*5.2. Validation of Numerical Results*

The numerical results for the internal and external flow domains were validated using the experimental data of Melton et al. [18]. Figure 7 shows the comparison between predicted and measured jet frequencies for the internal flow of the fluidic oscillator. The relative error is reduced as the mass flow rate increases and reaches about 2% at mass flow rate larger than 0.7 g/s.

In previous work [29], numerical results were obtained using the same numerical methods used in the present work and validated for the interaction between internal and external flows of the fluidic oscillators. The results were compared with experimental data [18] for the pressure distribution and lift coefficient of a NACA0015 airfoil with a flap angle of 40◦, as shown in Figure 8 and Table 4, respectively. In Figure 8, the distribution of the pressure coefficient shows some deviations near the leading edge on the lower surface in both cases with and without oscillators. However, it shows good agreement on the upper surface, which shows lower pressure. In the case of the lift coefficient, the difference between numerical and experimental [18] results decreases rapidly as the angle of attack increases, as shown in Table 4. Several factors such as flap angle, oscillator location, and flow rate seem to be involved in the error.

**Figure 7.** Validation of numerical results for frequency of fluidic oscillator using experimental data (Melton et al. [18]).

**Figure 8.** Validation of numerical results for pressure coefficient using experimental data (Melton et al. [18]) for the NACA 0015 airfoil with a flap and fluidic oscillators (x0/c = 0.7, α = 8◦, *δ<sup>f</sup>* = 40◦ and y/s = 0.5) performed by Kim and Kim [29]. (**a**) Case I and (**b**) Case II.


