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  • 1
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    A comparison of the acoustic and aerodynamic measurements of a model rotor tested in two anechoic wind tunnels (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Two aeroacoustic facilities--the CEPRA 19 in France and the DNW in the Netherlands--are compared. The two facilities have unique acoustic characteristics that make them appropriate for acoustic testing of model-scale helicopter rotors. An identical pressure-instrumented model-scale rotor was tested in each facility and acoustic test results are compared with full-scale-rotor test results. Blade surface pressures measured in both tunnels were used to correlated nominal rotor operating conditions in each tunnel, and also used to assess the steadiness of the rotor in each tunnel's flow. In-the-flow rotor acoustic signatures at moderate forward speeds (35-50 m/sec) are presented for each facility and discussed in relation to the differences in tunnel geometries and aeroacoustic characteristics. Both reports are presented in appendices to this paper. ;.);
    Keywords: AERODYNAMICS
    Type: NASA-TM-88364 , A-86417 , NAS 1.15:88364 , USAAVSCOM-TM-86-A-6 , PAPER-38-1 , AD-A175717
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  • 2
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    Helicopter model rotor-blade vortex interaction impulsive noise: Scalability and parametric variations (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: 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, inflight acoustic data under similar nondimensional test conditions. At low advance ratios (mu = 0.164 to 0.194), the data scale remarkable well in level and waveform shape, and also duplicate the directivity pattern of BVI impulsive noise. At moderate advance ratios (mu = 0.224 to 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. Carefully performed parametric variations over a complete matrix of testing conditions have shown that all of the four governing nondimensional parameters - tip Mach number at hover, advance ratio, local inflow ratio, and thrust coefficient - are highly sensitive to BVI noise radiation.
    Keywords: AERODYNAMICS
    Type: NASA-TM-86007 , A-9854 , NAS 1.15:86007 , TM-84-A-7 , AD-A159471
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  • 3
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    Transonic rotor noise: Theoretical and experimental comparisons (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Two complementary methods of describing the high speed rotor noise problem are discussed. The first method uses the second order transonic potential equation to define and characterize the nature of the aerodynamic and acoustic fields and to explain the appearance of radiating shock waves. The second employs the Ffowcs Williams and Hawkings equation to successfully calculate the acoustic far field. Good agreement between theoretical and experimental waveforms is shown for transonic hover tip Mach numbers from 0.8 to 0.9.
    Keywords: AERODYNAMICS
    Type: NASA-TM-81236 , A-8342 , AVRADCOM-TR-80-A-12
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  • 4
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    Aerodynamics of the model airplane. Part 1 - Airfoil measurements (1967)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Airfoil measurements that show behavior of wing sections in low-turbulence stream in Reynolds number range from 20,000 to 170,000
    Keywords: AERODYNAMICS
    Type: NASA-TM-X-60976 , RSIC-721-PT-1
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  • 5
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    Model helicopter rotor high-speed impulsive noise: Measured acoustics and blade pressures (1983)
    In:  CASI
    Details
    Publication Date: 2019-07-27
    Description: A 1/17-scale research model of the AH-1 series helicopter main rotor was tested. Model-rotor acoustic and simultaneous blade pressure data were recorded at high speeds where full-scale helicopter high-speed impulsive noise levels are known to be dominant. Model-rotor measurements of the peak acoustic pressure levels, waveform shapes, and directively patterns are directly compared with full-scale investigations, using an equivalent in-flight technique. Model acoustic data are shown to scale remarkably well in shape and in amplitude with full-scale results. Model rotor-blade pressures are presented for rotor operating conditions both with and without shock-like discontinuities in the radiated acoustic waveform. Acoustically, both model and full-scale measurements support current evidence that above certain high subsonic advancing-tip Mach numbers, local shock waves that exist on the rotor blades ""delocalize'' and radiate to the acoustic far-field.
    Keywords: AERODYNAMICS
    Type: NASA-TM-85850 , A-9463 , NAS 1.15:85850 , USAAVRADCOM-TR-83-A-14 , European Rotorcraft Forum; 13-15 Sep.; Stresa; Italy
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  • 6
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    The aerodynamics of small Reynolds numbers (1980)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Aerodynamic characteristics of wing model gliders and bird wings in particular are discussed. Wind tunnel measurements and aerodynamics of small Reynolds numbers are enumerated. Airfoil behavior in the critical transition from laminar to turbulent boundary layer, which is more important to bird wing models than to large airplanes, was observed. Experimental results are provided, and an artificial bird wing is described.
    Keywords: AERODYNAMICS
    Type: NASA-TM-75816 , Jahrbuch 1953 der Wiss. Ges. fuer Luftfahrt E. V. mit den Vortraegen der WGL-Tagung in Goettingen; May 26, 1953 - May 29, 1953; Braunschweig; Germany
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