Wildcard chars are allowed at begining or end or both but not the middle. The following would be allowed and would include your target row.
Dv.rowfilter="Name like '%a m%'"
Operator LIKE is used to include only values that match a pattern with wildcards. Wildcard character is * or %, it can be at the beginning of a pattern '*value', at the end 'value*', or at both '*value*'. Wildcard in the middle of a patern 'va*lue' is not allowed. From
DataView RowFilter Syntax [C#][
^]