Fardin,
It’s not any tetrahedral mesh, only a 4 node tet element. By default, Ansys will create a 10 node tet. You must change the Element Order to Linear on the Mesh to get a 4 node tet.
Complex shapes should deliver pure tet elements. You can turn on Mesh Quality metric to see that there are only tet elements.
Simpler shapes may generate Hex elements.
Insert a Mesh Method and select the body to force the mesh to be Tet elements. Note that there are two choices for Algorithm. Patch conforming forces the mesher to follow the edges of every face. Patch Independent allows the mesher to ignore some of face edges and generally results in fewer and better quality elements.
I used a Modal anlysis to mesh this and when I click on the Solution branch in the outline, I can click the Write Input File in the Tool section of the ribbon.
Ansys offers a choice of file extensions, either .dat or .inp but both give the same content. You can rename the file to .ans after it is written.
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