Effect of pulsating flow on mild/deep surge phenomena of turbocharger compressor

It is known that a compressor causes a flow instability phenomenon called surge when the flow rate becomes reduced. Previous studies performed a compressor performance test using an apparatus that simulated a turbocharger for cars. As a result, they have confirmed that surge frequencies differ depending on the capacity of the tank. In this study, performance tests of a compressor for a turbocharger were conducted to understand a mechanism of surge phenomena and to understand differences between them under the steady flow and the pulsating flow. The apparatus which was used at this time consists of a compressor, a pulsating flow generator, a tank, and a valve. Except for the compressor, they install on the downstream side of it in this apparatus. The pulsating flow generator and the tank are equivalent to an automobile engine. First, to understand the difference between the mild surge and the deep surge under steady flow, the flow rate and the pressure of the tank were measured by controlling the valve under five different rotational speeds. And the two types of surge phenomena (i.e. the mild surge and the deep surge) were determined. Compared to the mild surge and the deep surge, it was judged that the former has smaller fluctuations of the flow rate and weaker surge phenomena. And, Fast Fourier Transform (FFT) analysis was performed on the measured pressure. It was found that the higher the rotation speed became, the lower the surge frequencies of the deep surge were, and the lower the rotation speed became, the weaker the strength of the surge phenomenon became. Next, it was investigated the difference in surge frequencies between the mild surge and the deep surge under pulsating flow with the rotation speed fixed. It was found that in the mild surge, the effect of pulsating flow on the surge phenomenon was significant, and it was confirmed that the surge frequencies were drawn into the pulsating frequencies. On the other hand, in the deep surge, the pressure fluctuation of the surge phenomenon became stronger than that of the mild surge, and a pattern of drawing was changed. In addition, unlike the mild surge, in the deep surge, the frequency range of draw in the same magnification between the given pulsating frequency and the obtained surge frequency narrowed. And, it was confirmed that the surge frequency was drawn into the pulsating frequency at half times rate and two times rate.