Helicopter impulsive noise: Theoretical and experimental status
TL;DR: The theoretical and experimental status of helicopter impulsive noise is reviewed in this article, where two major sources of helicopter noise are addressed: high-speed impulsive noises and blade- vortex interaction noise.
About: This article is published in Journal of Sound and Vibration.The article was published on 1986-09-22 and is currently open access. It has received 129 citations till now. The article focuses on the topics: Noise & Impulse noise.
Summary (1 min read)
Jump to: and [A very good approximation t o these geometrical]
A very good approximation t o these geometrical
- As expected, the advancing-blade/ vortex interactions radiated most of their energy forward and were measured on the right wing-tip and nose-boom microphones.
- Blade/vortex interactions radiated to aft directions and were measured on the left wing tip and elevator microphones, were recorded on the right-wing-tip and nose-boom microphones, even though figure 74 shows that the advancing-blade interaction pressure variations are less than those measured on the retreating side.
- The conclusion to be drawn is that advancing-side BVIs are apparently "acoustically" more efficient than the retreating side B V I s , The retreating-.
Did you find this useful? Give us your feedback
Citations
More filters
TL;DR: In this article, the Kirchhoff formulation for moving surfaces is compared with the Ffowcs Williams Hawkings (FW-H) equation for the prediction of high-speed impulsive noise, in an effort to eliminate the need to compute the quadrupole contribution.
420 citations
Cites background from "Helicopter impulsive noise: Theoret..."
...By the 1980’s, the emphasis on theoretical development combined with several model scale and flight tests had led to a fairly complete understanding and classification of the physical sources of helicopter rotor noise [21]....
[...]
...George [20] and Schmitz and Yu [21] reviewed the status of helicopter noise in the late 1970’s and the early 1980’s, respectively....
[...]
Book•
01 Jan 2001
TL;DR: The second edition of Helicopter Dynamics by A.R. Bramwell as mentioned in this paper provides a detailed summary of helicopter aerodynamics, stability, control, structural dynamics, vibration, and aeroelastic and aeromechanical stability.
Abstract: 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.
315 citations
01 Nov 1991
TL;DR: 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 a wing.
Abstract: 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).
165 citations
Cites background from "Helicopter impulsive noise: Theoret..."
...7r3fl (c) 4 92160 fl-h (41 + fl(79C0 + llC1 +C2 + 316'3 + 42C4))Ch, (1-22)...
[...]
...2M2u)Mc_u (A-7) ACp = e(2- [2 - M2u]Cpu) (1-8) The above relations governing the corrections to Re, q_, M_, and Cp are assumed to apply to both 2D...
[...]
...0181 Note that equations (A-22) and (A-23) reduce to equations (A-20) and (A-21) when (1) the flow is incompressible (/3 = 1); (2) 2/c << 1; (3) c/h << 1; and (4) the airfoil is approximated by a single vortex at the quarter chord....
[...]
...Based on the measured pressure coefficient at a particular location near the leading edge, the velocity is determined from v = - Cp (incompressible) (1) The angle of attack that yields the above v/Voo at this particular _/c is found from...
[...]
...4M_u ) CdOu (1-17) where Ap is the planform area of the wing (Ap = cs for a rectangular wing), CdOu is the uncorrected drag coefficient at zero lift, and the test-section shape parameter A is given by (ref....
[...]
TL;DR: In this paper, the authors investigated different design concepts to reduce the blade-tip interaction noise and vibration by diffusing tip vortices, but these tip shapes have not been able to substantially reduce blade-vortex interaction noise without degradation of rotor performance.
141 citations
TL;DR: In this article, a detailed analysis of the complex vortical wakes generated by helicopter rotors is presented by means of several examples, including blade/vortex interactions, vortex perturbations, wake instabilities, and vortex/surface interaction phenomena.
Abstract: 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
88 citations
References
More filters
08 May 1969-Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences
TL;DR: In this article, sound generation by turbulence and surfaces in arbitrary motion is discussed, and sound and multipole fields and governing equations are discussed. But sound generation is not discussed in this paper.
Abstract: Monograph on sound generation by turbulence and surfaces in arbitrary motion, discussing sound and multipole fields and governing equations
3,121 citations
01 Aug 1978
TL;DR: In this article, a theoretical analysis for the harmonic noise of high speed, open rotors is presented, where the dominant sources are the volume displacement and the rho U(2) quadrupole, where u is the disturbance velocity component in the direction blade motion.
Abstract: A theoretical analysis is presented for the harmonic noise of high speed, open rotors. Far field acoustic radiation equations based on the Ffowcs-Williams/Hawkings theory are derived for a static rotor with thin blades and zero lift. Near the plane of rotation, the dominant sources are the volume displacement and the rho U(2) quadrupole, where u is the disturbance velocity component in the direction blade motion. These sources are compared in both the time domain and the frequency domain using two dimensional airfoil theories valid in the subsonic, transonic, and supersonic speed ranges. For nonlifting parabolic arc blades, the two sources are equally important at speeds between the section critical Mach number and a Mach number of one. However, for moderately subsonic or fully supersonic flow over thin blade sections, the quadrupole term is negligible. It is concluded for thin blades that significant quadrupole noise radiation is strictly a transonic phenomenon and that it can be suppressed with blade sweep. Noise calculations are presented for two rotors, one simulating a helicopter main rotor and the other a model propeller. For the latter, agreement with test data was substantially improved by including the quadrupole source term.
119 citations
TL;DR: In this article, a theoretical analysis for the harmonic noise of high speed, open rotors is presented, where the dominant sources are the volume displacement and the ϱu2 quadrupole, where u is the disturbance velocity component in the direction of blade motion.
119 citations
TL;DR: In this article, a theory is presented describing the noise generated by open rotors operating at supersonic tip speeds, based upon a combination of the LighthiIl aerodynamic sound theory and the Whitham weak shock theory.
87 citations
20 Jul 1976
68 citations