Cooling Fan Noise Reduction of Air-Cooled Diesel Engine by Engine Tests and Simulations 2020-01-0400
It is easy to identify flow induced noise on a flow bench or engine testing, but it is also equally essential to understand the fundamental mechanisms of fan noise generations. A methodology for optimizing cooling fan noise using 3-D CFD technique is presented in this paper. This work is an extension of Reference Nain, A. , where cooling fan dimensions like blade shape, number of blades, blade diameter etc. are optimized for achieving fuel efficiency targets. Any design modification in a fan should also be validated for any cause of noise generation. Initially engine noise sources are identified experimentally in anechoic chamber. Each noise source is categorized in order of their dominance on overall noise level. The cooling fan system impact is also extracted from overall noise spectrum. Then, a complete 3-D CFD simulation model is prepared which consists of fan impeller, fan shroud, top bracket and cylinder liner and sources of broad-band flow noise between 1.0 kHz - 5 kHz is obtained. The noise sources are captured by placing pressure probes around the outer periphery, center of cooling fan inlet and in-between fan/cylinder liner. These pressure signals are FFT processed and sound pressure level is obtained. SPL data confirm that fan outer periphery and fan/liner region shows dominant source as blade passing frequency and broad band noise in 1.0 kHz - 5 kHz frequency region. The sound pressure levels between base cooling system configuration and optimized cooling system configuration is compared and observed low dominance of broad band noise. The optimized system is again verified on genset/canopy level and observed average 1.5 dB (A) noise level reduction for all engine load points.