionFunction.htm
Hope this helps !!
i mean to say that small correctionit is not a visual pae in visual flow
How to store apex param passed value into visual flow variable