An official website of the United States government
Multirotor configurations introduce complicated aerodynamic and aeroacoustic interactions that must be considered during aircraft design. In this paper we explore two numerical methods to model the acoustic noise caused by aerodynamic rotor-on-rotor interactions of rotors in hover. The first method uses a conventional mesh-based unsteady Reynolds-average Navier-Stokes (URANS) solver, while the second consists of a meshless Lagrangian solver based on the viscous vortex particle method (VPM). Both methods are coupled with an aeroacoustics solver for tonal and broadband noise predictions. Noise predictions are validated for single and multi-rotor configurations, obtaining with the VPM a similar accuracy than URANS while being two orders of magnitude faster. We characterize the interactions of two side-by-side rotors in hover as the tip-to-tip distance and downstream spacing are varied. At an observer located six diameters away, multirotor noise is the strongest above and below the rotors, increasing by about 10 dBA directly underneath as the rotors are brought closer together. The interactions show no sensitivity to blade loading distribution, indicating that multirotor interactions are not alleviated with a lighter tip loading. We found that noise can be mitigated by spacing the rotors in the downstream direction—with the optimal spacing being about half a diameter—achieving a noise decrease of about 4 dBA without any aerodynamic penalties.
more »
« less
Experimental and Computational Aeroacoustic Investigation of Small Rotor Interactions in Hover
This paper investigates the aeroacoustic interactions of small hovering rotors, using both experiments and computations. The experiments were conducted in an anechoic chamber with arrays of microphones setup to evaluate the azimuthal and polar directivity. The computational methodology consists of high fidelity detached eddy simulations coupled to the Ffowcs-Williams and Hawkings equation, supplemented by a trailing edge broadband noise code. The aerodynamics and aeroacoustics of a single rotor are investigated first. The simulations capture a Reynolds number effect seen in the performance parameters that results in the coefficient of thrust changing with the RPM. The acoustic analysis enables the identification of self-induced noise sources. Next, dual side-by-side rotors are studied in both counter-rotating and co-rotating configurations to quantify the impact of their interactions. Higher harmonics appear due to the interactions and it is verified that the counter-rotating case leads to more noise and a less uniform azimuthal directivity. Difficulties that arise when trying to validate small rotor calculations against experiments are discussed. Comparisons of computational and experimental results yield further insight into the noise mechanisms that are captured by each methodology.
more »
« less
- Award ID(s):
- 1728277
- PAR ID:
- 10387748
- Date Published:
- Journal Name:
- Applied Sciences
- Volume:
- 11
- Issue:
- 21
- ISSN:
- 2076-3417
- Page Range / eLocation ID:
- 10016
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Multirotor configurations introduce complicated aerodynamic and aeroacoustic interactions that must be considered during aircraft design. In this paper we explore two numerical methods to model the acoustic noise caused by aerodynamic rotor-on-rotor interactions of rotors in hover. The first method uses a conventional mesh-based unsteady Reynolds-average Navier-Stokes (URANS) solver, while the second consists of a meshless Lagrangian solver based on the viscous vortex particle method (VPM). Both methods are coupled with an aeroacoustics solver for tonal and broadband noise predictions. Noise predictions are validated for single and multi-rotor configurations, obtaining with the VPM a similar accuracy than URANS while being two orders of magnitude faster. We characterize the interactions of two side-by-side rotors in hover as the tip-to-tip distance and downstream spacing are varied. At an observer located six diameters away, multirotor noise is the strongest above and below the rotors, increasing by about 10 dBA directly underneath as the rotors are brought closer together. The interactions show no sensitivity to blade loading distribution, indicating that multirotor interactions are not alleviated with a lighter tip loading. We found that noise can be mitigated by spacing the rotors in the downstream direction—with the optimal spacing being about half a diameter—achieving a noise decrease of about 4 dBA without any aerodynamic penalties.more » « less
-
View Video Presentation: https://doi.org/10.2514/6.2022-3218.vid The ability to accurately and rapidly assess unsteady interactional aerodynamics is a shortcoming and bottleneck in the design of various next-generation aerospace systems: from electric vertical takeoff and landing (eVTOL) aircraft to airborne wind energy (AWE) and wind farms. In this study, we present a meshless CFD framework based on the reformulated vortex particle method (rVPM) for the analysis of complex interactional aerodynamics. The rVPM is a large eddy simulation (LES) solving the Navier-Stokes equations in their vorticity form. It uses a meshless Lagrangian scheme, which not only avoids the hurdles of mesh generation, but it also conserves the vortical structure of wakes over long distances with minimal numerical dissipation, while being 100x faster than conventional mesh-based LES. Wings and rotating blades are introduced in the computational domain through actuator line and actuator surface models. Simulations are coupled with an aeroacoustics solver to predict tonal and broadband noise radiated by rotors. The framework, called FLOWUnsteady, is hereby released as an open-source code and extensively validated. Validation studies published in previous work by the authors are summarized, showcasing rotors across operating conditions with a rotor in hover, propellers, a wind turbine, and two side-by-side rotors in hover. Validation of rotor-wing interactions is presented simulating a tailplane with tip-mounted propellers and a blown wing with propellers mounted mid-span. The capabilities of the framework are showcased through the simulation of a tiltwing eVTOL vehicle and an AWE wind-harvesting aircraft, featuring rotors with variable RPM, variable pitch, tilting of wings and rotors, non-trivial flight paths, and complex aerodynamic interactions.more » « less
-
Continuously increasing offshore wind turbine scales require rotor designs that maximize power and performance. Downwind rotors offer advantages in lower mass due to reduced potential for tower strike, and is especially true at large scales, e.g., for a 25 MW turbine. In this study, three 25 MW downwind rotors, each with different prescribed lift coefficient distributions were designed (chord, geometry, and twist) and compared to maximize power production at unprecedented scales and Reynolds numbers, including a new approach to optimize rotor tilt and coning based on aeroelastic effects. To achieve this objective the design process was focused on achieving high power coefficients, while maximizing swept area and minimizing blade mass. Maximizing swept area was achieved by prescribing pre-cone and shaft tilt angles to ensure the aeroelastic orientation when the blades point upwards was nearly vertical at nearly rated conditions. Maximizing the power coefficient was achieved by prescribing axial induction factor and lift coefficient distributions which were then used as inputs for an inverse rotor design tool. The resulting rotors were then simulated to compare performance and subsequently optimized for minimum rotor mass. To achieve these goals, a high Reynolds number design space was developed using computational predictions as well as new empirical correlations for flatback airfoil drag and maximum lift. Within this design space, three rotors of small, medium and large chords were considered for clean airfoil conditions (effects of premature transition were also considered but did not significantly modify the design space). The results indicated that the medium chord design provided the best performance, producing the highest power in Region 2 from simulations while resulting in the lowest rotor mass, both of which support minimum LCOE. The methodology developed herein can be used for the design of other extreme-scale (upwind and downwind) turbines.more » « less
-
Abstract BackgroundCatheter ablation is associated with limited success rates in patients with persistent atrial fibrillation (AF). Currently, existing mapping systems fail to identify critical target sites for ablation. Recently, we proposed and validated several techniques (multiscale frequency [MSF], Shannon entropy [SE], kurtosis [Kt], and multiscale entropy [MSE]) to identify pivot point of rotors using ex‐vivo optical mapping animal experiments. However, the performance of these techniques is unclear for the clinically recorded intracardiac electrograms (EGMs), due to the different nature of the signals. ObjectiveThis study aims to evaluate the performance of MSF, MSE, SE, and Kt techniques to identify the pivot point of the rotor using unipolar and bipolar EGMs obtained from numerical simulations. MethodsStationary and meandering rotors were simulated in a 2D human atria. The performances of new approaches were quantified by comparing the “true” core of the rotor with the core identified by the techniques. Also, the performances of all techniques were evaluated in the presence of noise, scar, and for the case of the multielectrode multispline and grid catheters. ResultsOur results demonstrate that all the approaches are able to accurately identify the pivot point of both stationary and meandering rotors from both unipolar and bipolar EGMs. The presence of noise and scar tissue did not significantly affect the performance of the techniques. Finally, the core of the rotors was correctly identified for the case of multielectrode multispline and grid catheter simulations. ConclusionThe core of rotors can be successfully identified from EGMs using novel techniques; thus, providing motivation for future clinical implementations.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/app112110016
