Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session S17: Tandem and Flapping Wings |
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Chair: Bo Cheng, Pennsylvania State University Room: 4c4 |
Tuesday, November 26, 2019 10:31AM - 10:44AM |
S17.00001: Effect of the rear wing size on the thrust performance of the two-dimensional tandem flapping wing. Sunil Manohar Dash, Nishanth S, Jit Sinha, Kim Boon Lua In this numerical study, the effect of the size of the rear wing on the thrust performance of 2D elliptical tandem flapping wing is investigated. Here, size ratio (SR), defined as the ratio of the chord of the rear to the front wing, is varied from 0.5 to 1.5 at an interval of 0.25 while keeping the aspect ratio (ratio of wing chord to thickness) AR$=$8, wing spacing (distance from trailing-edge of front wing to leading-edge of rear wing) $\lambda =$chord of the front wing, and phase angle $\varphi =$0 deg constant. Reynolds number based on the chord and Strouhal number based on the excursion distance of the front wing are set as 5000 and 0.32, respectively. For different SRs, we notice that time-average (Ct) and peak transient (Ctp) thrust coefficients of the rear flapping wing in tandem configuration can be up to 80{\%} higher compare to those of single flapping wing of same size. This enhanced thrust performance in tandem wing flapping is attributed to the constructive interaction of the shed vortices from the front wing with the leading-edge vortex of the rear wing. Note that the formation and interaction of the vortices is modified with SR. When SR increases, Ctp shifts towards starting of the flapping stroke and maximum Ctp and Ct are seen at SR$=$0.5 and SR$=$0.75, respectively. [Preview Abstract] |
Tuesday, November 26, 2019 10:44AM - 10:57AM |
S17.00002: Multi-fidelity Kinematic Parameter Optimization of Flapping Airfoil Hongyu Zheng, Fangfang Xie, Yao Zheng We have constructed a multi-fidelity framework for kinetic optimization of flapping foil with inline motion. We employ multi-fidelity Gaussian process regression and Bayesian optimization to effectively synthesize the aerodynamic performance of flapping foil with the kinetic parameters under multi-resolution direct numerical simulations. The objective of this work is to demonstrate that the multi-fidelity framework can be used efficiently to discover optimal kinetic parameters of foil with desired aerodynamic performance using a limited number of expensive high-fidelity simulations combined with a larger number of inexpensive low-fidelity simulations. We efficiently identify the optimal kinetic parameters of asymmetric flapping foil with target aerodynamic forces in the design space of heaving amplitude, pitching amplitude, angle of attack (AOA) and the stroke angle. Specially, it is found that the AOA can affect the magnitude of the aerodynamic forces by violating the generation of leading-edge Vortex while its combination effect with the stoke angle can determine the attitude and trajectory of flapping airfoil. [Preview Abstract] |
Tuesday, November 26, 2019 10:57AM - 11:10AM |
S17.00003: Physics-informed Predictive Model of Flapping Flight Aerodynamics using Gaussian Process Regression Yagiz Bayiz, Keegan Harris, Yu Pan, Haibo Dong, Bo Cheng An accurate and computationally efficient model for predicting the aerodynamic force, moment and power of flapping flight can significantly advance the understanding animal flight and the design of bioinspired micro aerial vehicles. In this work, we develop such a predictive model based on Gaussian Process (GP), informed by quasi-steady aerodynamic model and trained by Computational Fluid Dynamics (CFD) simulation data for a wide range of flapping wing kinematics. The GP receives instantaneous wing kinematics as the input and uses statistical inference methods to predict the resulting forces, moment and power. The training set consists of a nominal wing trajectory and a set of trajectories highlighting a deviation from the vanilla trajectory in one particular kinematic feature. The resulting GP model is tested on a separate set of wing trajectories with a mixed change of kinematic features and is shown to provide more accurate predictions than the conventional quasi-steady models. The accuracy of the predictions relies on the proximity to the training set, and for a relatively wide range of trajectories, they show excellent agreement with the CFD results. The GP model also provides uncertainty information, indicating the regions where the prediction has a high variance. [Preview Abstract] |
Tuesday, November 26, 2019 11:10AM - 11:23AM |
S17.00004: Aerodynamic stability analysis of the dual-wing flapping flight for the large birds Tengyu Hou, Yang Xiang, Hong Liu By dual-wing flapping, large birds obtain lift and thrust to sustain flight. Insects obtain good maneuverability and dynamic stability through high frequency flap. The airliners show good performance based on the principle of steady aerodynamics. Different from the two examples before, birds have a lower flapping frequency to maintain their stability for forward flight. Through the observation of bird flap behavior and human speculation, we can easily generate the idea that the bird's flap can show stability only within a certain range of flapping frequency. In this article, we model birds based on a quasi-steady mathematical model, and observe the stability of the mathematical model by applying different perturbation excitations to the model. The results of theoretical analysis show that for a given parameter model, it is possible to maintain stable flight only within a certain range of flapping frequency. Moreover, we find that the model can resist disturbances of different degree in different frequency ranges. Then, we compare the dual-wing to the single-wing model. Our work shows that the flight stability of birds and the flapping frequency are closely related, which may provide effective theoretical guidance for the design of flapping wing air vehicles. [Preview Abstract] |
Tuesday, November 26, 2019 11:23AM - 11:36AM |
S17.00005: Rolling and twisting of finite foil Andhini Novrita Zurman Nasution, Bharathram Ganapathisubramani, Gabriel D. Weymouth Strip theory in flapping foils, i.e. reconstructing a 3-dimensional (3D) behavior from a spanwise sequence of 2D strips, has a potential to give fast predictions but the modeling errors are poorly understood. In this work, finite foils with an elliptic tip are simulated with a sinusoidal motion of pure rolling and combined rolling-twisting. Their spanwise cross-sections are compared with 2D simulations of the same kinematics. The 3D pressure distributions are strongly correlated with the 2D, but have very different amplitudes. The spanwise velocity of the cross-sections also increases with the local velocity caused by the kinematic. The pure rolling motion indicates that maximum lift coefficient ($C_L$) at each cross-section augments linearly with local velocity square except at the tip. It is discovered that the slope of $C_L$ along the span declines as the aspect ratio is reduced with the same scaling as Prandt'l finite-wing theory. Similar behavior is found by Green and Smits [2008] to scale the thrust coefficients of pitching panel for different aspect ratios. With these discoveries, the 2D $C_L$s can be corrected with the scaling to find their corresponding 3D cross-sections at different aspect ratios, enabling quantitative strip theory predictions of 3D flapping flight. [Preview Abstract] |
Tuesday, November 26, 2019 11:36AM - 11:49AM |
S17.00006: Vortex models for the unsteady aerodynamics of tandem foils. Javier Alaminos-Quesada, Jeff Eldredge Configurations of multiple wings and fins arise in various contexts, including biological flying and swimming, biologically-inspired and rotary wing vehicles, and formations of vehicles. Here, we present two-dimensional potential flow models for the separated flows of multiple unsteady foils. In the special case of a longitudinal tandem configuration, these models are evaluated and compared directly with high-fidelity numerical simulations at low Reynolds number. In addition, we have obtained the optimal configuration for an accelerating pair of foils with respect to the separation distance between them. Finally, we consider potential flow models of the trailing airfoil in which the effect of the leading airfoil's wake is replaced by a time-varying vorticity flux into the separated flow of the trailer. [Preview Abstract] |
Tuesday, November 26, 2019 11:49AM - 12:02PM |
S17.00007: A numerical study of flapping wings in tandem configuration at low Reynolds number Gonzalo Arranz, Oscar Flores, Manuel Garcia-Villalba Direct numerical simulations of wings in in-line tandem configuration are presented. \% The wings undergo a two-dimensional optimal kinematics. \% This optimal motion is a combination of heaving and pitching of the airfoils in a uniform free-stream at a Reynolds number 1000 and Strouhal number 0.7. \% The objective of the study is to analyze how three-dimensional effects influence the aerodynamic performance of the wings. \% To that end, wings of two different aspect ratios, 2 and 4, undergoing the two-dimensional kinematics are considered. \% Simulations show that the interaction between the vortical structures of the wings is similar to the 2D case. \% However, it is found that 3D effects are detrimental in terms of hind-wing's thrust generation. \% On the contrary, the propulsive efficiency remains constant both in 2D and 3D, for both aspect ratios. \% Simulations of flapping motion are also presented and compared to the previous wings in heaving motion. \% It is found that aerodynamic forces and propulsive efficiency decrease when the wings are in flapping motion due to a sub-optimal motion of the inboard region of the flapping wings. [Preview Abstract] |
Tuesday, November 26, 2019 12:02PM - 12:15PM |
S17.00008: Delaying Leading-Edge Vortex Detachment on a Pitching and Plunging Flat Plate using a DBD Plasma Actuator Johannes Kissing, Bastian Stumpf, Jochen Kriegseis, Cameron Tropea In order to achieve higher manoeuvrability, novel micro-air vehicle designs adapt flapping wings from biological flight to realize hovering and forward flight. The increased lift of flapping wings is mainly due to the circulatory lift of the leading-edge vortex (LEV), which forms on the wing and induces transient lift as it grows. Subsequently, the unsteady lift drops when the vortex detaches from the airfoil. In order to attain higher overall lift, the current project aims to delay the detachment of the LEV by manipulating the flow field at topologically critical locations with a dielectric barrier discharge plasma actuator (DBD-PA). Time-resolved particle-image velocimetry measurements are used to characterize the flow field around a flat plate, which executes a combined pitching and plunging motion at a Reynolds number of 24,000, a reduced frequency of 0.48 and a Strouhal number of 0.1. A prolongation of the growth phase of the LEV, marked by a longer circulation-accumulation phase and a decreased convection of the LEV, is achieved by compressing secondary structures ahead of the main vortex. Temporal variations of the excitation onset are found to be the key factor between spatial control authority of the DBD-PA and the determined effectiveness of flow control. [Preview Abstract] |
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