Airfoil turbulence interaction noise and the flow field up to and over the porous leading edge is experimentally studied. The porous leading edges were of the same base triply periodic minimal surface structure with varying porosity to enable us to understand how the porosity, permeability, and pore size affect the generated turbulence interaction noise. The turbulent flow was generated by means of a passive turbulence grid that does not affect the normal background noise of the wind tunnel. Far-field noise results were obtained from a polar microphone array to assess the directivity of the sound as well as the narrowband frequency contributions. Far-field noise results demonstrate that increasing porosity reduces the turbulence interaction noise over low-to-mid frequencies, with a penalty of a high frequency noise increase. Flow measurement results indicate hydrodynamic penetration of the flow into the porous structure at the leading edge. Furthermore, the two-point correlation analysis of the velocity fluctuations approaching the leading edge shows that the turbulent structures approaching the solid leading edge appear to deform into more two-dimensional structures, whereas in the case of the porous leading edge, the turbulent structures appear to retain a strong spanwise coherence up to the point of hydrodynamic penetration.

Experiments are performed to investigate the effect of porous treatment structure used at the leading edge on the aerodynamic and aeroacoustic characteristics of a National Advisory Committee for Aeronautics (NACA) 0012 airfoil. Three different triply periodic minimal surface porous structures of constant porosity are studied to explore their effect on the flow field and the relationship between airfoil response and far-field noise. The results show that the ratio between the porous structure pore size and the length scale of the turbulent flow plays an important role in the noise reduction capability of a porous leading edge. Changes to the turbulent flow properties in the vicinity of the airfoil are assessed to characterize the contributing physical behavior responsible for far-field noise manipulation. Velocity field analysis in front of the leading edge demonstrates a pronounced difference among porous structures. Furthermore, close to the airfoil surface and off from the stagnation line, all porous leading edges demonstrate a marked reduction in the low-frequency content of the velocity fluctuations. These results demonstrate the importance of the airfoil leading edge region and not just the stagnation line. The strong link evident in pressure–velocity coherence analysis of the solid airfoil is broken by the introduction of the porous leading edge. Furthermore, the porous leading edges reduce the near-field to far-field pressure coherence in both magnitude and frequency range.

The objective of this article is to characterize an aeroelastic system in terms of its dynamical behavior, which could be either chaotic or periodic before, during, and after achieving the flutter velocity. The aeroelastic system shown here is a wing with a high aspect ratio, which leads to a very flexible behavior subjected to unsteady flow. This paper compares the computational and experimental dynamical behavior of an aeroelastic system at the flutter velocity for the different dynamic stall models proposed. To understand the nonlinear behavior of this system, the traditional attractor reconstruction and Lyapunov exponent calculation are compared with the 0–1 test. In addition to this comparison, two dynamic stall semi-empirical models are applied directly to the time history. All these comparisons show that the computational and wind tunnel experiments are in good agreement, and the dynamic behavior usually gives close results for the 0–1 test and Lyapunov exponent. It is concluded that the system presents chaotic behavior when no dynamic stall correction is applied or when Gangwani’s correction is applied. However, Boeing–Vertol’s correction postpones the chaotic behavior, meaning that the chaotic behavior is only observed for velocities above the flutter.

Distributed electric propulsion systems in electric vertical takeoff and landing aircraft are expected to encounter unsteady inflow conditions in low-altitude flight, yet the interaction between discrete gusts and small-scale propellers remains insufficiently characterized. This study investigates the response of an isolated propeller subjected to a discrete one-minus-cosine like gust generated by a dual-vane gust generator. The propeller was tested at U∞=10 ms−1 and rotational speeds of 5000, 6000, and 7000 RPM, corresponding to advance ratios of J=0.47,0.39, and 0.34, respectively. Hot-wire anemometry and phase-synchronized stereo particle image velocimetry were used to characterize the incident gust and its evolution through the propeller disk, while synchronized six-axis load measurements quantified the corresponding unsteady propeller response. The results show that the propeller-induced swirl velocity redistributes the imposed gust field, locally attenuating the vertical gust velocity on the upstroke side of the disk and amplifying it on the downstroke side. A direct comparison between the measured combined velocity field and a local kinematic reconstruction confirmed that this gust–swirl interaction captures the main asymmetric inflow mechanism, while discrepancies near the blade-root region coincided with the loss of gust coherence observed in the particle image velocimetry fields, indicating gust breakdown and additional unsteady effects. This redistribution produces asymmetric out-of-plane torque responses and alters the induced velocity field in the wake. Increasing the propeller rotation speed from 5000 to 7000 RPM (J=0.47–0.34) reduced the thrust increment induced by the gust, but strengthened the distortion of the gust field, increasing the affected region by approximately 60%. The measurements identify the gust–swirl interaction and subsequent gust breakdown as the mechanism linking discrete-gust ingestion, asymmetric loading, and wake distortion and provide an experimental dataset for modeling unsteady propeller loading in non-uniform inflows.