Investigating the 'modified' complementary technique using pressure-velocity correlations of an axisymmetric jet

To investigate the validity of the 'modified' Complementary Technique ¹⁰ as applied to the axisymmetric jet, a quantitative measure of the strength of the cross-correlation between the pressure field near the nozzle exit (z/D=0.875) and the velocity field is examined. The jet nozzle used in these experiments has an exit diameter of 5.08cm, and is operated in the compressible flow regime at M=0.6, at an exit temperature of 25°C. The fluctuating pressure field is sampled by an azimuthal array of 15 dynamic pressure transducers, evenly spaced at 24 degrees apart. The velocity field is simultaneously captured using a single point LDA system, with a 3-Watt argon ion laser head, traversed along several streamwise and radial locations. The cross-correlation between the pressure and streamwise component of the velocity field are examined as a function of radial, streamwise, & azimuthal (r,z, θ) location. The greatest magnitudes, on the order of 25% correlation, are observed within the potential core region just outside the centerline. Streamwise convection velocities of 0.77U_j and 0.73U_j are calculated in the potential core and shear layer, respectively. In the future, a spectral comparison can then be employed to validate Tinney et al's ¹² application of the technique to the turbulent sound source regions of the axisymmetric jet.