I am facing problem in creating the .apk file using the ant script . The generated .apk named as _unaligned.apk instead of .apk and on installing the _unaligned.apk file to
What ant command are you running at the command / terminal prompt?
I have been having different problems with manually running ant (Repackage apk file to contain custom assets what build tool to use) and there might be some info on that thread to help you.
Alternatively, remember that one needs to sign the apk file before deploying it (see Joubarc's link).