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Random Data Analysis And Measurement Procedures

A first principles understanding of the sound field produced by multirotor drones in hover is presented. Propeller diameters ranging from 8 to 12 in. are examined and with configurations comprising...

Multirotor Drone Noise at Static Thrust

Integrated methodology for the prediction of helicopter rotor noise at mission level

In the past years, the aeroacoustic noise emission of a helicopter became one of the most important, but also challenging issues in helicopter development. The blade vortex interaction phenomenon is one of the dominant phenomena characterizing the helicopter's aeroacoustic footprint, which is insufficiently predicted by low fidelity computational methods. For a high fidelity noise prediction of a helicopter configuration, a multidisciplinary CFDCSD-CAA tool chain has been established at the Institute of Aerodynamics and Gas Dynamics of the University of Stuttgart. With higher order CFD computed noise generation at the near field and the noise convection using a Ffowcs-Williams Hawkings based CAA code, very good agreement to measured aeroacoustic noise in wind tunnel as well as free flight experiments of helicopters is achieved. However, the simulations had been limited to the main rotor's geometry up to now, where some residual deviations to the experiment still exist. In this paper, we present a high fidelity aeroacoustic simulation of a complete helicopter configuration and the benefit compared to an isolated rotor simulation in predicting its aeroacoustic noise emission. Shading and reflection effects are clearly resolved, influencing the behaviour of the helicopter's noise radiation. The simulated aeroacoustic noise emission of the helicopter lies within the experimental variation and shows therefore highly promising results for the next generation of aeroacoustic noise prediction.

Aeroacoustic Simulation of a Complete H145 Helicopter in Descent Flight

The forward flight stage of multicopters accounts for a relatively large amount of flight time in comparison with hovering, ascending, and descending conditions; therefore, understanding its aerody...

Aerodynamic and Aeroacoustic Performance of an Isolated Multicopter Rotor During Forward Flight

A new model for Blade-Vortex Interaction noise generation during maneuvering flight is developed in this paper. Acoustic and performance data from both flight and wind tunnels are used to derive a non-dimensional and analytical performance/acoustic model that describes BVI noise in steady flight. The model is extended to transient maneuvering flight (pure pitch and roll transients) by using quasisteady assumptions throughout the prescribed maneuvers. Ground noise measurements, taken during maneuvering flight of a Bell 206B helicopter, show that many of the noise radiation details are captured. The result is a computationally efficient Blade-Vortex Interaction noise model with sufficient accuracy to account for transient maneuvering flight. The code can be run in real time to predict transient maneuver noise and is suitable for use in an acoustic mission-planning tool.

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A Semi-Empirical Noise Modeling Method for Helicopter Maneuvering Flight Operations

A new methodology is developed for the construction of helicopter source noise models for use in mission planning tools from experimental measurements of helicopter external noise radiation. The models are constructed by employing a parameter identification method to an assumed analytical model of the rotor harmonic noise sources. This new method allows for the identification of individual rotor harmonic noise sources and allows them to be characterized in terms of their individual non-dimensional governing parameters. The method is applied to both wind tunnel measurements and ground noise measurements of two-bladed rotors. The method is shown to match the parametric trends of main rotor harmonic noise, allowing accurate estimates of the dominant rotorcraft noise sources to be made for operating conditions based on a small number of measurements taken at different operating conditions. The ability of this method to estimate changes in noise radiation due to changes in ambient conditions is also demonstrated.

/pdf/fundamental-rotorcraft-acoustic-modeling-from-experiments-4pkblletph.pdf

Fundamental Rotorcraft Acoustic Modeling from Experiments (FRAME)

A special acoustic flight test program was performed on the Bell 206B helicopter outfitted with an in-flight microphone boom/array attached to the helicopter while simultaneous acoustic measurements were made using a linear ground array of microphones arranged to be perpendicular to the flight path. Air and ground noise measurements were made in steady-state longitudinal and steady turning flight, and during selected dynamic maneuvers. Special instrumentation, including direct measurement of the helicopter s longitudinal tip-path-plane (TPP) angle, Differential Global Positioning System (DGPS) and Inertial Navigation Unit (INU) measurements, and a pursuit guidance display were used to measure important noise controlling parameters and to make the task of flying precise operating conditions and flight track easier for the pilot. Special care was also made to test only in very low winds. The resulting acoustic data is of relatively high quality and shows the value of carefully monitoring and controlling the helicopter s performance state. This paper has shown experimentally, that microphones close to the helicopter can be used to estimate the specific noise sources that radiate to the far field, if the microphones are positioned correctly relative to the noise source. Directivity patterns for steady, turning flight were also developed, for the first time, and connected to the turning performance of the helicopter. Some of the acoustic benefits of combining normally separated flight segments (i.e. an accelerated segment and a descending segment) were also demonstrated.

/pdf/measurement-and-characterization-of-helicopter-noise-in-57x5w0h68e.pdf

Measurement and Characterization of Helicopter Noise in Steady-State and Maneuvering Flight

Time frequency analysis of sound from a maneuvering rotorcraft

A cooperative flight test by NASA, Bell Helicopter and the U.S. Army to characterize the steady state acoustics and measure the maneuver noise of a Bell Helicopter 430 aircraft was accomplished. The test occurred during June/July, 2011 at Eglin Air Force Base, Florida. This test gathered a total of 410 data points over 10 test days and compiled an extensive data base of dynamic maneuver measurements. Three microphone configurations with up to 31 microphones in each configuration were used to acquire acoustic data. Aircraft data included DGPS, aircraft state and rotor state information. This paper provides an overview of the test.

/pdf/maneuver-acoustic-flight-test-of-the-bell-430-helicopter-sy7c8hzn17.pdf

Eric Greenwood

Papers

A Semi-Empirical Noise Modeling Method for Helicopter Maneuvering Flight Operations

Fundamental Rotorcraft Acoustic Modeling from Experiments (FRAME)

Measurement and Characterization of Helicopter Noise in Steady-State and Maneuvering Flight

Time frequency analysis of sound from a maneuvering rotorcraft

Maneuver Acoustic Flight Test of the Bell 430 Helicopter