One major problem that affects rotor blade aerodynamics is dynamic stall, characterized by a series of events where transient vortex shedding negatively affects drag and lift, leading to abrupt changes in the wing’s pitching moment. The present work focuses on the mitigation of such effects by using a modified NACA0012 airfoil: the NACA0012-IK30 airfoil, used previously for thrust enhancement in flapping propulsion. An experimental rig is designed and built to study the advantages of a time-varying pitching leading edge on a plunging wing, more specifically its influence on the aerodynamic coefficients over time. Results indicate that when the wing is not experiencing significant stall, the movable leading edge does not hold considerable influence on drag or lift. However, it can reduce the pitching moment intensity by indirectly shifting the pressure center. Contrarily, when the wing is under proper dynamic stall, the movable leading edge truly improves the aerodynamic characteristics while operating at smaller effective angles of attack. This study contributes to the long-standing discussion on how to mitigate the adverse effects of dynamic stall by providing an innovative yet simple solution.

One major problem affecting rotor blade aerodynamics is dynamic stall, characterized by a series of events where transient vortex shedding negatively affects drag and lift, leading to abrupt changes in the wing’s pitching moment. The present work focuses on the mitigation of such effects by using a modified NACA0012 airfoil—the NACA0012-IK30 airfoil—previously used for thrust enhancement in flapping propulsion. An experimental rig is designed to study the advantages of a deflectable leading edge on a plunging and pitching wing, more specifically its influence on the aerodynamic coefficients over time. In the first stage, results indicate that the proposed IK30 mechanism does mitigate the stall effects under static conditions, with stall visualization data corroborating it. Regarding time-varying conditions, the data presents the adequacy of the proposed geometry under different plunging and pitching conditions, which, when correctly used, can mitigate or even eradicate the adverse effects of dynamic stall experienced, leading to significant drag reductions and modest lift enhancements. In the absence of a dynamic stall, the movable leading edge can also provide operational advantages, where it does not negatively affect drag or lift but can reduce the pitching moment intensity by indirectly shifting the pressure center. This study contributes to the long-standing discussion on how to mitigate the adverse effects of dynamic stall by providing an innovative yet simple solution.

A real-time optimization strategy can provide any system with a considerable boost in performance on the fly, which in real-world applications can be translated to lower energy consumption or higher efficiency. This study investigates the particular case of using real-time optimization to improve wing aerodynamic performance with a dynamically activated deflectable leading edge. Its activation aims to minimize drag and maximize lift and is governed by real-time and gradient-based optimization. An extension to a classic method is suggested to enhance gradient estimation accuracy. Experimental data are obtained at a Reynolds number of with the wing fixed at five positions. For each of these positions, optimal leading-edge deflections are found. The results indicate that deflecting the leading edge has a negligible impact on drag and lift before the stall onset. However, the reduction in the pitching moment cannot be ignored. When the wing is experiencing a proper stall, the movable leading edge yields remarkable enhancements, with the lift being approximately raised by 45% together with a substantial increase in the critical angle of attack. The findings highlight the potential of real-time optimization in experimental aerodynamic studies, reinvigorating its application in improving aircraft performance.

Unsteady airfoils play a pivotal role in comprehending diverse aerospace applications, being one of those flapping propulsions. The present paper studies this topic by bringing back an old unsteady panel method to juxtapose its results against CFD data previously obtained. The central objective is to revive the interest in these reduced order models in the topic of unsteady airfoils, which can be extended to model highly nonlinear effects while keeping computational resources fairly low. The findings reveal that while the potential flow-based UPM (Unsteady Panel Method) struggles to accurately capture the airfoil’s propulsive power, it remains adept at estimating consumed power. Moreover, an investigation into the pressure coefficient shows the potential benefits of UPM in contexts where flow separation can be disregarded. Despite inherent limitations, these simplified methodologies offer an effective preliminary estimation of flapping airfoil propulsive capabilities.

Natural flight has consistently been the wellspring of many creative minds, yet recreating the propulsive systems of natural flyers is quite hard and challenging. Regarding propulsive systems design, biomimetics offers a wide variety of solutions that can be applied at low Reynolds numbers, achieving high performance and maneuverability systems. The main goal of the current work is to computationally investigate the thrust-power intricacies while operating at different Reynolds numbers, reduced frequencies, nondimensional amplitudes, and mean angles of attack of the oscillatory motion of a NACA0012 airfoil. Simulations are performed utilizing a RANS (Reynolds Averaged Navier-Stokes) approach for a Reynolds number between 8.5×10^3 and 3.4×10^4, reduced frequencies within 1 and 5, and Strouhal numbers from 0.1 to 0.4. The influence of the mean angle-of-attack is also studied in the range of 0º to 10º. The outcomes show ideal operational conditions for the diverse Reynolds numbers, and results regarding thrust-power correlations and the influence of the mean angle-of-attack on the aerodynamic coefficients and the propulsive efficiency are widely explored.

Animals and insects have been investigated because of their locomotion form that allows simultaneous thrust and lift production at low Reynolds numbers. The present study focuses on the experimental investigation of a plunging NACA0012 airfoil under asymmetric conditions. Tests are conducted with a Reynolds number of 1x10^4, considering two nondimensional velocities, kh=0.25 and 0.50. Each of these conditions is tested with different levels of asymmetry, depending on the limitations of the experimental apparatus. Flow visualization indicates that asymmetric movements produce both thrust and lift simultaneously and that increasing the asymmetry parameter and the reduced frequency have a similar impact: leading edge vortices to become stronger and are formed earlier. The present study is an earlier work that explores the existent void of experimental data regarding asymmetric conditions of unsteady airfoils.

In many research areas, such as rotor dynamics and biomimetics, the dynamics of oscillating airfoils are of great interest. The findings of this study provide great insight into the importance of the leading edge regarding the propulsive characteristics of flapping airfoils. The main objective of the present work is to analyze the influence of the leading-edge pitching amplitude of the NACA0012-IK30 airfoil at a Reynolds number of 1.4x10^4, constant Strouhal number of 0.15 with three different (k,h) combinations and five leading-edge pitching amplitudes (A_alpha=0º,5º,10º,15º,20º). Using a RANS approach with the turbulence model k-omega SST coupled with the Intermittency Transition Model, results show that changing the leading-edge pitching amplitude has great impact on thrust enhancement, although presenting a small influence when it comes to lower nondimensional amplitudes. The required power coefficient is typically reduced while increasing the leading-edge pitching amplitude which, in some cases, provides an increase up to 211% in propulsive efficiency.

The kinematics of oscillating airfoils are crucial to understanding subjects such as rotor dynamics and bio-inspired flows. Unsteady airfoils have been studied extensively, but there is an overall lack of knowledge regarding newer and more complex kinematics. The present paper builds upon previous studies of the NACA0012-IK30 airfoil by implementing a gradient-based method that searches for a leading-edge pitching amplitude that maximizes propulsive power. All of this is done numerically by solving the Reynolds-Averaged Navier-Stokes equations coupled with the Intermittency Transition model. Results indicate that for higher reduced frequencies, higher leading-edge pitching amplitudes are required to maximize the mean propulsive power. Additionally, propulsive power is achieved with near-optimal propulsive efficiency, which is a common limitation of traditional flapping airfoils.

The aerodynamics of oscillating airfoils are crucial to understanding subjects such as rotor dynamics and bio-inspired flows. Unsteady airfoils have been studied extensively, but there is an overall lack of knowledge regarding newer and more complex kinematics. The present paper builds upon our modified version of the NACA0012 by numerically comparing its way of flapping with the standard flapping that is common in the literature. The comparison is conducted parametrically at a Reynolds number of 104 for two nondimensional amplitudes. Then, using a gradient-based optimization method, we search for pitching amplitudes that maximize the propulsive power and efficiency for both flapping modes. Results indicate that the proposed flapping methodology is more promising than conventional flapping, with thrust increases up to approximately 40%. Furthermore, the proposed mechanism achieves maximum propulsive power with near-optimal efficiency, a common limitation of traditional flapping airfoils.

Unsteady aerodynamics is the study of flows that pass an object subjected to oscillations, which has a strong association with bioinspired flows and rotor dynamics. The central objective of the paper is to study the propulsive characteristics of two plates at a Reynolds number of 3.1x10^3 with straight and sharp trailing edges. The reduced frequency is kept between 1.0 and 5.0 with a nondimensional amplitude ranging between 0.125 and 0.500. The problem was solved numerically using CFD (Computational Fluid Dynamics), and results show that differently from what is usually observed in airfoils, the mean thrust coefficient does not increase monotonously with the reduced frequency, having a dip around k = 3.0. The same is not verified for the mean power coefficient, which increases continuously with the reduced frequency. Two phenomenon responsible for the reduction of the mean thrust coefficient is identified. Through analysis of pressure contours around the flat plates, a low-pressure zone was seen near the trailing edge, creating a suction effect in that zone. The influence of k on the formation of the LEV is analyzed, via its approximate radius, evidencing a behavior similar to the mean Ct . Furthermore, the trailing-edge shape revealed to be an important factor on thrust reduction.