Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session A02: Aerodynamics: General |
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Chair: Ignacio Maria Viola, University of Edinburgh Room: 130 |
Sunday, November 20, 2022 8:00AM - 8:13AM |
A02.00001: Spectral and Statistical Evaluation of Reconstructed Pressure Scanner Measurements for Unsteady Aerodynamic Applications Pourya Nikoueeyan, Michael Hind, Marvin Perry, Benjamin Wimpenny, John Strike, Jonathan W Naughton Hindering the use of pressure scanners for unsteady measurements is the connecting tubing that inherently introduces time lags and pneumatic distortion to the pressure signal received at the sensing element inside the pressure scanner. The character of the distortion varies and can be due to attenuation or resonant amplification. The exact behavior depends on the geometry of the tubing, as well as the environmental conditions. However, the Wiener-filtered inverse system response model (WF-iSRM) developed by Whitmore has been proven effective in reconstructing complex unsteady pressure signals in various low-speed wind tunnel testing applications. |
Sunday, November 20, 2022 8:13AM - 8:26AM |
A02.00002: Effect of yaw angle on aerodynamics of a square inclined flat plate in ground effect Thelge S Pieris, Serhiy Yarusevych, Sean D Peterson The aerodynamics of a square inclined flat plate is investigated using flow and force measurements for yaw angles between 0° and 180°. The Reynolds number is 50,000 and the angle of attack is 30°. The minimum clearance between the ground and the plate is varied between 0.1 and 1 chord length. Lift and drag are measured using a load cell. Surface oil flow visualizations provides a holistic view of the highly three dimensional flow development over the suction side, which are accompanied by cross-flow stereo particle image velocimetry measurements at the leeward point of the model. The results reveal strong tip effects at yaw angles of 0° and 180° in free flight, causing leading edge shear layer reattachment over the plate, leading to relatively high lift and drag coefficients. As yaw angle of 90° is approached, tip effects diminish, and the loads decrease under both free flight and ground effect conditions. Ground effect on loading is dependent on the yaw angle and whether the suction or the pressure side is exposed to the ground, with the former experiencing a decrease in forces, while the latter observes an increase in forces with decreasing ground height. |
Sunday, November 20, 2022 8:26AM - 8:39AM |
A02.00003: Development and validation of a facility to study the unsteady aerodynamic interactions between lifting surfaces Lokesh Silwal, Vrishank Raghav From the interactions between tandem insect wings to that between the rotors in multi-rotor aerial vehicles, unsteady aerodynamic interference between multiple lifting bodies dictates the efficiency and stability of these systems. While studies have focused on investigating the unsteady aerodynamics of multiple lifting bodies translating in the same direction, research on unsteady interactions between two lifting surfaces translating in opposite directions has been scarce. As such, this study details the development and validation of a towing tank facility, enabling the study of unsteady interactions between two moving lifting surfaces. The facility consists of a translation system for wings with chord length c = 0.036m and a translation length of 24c. The wings are equipped with strain gauge loadcells to quantify the blade airloads, and flow visualization is employed to understand the underlying flow physics. For the validation of the facility, single-wing experiments are conducted, and the results are compared with the literature. Initially, the influence of acceleration on the steady-state characteristics of a single wing is investigated. The steady-state characteristics of the wing airloads are then analyzed across a range of Reynolds number conditions. |
Sunday, November 20, 2022 8:39AM - 8:52AM |
A02.00004: Physics-informed Deep Learning for simultaneous Surrogate Modelling and PDE-constrained Optimization Yubiao Sun, Ushnish Sengupta, Matthew P Juniper We model the flow around an airfoil with a physics-informed neural network (PINN) while simultaneously optimizing the airfoil geometry to maximize its lift-to-drag ratio. The parameters of the airfoil shape are provided as inputs to the PINN and the multidimensional search space of shape parameters is populated with collocation points to ensure that the Navier-Stokes equations are approximately satisfied throughout. We use the fact that the PINN is automatically differentiable to calculate gradients of the lift-to-drag ratio with respect to the parameter values. This allows us to use the L-BFGS gradient-based optimization algorithm, which is more efficient than non-gradient-based algorithms. We train the PINN with adaptive sampling of collocation points, such that the accuracy of the solution is enhanced. We demonstrate this method on two examples: one that optimizes a single parameter, and another that optimizes eleven parameters. The method is successful and, by comparison with conventional CFD, we find that the velocity and pressure fields have small pointwise errors and that the method converges to optimal parameters. We find that different PINNs converge to slightly different parameters, reflecting the fact that there are many closely-spaced local minima when using stochastic gradient descent. This method can be applied relatively easily to other optimization problems and avoids the difficult process of writing adjoint codes. As knowledge about how to train PINNs improves and hardware dedicated to neural networks becomes faster, this method of simultaneous training and optimization with PINNs could become easier and faster than using adjoint codes. |
Sunday, November 20, 2022 8:52AM - 9:05AM |
A02.00005: Physics Informed Neural Network model for wind field prediction in urban spaces for small Unmanned Aerial Systems. Rohit Kameshwara Sampath Sai Vuppala, Kursat Kara In recent years there has been significant interest in using Unmanned Aerial Systems for various applications in urban spaces, including disaster management, law enforcement, delivery/catering services, and Advanced Air Mobility. However, Unmanned Aerial Systems are highly sensitive to the abrupt wind patterns generated in urban spaces due to obstacles like buildings and other structures. It is especially difficult for Small Unmanned Aerial Vehicles owing to their lightweight and smaller overall structure. Safe Wind-Aware navigation is thus an essential part of small Unmanned Aerial Systems operation and deployment. Although Computational Fluid Dynamics solvers could provide accurate solutions, they are computationally expensive and cannot be used for real-time or close to real-time wind predictions. Non-intrusive Data-driven, Reduced Order Models could offer a viable alternative for wind-filed predictions by relying on offline training using these high-fidelity solutions. However, they are not easily generalizable for different flow conditions since they depend highly on the training data. |
Sunday, November 20, 2022 9:05AM - 9:18AM |
A02.00006: On Inviscid Modeling of Vortex-Wall Interactions James Paulson, Thierry Jardin, James H Buchholz A vortex near the surface of an aerodynamic body necessarily results in the generation of secondary vorticity to enforce the no-slip condition on the boundary. Interaction between the primary and secondary vorticity can lead to modified vortex evolution, including weakening of the primary vortex through entrainment and cross-cancelation of the secondary vorticity. These phenomena are omitted in the inviscid modeling of vortex-dominated flows. In this study we investigate the physics of the vortex-wall interaction by comparing simulations of two revolving wings under identical inflow conditions. In one case the no-slip condition is applied to the full surface of the wing whereas in the other case, a free-slip condition is applied to the suction surface that interacts with the leading-edge vortex (LEV). A difference in LEV circulation is observed. A vorticity transport framework is used to elucidate differences in the evolution of the vortices between the two cases. Whereas in the no-slip case, the diffusive flux of secondary vorticity is found to be a significant factor regulating wing circulation, other transport mechanisms become more important in the free-slip case. |
Sunday, November 20, 2022 9:18AM - 9:31AM |
A02.00007: Gust Response and Mitigation Through Passive Pitching Yabin Liu, Stefano Gambuzza, Shūji Ōtomo, Eddie McCarthy, Anna Young, Riccardo Broglia, Ignazio Maria Viola The pitching motion around an elastic joint enables natural wings to keep steady flight by passively responding to gusts. To understand the underlying principles, we investigate a two-dimensional foil free to pitch in a uniform stream. An external pitch moment proportional to the pitch angle is applied to the foil, representing the effect of a torsional spring. We first demonstrate analytically that the quasi-steady variation of any force component, e.g. the lift, can be cancelled by setting the pitching axis through any point along along a straight line that depends only on the geometry and the Reynolds number. Then, we investigate numerically the transient response of a NACA0012 foil to a streamwise gust. We consider initial chord-based Reynolds number values of 1000, 50k and 1M; a solid-to-fluid density ratio of 5; a torsional spring preload of 30 degrees; and a spring stiffness such that the initial angle of attack is 5 degrees. The incompressible Navier-Stokes equations for a Newtonian fluid are weakly coupled with a rotational harmonic oscillator within OpenFOAM. For a fast gust with a duration shorter than a convective length, and with an amplitude of the fluctuation of the same order of the mean flow (e.g. doubling the free stream velocity), the transient forces are governed by the generation of added mass vorticity and their shedding. We find that the amplitude of the lift fluctuations decreases asymptotically with the distance of the pitching axis from the foil, and are already reduced by an order of magnitude when the distance is about one chord length. The kinematics of the pitching foil is well predicted by solving the Newton-Euler equation of motion considering quasi-steady circulatory and added mass forces. Additionally, we find that vortex shedding triggered by the gust at high Reynolds numbers can be suppressed by passive pitching. These results provide new insights into the mechanism by which unsteady loads are generated and on the technology by which they might be mitigated. |
Sunday, November 20, 2022 9:31AM - 9:44AM |
A02.00008: Early detection of self-sustained low-frequency flow oscillations over an airfoil Xiangyu Zhai, Vikrant Gupta, Stephane Redonnet, Larry K.B. Li We perform output-only system identification for early detection of self-sustained low-frequency flow oscillations (LFOs) over a prototypical airfoil near stall conditions. We treat the LFO statistics as a Markov process and model the lift force fluctuations with a Van der Pol oscillator subjected to stochastic intrinsic noise representing freestream turbulence. Using time-series data acquired with a load cell, we estimate the first two Kramers-Moyal coefficients (drift and diffusion coefficients) of the corresponding Fokker-Planck equation via an adjoint-based optimization algorithm. By reconstructing the probability distribution of the oscillation amplitude with the identified model parameters, we validate this modeling approach and confirm that the LFOs emerge via a supercritical Hopf bifurcation. Crucially, we show that even when equipped with only pre-bifurcation data, one can forecast the location of the Hopf point as well as the amplitude of the post-bifurcation limit cycle. This approach to early detection of LFOs could find use in future stall-avoidance strategies. |
Sunday, November 20, 2022 9:44AM - 9:57AM |
A02.00009: On the interaction between a rigid parachute and the supersonic wake behind a probe during the descent phase on Mars Francesco Picano, Luca Placco, Giulio Soldati, Matteo Bernardini, Alessio Aboudan, Francesca Ferri, Stefano Debei The number of recent missions on Mars highlights the renovated importance of this planet exploration. Nevertheless, recent and past failures clearly show how critical the landing phases are for these missions. Entry and descent phases of interplanetary probes are characterized by complex aerodynamic phenomena as the capsule gradually encounters the planet's atmosphere. In the present study we use accurate 3D Large-Eddy-Simulations to simulate the interaction between the wake behind the probe and a rigid parachute in a supersonic regime matching the typical Mars descent conditions. Firstly, the supersonic wake behavior will be characterized in terms of fluctuation intensities, typical frequencies and a Proper-Orthogonal-Decomposition analysis. Then the interaction between the wake and the parachute will be discussed. We will show how the unsteady turbulent wake forces the breathing of the bow shock in front of the parachute causing strong unsteadyness of the aerodynamic behavior. We will also discuss a simple model able to capture this interaction well reproducing the main flow features. More details will be given in the final paper. |
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