Hello packets used to construct neighbor table for all the nodes. IN AODV you can use Hello packets or Link layer detection to create a neighbor list. in default AODV works with link layer detection. If you want to use hello packets you have to command the below lines in aodv.cc
//#ifndef AODV_LINK_LAYER_DETECTION
//#endif // LINK LAYER DETECTION
now you can verify hello packets operation using your trace files.