A simpler model for concentrated vortices

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.

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“…The Vatistas (Ref. 26) model with n = 2 is used, which can be described with the following relation for non-dimensional swirl velocity: …”

Section: Appendix: Mathematical Description Of the Frame-d Bvi Noise mentioning

confidence: 99%

A Semiempirical Noise Modeling Method for Helicopter Maneuvering Flight Operations

Greenwood¹,

Schmitz²,

Sickenberger³

2015

j am helicopter soc

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“…17), and the appropriateness of simple vortex models (ref. 18). In response to these questions, an experiment was performed to provide data that focuses specifically on cross sections of the trailing vortex during a complete revolution of the rotor.…”

Section: Introductionmentioning

confidence: 99%

Rotor Wake Development During the First Revolution

Mcalister¹

2004

j am helicopter soc

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The wake behind a two-bladed model rotor in light climb was measured using particle image velocimetry, with particular emphasis on the development of the trailing vortex during the first revolution of the rotor. The distribution of vorticity was distinguished from the slightly elliptical swirl pattern. Peculiar dynamics within the "void" region may explain why the peak vorticity appeared to shift away from the center as the vortex aged, suggesting the onset of instability. The swirl and axial velocities (which reached 44 and 12 percent of the rotor-tip speed, respectively) were found to be asymmetric relative to the vortex center. In particular, the axial flow was composed of two concentrated zones moving in opposite directions. The radial distribution of the circulation rapidly increased in magnitude until reaching a point just beyond the core radius, after which the rate of growth decreased significantly. The core-radius circulation increased slightly with wake age, but the large-radius circulation appeared to remain relatively constant. The radial distributions of swirl velocity and vorticity exhibit self-similar behaviors, especially within the core. The diameter of the vortex core was initially about 10 percent of the rotor-blade chord, but more than doubled its size after one revolution of the rotor. According to vortex models that approximate the measured data, the core-radius circulation was about 79 percent of the large-radius circulation, and the large-radius circulation was about 67 percent of the maximum bound circulation on the rotor blade. On average, about 53 percent of the maximum bound circulation resides within the vortex core during the first revolution of the rotor.

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“…The induced inflow is calculated using Biot-Savart formula. In addition, Vatistas's vortex-core model [11] is used to resolve the singularity at the center of the vortex. In order to artificially add the viscous diffusion effect on the vortex, Squire's vortex-core growth model [12] is used as follows:…”

Section: Wake Modelmentioning

confidence: 99%

Development of an Unsteady Aerodynamic Analysis Module for Rotor Comprehensive Analysis Code

Lee

Yee²,

Oh³

et al. 2009

International Journal of Aeronautical and Space Sciences

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The inherent aeromechanical complexity of a rotor system necessitated the comprehensive analysis code for helicopter rotor system. In the present study, an aerodynamic analysis module has been developed as a part of rotorcraft comprehensive program. Aerodynamic analysis module is largely classified into airload calculation routine and inflow analysis routine. For airload calculation, quasi-steady analysis model is employed based on the blade element method with the correction of unsteady aerodynamic effects. In order to take unsteady effects -body motion effects and dynamic stall -into account, aerodynamic coefficients are corrected by considering Leishman-Beddoes's unsteady model. Various inflow models and vortex wake models are implemented in the aerodynamic module to consider wake induced inflow. Specifically, linear inflow, dynamic inflow, prescribed wake and free wake model are integrated into the present module. The aerodynamic characteristics of each method are compared and validated against available experimental data such as Elliot's induced inflow distribution and sectional normal force coefficients of AH-1G. In order to validate unsteady aerodynamic model, 2-D unsteady model for NACA0012 airfoil is validated against aerodynamic coefficients of McAlister's experimental data.

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A simpler model for concentrated vortices

Cited by 311 publications

References 8 publications

A Semiempirical Noise Modeling Method for Helicopter Maneuvering Flight Operations

A Semiempirical Noise Modeling Method for Helicopter Maneuvering Flight Operations

Rotor Wake Development During the First Revolution

Development of an Unsteady Aerodynamic Analysis Module for Rotor Comprehensive Analysis Code

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