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 B17: Aerodynamics: Multi-Rotor Vehicles |
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Chair: Morteza Gharib, Caltech Room: 4c4 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B17.00001: Experimental investigation of the unbalanced coaxial rotor configuration for unmanned aerial vehicles Emile Oshima, Katia Luis-Diaz, Morteza Gharib The coaxial rotor configuration on a helicopter eliminates the need for a torque-balancing tail rotor, but also induces large aerodynamic interference losses. For multirotor unmanned aerial vehicle (UAV) designs, however, such losses may be reduced by relaxing the torque-balancing restriction on each coaxial pair. The two rotors can have mismatched diameters, blade geometries, and rotation rates. This is a promising design approach for increasing the efficiency and maneuverability of UAVs in various applications such as package delivery, emergency response, and space exploration. A test stand for measuring the hover thrust of coaxial systems is built, with design emphasis on the ease of geometry alterations. Experimental results show that unbalanced configurations perform better than the traditional torque-balanced configuration. In particular, the thrust-to-power ratio is highest when the diameter and rotation rate of the upstream rotor are less than those of the downstream rotor. Various axial separation distances and mounting structures are also investigated. Flows for selected cases are then quantitatively visualized using particle image velocimetry. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B17.00002: Modeling rotor wakes of a quadrotor UAV in hovering mode Seungcheol Lee, Hungsun Son, Jooha Kim For rotary-wing aircraft, predicting the locations of the rotor-tip vortices plays an important role in determining the rotor performance. Thus, there have been various attempts to model the rotor wake geometry for a single rotor. However, when these models are applied to multi-rotor UAVs, the interaction between rotor wakes, such as wake deflection, cannot be modeled. In the present study, we develop an empirical model that can predict the wake geometry for a quadrotor UAV in hover. The experiment is performed in a chamber at Re $=$ 34,000, where Re is the Reynolds number based on the rotor chord length and the rotor-tip speed. By varying the normalized rotor separation distance (d/D) from 0.06 to 1.18, we directly measure the thrust force and the velocity field in the rotor wake using PIV, where d is the distance between adjacent rotor tips and D is the rotor diameter. With decreasing the normalized rotor separation distance, the extent of rotor-rotor interaction increases, and thus the wake center moves more to the center of UAV as the wake develops downstream. The wake geometry is predicted by modeling the locations of the wake center and the wake diameter as functions of the normalized rotor separation distance. Details will be discussed in the presentation. [Preview Abstract] |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B17.00003: Characterization of Rotor-Rotor Aerodynamic Interactions for Free Flight Studies of Multirotor Systems Marcel Veismann, Morteza Gharib As multirotor systems are increasingly utilized for academic as well as commercial purposes, their aerodynamics require precise identification for performance evaluation and more reliable predictive models. However, the interactions between closely arranged rotors have been given little attention. In order to account for the interactional effects on generated thrust, we developed an analytic expression derived from experimental data that is dependent on geometric and operational parameters, specifically rotor separation, rotational speeds, and Reynolds number. We find that the thrust reduction caused by the flow of neighboring rotors must be considered to accurately predict a multirotor system's cumulative propulsive force. Using this analytical model, we aim to quantify rotor performance in various free flight conditions. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B17.00004: Experimental Measurement of Flow Field Around a Rotary Wing Unmanned Aircraft for Evaluation of Onboard Anemometer Placement Alyssa Avery, Seabrook Whyte, James Brenner, Victoria Natalie, Jamey Jacob CLOUD-MAP is a collaboration between multiple universities to develop and evaluate unmanned aircraft technologies to place atmospheric sensors in otherwise hard to reach areas in the atmosphere. To determine the effectiveness of ultrasonic anemometers mounted on rotary wing aircraft, multirotor aircraft have been outfitted with sonic anemometers to measure windspeed and direction of winds aloft. The experiment maps the in-flow around a multirotor using multiple diagnostics, including PIV, ultrasonic anemometers, multi-hole probes, and impeller anemometers. Evaluation begins with flow measurements around a fixed single multirotor arm and followed up with multiple rotors with increasing fidelity for in-flight UAS. Multirotors are also be placed in a wind tunnel and angled to simulate a sonic anemometer crosswind measurement. Comparisons with flight modes are made utilizing the OSU Gust and Shear Wind Tunnel Areas while validation tests are performed with tower mounted anemometers both at the Oklahoma Mesonet and the DOE ARM SGP Site. Areas of general quiescent flow are found absent of large scale disturbances or turbulent fluctuations. Results detail the accuracy of sonic anemometer measurements from mounted while on the multirotor in flight. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B17.00005: Flight performance of autonomous quadrotors in von Karman wakes Kasey Laurent, Joshua Solberg, Marigot Fackenthal, Grace Ding, Gregory Bewley Natural environments are highly variable and present significant challenges for autonomous aircraft. As the size of aircraft decreases, they become more susceptible to~flow~disturbances and typical control schemes fail. An understanding of the effects of turbulence on flight becomes crucial when developing new control schemes to optimize the performance of smaller aircraft. We designed an experiment in which an autonomous controller flies a small quadrotor in the von Karman vortex street behind a cylinder in a wind tunnel. We varied controller parameters as well as properties of the flow, such as mean airspeeds up to 3 m/s and wake dimensions as well as flow time scales between 0.5 and 2 times the quadrotor dimensions and response times, to find relationships between the controller and the response of the quadrotor. We measured displacements and power consumption in flight in the wake and compared this to the performance of the quadrotor in quiescent flow. Finally, we compare to the behavior of the quadrotor in active grid turbulence, with turbulence intensities up to 26{\%}.~ We find that the quadrotor dynamics are set by an interplay between the turbulence and the controller. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B17.00006: Potential Flow Model for Wall Effects on Quadrotor UAVs Dimitri Calomiris, Jovan Nedic Solid surfaces are known to directly influence the flow surrounding propellers when they are close to each other by altering the thrust force. One of the most common potential flow models, developed by Cheeseman and Bennett, predicts the relative increase of a rotor's thrust as a function of ground distance (for constant power operation), within four rotor radii ($i.e.$ in ground effect). Recently, Sanchez-Cuevas \textit{et al.} extended this single propeller model to a quadrotor, which experiences a much larger influence from the ground. However, no such characterization has been done for walls. A potential flow model to account for wall effects will be presented and the results compared to experimental data. Initial measurements have qualitatively shown that the presence of the wall causes the quadrotor UAV to pitch down, essentially flipping it into the wall. [Preview Abstract] |
Saturday, November 23, 2019 5:58PM - 6:11PM |
B17.00007: Multi-rotor Unmanned Aerial Vehicle (UAV) performance under shear flow Ningshan Wang, Aleksandar Dzodic, Dom DiDominic III, Amit Sanyal, Mark Glauser Several multi-rotor UAV test flights under shear flow turbulence are carried out. This research targets evaluating the flight performance of the multi-rotor UAV when exposed to shear flow. The UAV deployed with different types of control schemes is exposed to shear flow with different shear rates and freestream velocities to gain its performance under a variety of conditions. Characterization of the shear flow field is evaluated by an array of total pressure scanners to measure the shear rate and free stream velocity spatially. The flight performance data is achieved through the Inertial Measurement Unit (IMU) integrated inside the UAV controller. [Preview Abstract] |
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