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 Q12: Vortex Dynamics and Vortex Flow: General II |
Hide Abstracts |
Chair: Carlo Scalo, Purdue University Room: 303 |
Tuesday, November 26, 2019 7:45AM - 7:58AM |
Q12.00001: Modification of Tip-Vortices using Chevron Wing Tips Anushka Goyal, Jovan Nedic The aerodynamic performance of chevrons with varying depths, cut directly into the tips of a flat plate with a semi aspect ratio of 3 were investigated using a time resolved six axis force/torque sensor at a Reynolds number of 67,000. Results show that shallower chevrons cut directly into the tips of wings lead to a higher peak $\frac{L}{D}$ ratio at an angle of attack of 5$^\circ$. It is known that the formation of a tip vortex depends on the geometry of the wing tip (Sarpkaya 1983, Giuni and Green 2013). The chevrons plates formed tip vortices that have lower peak tangential velocities and larger core radii as compared to a flat plate, based on measurements taken by using a four sensor hot wire. The tip vortices formed on wing tips with deeper chevrons exhibited a turbulent core, as opposed to those formed on a flat plate. It was also found that deeper chevron plates had an impact on the wandering of the tip vortex. [Preview Abstract] |
Tuesday, November 26, 2019 7:58AM - 8:11AM |
Q12.00002: Wavelength variation in seal whisker geometries and the effect on vortex structure Christin T. Murphy, Kathleen M. Lyons, William A. Haddock, William N. Martin, Aren M. Hellum, Kenneth S. Breuer, Jennifer A. Franck Seal whiskers have a unique undulated geometry that affects water flow over the structure and influences downstream shedding. By intensifying and modifying geometric features in whisker models, we can observe their effects more clearly. In a multi-parameter analysis, wavelength is shown to be an important parameter, especially if interacting with other geometry features. This study isolated the effect of wavelength by creating four physical models of different wavelength but constant streamwise and transverse amplitudes, peak shift, and symmetry. Flow visualization in a water tunnel, in the biologically relevant Reynolds number range of 500-2000, demonstrates the ability of the undulations to enhance the spanwise momentum transport, reduce the recirculation region, and modify the frequency spectra in the recirculation region behind the whisker. To complement the experiments, direct numerical simulations (DNS) at Re 500 are performed on the four models to correlate the flow structure visualization with resulting drag coefficients, root-mean-square lift coefficients and reduced frequencies. Agreement between experiments and simulations isolates the dominant flow structures responsible for shifts in the frequency spectra over the range of wavelengths investigated. [Preview Abstract] |
Tuesday, November 26, 2019 8:11AM - 8:24AM |
Q12.00003: Direct numerical simulation of trefoil knotted vortices Xinran Zhao, Carlo Scalo 3D viscous vortex reconnection has been a topic of strong interest for the fluid mechanics community over the past several decades. This paper investigates pre- and post-reconnection dynamics of a trefoil knotted vortex for Reynolds numbers up to Re $=$ 20,000 by means of DNS with adaptive mesh refinement. The compressible Navier-Stokes equations are solved on the block-structured computational domain with compact-finite difference scheme. An overall high-order accuracy in space can be achieved with the combination of high-order compact restriction/prolongation operators. The test refinement function is given by a Coherent-vorticity-perserving (CvP) sensor (Chapelier, Wasistho, and Scalo, 2018. J. Comput. Physics., 359, 164-182) from our previous work. The simulation on the trefoil vortex problem has shown that this sensor is capable of capturing and refining the location where the reconnection occurs and local turbulence is produced. The complete flow evolution is resolved by the DNS simulation, including the turbulence production upon reconnection, subsequent separation into a smaller and a larger vortex ring, and, finally, the formation of Kelvin waves. The DNS simulation depicts the mechanism how helicity is produced due to small-scale vortical events during the bridging process. A qualitative comparison between the present simulations and existing experiments has also been conducted and an excellent match has been found in terms of flow topology. [Preview Abstract] |
Tuesday, November 26, 2019 8:24AM - 8:37AM |
Q12.00004: Vortex Force Map Method for Unsteady Incompressible Viscous Flows Juan LI, Xiaowei Zhao Recently, Li {\&} Wu (2017, 2018) proposed a vortex force map method for a flat plate and extended it to general airfoils at high Reynolds numbers by adopting Howe's (1995) force formula for the derivation of the vortex force vectors. Here, the vortex force map method is refined to have the capability of dealing with more general cases for a larger range of Reynolds numbers. Updated vortex-pressure force maps, which ensure vortices far away from the body have negligible effect on body-force, are built based on the vortex-pressure force factors derived from viscous governing equations. These maps help us identify the force contribution role of each given vortex more precisely than the ones presented previously. The impulsively started flows around a cylinder and a NACA0012 airfoil are used to demonstrate the applications of this vortex force map method. CFD is used to provide the velocity and vorticity data, as well as for validations by comparing the forces directly given by it with those from the proposed vortex force map method. In order to explore the possibility of applying this method to extracting forces from PIV data, the accuracy of this approach on small domains and under coarse sampling is demonstrated. [Preview Abstract] |
Tuesday, November 26, 2019 8:37AM - 8:50AM |
Q12.00005: Vortex dynamics from a vibrating leaf upon drop impact Zixuan Wu, Seungho Kim, Sunghwan Jung Raindrop impact have been shown to discharge rust spores and induce dispersal from leave surface through fluid-elasticity interactions and vortex ring formations. In contrary to impacts on rigid surface, here we present an exposition on the vortex dynamics transformations resulting from drop-induced leave oscillations. Experimentally, we utilized high-speed imaging to probe the complex vortex dynamics and S(Single)-P(Pair) shedding schemes from a damped harmonic oscillator (drop impacted a flexible, free-end beam) without a prescribed background flow. While low impact inertia is shown to yield single vortex shedding behavior, epitomized by the von Karman street, beam fluctuations from high inertia and even longitudinal twisting motions can give ways to paired vortex schemes and atypical vorticity generations. By tuning such interactions between drop inertia and beam elasticity, the beam vibrations show different frequency and amplitude regimes, with damping effect from lingering vortices and residual drop oscillations. Vorticity behavior of the induced airflow can then provide potential insights on more spore dispersal from simple mechanically induced vibrations. [Preview Abstract] |
Tuesday, November 26, 2019 8:50AM - 9:03AM |
Q12.00006: The Propulsive Performance of Side-By-Side Foils at a Range of Re and St Ahmet Gungor, Arman Hemmati The hydrodynamic interactions between two foils placed in side-by-side arrangement are investigated using Direct Numerical Simulation at Reynolds numbers of 1000, 2000 and 4000, and Strouhal numbers (St) ranging from 0.25 to 0.5. The transverse spacing and phase difference between the foils are kept constant. Dynamic motions of the foils are simulated using dynamic mesh morphing technique in OpenFOAM. Coefficients of thrust and power, as well as efficiency, are used to compare the performance of foils. The interactions between foils are also studied through varying the St of individual foils. The performance parameters of the system are observed to depend on both St and Re. In the range of St, the combined efficiency of the system reaches the maximum at St$=$0.4. The system experiences a thrust enhancement with increasing Re although the coefficient of power remains stable in the Re range. The results are used to evaluate the applicability of the scaling law developed by Floryan et al. (2017) on an isolated foil. The scaling laws for tandem foils in side-by-side arrangements are also developed. [Preview Abstract] |
Tuesday, November 26, 2019 9:03AM - 9:16AM |
Q12.00007: ABSTRACT WITHDRAWN |
Tuesday, November 26, 2019 9:16AM - 9:29AM |
Q12.00008: Drag Estimation of Isolated, Surface-mounted, Droplet-inspired Geometries Xueqing Zhang, Burak A. Tuna, Serhiy Yarusevych, Sean D. Peterson Droplet mobility on a substrate due to aerodynamic loading is of interest of many industrial applications. However, modeling this phenomenon is hindered by a lack of reliable estimations of aerodynamic forces on representative shapes. The present study investigates the wake development downstream of isolated, surface-mounted, three-dimensional droplet shapes submerged in a laminar boundary layer. The obstacle geometries considered are representative of the droplet morphologies at sessile state (`sessile') and at depinning (`runback'). The incoming flow has a Reynolds number based on obstacle height of $\mathrm{Re}_h = 2070$ and a boundary layer thickness of around one obstacle height, simulating the critical flow conditions at droplet depinning. Aerodynamic loading on the obstacles is estimated using the wake integral method extended to drag estimation for obstacles with high boundary layer submergence. With a laminar incoming boundary layer, the drag coefficient of the `sessile' model is larger than that of the `runback' model. The drag reduction for the `runback' model is ascribed to the tapered front-body and short aft-body geometry, which makes the obstacle more aerodynamic. For both cases, drag coefficients decrease with increasing turbulence level in the incoming flow. [Preview Abstract] |
Tuesday, November 26, 2019 9:29AM - 9:42AM |
Q12.00009: Definition of local vortical axis flow geometry Katsuyuki Nakayama Local vortical axis flow is defined in the vortical region in the velocity gradient field, which specifies the characteristics of the passage of a vortical axis in the core region of a vortex. The axis vector field derived from vortical axes (identified by a definition of the vortical axis) is defined, and the local axis geometry of the axis vector field is specified by the gradient tensor of its axis vector. Even though the eigenvalues of the tensor may exhibit the feature of the axis curve, it is not associated with the characteristics of the passage of the core region of a vortex. The present study specifies the convergence/divergence/rotation of a bundle of the axes in swirl plane of a vortex. The swirlity and sourcity that represent the unidirectionality and intensity of respective azimuthal and radial flows in the plane are applied to specify the characteristics of local axis geometry in the swirl plane, as a characteristic of a bundle of the axis. It shows that the bundle feature of a vortical axis such as the eigen-vortical-axis line (EVAL) or pressure minimum line is associated with the velocity structure of a vortex, and that the vortical axis associated with the local vortical flow (EVAL) tends to be stable in the intense vortical region. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700