I have two sets of output files i.e., rm2turbPipe0.f00001 and rmsturbPipe0.f00001 from Nek5000. The files are with the same mesh and I want to use them to calculator. I had followed the previosu topic Calculator from different field sources?, but my Append Attributes 1 and Append Attributes 2 (please see the attchment) stay under the two different files, so that the calcualtor cannot to combine them together. I am not sure it is because my operation, the version of Paraview or the output file of Nek5000. Could anyone give any suggestions? Much appreciated.
On the Pipeline Browser, with both rm2turbPipe0.f00001 and rmsturbPipe0.f00001 selected while holding down the Ctrl key, then Append Attributes filter must be applied.
Great, it works. 
Kyoshimi, thanks for you instant reply!