Nowadays, attention to environmental energies and using them as a source of energy for low-power and wireless electronic equipment have been highlighted. There are several ways to harvest environmental energies, including use of piezoelectric patches which are widely used on a micro scale due to their simplicity and high flexibility. The fluid flow is one of the most important and most widely available sources for energy harvesting. But the effective conversion of the kinetic energy in a fluid into the strain energy of the piezoelectric structure has always been one of the challenges ahead. In this study, a fluidic oscillator was used to solve this problem. Fluidic oscillators without any external and moving bodies cause fluctuations in fluid flow. The activities carried out in this study are divided into two experimental and numerical sections. In the first step, the oscillator characteristic curve, which shows the relation between the flow velocity and the frequency of fluid oscillations, have been obtained experimentally. According to the results, the oscillator characteristic curve is linear so that Strouhal number is almost constant and equal to 0.13 for the Reynolds number in the range of 10000-33000. Then, by placing a piezoelectric beam in different positions, the effects of the parameters such as the inlet flow velocity and the position of the beam on the energy harvesting have been investigated. By examining the output voltage of the piezoelectric patch, it was observed that the piezoelectric beam vibrates with a combination of natural frequency and the frequency of fluid oscillations. When the frequency of fluid oscillations is equal to the natural frequency of the piezoelectric beam, the resonance occurs and harvesting energy reaches its maximum and then decreases. In the following, the effect of the added mass and the equivalent electrical resistance on the output electrical power is investigated. The maximum effective electrical power density, which is normalized with the inlet flow velocity, is equal to 379.7 W.s/m 4 at the Reynolds number of 37000 and the energy harvesting efficiency is 0.73%. It is important to note that the goal of micro-scale energy harvesting is to use the wasted energies in the surrounding environment and its efficiency should not be compared with the methods such as thermal power plants, wind turbines and etc. In some flow control applications, it is necessary that the frequency of fluid oscillations within the oscillator be constant and independent of the inlet flow velocity. To achieve this goal, by placing aluminum beams with different natural frequencies inside the main chamber, the frequency of fluid oscillations are independent of the inlet velocity and for a specified range of inlet velocity, it is within the natural frequency range of the beam. Then, through ANSYS CFX software and two-dimensional and transient numerical simulation, the flow pattern and the oscillator characteristic curve is obtained. In the Reynolds numbers less than 33000, the average of deviations from the experimental data are about 3.18%. Then, by simulating a three-dimensional and transient fluid-structure interaction, the piezoelectric beam was simulated in the oscillator output and the oscillatory behavior of the beam and the pattern of flow around the beam was investigated. By examining the vertical displacement of the free end of beam, it was observed that, like experimental data, the beam vibrates with a combination of natural frequency and the frequency of fluid oscillations. As the beam becomes farther away from the oscillator output, the interaction of the beam and output jet flow decreases so that the beam displacement decreases. Finally, by simulating the interaction of the aluminum beams and the fluid flow, controlling the frequency of the fluid oscillations in the oscillator was investigated. According to the results, the fluid oscillations are independent of the inlet velocity and as the length of the beam increases, the pressure oscillations inside the oscillator are amortized. Keywords: Energy harvesting, Piezoelectric patches, Fluidic oscillator, Fluid oscillations, Resonance, Fluid-structure interaction, Frequency control of the fluid oscillations