Two-point laser Doppler velocimetry measurements in a Mach 1.2 cold supersonic jet for statistical aeroacoustic source model |
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Authors: | Email author" target="_blank">F?KerhervéEmail author P?Jordan Y?Gervais J-C?Valière P?Braud |
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Institution: | (1) Laboratoire d Etudes Aérodynamiques, Bâtiment K, UMR Centre National de la Recherche Scientifique 6609, 40 Avenue du Recteur Pineau, 86000 Poitiers, France |
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Abstract: | Single and multi-point laser Doppler velocimetry measurements performed in a cold Mach 1.2 jet flow are used to assess those properties of the aerodynamic field most relevant in the generation of turbulence mixing noise. Single point measurements yield mean velocity profiles, turbulence intensity profiles and power spectral densities of both the velocity and Reynolds stress fields at seven axial stations between the jet exit and the end of the potential core. The longitudinal components of the second-order and fourth-order two-point velocity correlation tensor are obtained from a series of multi-point LDV measurements, whence a cartography of integral space and time scales, convection velocities and acoustic compactness is effected. These results are used to examine differences between subsonic and supersonic jet aerodynamics in terms of their sound generating potential. Finally analytical expressions are proposed for the spatial and temporal parts of the longitudinal correlation coefficient function. These are scaled using the integral space and time scales of the velocity and Reynolds stress fields, and excellent agreement is found with experimentally determined functions.Nomenclature co
Sound speed
- D
Exit nozzle diameter
- f, f
Spatial correlation function
- g, g
Temporal correlation function
- fSt
Frequency based Strouhal number
- i
2nd-order integral length scales in i-th direction
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4th-order integral length scales in
i-th direction - Mc
Convective Mach number - Mj Jet exit Mach number - q Quantity q evaluated at location y into the flow - Time average of the quantity
q - r Radial distance from the jet exit - r0.5
Radial location of the shear layer axis - r* Normalised radial coordinate - rij Second-order velocity correlation - rijkl Fourth-order velocity correlation - St Jet Strouhal number - Uc Convective velocity - Ue Subsonic coflow velocity - Uj Jet exit velocity - Ui Mean part of ui - ui Local velocity in i-th direction - uti Fluctuating part of ui - x Distance from the exit nozzle - y Location test point - i Variance of the velocity component ui - ij Variance of the velocity product uiuj - Constant value - ij Kronecker delta - c Shear layer thickness - ti Interarrival time between two ldv samples - Separation distance in the moving pattern (components i
) - Polynomial function - Separation distance in the fixed pattern (components
i
) -
Time delay -
2nd-order time scale in the fixed pattern -
2nd-order time scale in the moving pattern -
4th-order time scale in the fixed pattern -
4th-order time scale in the moving pattern -
Typical radian frequency where
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