The information below was gathered from the 2018 Simcenter Conference - Americas that took place October 15-17 in Detroit, Michigan.
Author: Ahsanul Karim, Ph.D., Product Design Engineer
A new compressor wheel proposed for 2017 3.5L Raptor needed a 30% improvement in flow to meet the 450HP performance level (see slide 20). The initial plan was to implement the same compressor across all 2017 3.5L application for the F150. This requirement dictated a new aerodynamic design of the compressor wheel to maintain surge margin, low-end torque, and peak power over the outgoing compressor wheel. The changes in the aerodynamics resulted in an increase in NVH of 12-14 dB OSPL in the whoosh region of the map (4-12 kHz). This made the product unsellable in the baseline F-150, so a second compressor has to be implemented resulting in product complexity for 2017 product line. Implementation of the higher performance levels in the Navigator for 2018MY would require adding metal High-Pressure AIS (HP-AIS) ducts to reduce the audible NVH levels resulting in a cost hit of ~$2M/year A novel solution to use a ported shroud casing treatment on a gasoline turbocharger for NVH benefits was pursued. The ported shroud reduced the whoosh NVH characteristics by 10-12 dB but created two additional error states: an objectionable increase in Blade Pass Frequency (BPF) and a 1st order compressor outlet whine (~ 2.3kHz). Computational Aero-Acoustics Analysis (CAA) is used to analytically find design solutions for the BPF and outlet whine noise. The new ported shroud casing treatment design decreased narrowband tonal noise sound pressure level by 3-6 dB in the low to mid flow region compared to the baseline design. Computational Fluid Dynamics (CFD) tools Siemens’s STAR-CCM+ was used to develop this casing treatment design.