Velocity measurements in jets with application to noise source modeling

This paper describes an experimental investigation of the statistical properties of turbulent velocity fluctuations in an axisymmetric jet. The focus is on those properties that are relevant to the prediction of noise. Measurements are performed using two single hot-wire anemometers as well as a two-component anemometer. Two-point cross correlations of the axial velocity fluctuations and of the fluctuations in the square of the axial velocity fluctuations are presented. Several reference locations in the jet are used including points on the jet lip and centerline. The scales of the turbulence and the convection velocity are determined, both in an overall sense as well as a function of frequency. The relationship between the second and fourth order correlations is developed and compared with the experimental data. The implications of the use of dimensional as well as non-dimensional correlations are considered. Finally, a comparison is made between the length scales deduced from the flow measurements and a RANS CFD calculation.