Helicopter Model Rotor‐Blade Vortex Interaction Impulsive Noise: Scalability and Parametric Variations

1 January 1987

journal article
Published by AHS International dba Vertical Flight Society in Journal of the American Helicopter Society

Vol. 32 (1) , 3-12
https://doi.org/10.4050/jahs.32.1.3

Abstract

Acoustic data taken in the anechoic Deutsch‐Niederlaendischer Windkanal (DNW) have documented the blade‐vortex interaction (BVI) impulsive noise radiated from a 1/7‐scale model main rotor of the AH‐1 series helicopter. Averaged model‐scale data were compared with averaged full‐scale, in‐flight acoustic data under similar non‐dimensional test conditions using an improved data analysis technique. At low advance ratios (μ = 0.164−0.194), the BVI impulsive noise data scale remarkably well in level, waveform, and directivity patterns. At moderate advance ratios (μ = 0.224−0.270), the scaling deteriorates, suggesting that the model‐scale rotor is not adequately simulating the full‐scale BVI noise. Presently, no proved explanation of this discrepancy exists. Measured BVI noise radiation is highly sensitive to all of the four governing nondimensional parameters—hover tip Mach number, advance ratio, local inflow ratio, and thrust coefficient.

Keywords

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