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

Modeling aerodynamically generated sound of helicopter rotors

Since the original publication of Helicopter Dynamics by A.R.S. Bramwell in 1976, this book has become the definitive text on helicopter dynamics. As such it is an essential aid to those studying the behavior of helicopters. The second edition builds on the strengths of the original, and hence the approach of the first edition is retained. The authors provide a detailed summary of helicopter aerodynamics, stability, control, structural dynamics, vibration, and aeroelastic and aeromechanical stability.

Bramwell's Helicopter Dynamics

A NACA 0015 semispan wing was placed in a low-speed wind tunnel, and measurements were made of the pressure on the upper and lower surface of the wing and of velocity across the vortex trailing downstream from the tip of the wing. Pressure data were obtained for both 2-D and 3-D configurations. These data feature a detailed comparison between wing tips with square and round lateral edges. A two-component laser velocimeter was used to measure velocity profiles across the vortex at numerous stations behind the wing and for various combinations of conditions. These conditions include three aspect ratios, three chord lengths, a square- and a round lateral-tip, presence or absence of a boundary-layer trip, and three image plane positions located opposite the wing tip. Both pressure and velocity measurements were made for the angles of attack 4 deg less than or equal to alpha less than or equal to 12 deg and for Reynolds numbers 1 x 10(exp 6) less than or equal to Re less than or equal to 3 x 10(exp 6).

/pdf/naca-0015-wing-pressure-and-trailing-vortex-measurements-4qdk6anb81.pdf

NACA 0015 Wing Pressure and Trailing Vortex Measurements

Rotor blade–vortex interaction noise

Many experimental challenges are encountered when attempting to understand the complex vortical wakes generated by helicopter rotors. The problems are illustrated by means of several examples, including blade/vortex interactions, vortex perturbations, wake instabilities, and vortex/surface interaction phenomena. Specific emphasis is placed on flow visualization and quantitative measurements using laser Doppler velocimetry

Challenges in Understanding the Vortex Dynamics of Helicopter Rotor Wakes

Helicopter impulsive noise: Theoretical and experimental status

The theoretical and experimental status of helicopter impulsive noise is reviewed. The two major source mechanisms of helicopter impulsive noise are addressed: high-speed impulsive noise and blade- vortex interaction impulsive noise. A thorough physical explanation of both generating mechanisms is presented together with model and full-scale measurements of the phenomena. Current theoretical prediction methods are compared with experimental findings of isolated rotor tests. The noise generating mechanisms of high speed impulsive noise are fairly well understood—theory and experiment compare nicely over Mach number ranges typical of today’s helicopters. For the case of blade-vortex interaction noise, understanding of noise generating mechanisms and theoretical comparison with experiment are less satisfactory. Several methods for improving theory/experiment are suggested.

Y. H. Yu

Papers

Helicopter impulsive noise: Theoretical and experimental status

Helicopter impulsive noise: Theoretical and experimental status

Prediction of rotor high-speed impulsive noise with a combined cfd–kirchoff method