Not able to install .ipa via iTunes after updating to iOS 9.3.1
Finally, I know we need the enterprise account for in house distributions. 

Alternate solutions are using


Using third party's solution, I used https://www.diawi.com/. It works perfect.
Using your apple developer account, add your devices' UDID number and used development team profile to install. Only 100 devices are allowed.
Good luck!