Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E14: Vehicle Aerodynamics |
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Chair: James Buchholz, University of Iowa Room: Georgia World Congress Center B301 |
Sunday, November 18, 2018 5:10PM - 5:23PM |
E14.00001: Effect of boundary layer thickness on drag and wake structure of the Ahmed body Ryosuke Oda, Jun Sakakibara A simple car model ‘Ahmed body’ proposed by Ahmed et al [SAE Technical Paper, 840300, 1984] has a slant surface on the rear upper surface, and its aerodynamics characteristics are significantly affected by the slant angle. Since the model is installed near the wall, the influence of the boundary layer is large. We measured the drag acting on the model exposed in boundary layer having a variety of thickness. We also measured velocity distribution around the model with the slant angle 25° and 30° using PIV. Free stream velocity was set at 15 m/s, and Reynolds number based on the square root of the frontal area was 3.13×104. The drag acting on the model tended to increase as boundary layer thickness increased. As increasing boundary layer thickness at the slant angle being 25°, velocity of flow through model undersurface was reduced. At the slant angle being 30°, the increase of the boundary layer thickness exhibited sudden reduction of drag and elongation of the streamwise vortices in wall normal direction. |
Sunday, November 18, 2018 5:23PM - 5:36PM |
E14.00002: Experimental Measurement of Flow Field Around a Rotary Wing Unmanned Aircraft Seabrook Whyte, Jamey D Jacob Multirotor aircraft are outfitted with sonic anemometers to measures wind speed and direction of winds aloft for atmospheric boundary layer measurements. This effort maps the flow field around a multirotor with a sonic anemometer attached to the top of it to determine accuracy of the mounted anemometer measurements while on the vehicle in flight as air being pulled into the propellers can cause discrepancies in anemometer measurements. The project begins with flow measurements on the anemometer in a wind tunnel and continues with 5 hole probes and hot-wires an vehicle in flight. Flow visualization and particle image velocimetry are being used to map and analyze the flow. Validations are made using towers in the field including the Oklahoma Mesonet and DOE ARM SGP site as well as lidar. |
Sunday, November 18, 2018 5:36PM - 5:49PM |
E14.00003: Unsteady simulations of flow around a multicopter using an actuator disk model Junseong Lee, Teasoon Kim, Junkyu Kim, Solkeun Jee Computations of flow around a multicopter are conducted using an actuator disk model. The purpose of the current study is to investigate the actuator disk model for cost-effective simulations. Details of the blade geometry are not required for the current approach. Instead, thrust and torque on the rotor disk are approximated based on a control volume analysis. It is anticipated that numerical cost would be significantly reduced while the flow field is reasonably reproduced. Computational results will be compared with relevant test data. |
Sunday, November 18, 2018 5:49PM - 6:02PM |
E14.00004: Flow Field and Spectral Characteristics of a Ship Airwake with Wave-induced Motions Austin F. Krebill, James H. J. Buchholz, Gregory M. Dooley, Juan E. Martin, Pablo M. Carrica A rotorcraft landing on a ship deck interacts with a highly unsteady aerodynamic environment due to atmospheric boundary layer turbulence and the unsteady airwake shed by the ship superstructure, which may be influenced by wave-induced motion of the ship. Applying PIV and LDV measurements on a 2-m-long ship model and DES numerical simulations using a dynamic overset grid technique, we consider the wind flow field over the ONR Tumblehome geometry with uniform inflow at a Reynolds number of 106, with and without imposed pitch and heave motions derived from wave interactions. Whereas at Re=O(104), discrete flow structures shed from the fore of the superstructure synchronize with arch structures to form a highly periodic shedding pattern over the landing deck, at Re=106, the diminished scale of the fore structures and broader range of spatial scales makes the flow much more complex. Mean velocity fields and spectra in the vicinity of the landing deck are compared with and without periodic ship motions to provide insight into the dynamics of the airwake and the influence of ship motion. |
Sunday, November 18, 2018 6:02PM - 6:15PM |
E14.00005: Dynamic response of a helicopter hovering above a ship’s flight deck Gregory M. Dooley, Juan E. Martin, Austin F Krebill, James H. J. Buchholz, Pablo M. Carrica We present a CFD study of a helicopter hovering 9 m above the flight deck of the full-scale ONR Tumblehome ship. Regular head waves for sea states 3 and 6 are analyzed with wind speeds of 15 and 35 knots, respectively, while the ship advances at 15 knots. Two approaches are used. In one-way coupling the water and air flow, and ship motion are predicted without the rotorcraft, while independent performance curves of a generic 4-bladed rotor based on the SH-60 Seahawk are computed. Then the thrust on the rotor is computed for large and small helicopters (SH-60 and Robinson R22 sizes) and a small drone (0.75 m rotor diameter). Small scale turbulent fluctuations are mostly filtered by the larger craft, but the drone is strongly affected by small scales. The response to the wave encounter frequency is considerable for all cases. A two-way analysis was performed for SH-60, computing air/water flow and motion in waves maintaining the helicopter (with rotating main and tail rotors) at constant altitude. Baseline cases with no ship motions and of the helicopter were also computed. The thrust shows a strong peak at the blade passing and wave encounter frequency and harmonics. |
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