Put this formula where you want the result
=SeriesSum(AA11:B12)
And create this VBA Function
Function SumSeries(myRange As Range) As Variant
Dim rStr As String
Dim sh As Worksheet
rStr = myRange.Address
For Each sh In ThisWorkbook.Worksheets
If Left(sh.Name, 6) = "Series" Then SumSeries = SumSeries + Application.WorksheetFunction.Sum(sh.Range(rStr))
Next sh
End Function