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- Predicting the NACA0012-IK30 Airfoil Propulsive Capabilities with a Panel MethodPublication . Camacho, E. A. R.; Marques, Flávio D.; Silva, A. R. R.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.
- Effects of a Dynamic Leading Edge on a Plunging AirfoilPublication . Camacho, Emanuel; Neves, Fernando M. S. P.; Marques, Flávio D.; Barata, Jorge M M; Silva, AndréThe dynamics of oscillating airfoils are of great interest in many research areas such as rotor dynamics and biomimetics. The results reported in this research provide an insight into the mechanics of birds’ leading edge and how the dynamic curvature of the airfoil can highly benefit the aerodynamic and propulsive performance, especially at high angles of attack. The main goal of the current work is to numerically investigate the influence of a deflecting leading edge on the propulsive coefficients and flowfield created by a plunging airfoil at a Reynolds number of 1.4 × 104 and a constant Strouhal number of 0.15 with different ( k, ℎ) combinations. Employing a RANS approach with the proposed NACA0012-IK30 airfoil, results show that dynamically deflecting the leading edge significantly improves the propulsive efficiency of the airfoil by either reducing the required power or improving the thrust production. The outcomes regarding the propulsive efficiency show a considerable increase of up to 92% when the higher nondimensional amplitude was considered.
- Leading-Edge Parametric Study of the NACA0012-IK30 AirfoilPublication . Camacho, Emanuel; Marques, Flávio D.; Silva, A. R. R.; Barata, Jorge M MIn 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.
- Dynamic Stall Mitigation Using a Deflectable Leading Edge: The IK30 MechanismPublication . Camacho, Emanuel A. R.; Silva, A. R. R.; Marques, Flávio D.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.
- Theoretical and Numerical Analysis of Oscillating Airfoil Including Viscous EffectsPublication . Torres, George Lucas; Camacho, Emanuel; Marques, Flávio D.; Silva, AndréUnsteady airfoils are the way to explore new aerodynamic phenomena which do not appear in ordinarily aeronautical applications. At lower Reynolds numbers, unsteady flow can make way to newer technologies to be implemented in areas such as extraterrestrial exploration. In the present work, the Theodorsen classical unsteady theory and a viscous extension to this model are implemented. Results from those computations are then compared with high fidelity CFD simulations using laminar and turbulent assumptions. Results obtained by using the viscous model indicate a good agreement with CFD data, although there are still some discrepancies at the trailing edge.
- Simulations of a Plunging Airfoil Undergoing Unequal Ascending and Descending Velocities at Low Reynolds NumbersPublication . Torres, George L. S.; Camacho, Emanuel; Marques, Flávio D.; Silva, AndréDynamic stall is an effect frequently seen in nature and rotary wings where flow separation induces strong force oscillations. In order to simulate such phenomena, reduced-order models (ROMs) such as the LESP-modulated discrete-vortex method (LDVM) are often used whose applicability at low Reynolds number is discussed here. CFD computations with the SST were conducted to obtain the critical leading-edge suction parameter (LESP) by analyzing the skin friction coefficient distribution for the Reynolds number tested of 1,500. Results explore both symmetrical and asymmetrical plunging of a NACA0012 airfoil following a triangular velocity profile, indicating a good agreement between experimental, CFD, and LDVM computations, which makes the latter, a very efficient and adequate method to study wake configurations of oscillating airfoils at low Reynolds numbers.
- Flapping Airfoil Aerodynamics using Recurrent Neural NetworkPublication . Pereira, João A.; Camacho, Emanuel A. R.; Marques, Flávio D.; Silva, AndréThe recent increase in interest in artificial intelligence and neural networks has stirred up various industries. Inevitably, its application will trickle down to the most fundamental studies, for instance, unsteady aerodynamics. The present paper serves the purpose of exploring the ability of a recurrent neural network to predict flapping airfoil aerodynamics, in particular the lift coefficient of a plunging NACA0012 airfoil. Thus, a neural network is designed and trained using motion parameters, such as motion frequency and effective angle of attack, to output the instantaneous lift coefficient over a plunging period. Training data is generated using a panel code (HSPM) for fast generation and early testing. Results show that the neural network can adequately predict the lift coefficient for various conditions, including plunging kinematics that are far from the training domain. Future work will build on this framework and extend it to other aerodynamic coefficients using CFD results and experiments, which should enhance the value of the estimates.
- Optimal Operation of the NACA0012-IK30 AirfoilPublication . Camacho, Emanuel A. R.; Silva, A. R. R.; Marques, Flávio D.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.
- Fast Flapping Aerodynamics Prediction Using a Recurrent Neural NetworkPublication . Pereira, João A. F.; Camacho, Emanuel A. R.; Marques, Flávio D.; Silva, A. R. R.One of the major tasks of aerodynamics is the study of the flow around airfoils. While most conventional methods deal well with steady flows, unsteady airfoils, like the ones on helicopter blades, are subject to such complex dynamic flows that their study can impose substantial difficulties. However, recent applications of machine learning, in the form of neural networks, have shown very promising results when dealing with complex dynamic aerodynamic phenomena. For this reason, this paper proposes the implementation of a recurrent neural network for the time-wise prediction of the lift, momentum, and drag coefficients for an airfoil subject to plunging motion, using the 𝑅𝑒, k, h, 𝑘ℎ, and the time history of the effective angle of attack as inputs. Results from early training already suggest the network’s capability to approximate the desired outputs, even if with some limitations. However, the network configuration is flexible enough to be fed with either experimental or numerical data in the future.
- Influence of a Deflectable Leading-Edge on a Flapping AirfoilPublication . Camacho, Emanuel A. R.; Marques, Flávio D.; Silva, A. R. R.Flapping wing dynamics are of great interest in many research areas, such as bioinspired systems and aircraft aeroelasticity. The findings of the present study provide significant insight into the importance of the leading-edge dynamic incidence on the propulsive performance of flapping airfoils. The main objective is to improve the propulsive characteristics by adding a pitching leading-edge to a conventional NACA0012 airfoil at the lower spectrum of the Reynolds number. The problem is solved numerically at a Reynolds number of 104 under various flapping conditions. The results show that the leading-edge pitching amplitude has a great impact on the propulsive power and efficiency, providing meaningful improvements. The required power coefficient is reduced overall, although not as significantly as the propulsive power. The influence of the movable leading-edge on the pressure distribution is analyzed, showing that the enlargement of the frontal area is the root cause of propulsive augmentation. The proposed geometry provides an innovative way of flapping an airfoil with propulsive purposes, offering remarkable improvements that can defy conventional flapping.