Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session J04: Rotor Aerodynamics and Interactions |
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Chair: Vrishank Raghav, Auburn University Room: 101 |
Sunday, November 19, 2023 4:35PM - 4:48PM |
J04.00001: Study on the effects of blade crossover on the blade airloads Lokesh Silwal, Carson R Youngblood, Vrishank Raghav Blade crossover, a periodic interaction between two blades rotating in opposite directions, is commonly observed in urban air mobility aerial vehicles with counter-rotating coaxial rotor configurations. These interactions lead to increased vehicle vibrations and alterations to the vehicle's acoustic signature. However, the underlying physics of these interactions are not well understood. This work aims to study the effects of blade crossover on blade airloads and understand the underlying physics. A towing tank facility was developed, enabling the translation of two infinite wings in opposite directions. Each blade was mounted with multi-axis strain gauge load cells to measure the blade airloads. Quantification of the temporal scale (ratio of blade chord to translation velocity) for the current problem shows that the time scale is always constant and implies that the airloads should exhibit self-similar characteristics. The validity of this observation is currently being explored by conducting experiments at different translation speeds and blade chord lengths. This parametric space provided insights into varying length and time scale effects on the airload characteristics during the blade crossover. Initial results show that the airload characteristics are independent of the translation speed exhibiting self-similar characteristics. Further analysis of the airloads self-similarity characteristics across different length scales will be presented. |
Sunday, November 19, 2023 4:48PM - 5:01PM |
J04.00002: Abstract Withdrawn
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Sunday, November 19, 2023 5:01PM - 5:14PM |
J04.00003: Pressure Variations for a Shrouded Tail Rotor in Edgewise Flight Purui Chen, Jovan Nedic The concept of a shrouded rotor has gained considerable attention in modern rotorcraft design due to its potential to improve the aerodynamic and aeroacoustics performance of the rotor. By enclosing the rotor within a cylindrical shroud, additional thrust can be generated while achieving considerable noise reduction. Most existing research has focused on the hovering condition, assuming a zero-freestream velocity. However, during the climb and descent, the shrouded tail rotor operates in an edgewise flight condition, leading to observable inflow distortion. In this study, a shrouded rotor was experimentally examined in a wind tunnel at various tip-to-freestream velocity ratios μ. Measurements of the pressure distribution on the shroud inner surface were investigated, which showed a clear change in topology as μ increased. A peak positive pressure was observed on the downwind side of the shroud, which moved towards the shroud exit as μ increased. |
Sunday, November 19, 2023 5:14PM - 5:27PM |
J04.00004: The Effects of Freestream Turbulence on Edgewise Flight Fixed-Pitch Rotor Noise and Forces Lawrence Ukeiley, James Goldschmidt, Riley Hackworth The use of eVTOL vehicles as a means of urban transportation forces the fixed-pitch rotors to operate in high levels of atmospheric turbulence. This makes it imperative to understand the basic effects of freestream turbulence on rotor noise and forces. To analyze these effects, a fixed-pitch APC 9x6E rotor was operated in a range of edgewise flight conditions. The experiments were conducted in the UF Anechoic Wind Tunnel Facility, which was outfitted to include three sets of passive grids for varying freestream turbulence conditions. The grid generated turbulence intensity and integral length scales were characterized with stereoscopic Particle Image Velocimetry (sPIV). sPIV measurements were also conducted above the rotor, operating in both clean and turbulent freestream conditions to investigate the effects of mean flow distortion on turbulence properties. The results showed that the mean induced flow to the rotor plane altered the turbulence statistics when compared to the baseline grid characterization measurements. The rotor forces and noise were also measured in similar conditions and the results indicated that the increased freestream turbulence intensity reduced rotor efficiency. |
Sunday, November 19, 2023 5:27PM - 5:40PM |
J04.00005: Developing a cyber-physical system to simulate an amphibious UAV's transition between water and air Logan P Honts, Yuanhang Zhu, Daniel Quinn Amphibious unmanned aerial vehicles (UAVs) are rising in popularity in robotics and fluids research with their applications in exploration, delivery, and reconnaissance. These missions require an efficient and agile UAV that smoothly transitions between the water and air. Such UAVs exist, but lack innovation in the rotors used or the method of transition. The goal of this project is to push the limits of these vehicles by studying the hydrodynamics governing rotors as they move between the two media. We will do this by implementing a cyber-physical system using feedback control to mimic the real-time transition of an entire UAV between water and air. This allows a focus on the unsteady, multiphase flow around differing rotors, and simulation of many differently sized UAVs with high accuracy. We tested nine rotors of varying diameters and number of blades. The rotors were tested over a range of rotational frequencies and distances from the water-air interface. Time-averaged thrust and power consumption at each distance will be used to investigate control strategies and rotor designs that minimize the transition time and maximize efficiency. |
Sunday, November 19, 2023 5:40PM - 5:53PM |
J04.00006: Influence of quadrotor downwash on close proximity flight Anoop Kiran, Nora Ayanian, Kenneth Breuer Quadrotors have found widespread use in numerous applications including search and rescue, transportation of goods, remote sensing, and package delivery. However, the aerodynamic interference of rotor wakes between adjacent vehicles can be detrimental to the stability of dense quadrotor swarms. The ability to characterize and model the flow between neighboring quadrotors could lead to more stable formation flight and improve flight efficiency. We present data from a series of experiments using a pair of Crazyflie quadrotors mounted on stings attached to a translational stage, positioned with varying horizontal and vertical separation. Force and torque measurements (using a six-axis F/T transducer) and velocity measurements (using PIV) were recorded over a wide range of spatial separations. For small vertical separations, the downwash from the upper quadrotor has a pronounced effect, reducing the aerodynamic thrust on the lower quadrotor. Furthermore, for small horizontal separations, a roll moment is induced on the lower quadrotor, requiring a restoring moment to maintain stability. These findings are compared with predictions using actuator disk theory and scaling laws, potentially enabling their application to quadrotors of various sizes. |
Sunday, November 19, 2023 5:53PM - 6:06PM |
J04.00007: Experimental study to characterize flow dynamics and drag response of a multi-propeller system Ben L Silva, Prasoon Suchandra, Shabnam Raayai Recent advances in unmanned aerial vehicle (UAV) technologies have given rise to a variety of drone swarm strategies, particularly useful for security and surveillance, provision of wireless connectivity, delivery of goods, and environmental monitoring. Most of the current literature on UAV swarms is concerned with control algorithms, with little focus on aerodynamics of these formation strategies. Understanding the mechanics of flow around motorized multi-propeller systems can be used as an optimization tool to achieve certain outputs, like minimizing energy expenditure in a swarm of drones. In this talk, we will focus on the dynamics of flow past a multi-propeller system, containing up to 7 propellers, with varying orientations with respect to the freestream at moderate angular velocities. Our propellers are comprised of two-blade cross-sectional shapes following 4-digit series NACA profiles, with a maximum blade twist of 45○ at the root. The performance of an individual propeller is characterized using a load cell and motor to allow for comparison with the multi-propeller configuration. These propellers are suspended in various formations in a water tunnel where we perform 2D-2C high-resolution and high-speed particle image velocimetry (PIV). We will use the PIV data to explore the complex vortex dynamics and the associated turbulence statistics. We will also obtain the pressure and calculate the forces experienced by each propeller to determine the optimum orientation for minimizing the total drag of this propeller system. Lastly, we will also use the time-resolved PIV to characterize the vortex shedding and the turbulent energy spectrum. |
Sunday, November 19, 2023 6:06PM - 6:19PM |
J04.00008: Numerical analysis of blade-tip vortex effect on turbulence in a cyclorotor system Manabu Saito, Jun Nagao, Ryoichi Kurose A cyclorotor is a propulsion system that has multiple blades rotating around an axis parallel to the blades' spanwise direction and generates thrusts by dynamically controlling the angle of attack of each blade. It is capable of instantaneous thrust vectoring in any direction and magnitude. In addition to the benefit of maneuverability, due to its lower blade-tip velocity compared with a conventional propeller, it features lower noise generation. However, few aerodynamic investigations have been conducted through experimental and numerical analyses. In this study, large-eddy simulations (LES) of a cyclorotor are conducted to investigate the effect of the blade-tip vortex on the turbulence generation and consequently the aerodynamic performance of a cyclorotor. Specifically, the results of an LES with an infinite spanwise length by setting the spanwise boundary as periodic and another LES with a finite spanwise length to consider the blade-tip vortex effect are compared. Results show that, when the blades have blade tips, the spanwise inlet towards the center of the cyclorotor induces a significant change in the formation of the turbulence. |
Sunday, November 19, 2023 6:19PM - 6:32PM |
J04.00009: Aeroacoustics of Unconventional Drone Rotors - From Leonardo da Vinci's Designs to Toroidal Loops Suryansh Prakhar, Jung-Hee Seo, Rajat Mittal Unmanned Aerial Vehicles (UAVs) are transforming everything from agriculture to product delivery, environmental monitoring, and disaster relief. Delivery drones have a lower environmental footprint compared to other modes of delivery, but the noise generated by traditional rotary drones hinders their widespread use. As the demand for drones grows, the need for a quieter propeller becomes paramount. da Vinci envisioned an aerial screw long before the first flying machine was built. While propeller with loops were designed way back in the 1890s for steamships (C Myers' screw propeller), recently a novel design of a toroidal rotor has emerged for UAVs which aims to reduce broadband noise compared to traditional propellers. In our study, we explore the aerodynamics and aeroacoustics of da Vinci's aerial screw and the toroidal propeller via simulations. Since the unsteady surface pressure on the rotor blade, which is the source of aeroacoustic noise, is simultaneously affected by all the structures in the flow, we use the Force Partitioning Method (FPM) to calculate the pressure forces induced by various vortex structures. We then employ the Ffowcs Williams–Hawkings based acoustic partitioning method to get the corresponding far-field noise due to these propellers and quantify the effectiveness of these designs. |
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