When a flying vehicle approaches a surface of water or land, changes occur in the pattern of the fluid flow field around it. This change in flow field eliminates the direct effect on aerodynamics and control of the vehicle. This is more common when the vehicle is landing and taking off, as well as flying at low altitudes, which is called the surface effect. In this research, the phenomenon of surface effect and its effect on aerodynamic coefficients and flow pattern around NACA0012 airfoil in the static incompressible subsonic regime have been investigated numerically and experimentally. Experimental tests were performed in the incompressible subsonic wind tunnel of the Ghadr National Aerodynamics Research Center of Imam Hossein University with a cross-sectional area of 80 by 100 cm. The simulation of the phenomenon is a fixed ground with the minimum possible thickness of the boundary layer in the wind tunnel. Solve the flow field numerically based on Navier Stokes equations along with the Transition-SST viscous model. The impact of the surface effect phenomenon on the change of aerodynamic coefficients has been investigated by considering different distances from the surface in the static state. The pressure distribution on the airfoil surface is measured by an accurate pressure sensor and is due to the surface effect phenomenon at close distances to the surface. The results of the static analysis show an increase in lift force and a decrease in drag force.

Aerodynamic noise generated by airfoils poses a serious industrial challenge because of its detrimental impact on human hearing and on the performance of vehicles and wind turbines. This noise rooted in geometric parameters, vortex shedding and flow separation can be mitigated by mounting triangular serrations on the trailing edge. In the present study, the aeroacoustic behaviour of an oscillating NACA 0012 airfoil with a ±10° pitching amplitude and oscillation frequencies between 5 and 25 Hz about its aerodynamic center was evaluated numerically. The flow field was solved with the Unsteady Reynolds-averaged Navier–Stokes equations with the k-ω SST turbulence model, while the surrounding acoustic field was predicted through the Ffowcs Williams–Hawkings (FW-H) acoustic analogy. Acoustic metrics, including sound pressure level and power spectral density,were recorded at several downstream positions from the trailing edge. results demonstrate that the serrationsfragmented large scale vortices into smaller structures and, on average, lowered vortex-induced noise by 4.58 dB from 51.18 dB equivalent to a 8.95% reduction. This attenuation is attributed to weakened dominant vortices, reduced velocity fluctuations and creating phase shifts in acoustic wave propagation, which collectively suppresswake turbulence and limit acoustic energy propagation, thereby enhancing aeroacoustic performance. Theeffectiveness of serrations was frequency dependent, exhibiting greater efficacy at lower oscillation frequencies and reduced effectiveness at higher frequencies due to intensified flow instabilities.

In this manuscript, the vortex generated by the main frequency excitation of the shedding vortex at various attack angles is investigated by employing the synthetic jet control technique. We also analyzed the impact of the vortex structure on the fled flow around the wing and the spectral characteristics corresponding to the vortex. The dominant frequency and harmonic frequency corresponding to the wave rule of the shedding vortex at various attack angles without the absence of a synthetic jet are selected as the synthetic jet excitation frequency. The results indicate that under the excitation of fixed frequency synthetic jet, the shape of the shedding vortex in the flow field turns correspondingly. Compared with the flow field without jet excitation, it is found that the field with the jet at most attack angles is stable in 2S (Single) mode, and the flow field at a small attack angle is stable in a chaotic state. The angle of attack with a chaotic state is delayed by adding a jet, which makes the curves and corresponding spectral characteristics more orderly. At a defined attack angle, the combined frequency synthetic jet will cause the lift coefficient to fluctuate regularly. At this time, the multiple small-scale vortex structures lead to lift reduction.

Imitating Dolphin fish-like movement is productive method for enhancing their hydrodynamic capabilities. This work aims to analyze and understand the oscillations of tail fluke of Dolphin, which can be used as a propulsive mechanism for underwater fish robots and vehicles. The objective of the work is to achieve the desired oscillating amplitude by simulating the NACA 0012 profile using computational models and Set up the swimming movement of the dolphin, imitating a fish like model. Computational techniques were employed to examine the propulsive capabilities of the oscillating hydrofoil, inspired by the dolphin's biological propulsion. The evolutionary of fluid pattern in the field surrounding both Dolphin fish model and the NACA0012 hydrofoil, from initial motion to cruising, was established, and the hydrodynamic impact was subsequently studied. An user-defined function (UDF) was developed to create a dynamic mesh interface with CFD code ANSYS FLUENT for establishing the oscillations of Dolphin tail across the flow field. Influencing hydrodynamic coefficients such as lift and drag coefficients at different frequencies were also obtained. The findings shown that when the acceleration of the Dolphin fish model increases, the time averaged drag force coefficient drops because The wake field's vortex disperses to have some beneficial effects and pressure of water surrounding the fish head intensifies to produce a large resistance force. Simulation results show a 98% agreement at lower frequency and speed levels but a 5% deviation at higher frequency and speed due to turbulence effects in both models. It was established that the vortex superposition enhances the Dolphin fish like model rather than lowering its positive impacts.  The Strouhal number, which is obtained by the fluid field's evolution rule, can be linked to the Kármán vortex street span with reverse.

Traveling wave is an innovative active flow control technique that can remarkably mitigate flow separation. This paper employs numerical simulation to examine how traveling wave structures affect the NACA0012 airfoil. The traveling wave structure is situated at 0.5%c from the leading edge. In the chord direction, its projection length is 0.1c. Through numerical simulation, the impacts of dimensionless length-width ratio and velocity of traveling wave on flow separation are investigated, and the relationship between the traveling wave's optimal parameters and angle of attack is explored. The outcomes demonstrate that traveling waves with suitable length-width ratios and velocities can effectively suppress flow separation. When AoA=16°, traveling wave airfoil with dimensionless velocity U=1.1 and length-width ratio A=1 achieves the best performance, and its lift-drag ratio is 9.24 times that of the original NACA0012 airfoil. The optimal dimensionless length-width ratio and velocity of the traveling wave airfoil are associated with the angle of attack, and different parameters need to be chosen at various angles of attack to attain optimum effect.

Airfoil self-noise is one of the dominant sources of airframe noises which causes limitations in many applications such as wind turbines. This paper investigates and quantifies the sensitivity of airfoil self-noise prediction to the grid resolution using large eddy simulation. Three-dimensional incompressible fluid flow around a NACA0012 airfoil at zero angle of attack with a chord-based Reynolds number of 6.4×105 is numerically analyzed in this paper. Far-field noise is predicted by Ffowcs-Williams & Hawkings model using the results of large eddy simulation. Three different grid sizes are used to investigate the effect of grid resolution on the accuracy of self-noise prediction. Results are compared with the experimental data of wind tunnel tests and noise measurements with microphones. Although the aerodynamic properties are calculated accurately in all grids, the grid resolution over the surface has a significant effect on the accuracy of the noise prediction. This effect of grid resolution is quantified in this paper. By the increase of grid points in the spanwise and streamwise directions on the surface, numerical noise prediction has approached the experimental data. The difference with the experimental data decreases from 20 dB to 3 dB in some frequencies. In addition, having doubled the number of surface grid points in both directions the average percentage of difference with the experimental data decreases from 5% to 2%.

In this study, the effect of blowing jet parameters, which include location, blowing angle, momentum coefficient, and orifice area, on the average aerodynamic coefficients and aerodynamic performance parameter of the NACA0012 is investigated. The airfoil has a sinusoidal oscillating motion around a quarter of the chord. As a result of this movement, the angle of attack of the airfoil changes from -5 to 25 degrees. Five locations by 1, 4, 6, 10, and 20% of the chord length were examined and the results showed that the placement of the jet at 1% of the chord length is more appropriate than the other locations and significantly improves performance and have more impact on the flow control. Three angles of 30, 60, and 90 degrees were considered as the angles of the blowing jet and it was observed that the angle of 60 degrees is better in controlling the flow than the other two angles and this effective angle decreases when orifice length increases. The results show that there is no regular uptrend or downtrend for the angle effect. For the jet momentum coefficient, which actually aimed to investigate the effect of blowing jet velocity, the values of 0.14, 0.08, and 0.04 were considered while the orifice length is considered constants for these cases. The results showed that increasing the blowing jet velocity as well as increasing the jet orifice length improves aerodynamic performance, although increasing the orifice length at a constant momentum coefficient decreases the mean of lift coefficient.