Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session R30: Fluid-Structure Interactions, Membranes, Flutter I |
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Chair: Ross Cruikshank, Michigan State University Room: 255 B |
Monday, November 25, 2024 1:50PM - 2:03PM |
R30.00001: A novel morphing vehicle design for improved fuel economy Sina Kazemipour, Peng Zhang Optimizing the body shapes of road vehicles is essential to enhancing their aerodynamic efficiency and improving their fuel economy. Heavy-duty vehicles, such as commercial and pickup trucks, have poor aerodynamic performances due to a lack of streamlined body shapes. To address this issue, we propose a low-cost, noninvasive morphing vehicle concept toward minimizing the aerodynamic drag, thereby improving the energy efficiency of the vehicle. Using a generic pickup truck model as the base geometry, morphing is enabled by retrofitting active flexible structures on its roof, which can actively interact with the surrounding airflow. To guide real-time, active morphing, we employ a combined parameterized genetic algorithm – computational fluid dynamics framework to identify the optimal shapes of the active structures for a range of realistic driving speeds. This optimization framework identifies a series of morphing strategies that could lead to 7% - 12% reductions in the aerodynamic drag. Analysis of the flow field uncovers the role of the morphing structures in modulating the wake flow and facilitating drag reduction. This novel non-invasive morphing vehicle concept could lead to outstanding energy savings and contribute to enhanced fuel economy for heavy-duty vehicles. |
Monday, November 25, 2024 2:03PM - 2:16PM |
R30.00002: Direct Numerical Simulations of the Aerodynamics of Insect Inspired Gliders Sahaj Sunil Jain, Kyung Jun Paul Lee, Aimy Wissa, Jung-Hee Seo, Rajat Mittal While insects have often served as bioinspiration for flapping wing micro-aerial vehicles, several large insects such as grasshoppers, butterflies, moths, and dragonflies also exhibit excellent capabilities for gliding. We employ direct numerical simulations using an in-house ghost cell immersed boundary method-based CFD code to investigate the aerodynamics of a grasshopper-inspired glider. The glider is modeled as a thin membrane structure, and we examine the glider's performance in the context of various aerodynamic parameters such as Reynolds number, angle-of-attack, and roll angle and their impacts on the aerodynamics as well as quantities such as drag and lift coefficients. The effect of the presence of wing corrugations is also studied in this framework, along with the contribution of different flow structures such as wake and wing tip vortices using the Force and Moment Partitioning Method (FMPM). A special emphasis is placed on understanding the roll and pitch moment characteristics that ultimately affect the glider's stability. |
Monday, November 25, 2024 2:16PM - 2:29PM |
R30.00003: Stabilizing Flows: The Role of Poro-Elasticity in Reducing Unsteady Drag Forces Alexander Gehrke, Zoe King, Kenneth S Breuer In nature, flexibility and porosity enable structures like feathers, leaves, and seeds to adapt to strong winds, making them more resilient and lightweight. However, few aerodynamic applications and experimental studies have explored the effect of poro-elasticity on the forces and coherent flow structures behind these objects. Our work investigates the effects of poro-elasticity on thin circular membrane disks under different fluid loadings. We measure the unsteady deformation, vortex-dominated flow fields, and drag forces for varying porosity levels. As dynamic pressure increases, non-porous disks deform into spherical cap shapes, leading to increased drag compared to flat disks due to higher turbulent kinetic energy in the wake. However, increasing porosity significantly reduces the average drag and drag fluctuations. Time-resolved PIV measurements reveal that poro-elasticity stabilizes the unsteady wake behind the membranes, similar to natural mechanisms. Using a frequency analysis on the unsteady membrane deformation, drag forces, and flow fields, we find that poro-elasticity suppresses the shear-layer instability associated with the high unsteady forces experienced by non-porous membranes. We present a coupled aero-elastic scaling for membrane deformation and porosity that predicts the membrane shape and drag forces experienced by the membrane. Our findings highlight the potential of poro-elastic structures, particularly for the reduction of unsteady drag forces. |
Monday, November 25, 2024 2:29PM - 2:42PM |
R30.00004: Experimental investigation of the fluttering flag using FSI-POD Rodrigo Padilla, Vibhav Durgesh, Tao Xing, Anas M Nawafleh Fluttering flag exhibit complex behavior due to the continuous energy exchange between a deforming structure and a flowing fluid. Fluid-structure interaction-proper orthogonal decomposition (FSI-POD) was proposed by Goza & Colonius [JF&S:2018], and they successfully applied it to a computational flag FSI studies. One benefit of using FSI-POD is that it couples the fluid and structure energy together, elucidating the interplay between the fluid and structure observed in FSI problems. This study focuses on developing FSI-POD for the experimental investigation of a fluttering flag. For this purpose, particle image velocimetry (PIV) measurements were performed on the flag fluttering in an open jet. The flag had a mass ratio of 1.47, an aspect ratio of 0.25, a dimensionless rigidity of , and a Reynolds number based on flag length is . The raw PIV images were used to estimate the position and velocity of the structure using an algorithm developed in-house. The position and velocity of the flag allowed for the estimation of the energy of the structure required for the FSI-POD implementation. The velocity flow field data were obtained using the traditional PIV cross-correlation technique. These results showed it is possible to implement FSI-POD for fluttering flags using only the PIV measurements. Additionally, the results highlight the complex energy exchange between the fluid and flag during limit-cycle oscillation, which would not have been possible otherwise. |
Monday, November 25, 2024 2:42PM - 2:55PM |
R30.00005: Evaluation of Aeroelastic Coupling between a Shock Boundary Layer Interaction and Compliant Surface Matthew J Kronheimer, Datta V Gaitonde, Jack J McNamara An inadequate understanding of the role of inherently unsteady flow features in interactions between lightweight aircraft structures and turbulent flows impedes rapid and accurate computational aeroelastic analysis. In this work, a large-eddy simulation flow solver is coupled to a finite element structural solver to investigate the interaction and coupling mechanisms between an impinging shock boundary layer interaction (SBLI) and a compliant surface. The large separation region associated with the strong SBLI subjects the compliant surface to a wide range of turbulent fluctuations, which complicate the task of identifying and classifying aeroelastic responses with significant levels of coupling. Of particular interest is the possibility for static and dynamic feedback from the structure to the inherent flow unsteadiness. To elucidate the potential alteration of the intrinsic flow unsteadiness and to distinguish between the mean flow, structurally induced flow, and background fluctuations, a triple decomposition of the flow is adopted. Careful analysis of the coupled structural response allows for subsequent fluid-only simulations that harmonically force the flow through prescribed structural motions. Thus, an exact extraction of a representative induced flow response is obtained. Analysis of the remaining turbulent fluctuations allows for key insights into the predominant coupling mechanisms that must be considered when performing reduced-order aeroelastic computations. |
Monday, November 25, 2024 2:55PM - 3:08PM |
R30.00006: Non-linear Panel Response to Turbulent Loads in Compound Shock-Wave/Boundary Layer Interactions Anshul Suri, Jack J McNamara, Datta V Gaitonde, Serdar Seckin, Farrukh Sabbah Alvi Fluid-structure interactions (FSI), induced by shock-wave/boundary layer interactions (SBLI), significantly influence the design and performance of high-speed vehicles. This study investigates the response of compliant panels to 3D swept SBLI, focusing on double-fin (or crossing-shock) SBLI using one-way fluid-to-structure interactions. Time-resolved pressure-sensitive paint (PSP) measurements for the SBLI with a rigid surface, are employed for turbulent pressure loading on the panel area. The study explores dynamically non-linear panel responses, induced by high cavity pressure differentials. Concurrently, the panel response is evaluated at different non-dimensional dynamic pressures (λ). The low-frequency dynamics of compound SBLI exhibits complex motions moving in both streamwise and spanwise directions, imposing relatively complicated pressure fluctuation loads that are not aligned with any of the principal directions. Beyond a critical λ threshold, the panel response features multiple limit cycles, with intermittent switching between large and small amplitude oscillations. These nonlinearities facilitate energy exchange among different panel modes, which is elucidated using bispectrum analysis. This study highlights the utility of PSP data in parametric FSI analyses. |
Monday, November 25, 2024 3:08PM - 3:21PM |
R30.00007: On the Connection between the Transverse Force and Flow Separation on Galloping Prone Rectangular Cylinders Ahmed M Naguib, Alireza Safaripour, Manoochehr M Koochesfahani Symmetric bluff bodies that are prone to flow induced vibration due to transverse galloping are characterized by the formation of open separation along their sides at zero angle of attack (AoA). As the AoA increases, the magnitude of the mean transverse force coefficient increases from zero until it reaches a maximum at the critical AoA αc. In the galloping literature (e.g. Naudascher & Rockwell, 2005), there is a consensus that αc corresponds to the AoA where the shear layer reattaches on the windward side of the body. In this talk, we use high-resolution single-component molecular tagging velocimetry to capture the boundary layer behavior around high-aspect-ratio rectangular cylinders with side ratio of 2 in the Reynolds number range (based on model thickness) 1,000<Red<10,000. The results show that significant deviation could exist between and the AoA at which the shear layer reattaches on the body. The deviation seems to be connected to the geometry (corner roundness) and/or the Reynolds number. |
Monday, November 25, 2024 3:21PM - 3:34PM |
R30.00008: Interpretation of the flow-induced transverse vibrations of a rectangular cylinder through energy portraits Ross J Cruikshank, David A Olson, Ahmed M Naguib, Manoochehr M Koochesfahani The flow-induced vibrations (FIV) of bluff bodies is of research interest due to their importance in many engineering problems, such as energy harvesting and structural design. This study is motivated by the vibrations of precision airdrop suspension lines, which typically operate at Reynolds numbers Red, based on the body thickness d, below 10,000. The present study experimentally investigates the transverse oscillations of a rectangular cylinder with a chord to thickness ratio of 2. The separated shear layers of this type of body interact to form a vortex street, making the body susceptible to vortex-induced vibrations. Additionally, unlike circular cylinders, this body is unstable to galloping under certain conditions. In this study, forced transverse sinusoidal oscillations are applied to the body in a water tunnel at Red = 2,500 and the fluid-induced forces in the transverse direction are measured over a wide range of frequencies and amplitudes. The motion and measured forces are interpreted through energy portraits, relating the net energy transfer between the fluid and the body. Following the work of Menon & Mital (JFM 2019), the energy portraits are used to help identify various FIV regimes and how they are influenced by different oscillator parameters. |
Monday, November 25, 2024 3:34PM - 3:47PM |
R30.00009: Unravelling the Influence of Taper Ratio on 2-DOF Vortex-Induced Vibration Characteristics of a Circular Cylinder Mayank Verma, Ashoke De The present study discusses the effect of the taper of the circular cylinder on its vortex-induced vibration characteristics when subjected to an incoming flow with a Reynolds number (based on the average diameter) of 500. The tapered cylinder (with a mass ratio of 10) is mounted with the help of linear springs (with a natural frequency of 1.0) and the dampers (with a damping coefficient of 0.02) such that it is free to oscillate in both the inline and the cross-flow direction. The three-dimensional numerical simulations are performed over taper ratios (defined as: τ=l/(d2 - d1): 12, 20, and 40) for a range of reduced velocities (3 ≤ Ur ≤ 16). The findings indicate that increasing the taper ratio leads to delayed branch transition between the initial and lower branches with higher peak oscillation amplitude than the uniform cylinder. The combined study of the vortex distribution and the time-frequency spectrum of the probe data reveals the presence of oblique shedding and vortex stretching/dislocations. The pressure-driven secondary motion on the taper cylinders at the front stagnation regime travels from the wide end towards the narrow end and becomes weak near the narrow end, while behind the cylinder, it doesn’t have any preference for the flow-direction in the near or far wake of the cylinder. |
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