The influence of structural vibrations on piezoelectric energy harvesters' performance is already documented in the literature. Testing of cantilevered type piezoelectric transducers was performed in this work, which confirmed that the voltage output of the piezo-film transducers largely used in studies assuming flow-induced excitation is affected by structural vibrations transported to its base. Aiming to exclude the base vibration effect, two piezoelectric energy harvesting (PEH) test rigs isolated from structural vibrations were constructed and tested at the Laboratory of Fluid Mechanics and Turbomachinery in the Aristotle University of Thessaloniki (LFMT, AUTh). In both cases plastic attachments were mounted on the piezo-films to increase their voltage output range. The first set up created air flow excitation using a low power axial fan (set up A) and the second using a centrifugal fan (set up B). The Reynolds numbers ranged at 5000-110,000. The maximum swirl number was 0.5 in both set ups. Traverse mechanisms were employed to study the effect of the harvesters' distance from the source of excitation on their power output. Both harvesters demonstrated higher power outputs for higher fan speeds. The power output of the harvesters was found to increase with the increase of the voltage root mean square (rms) value. The maximum power harvested was 3.75 mu W and it was observed at the highest fan speed of set up B.