An experimental program is carried out to assess the effects of forward flight on both turbulent mixing noise and broadband shock-associated noise from single-stream jets. Far-field spectral measurements are made over a wide range of jet operating conditions and at seven tunnel Mach numbers, in an open freejet anechoic facility. The tunnel Mach number Mt spans a range from 0.0 to 0.32. The values of the flight velocity exponent k, obtained from a least-squares fit of the variation of the reduction in overall sound pressure levels with relative velocity (10Log[Vj/(Vj - Vt)]), have been calculated at all angles from the database. The flight velocity exponent has no discernible dependence on jet Mach number or temperature ratio. There is a distinct variation with angle: a slow increase from nearly equal 2.9 to nearl equal 3.5 at the lower polar angles from 50 to nearly equal 105 deg and a steeper increase from nearly equal 3.5 to nearly equal 7.6 from nearly equal 105 to 150 deg.. Two different characteristic velocities may be identified for jets in forward flight: jet velocity Vj and relative velocity (Vj - Vt). Though the Strouhal numbers based on both provide good collapse of the spectra at the lower polar angles, the jet velocity Vj rather than (Vj - Vt) is shown to be the correct characteristic velocity at large aft angles. Thus, it is established that the regular Strouhal number based on Vj is the correct nondimensional frequency for scaling spectra. The scaling of spectra at large aft angles is not straightforward and additional issues need to be considered. For jets in the presence of forward flight, it is established that the phenomenon of nonlinear propagation is observed when the relative velocity (Vj - Vt) becomes convectively supersonic. This is a new result and has not been reported in any prior study. An effective jet velocity, which is a combination of both the jet velocity and the ambient speed of sound, is required to collapse spectra from unheated jets only at large aft angles. The use of an effective velocity is not required for heated jets; the regular Strouhal number is the correct nondimensional frequency at all angles, with or without forward flight. The effect of forward flight on broadband shock-associated spectra is minor. The effects of flight on spectra at various angles need to be modeled for the development of a practical prediction scheme for jet noise. A simple additional term to the recent scaling method is shown to collapse the spectra obtained in the presence of forward flight. It is quite remarkable that the characteristics of the mixing noise spectra from single-stream jets at all angles, with or without the presence of forward flight, can be represented by a single equation. The negligible dependence of the flight velocity exponent on jet conditions allows for the following practical benefit: it is possible to predict the flight effect for lower-velocity jets for which the measurement of flight effect may not be feasible because of high tunnel-noise floor. This key finding perhaps represents the greatest value of this investigation.


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    Titel :

    Measurement and modeling of effect of forward flight on jet noise


    Weitere Titelangaben:

    Messung und Modellierung des Horizontalflugeinflusses auf den Strahllärm


    Beteiligte:
    Viswanathan, K. (Autor:in) / Czech, M.J. (Autor:in)

    Erschienen in:

    AIAA Journal ; 49 , 1 ; 216-234


    Erscheinungsdatum :

    2011


    Format / Umfang :

    19 Seiten, 35 Bilder, 1 Tabelle, 35 Quellen



    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch




    Measurement and Modeling of Effect of Forward Flight on Jet Noise

    Viswanathan, K. / Czech, M. J. | AIAA | 2011



    Measurement and Modeling of Effect of Forward Flight on Jet Noise

    Viswanathan, Krishna / Czech, Michael | AIAA | 2010


    Forward flight effects on EBF noise

    Fink, M. R. | NTRS | 1977