Acoustic data t a k e n i n t h e a n e c h o i c Deutsch-Niederlaendischer Windkanal (DNW) have documented t h e b l a d e -v o r t e x i n t e r a c t i o n (BVI) i m p u l s i v e n o i s e radiated from a 1 / 7 -s c a l e model main r o t o r of t h e AH-1 series helicopter. Averaged model-scale data were compared w i t h averaged f u l l -s c a l e , i n -f l i g h t a c o u s t i c data under similar nondimensional test c o n d i t i o n s . A t low advance ratios (IJ = 0.164-0.1941, t h e data s c a l e remarkably well i n l e v e l and waveform shape, and also d u p l i c a t e t h e d i r e c t i vi t y p a t t e r n of BVI i m p u l s i v e noise. A t moderate advance r a t i o s (IJ = 0.224-0.2701, t h e s c a l i n g d e t e r i o r a t e s , s u g g e s t i n g t h a t t h e model-scale rotor is not a d e q u a t e l y s i m u l a t i n g t h e f u l l -s c a l e BVI n o i s e ; p r e s e n t l y , no proved e x p l a n a t i o n of t h i s d i screpancy e x i s t s . C a r e f u l l y performed p a r a m e t r i c v a r i a t i o n s over a complete m a t r i x of t e s t i n g c o n d i t i o n s have shown t h a t a l l of t h e f o u r governing nondimensional parameters--tip Mach number a t hover, advance r a t i o , local i n f l o w ratio, and t h r u s t c o e f f i c i e n t --a r e h i g h l y s e n s i t i v e t o BVI n o i s e r a d i a t i o n .
A model-rotor acoustic experiment in a three-meter open-section anechoic wind tunnel (CEPRA-19) is described. The important scaling parameters are reviewed and some an-line acoustic data are presented for conditions known to produce blade-vortex interaction noise on a single rotor helicopter. Time averages of the model-scale aeonslic pulses are compared with similar iull-scale data tsken in-flight under the same nondimensionallzed conditions. Good agreement between model and full-scale shapes and amplitudes of blsdevorlex interaction noise is shown far one advance ratio over a ranee of inflow conditions for the rotor. Directivity sweeps for onr condition known lo genrrute blade-vorlex inleractionr are presenled. Snme model rotor testing limitations of the CEI'KA-19 t~tcility in itr prerentconfipratiun are indicated.
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