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Numerical investigation of marine diesel engine turbocharger compressor tonal noise

The compressor tonal noise of a low-speed marine diesel engine turbocharger is investigated with numerical method. Nine operating conditions on four different rotating speed lines are analyzed; the conditions include near-choke conditions, near-surge conditions, and peak efficiency conditions. Numerical predictions of compressor global variables are compared with experimental measurements, and a good agreement is achieved. The pressure fluctuation at all operating conditions presents strong periodicity, and the prominent peaks of pressure amplitude appear at the blade passing frequency and its harmonics after Fast Fourier transform algorithm. Furthermore, the fluctuation strength varies with the changes in operating conditions. Then, the pressure fluctuation is used to acquire the aero-acoustic source, and the compressor tonal noise and the compressor broadband noise are calculated by the boundary element method. The compressor tonal noise increases with operating conditions shift to high rotating speed and the surge line. The acoustic directivity of radiated tonal noise at inlet duct nozzle is obvious, which is particularly detectable at the blade passing frequency. The further analysis shows that the acoustic directivity is greatly influenced by the frequency, compressor rotating speed, and total-to-total pressure ratio.