Bulletin of the American Physical Society
74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021; Phoenix Convention Center, Phoenix, Arizona
Session E16: General Fluid Dynamics; Rotating Flows & Drag Reduction |
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Chair: Amirfarhang Mehdizadeh, University of Missouri-Kansas City Room: North 130 |
Sunday, November 21, 2021 2:45PM - 2:58PM Not Participating |
E16.00001: A triple-deck analysis of the steady flow over a rotating disk with surface roughness Claudio Chicchiero, Antonio Segalini, Simone Camarri The flow over a rotating disk in still fluid is a canonical flow case that has attracted much attention with several studies focused on its stability properties. For a smooth disk, the steady laminar flow is described by the self-similar solution provided by Von Kármán. |
Sunday, November 21, 2021 2:58PM - 3:11PM |
E16.00002: Flow Separation Behind a Bulge in Rotating Turbulent Channel Flows Wen Wu In a channel rotating about the spanwise axis, the turbulence near the wall where the mean vorticity has the opposite sign of the rotation may be either de-stabilized or stabilized; the other side tends to become more stable or even relaminarized. The response of a flow separation induced by a protuberance on one of the walls of an otherwise planar turbulent channel is investigated using DNS. The bulk Reynolds number of the channel is 2,500. The bump is placed on either the stable or unstable side of the channel, modeled using an immersed boundary method. Two rotating rates ($Ro_b=2\Omega\delta/U_{b}$ = 0.42 and 1.0) were used to compared with the non-rotating baseline case. When the bulge is placed on the unstable side, rotation reduces the size of the mean separation region. At the high Rotation number, the separation is nearly completely suppressed. When the bulge is placed on the stable side, the quasi-laminar boundary layer separates earlier behind the bump and forms more coherent 2D roller vortices in the separated shear layer. The mean separation bubble reattaches much later compared with the non-rotating case. The effects of the Coriolis force on the separating shear layer will be discussed. |
Sunday, November 21, 2021 3:11PM - 3:24PM |
E16.00003: Intricate patterns of three-dimensional inertial wavebeams in a tilted librating cube Ke Wu, Juan M Lopez, Bruno D Welfert A fluid-filled cube rotating about an axis passing through the midpoints |
Sunday, November 21, 2021 3:24PM - 3:37PM |
E16.00004: Visualization of flow structures in an isothermal swirling flow in a confined domain Rahul Sharma, Mayank Kumar A computational study of flow structure have been carried in the current study. The swirling flow involves much more complexity than the non-swirl flow due to higher probabilities of instabilities, asymmetric vortex core, precessing vortex core, Internal recirculation zone (IRZ), vortex breakdown, and other coherent flow structures. This brings attention to study and analyze these effects by visualizing the flow with such a method so that each type of structure can be more understandable than previous studies. We visualized the swirling flow in a confined domain by simulating the transient isothermal flow using RANS modeling on Ansys fluent platform. The results reveal that the patterns of flow structures are in a vast range as the vortex core and IRZ keeps on switching their state from symmetric and steady to asymmetric and transient. These precarious states are found to be dependent on Reynolds number, swirl strength, method of generating swirl and domain type. |
Sunday, November 21, 2021 3:37PM - 3:50PM Not Participating |
E16.00005: Simulations of Plano-Taylor-Couette Flow Devin Kenney, Varghese Mathai The flow between moving, parallel plates (plane-Couette) and the flow between concentric, rotating cylinders (Taylor-Couette) represent two canonical fluid flow configurations that have been studied in great detail. Here we use numerical simulations to study the flow between conveyor belts composed of a linear region resembling the plane-Couette geometry, and a curved, corner region resembling the Taylor-Couette geometry. The linear region, of length L, smoothly merges into the circular corners with inner and outer belt curvatures, L / ri and L / ro, respectively. This system presents a single geometry that includes zones of two classically studied wall-bounded flows, and allows for a continuous topology transformation between the two limits. For L / ri << 1, the system tends to a pure Taylor-Couette flow, while in the other limit of L / ri >> 1 the geometry is dominated by the plane-Couette flow. We explore the case of pure inner-belt motion, for which the control parameters are the inner-belt Reynolds Number, Re = riωid / ν and the dimensionless curvature of the corner, κ ≡ L / ri, where d = ro - ri is the gap between the belts, and ωi is the angular speed of the inner belt at the corner. We decompose the total dissipation in the system into contributions from the dimensionless torque and the dimensionless drag for varying L / ri, for a range of Reynolds numbers at a fixed curvature ratio (or radius ratio). The flow structures in both the linear and the curved regions are evaluated, as well as those in the merging zone. |
Sunday, November 21, 2021 3:50PM - 4:03PM |
E16.00006: Artificial denticle-covered textures in Taylor-Couette flows Lars F Caspersen, Shabnam Raayai Riblet-textured surfaces, inspired by ribs on the denticles of sharks, have been demonstrated as an effective method to reduce the frictional drag force exerted on the wall. The response of these 2D grooves vary depending on their cross-sectional geometry, with previous research largely focused on V-grooves. However, shark denticles protrude outwards at an angle from the plane of the skin and overlap with the neighbors. In this talk, we investigate how the addition of this protrusion defined as an offset angle with respect to the base surface impacts the flow. We present the results of our experiments performed in a Taylor-Couette cell with textured 3D-printed inner rotors. Texture of each rotor consists of V-groove riblets broken up into separate denticles placed at an offset angle to the circumference of the base rotor. To achieve this design in a cylindrical coordinate system, the riblets are set to protrude from the rotor along the path of a logarithmic spiral. We will show our torque and velocity measurements in Couette flow and Taylor vortex flow regimes as a function of the Reynolds number and the geometry of the artificial denticles, and ultimately compare the results across the denticle-covered rotors and with base rotors with circumferential V-groove textures. |
Sunday, November 21, 2021 4:03PM - 4:16PM |
E16.00007: Ventilated supercavitation around a moving body in a still fluid Yeunwoo Cho, Jaeho Chung This experimental study examines ventilated supercavity formation in a free-surface bounded environment where a body is in motion and the fluid is at rest. For a given torpedo-shaped body and water depth (H), depending on the cavitator diameter (dc) and the submergence depth (hs), four different cases are investigated according to the blockage ratio (B=dc/dh, where dh is the hydraulic diameter) and the dimensionless submergence depth (h*=hs/H). Cases 1~4 are no cavitator in fully submerged (B=0, h*=0.5), small blockage in fully submerged (B=15%, h*=0.5), small blockage in shallowly submerged (B=1.5%, h*=0.17) and large blockage in fully submerged (B=3%, h*=0.5) cases. In case 1, no supercavitation is observed and only a bubbly flow (B) and a foamy cavity (FC) are observed. In cases 2 and 3, a twin-vortex supercavity (TV), a reentrant-jet supercavity (RJ), a half-supercavity with foamy cavity downstream (HSF), B and FC are observed. In case 4, a half-supercavity with a ring-type vortex shedding downstream (HSV), double-layer supercavities (RJ inside and TV outside (RJTV), TV inside and TV outside (TVTV), RJ inside and RJ outside (RJRJ)), B, FC and TV are observed. The body-frontal-area-based drag coefficient for a moving torpedo-shaped body with a supercavity is measured to be approximately 0.11 while that for a cavitator-free moving body without a supercavity is approximately 0.4. |
Sunday, November 21, 2021 4:16PM - 4:29PM |
E16.00008: Experimental drag minimization of a morphing soft silicone-shell robot. Mark Hermes, Mitul Luhar Despite the overwhelming dominance of bilateral symmetries in animal morphologies, examples of Radial Symmetries (RS) are not uncommon in aquatic environments. Some RS animals have developed exceptional abilities to survive repeated exposure to extreme fluid flow events. Species living in intertidal regions, for example, must be able to withstand wave velocities up to 8m/s. These animals have developed inspiring strategies to survive these loads. The sea star, Pisaster Ochraceus, produces passive downforce due to their pentaradial pyramid-like geometry, which may serve to enhance attachment to surfaces during wave exposure. These sea stars are also known to exhibit morphological plasticity in response to fluid flow intensity. Inspired by these observations, we developed a soft silicone-shell 7 degree-of-freedom (5 arm extensors, 1 height extensor, 1 volume inflator) robot that changes its shape to minimize drag and lift forces. We applied a Bayesian Optimization algorithm with a coarse grid search initial dataset to rapidly converge to an optimal shape configuration. This work shows that emerging soft robotic technologies can be used to advance hydrodynamic shape optimization and such systems could tune fluid-structure interactions for performance gain. |
Sunday, November 21, 2021 4:29PM - 4:42PM |
E16.00009: Study of drag reduction potential in textured microchannels Nastaran Rabiei, Massimo DiMuzio, Carlos H Hidrovo Reduced length-scales in microchannels is highly favorable for efficient manipulation of the flow and mixing in biochemical devices as well as enhancing heat transfer which makes them an ideal candidate for microelectronics cooling applications. However, these benefits come at the cost of higher pumping power requirements that can be alleviated using surface mixrotexturing. While the results of some of the studies in this field may have been misconstrued due to the lack of a proper smooth reference channel selection, it is critical to understand this in order to conduct valid comparisons. Considering a smooth reference channel that occupies the same volume as the textured microchannels, we have performed numerical simulations and experiments to study the effect of important geometrical parameters of the trenches on the Poiseuille number, which represents the non-dimensional hydraulic resistance of a channel. |
Sunday, November 21, 2021 4:42PM - 4:55PM |
E16.00010: Rowing Race Strategy : find the optimum through hydrodynamics, biomechanics and physiologics constraints. Alice Boillet, Hugo Maciejewski, Christophe Clanet, Laurent Messonnier, Caroline Cohen During a race, rowers have to travel a cosntant length: 2000 meters. They do it in approximately 240 strokes, oscillating on a thin shaped boat while pulling their oars. During this 6 to 7 minutes effort, they have to choose their energy managing strategy: some of them start very fast but are unable to maintain the high pace until the end of the race; on the contrary, some others accept to start behind in order to have enough energy to finish faster (negative split strategy). Inspired by the seminal work of J.B. Keller on running races, the goal of this stufy is to derive a theoretical model of the rowing race, taking into account hydrodynamic frictions of the rowing boat (added mass, skin friction, wave resistance), and the biomechnaics and physiology of human rowing propulsion, in order to find the optimal strategy to run the race. |
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