I found this plant in Hyderabad city of Telangana State,India.Many people of Hyderabad city have planted this flowering plant.I don't know the name of this plant.If it's flower treated as a circle,the flower has diameter of nearly 6cm length.Can any one tell me what is the name of this plant?
From the twisted overlapping appearance of the petals it is a member of the Apocynaceae family. So I searched for "Apocyanaceae india" and found images consistent with your picture. Good chance it is Allamanda blanchetii or Purple Allamanda. Here is a picture comparable to yours (source/CC0).