LabVIEW wil take care of the memory management. Thus, there is no explicit way for you to free memory in LabVIEW. In fact, I don't think you should do that by yourself. LabVIEW has quite good memory optimation strategy and it wll track all the memory usage in your VI and reuse/free memory when there is no reference to it. As for TDMS, once the data is read out from the TDMS VIs, there will be no additional data copy inside.
