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  • 1
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    Computational Aerodynamic Modeling of Small Quadcopter Vehicles (2017)
    In:  CASI
    Details
    Publication Date: 2018-03-07
    Description: High-fidelity computational simulations have been performed which focus on rotor-fuselage and rotor-rotor aerodynamic interactions of small quad-rotor vehicle systems. The three-dimensional unsteady Navier-Stokes equations are solved on overset grids using high-order accurate schemes, dual-time stepping, low Mach number preconditioning, and hybrid turbulence modeling. Computational results for isolated rotors are shown to compare well with available experimental data. Computational results in hover reveal the differences between a conventional configuration where the rotors are mounted above the fuselage and an unconventional configuration where the rotors are mounted below the fuselage. Complex flow physics in forward flight is investigated. The goal of this work is to demonstrate that understanding of interactional aerodynamics can be an important factor in design decisions regarding rotor and fuselage placement for next-generation multi-rotor drones.
    Keywords: Numerical Analysis; Aerodynamics; Aircraft Design, Testing and Performance; Computer Systems
    Type: ARC-E-DAA-TN40938 , Annual American Helicopter Society (AHS) Forum and Technology Display 2017; 9-11 May 2017; Fort Worth, TX; United States
    Format: application/pdf
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  • 2
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    Investigation of Rotor-Airframe Interaction Noise Associated with Small-Scale Rotary-Wing Unmanned Aircraft Systems (2017)
    In:  CASI
    Details
    Publication Date: 2019-08-03
    Description: In this study, hover acoustic measurements are taken on isolated rotor-airframe configurations representative of smallscale, rotary-wing unmanned aircraft systems (UAS). Each rotor-airframe configuration consists of two fixed-pitch blades powered by a brushless motor, with a simplified airframe geometry intended to represent a generic multicopter arm. In addition to acoustic measurements, CFD-based aeroacoustic predictions are implemented on a subset of the experimentally tested rotor-airframe configurations in an effort to better understand the noise content of the rotor-airframe systems. Favorable agreements are obtained between acoustic measurements and predictions, based on both time- and frequency-domain post-processing techniques. Results indicate that close proximity of airframe surfaces result in the generation of considerable tonal acoustic content in the form of harmonics of the rotor blade passage frequency (BPF). Analysis of the acoustic prediction data shows that the presence of the airframe surfaces can generate noise levels either comparable to or greater than the rotor blade surfaces under certain rotor tip clearance conditions. Analysis of the on-surface Ffowcs Williams and Hawkings (FW-H) source terms provide insight as to the predicted physical noise-generating mechanisms on the rotor and airframe surfaces.
    Keywords: Acoustics
    Type: NF1676L-29371 , NF1676L-25342 , AHS Annual Forum and Technology Display; May 09, 2017 - May 11, 2017; Fort Worth, TX; United States
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  • 3
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    Combined Experimental and Computational Aeroacoustic Analysis of an Isolated UAV-Scale Propeller (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21236 , Acoustics Technical Working Group Meeting (Acoustics TWG 2015); Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 4
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    An Assessment of Comprehensive Code Prediction State-of-the-Art Using the HART II International Workshop Data (2012)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Despite significant advancements in computational fluid dynamics and their coupling with computational structural dynamics (= CSD, or comprehensive codes) for rotorcraft applications, CSD codes with their engineering level of modeling the rotor blade dynamics, the unsteady sectional aerodynamics and the vortical wake are still the workhorse for the majority of applications. This is especially true when a large number of parameter variations is to be performed and their impact on performance, structural loads, vibration and noise is to be judged in an approximate yet reliable and as accurate as possible manner. In this paper, the capabilities of such codes are evaluated using the HART II Inter- national Workshop data base, focusing on a typical descent operating condition which includes strong blade-vortex interactions. Three cases are of interest: the baseline case and two cases with 3/rev higher harmonic blade root pitch control (HHC) with different control phases employed. One setting is for minimum blade-vortex interaction noise radiation and the other one for minimum vibration generation. The challenge is to correctly predict the wake physics - especially for the cases with HHC - and all the dynamics, aerodynamics, modifications of the wake structure and the aero-acoustics coming with it. It is observed that the comprehensive codes used today have a surprisingly good predictive capability when they appropriately account for all of the physics involved. The minimum requirements to obtain these results are outlined.
    Keywords: Aerodynamics
    Type: NF1676L-13597 , American Helicopter Society 68th Annual Forum and Technology Display; May 01, 2012 - May 03, 2012; Forth Worth, TX; United States
    Format: text
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  • 5
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    Use of HART-II Measured Motion in CFD (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-27
    Description: This presentation examines the use of HART-II measured rotor blade motion in computational fluid dynamics (CFD). Historically, comprehensive analyses were used for input to acoustic calculations. These analyses focused on lifting line aerodynamics and beam models. However, there is a a need to evolve lifting line aerodynamics to first principles, notably the use of CFD instead of lifting line. The current analysis focuses on CFD and computational structural dynamics (CSD) coupling. Beam models are still very good (CSD is typically from comprehensive analysis), but generally CFD replaced aerodynamics in comprehensive analysis. This presentation examines both CFD and CSD individually and includes predictions using measured motion as well as predictions using measured motion versus coupled motion and calculations of "correct" airloads, noise and vibration.
    Keywords: Fluid Mechanics and Thermodynamics
    Type: 5th International HART-II Workshop at the 64th American Helicopter Society Annual Forum and Technology Display; 29 Apr.?1 May, 2008; Montreal; Canada
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  • 6
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    Design of Quiet Rotorcraft Approach Trajectories (2009)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A optimization procedure for identifying quiet rotorcraft approach trajectories is proposed and demonstrated. The procedure employs a multi-objective genetic algorithm in order to reduce noise and create approach paths that will be acceptable to pilots and passengers. The concept is demonstrated by application to two different helicopters. The optimized paths are compared with one another and to a standard 6-deg approach path. The two demonstration cases validate the optimization procedure but highlight the need for improved noise prediction techniques and for additional rotorcraft acoustic data sets.
    Keywords: Acoustics
    Type: NASA/TM-2009-215771 , L-19701 , LF99-9005
    Format: application/pdf
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  • 7
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    Aeroacoustic Codes for Rotor Harmonic and BVI Noise. CAMRAD.Mod1/HIRES: Methodology and Users' Manual (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: This document details the methodology and use of the CAMRAD.Mod1/HIRES codes, which were developed at NASA Langley Research Center for the prediction of helicopter harmonic and Blade-Vortex Interaction (BVI) noise. CANMAD.Mod1 is a substantially modified version of the performance/trim/wake code CANMAD. High resolution blade loading is determined in post-processing by HIRES and an associated indicial aerodynamics code. Extensive capabilities of importance to noise prediction accuracy are documented, including a new multi-core tip vortex roll-up wake model, higher harmonic and individual blade control, tunnel and fuselage correction input, diagnostic blade motion input, and interfaces for acoustic and CFD aerodynamics codes. Modifications and new code capabilities are documented with examples. A users' job preparation guide and listings of variables and namelists are given.
    Keywords: Acoustics
    Type: NASA/TM-1998-207640 , L-17697 , NAS 1.26:207640
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  • 8
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    Challenges in Rotorcraft Acoustic Flight Prediction and Validation (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Challenges associated with rotorcraft acoustic flight prediction and validation are examined. First, an outline of a state-of-the-art rotorcraft aeroacoustic prediction methodology is presented. Components including rotorcraft aeromechanics, high resolution reconstruction, and rotorcraft acoustic prediction arc discussed. Next, to illustrate challenges and issues involved, a case study is presented in which an analysis of flight data from a specific XV-15 tiltrotor acoustic flight test is discussed in detail. Issues related to validation of methodologies using flight test data are discussed. Primary flight parameters such as velocity, altitude, and attitude are discussed and compared for repeated flight conditions. Other measured steady state flight conditions are examined for consistency and steadiness. A representative example prediction is presented and suggestions are made for future research.
    Keywords: Acoustics
    Type: AIAA Paper 2003-0709 , 41st AIAA Aerospace Sciences Meeting; Jan 06, 2003 - Jan 09, 2003; Reno, NV; United States
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  • 9
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    Full Scale Rotor Aeroacoustic Predictions and the Link to Model Scale Rotor Data (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The NASA Aeroacoustic Prediction System (NAPS) is used to establish a link between model-scale and full-scale rotor predictions and is partially validated against measured wind tunnel and flight aeroacoustic data. The prediction approach of NAPS couples a comprehensive rotorcraft analysis with acoustic source noise and propagation codes. The comprehensive analysis selected for this study is CAMRAD-II, which provides the performance/trim/wake solution for a given rotor or flight condition. The post-trim capabilities of CAMRAD-II are used to compute high-resolution sectional airloads for the acoustic tone noise analysis, WOPMOD. The tone noise is propagated to observers on the ground with the propagation code, RNM (Rotor Noise Model). Aeroacoustic predictions are made with NAPS for an isolated rotor and compared to results of the second Harmonic Aeroacoustic Rotor Test (HART-II) program, which tested a 40% dynamically and Mach-scaled BO-105 main rotor at the DNW. The NAPS is validated with comparisons for three rotor conditions: a baseline condition and two Higher Harmonic Control (HHC) conditions. To establish a link between model and full-scale rotor predictions, a full-scale BO-105 main rotor input deck for NAPS is created from the 40% scale rotor input deck. The full-scale isolated rotor predictions are then compared to the model predictions. The comparisons include aerodynamic loading, acoustic levels, and acoustic pressure time histories for each of the three conditions. With this link established, full-scale predictions are made for a range of descent flight conditions and compared with measured trends from the recent Rotorcraft Operational Noise Abatement Procedures (RONAP) flight test conducted by DLR and ONERA. Additionally, the effectiveness of two HHC conditions from the HART-II program is demonstrated for the full-scale rotor in flight.
    Keywords: Acoustics
    Type: American Helicopter Society 4th Decennial Specialists Conference on Aeromechanics; Jan 21, 2004 - Jan 23, 2004; San Francisco, CA; United States
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  • 10
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    A Computational Model for Rotor-Fuselage Interactional Aerodynamics (2000)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A novel unsteady rotor-fuselage interactional aerodynamics model has been developed. This model loosely couples a Generalized Dynamic Wake Theory (GDWT) to a thin-layer Navier-Stokes solution procedure. This coupling is achieved using an unsteady pressure jump boundary condition in the Navier-Stokes model. The new unsteady pressure jump boundary condition models each rotor blade as a moving pressure jump which travels around the rotor azimuth and is applied between two adjacent planes in a cylindrical, non-rotating grid. Comparisons are made between measured and predicted time-averaged and time-accurate rotor inflow ratios. Additional comparisons are made between measured and predicted unsteady surface pressures on the top centerline and sides of the fuselage.
    Keywords: Aerodynamics
    Type: AIAA Paper 2000-0256 , 38th Aerospace Sciences Meeting and Exhibit; Jan 10, 2000 - Jan 13, 2000; Reno, NV; United States
    Format: text
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