This work is concerned with finding the optimal nozzle length for a piezoelectric harvester. Studies are carried out experimentally and numerically. First, the optimum Reynolds number is found. It was then numerically studied to find the optimum nozzle length. As a result, the most efficient design is produced and studied experimentally. The results found are compared. The "target function" is to find the best turbulent kinetic energy at the appropriate nozzle length.