https://www.cs.odu.edu/~mln/ltrs-pdfs/NASA-2003-pas-ksb.pdf

Modeling aerodynamically generated sound of helicopter rotors

Rotor blade–vortex interaction noise

Modern helicopter rotor aerodynamics

A direct panel method based on a novel boundary integral formulation for the velocity potential is presented and applied to helicopter rotors experiencing blade-vortex interaction. It avoids the numerical instabilities arising in the standard direct panel method in case of blade/wake impingement. This aerodynamic formulation yields a unified approach for the calculation of free-wake evolution and the blade-pressure field; it is fully 3-D, includes body-thickness effects, and can be applied to blades with arbitrary shape and motion. Blade-pressure predictions and the corresponding acoustic fields correlate well with wind-tunnel test data for helicopter rotors in descent flight, in which severe blade-vortex interaction occurs.

Novel Boundary Integral Formulation for Blade-Vortex Interaction Aerodynamics of Helicopter Rotors

: In a major cooperative program within the existing US-German and US-French Memoranda of Understanding/Agreements (MOU/MOA), researchers from German DLR, French ONERA, NASA Langley, and the US Army Aeroflightdynamics Directorate (AFDD) conducted a comprehensive experimental program in October 2001 with a 40%-geometrically and aeroelastically scaled model of a BO-105 main rotor in the open-jet anechoic test section of the German-Dutch Windtunnel (DNW). This international cooperative program carries the acronym HART-II (Higher harmonic control Aeroacoustics Rotor Test). The main objective of the program is to improve the basic understanding and the analytical modeling capabilities of rotor blade-vortex interaction noise with and without higher harmonic pitch control (HHC) inputs, particularly the effect of rotor wakes on rotor noise and vibration. Comprehensive acoustic, rotor wakes, aerodynamic, and blade deformation data were obtained with pressure-instrumented blades. The test plan has been concentrated on measuring extensive rotor wakes with a 3-component Particle Image Velocimetry (PIV) technique, along with measurements of acoustics, blade surface pressures, and blade deformations. The prediction team with researchers from DLR, ONERA, NASA-Langley and AFDD was actively involved with the pre-test activities to formulate a test plan and measurement areas of the PIV technique. The prediction team predicted all the test results in advance before performing the wind tunnel test. This was done to obtain the best quality of test data, to improve the speed of measurements, and to determine the necessary measurement information for code validation. In this paper, an overview of the HART-II program and some representative measured and predicted results are presented.

/pdf/the-hart-ii-test-rotor-wakes-and-aeroacoustics-with-higher-142ae1o4pn.pdf

The HART-II Test: Rotor Wakes and Aeroacoustics with Higher-Harmonic Pitch Control (HHC) Inputs - The Joint German/French/Dutch/US Project

https://ntrs.nasa.gov/api/citations/19980032586/downloads/19980032586.pdf

Reduction of helicopter blade-vortex interaction noise by active rotor control technology

The HART II Test in the LLF of the DNW - a Major Step towards Rotor Wake Understanding

In a major cooperative research program within existing US-German and US-French Memoranda of Understanding (MoU's), a comprehensive study was conducted with a 40-percent geometrically and dynamically scaled BO-105 main rotor operated in the open-jet anechoic test section of the German-Dutch Wind Tunnel (DNW). The objectives of the program were to improve the physical understanding and the mathematical modelling of the effects of the higher harmonic blade pitch control technique on blade-vortex interaction (BVI) impulsive noise and vibration reduction. A unique set of acoustic, aerodynamic,dynamic response, performance, and rotor wake data were acquired witha pressure and strain gauge instrumented blade and by application of non-intrusive measurement techniques. This paper is focused on the experimental part of this research program, termed Higher-harmonic- control Aeroacoustic Rotor Test (HART) which was jointly performed by researchers from the US Army Aeroflightdynamics Directorate (AFDD) and NASA Langley, the DNW, and the French and German Aeropace Research Establishments ONERA and DLR. The applied test procedures and obtained key results are presented.

Yung H. Yu

Papers

Rotor blade–vortex interaction noise

The HART-II Test: Rotor Wakes and Aeroacoustics with Higher-Harmonic Pitch Control (HHC) Inputs - The Joint German/French/Dutch/US Project

Reduction of helicopter blade-vortex interaction noise by active rotor control technology

The HART II Test in the LLF of the DNW - a Major Step towards Rotor Wake Understanding

Initial Results from the Higher Harmonic Control Aeroacoustic Rotor Test (HART) in the German-Dutch Wind Tunnel.