Design of a Facility for Studying Shock-Cell Noise on Single and Coaxial Jets

Abstract

Shock-cell noise occurs in aero-engines when the nozzle exhaust is supersonic and shock-cells are present in the jet. In commercial turbofan engines, at cruise, the secondary flow is often supersonic underexpanded, with the formation of annular shock-cells in the jet and consequent onset of shock-cell noise. This paper aims at describing the design process of the new facility FAST (Free jet AeroacouSTic laboratory) at the von Karman Institute, aimed at the investigation of the shock-cell noise phenomenon on a dual stream jet. The rig consists of a coaxial open jet, with supersonic capability for both the primary and secondary flow. A coaxial silencer was designed to suppress the spurious noise coming from the feeding lines. Computational fluid dynamics (CFD) simulations of the coaxial jet and acoustic simulations of the silencer have been carried out to support the design choices. Finally, the rig has been validated by performing experimental measurements on a supersonic single stream jet and comparing the results with the literature. Fine-scale PIV (Particle Image Velocimetry) coupled with a microphone array in the far field have been used in this scope. Preliminary results of the dual stream jet are also shown.

Minimum Quantity Lubrication Jet Noise: Passive Control

“…When the expansion wave reaches the inner shear layer of the airflow, it is reflected to form a shock wave. The shock wave passes through the jet core region, reaching the outer shear layer of the airflow and reflecting to form an expansion wave [29,30]. As the airflow propagates downstream, the expansion and shock waves alternate, which leads to alternating low and high air pressure [31,32].…”

Effects of Nozzle Pressure Ratio and Nozzle-to-Plate Distance to Flowfield Characteristics of an Under-Expanded Jet Impinging on a Flat Surface

“…An experimental setup combining a PIV system for velocity measurement and microphone system for acoustic measurement could provide details about the flowfield and noise characteristics of supersonic free jets and impinging jets. Experimental measurements of flowfield and acoustics as can be reviewed in numerous studies of Krothapalli et al [3], Henderson [16], Henderson et al [17], Sinibaldi et al [18], Alvi and Iyer [43], and Guariglia et al [55], to name a few. With the recent improvement in digital imaging cameras, high-speed schlieren is enable to acquire large datasets of time-resolved flowfield information (Berry et al [56]), although the measured quantities are scalars derived from density gradients (Berry et al [54]).…”