Broadband Liner Optimization for the Source Diagnostic Test Fan

Abstract

The broadband component of fan noise has grown in relevance with the utilization of increased bypass ratio and advanced fan designs. Thus, while the attenuation of fan tones remains paramount, the ability to simultaneously reduce broadband fan noise levels has become more appealing. This paper describes a broadband acoustic liner optimization study for the scale model Source Diagnostic Test fan. Specifically, in-duct attenuation predictions with a statistical fan source model are used to obtain optimum impedance spectra over a number of flow conditions for three liner locations in the bypass duct. The predicted optimum impedance information is then used with acoustic liner modeling tools to design liners aimed at producing impedance spectra that most closely match the predicted optimum values. Design selection is based on an acceptance criterion that provides the ability to apply increased weighting to specific frequencies and/or operating conditions. Typical tonal liner designs targeting single frequencies at one operating condition are first produced to provide baseline performance information. These are followed by multiple broadband design approaches culminating in a broadband liner targeting the full range of frequencies and operating conditions. The broadband liner is found to satisfy the optimum impedance objectives much better than the tonal liner designs. In addition, the broadband liner is found to provide better attenuation than the tonal designs over the full range of frequencies and operating conditions considered. Thus, the current study successfully establishes a process for the initial design and evaluation of novel broadband liner concepts for complex engine configurations.

Design and Acoustic Efficacy of a Broadband Liner for the Inlet of the DGEN Aero-propulsion Research Turbofan

“…As with previous liner optimization studies 1,3,5 , induct attenuation was chosen as the cost function for the impedance optimization. Thus, optimum impedance values were predicted using the propagation module of the CDL code (with the aforementioned source model) coupled with optimization routines.…”

“…Thus, improved broadband liner designs must account for these constraints and take advantage of novel liner configurations. With these observations in mind, the development and assessment of a broadband acoustic liner optimization process has been pursued through a series of recent design and experimental studies 1,2,3,4,5,6,7 .…”

Broadband Inlet Liner Design for the DGEN Aero-propulsion Research Turbofan

“…As with previous liner optimization studies, 1,3,5 the cost function was formulated to maximize in-duct attenuation. Thus, optimum impedance values were predicted using the propagation module of the CDL code (with the aforementioned source model) coupled with optimization routines.…”

“…Thus, improved broadband liner designs must account for these constraints and take advantage of novel liner configurations.With these observations in mind, the development and assessment of a broadband acoustic liner optimization process has been pursued through a series of recent design and experimental studies. [1][2][3][4][5][6] In this design process, an acoustic duct propagation code is used to predict optimum impedance spectra over a number of frequencies and flow conditions. Acoustic liner modeling tools are then used to identify geometric liner parameters (within manufacturing constraints) necessary to produce impedance spectra that most closely match the predicted optimum values.…”

Improved Broadband Liner Optimization Applied to the Advanced Noise Control Fan

“…With these observations in mind, a process for the design and evaluation of novel broadband acoustic liner concepts with limited fan source information was established in a previous study. 1 Specifically, a statistical fan source model was used within an acoustic duct propagation code to predict optimum impedance spectra for the Source Diagnostic Test (SDT) fan (see Figure1a). Acoustic liner modeling tools were then used to identify geometric liner parameters (within manufacturing constraints) necessary to produce impedance spectra that most closely matched the predicted optimum values.…”