Experimental characterization of velocity and acoustic fields of single-stream subsonic jets

The characterization of velocity and acoustic fields from a single-stream free jet operating at subsonic regimes is essential for aeronautical applications. For instance, the investigation of exhaust gases from single or coaxial nozzles or from bleed valve in turbojets and turbofan engines is crucial for understanding the mechanisms of noise generation and propagation and eventually for finding ways to reduce aircraft noise. This article evaluates the velocity and acoustic fields of an isothermal single jet discharging from a circular 38.1 mm conical nozzle at three different Mach and Reynolds numbers of 0.25 (Re = 2.5 × 105), 0.50 (Re = 4.9 × 105) and 0.75 (Re = 6.8 × 105), respectively. Pitot-tube and hot-wire probes were used to identify the mean velocity profiles in longitudinal and transversal directions in the wake of the jet. The hot-wire anemometry system was also used to evaluate the turbulence intensity distribution over eleven axial lines, from the centerline to the edge of the nozzle. The accuracy of hot-wire anemometers for turbulent intensities lower than 15% at low and high subsonic Mach numbers was evaluated by comparing the experimental measurements with available data from the literature. An acoustic investigation was carried out by analyzing the sound pressure level obtained at six positions in the far field, with viewing angles ranging from 40° to 110°. The results were integrated to a database with sound pressure level as a function of Strouhal number, aiming to provide a benchmark for further RANS-based methods applied to aeroacoustic simulations of single jets.