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 T33: Flow Control III: Separation |
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Chair: Shabnam Raayai, Harvard University Room: 255 E |
Monday, November 25, 2024 4:45PM - 4:58PM |
T33.00001: Passive Turbulent Boundary Layer Control through 3D-Printed Dolphin Skin Devin Alexander Kodsi, Amy W Lang, Emma Rose Hill, Andrew James Bonacci Various mechanisms for drag and flow separation reduction are continually analyzed and developed across multiple fields. This study examines the efficacy of 3D-printed transverse sinusoidal grooves modeled after dolphin skin to mitigate boundary layer separation as a form of passive flow control, energizing the flow near the wall. A water tunnel generates a turbulent boundary layer across the vertical test plate with a tripped boundary layer, and a rotating cylinder induces flow separation by creating an adverse pressure gradient. The dolphin-inspired models are tested in a range of Re values of 105 with a constant amplitude of 0.9 mm and varying groove spacings from 2.5 mm to 10 mm. It is hypothesized that the model with decreased groove spacing will better capture the flow and enhance momentum near the wall, thereby reducing boundary layer detachment. Time-resolved digital particle image velocimetry (TR-DPIV) is employed to document the flow behavior and quantify flow separation, and the resulting boundary layer profiles, backflow coefficients, and Reynolds stresses are visualized from the data. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T33.00002: Investigation of Separation Control in a Turbulent Boundary Layer Using Passive 3D-Printed Shark Denticles Alexander G Alberson, Amy W Lang, Andrew James Bonacci Separated turbulent boundary layers are an engineering problem due to their drag-inducing properties. A possible solution may lie with the shortfin mako shark whose scales’ flow-activated bristling under reversing flow conditions may passively control separated flow. An adverse pressure gradient is induced through a rotating cylinder to produce the backflow near the wall over the 3D printed array of shark scales. This passive bristling has been observed by biologists to be caused by reversing flow on real shark skin samples. Controlling effects of these scales have been seen within a 2-D separating turbulent boundary layer from previous researchers. Several shark-inspired 3D-printed models have been constructed to analyze flow control capabilities of man-man models. Data acquisition is conducted using DPIV in a water tunnel to document flow control capability, and investigate the range of permissible actuating height needed to implement flow control. Re ranging up to 8.8x10^5 in the boundary layer were tested, to vary both the boundary layer thickness and reversing flow speeds over the 3D printed models. Results are compared also to a smooth flat plate to discern the amount of separation control for a given flow regime. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T33.00003: Investigation of Turbulent Boundary Layer Separation Control Using both Flexible and Rigid 3D Printed Shark Skin Models James Bercaw, Amy W Lang, Andrew James Bonacci The separation of a turbulent boundary layer can cause reversing flow in the region aft of the separation point and close to the wall, leading to an increase in drag. However, nature may offer a way to reduce this drag in the form of passively actuated scales from the shortfin mako shark. Previous experiments have shown that both real shark skin and flexible shark scale models exhibit passive control of the flow separation. This experiment used 3D printed rigid shark skin models to study the effect on flow separation and confirm that the flexible nature of the scales is key to the separation control mechanism. The measurements were collected in a water tunnel using a DPIV system, and a rotating cylinder was placed just before the test section to induce an adverse pressure gradient and flow separation of a tripped turbulent boundary layer. Baseline experiments used a smooth flat plate in the test section with a maximum Re of 8.5 x 105. The second set of data used a Micro-actuated Array for Kinematic Optimization (MAKO) model that is geometrically similar to the scales found on the flank of the shortfin mako where scales are capable of bristling to an angle of 50 degrees. A third set of experiments used unactuated, rigid 3D printed shark scales, and a fourth experiment tested the same scales at a fixed actuation angle of 50 degrees. Results show that the separation control occurs due to the flexibility of the scales while the rigid models lose the ability to control flow separation. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T33.00004: Shark Inspired Separation Flow Control in Unsteady Laminar Boundary Layer Conditions Katelyn Heglas, Amy W Lang, Andrew James Bonacci, Jessie Laine Chiella, Alexander G Alberson Previous work suggests that the flexible scales on the shortfin mako shark exhibit flow control, specifically in both turbulent and laminar boundary layers to mitigate separation. As the flow reverses close to the skin, the scales bristle and impede further flow reversal. 3D printed flexible scale surfaces, designated as a Micro-adaptive Array for Kinematic Optimization or MAKO surface, that are geometrically similar to shortfin mako scales have been manufactured to determine if these flow control results can be recreated for a man-made surface. This study specifically documents when the scales are actuated for unsteady, laminar conditions in a boundary layer subjected to an increasing adverse pressure gradient (APG). Two MAKO models, with scale crown lengths of 2.5 mm and 3.6 mm, have been tested in a water tunnel with a boundary layer grown over a flat plate for Re up to 4x105. The APG was induced to create a separation bubble using a spinning cylinder located just upstream from the MAKO surface. The unsteady APG was created by moving this spinning cylinder vertically toward the plate from a distance of 14 cm to 4 cm. Using DPIV, the formation of the separated region can be visualized, for both a smooth surface and over the MAKO models so this passive flow control mechanism can be studied. Instantaneous flow fields capture the bristling motion of the scales, and results will show if bristling of the scales impedes the formation of reversing flow. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T33.00005: Control of Dynamic Stall on a Pitching Airfoil using Pulsed Bleed Actuation Michael DeSalvo, Ari N Glezer
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Monday, November 25, 2024 5:50PM - 6:03PM |
T33.00006: Response Time Reduction with Porosity: A Study on Flow Separation Control Xuanhong An, Alberto Medina, Sidaard Gunasekaran, Michael Mongin Porous structures have significant potential for enhancing the performance of various aerodynamic applications. This study explores the impact of porous surfaces on wings subjected to unsteady flows generated by wing motion and active flow control actuation. Both experimental methods and numerical simulations are utilized. Wind tunnel experiments were performed on a nominally 2-D wing undergoing unsteady motion with plasma actuators, and a corresponding 2-D Direct Numerical Simulation (DNS) was conducted. The analysis focuses on comparing aerodynamic loads, including lift, drag, and pitching moment, between wings with and without porous surfaces. Additionally, flow field analysis is carried out to examine the flow characteristics, offering insights for future wing designs incorporating porous surfaces. |
Monday, November 25, 2024 6:03PM - 6:16PM |
T33.00007: Circulation Control of a Circular Cylinder using Discrete, 3-D Coanda Wall Jets Nathan Rackers, Michael DeSalvo, Bojan Vukasinovic, Ari N Glezer Controlled circulation over wings to effect significant lift increments has been realized by the Coanda effect of a nominally 2-D wall jet over a bluff trailing edge or the flap. The present wind tunnel investigation explores the utility of segmented Coanda actuation for generating streamwise and cross-stream loads using spanwise arrays of fluidically oscillating wall jets integrated into a 2-D cylinder model with specific emphasis on the interaction of the control jets with the cross flow and their effects on the near wake. It is shown that compared to a conventional 2-D wall jet, 3-D jets having the same momentum coefficient effect substantial improvements in attained lift increments without significant changes in induced drag. The effects of the 2- and 3-D wall jets on separation in adverse pressure gradient over the cylinder’s curved surface are investigated using stereo PIV measurements revealing differences in structural features of induced streamwise vorticity concentrations that alter the spanwise interactions with the cross flow and thereby suppress separation. The 3-D features of boundary layer entrainment, separation, and vorticity transport and interactions between adjacent jets are assessed using POD analysis of the instantaneous velocity data. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T33.00008: Flow separation control on a backward facing step using wall information ANUSHKA SUBEDI, Yulia T Peet
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