Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session E17: Aerodynamics: VehiclesAerodynamics
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Chair: Ivaylo Nedyalkov, University of New Hampshire Room: 605 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E17.00001: Aerodynamics of the superstructure of a moving ship in a turbulent boundary layer Gregory Dooley, Austin Krebill, J. Ezequiel Martin, James Buchholz, Pablo Carrica The airwake behind a ship is a problem of practical and fundamental interest. The complex flow resulting from the interaction of the wake from the blunt superstructure with the wave-induced motions of the ship and background turbulence of the incoming wind result in a variety of turbulent structures with scales strongly dependent on the characteristics of the ship and incoming flow. Characterization of the flow field is relevant in the context of aircraft operation in the wake region. Better understanding of the interactions between the different mechanisms driving the flow can lead to reduced order models of the case, useful for design and operational guidance for landing aircraft. REX, a ship hydrodynamics computational fluid dynamics suite able to solve both air and water phases around a moving ship has been used to explore the characteristics of the airwake. A 6-DOF solver and course-keeping controllers are used to realistically simulate the advancing ship; overset technology is used to connect the structured grids defining the computational domain. Examples of the flow around a modern surface combatant, including motions in irregular waves and turbulent fluctuations of the boundary layer as prescribed with Mann's atmospheric boundary layer model will be presented. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E17.00002: Drag and Side Force Reduction for Cyclicsts in Echelon Formation Ivaylo Nedyalkov, Alec Cunningham, Adam Lovell When riding directly behind another cyclist (drafting), a rider can use up to 30\% less energy. This technique is often used during competitions, yet drafting in the presence of a cross wind has not been studied extensively. To investigate the effect of side-wind on drafting, 1:11 scale models of two different cyclists were rapid-prototyped and tested in a wind tunnel. The drag and side forces were measured in formations of up to 4 models. The results suggest that there is a significant decrease in both drag and side force when a cyclist is riding in another cyclist’s wake. Positioning with no off-stream-wise offset result in the largest reduction of forces. When riding in a group of four cyclists, the second and third cyclist experience the largest force reduction. The size of the leading cyclist affects the reduction of forces, particularly when the leading cyclist is smaller. The results are dependent on the Reynolds number, but appear to be independent at higher Reynolds numbers. Initial full scale tests were conducted at the UNH Flow Physics Facility. [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E17.00003: Novel Aerodynamic Design for Formula SAE Vehicles Samuel Sentongo, Austin Carter, Christopher Cecil, Ioan Feier This paper identifies and evaluates the design characteristics of a novel airfoil that harnesses the Magnus Effect, applying a moving-surface boundary-layer control (MSBC) method to a Formula SAE Vehicle. The MSBC minimizes adverse pressure gradient and delays boundary layer separation through the use of a conveyor belt that interacts with the airfoil boundary layer. The MSBC allows dynamic control of the aerodynamic coefficients by variation of the belt speed, minimizing drag in high speed straights and maximizing downforce during vehicle cornering. A conveyer belt wing measuring approximately 0.9 x 0.9m in planform was designed and built to test the mechanical setup for such a MSBC wing. This study follows the relationship between inputted power and outputted surface velocity, with the goal being to maximize speed output vs. power input. The greatest hindrance to maximizing speed output is friction among belts, rollers, and stationary members. The maximum belt speed achieved during testing was 5.9 m/s with a power input of 48.8 W, which corresponds to 45.8 N of downforce based on 2D CFD results. Ongoing progress on this project is presented. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E17.00004: Large-eddy simulation of a turbulent flow over the DrivAer fastback vehicle model Mario Ruettgers, Junshin Park, Donghyun You In 2012 the Technical University of Munich (TUM) made realistic generic car models called DrivAer available to the public. These detailed models allow a precise calculation of the flow around a lifelike car which was limited to simplified geometries in the past. In the present study, the turbulent flow around one of the models, the DrivAer Fastback model, is simulated using large-eddy simulation (LES). The goal of the study is to give a deeper physical understanding of highly turbulent regions around the car, like at the side mirror or at the rear end. For each region the contribution to the total drag is worked out. The results have shown that almost 35\% of the drag is generated from the car wheels whereas the side mirror only contributes 4\% of the total drag. Detailed frequency analysis on velocity signals in each wake region have also been conducted and found 3 dominant frequencies which correspond to the dominant frequency of the total drag. Furthermore, vortical structures are visualized and highly energetic points are identified. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E17.00005: Flow behavior at different boattail angles of an axisymmetric body in low-speed regime. Tran The Hung, Takumi Ambo, Taekjin Lee, Taku Nonomura, Keisuke Asai A boattail, added to a blunt base of an axisymmetric body, is a well-known means for drag reduction and has been studied widely. Despite a huge number of investigations, the information relating to the effect of boattail angle on flow pattern at the slant surface in low-speed regime is still limited. To obtain more clearly flow behavior, an experiment on axisymmetric bodies with different conical boattail angles, ranging from 10 to 25 degrees, has been performed. A global luminescent oil-film skin friction meter was employed to extract skin friction and analyze the flow pattern. The skin friction results indicate three types of flow on the slant surface: unseparated at the angle of 10 degrees, separated and reattached at angles from 12 to 20 degrees and totally separated at the angle of 25 degrees. Interestingly, when angle increase from 12 to 20 degrees, the separation points stay nearly at the fixed position while reattachment points move downstream. An average skin friction value indicates an increase of skin friction magnitude inside and a decreasing trend behind the separation bubble as the result of increasing angles. At high angles, the flow fully separates near the boattail shoulder and the whole afterbody is located inside the wake region. [Preview Abstract] |
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