Question: i have added a splash screen to my application by adding Default.png.
the splash screen works fine in the simulator but not showing on real device

Answer: 
The file name must be Default.png (with a capital D). Also, do a clean/rebuild of the entire project to ensure the most recent version of the file is being included in the project.
Sometimes this issue hapens, when .png file was renamed from .jpg file. 
So, for example, you had image.jpg, you've renamed in to image.png, and using this image.png. It'll be correctly displayed in simulator, and won't work on device