The behavior of the compression system in turbochargers is studied with a one-dimensional engine simulation code. The system consists of an upstream compressor duct open to ambient, a centrifugal compressor, a downstream compressor duct, a plenum, and a throttle valve exhausting to ambient. The compression system is designed such that surge is the low mass flow rate instability mode, as opposed to stall. The compressor performance is represented through an extrapolated steady-state map. Instead of incorporating a turbine into the model, a drive torque is applied to the turbocharger shaft for simplification. Unsteady compression system mild surge physics is then examined computationally by reducing the throttle valve diameter from a stable operating point. Such an increasing resistance decreases the mass flow rate through the compression system and promotes surge. Mild surge is predicted as the mass flow rate is decreased below the stability limit, with oscillations of mass flow rate and pressure exhibited at the Helmholtz resonance frequency of the compression system. The computational results are shown to be able to reproduce the experimental observations available in the literature.
The unsteady surge behavior of a turbocharger compression system is studied computationally by employing a onedimensional engine simulation code. The system modeled represents a new turbocharger test stand consisting of a compressor inlet duct breathing from ambient, a centrifugal compressor, an exit duct connected to an adjustable-volume plenum, followed by another duct which incorporates a control valve and an orifice flow meter before exhausting to ambient. Characteristics of mild and deep surge are captured as the mass flow rate is reduced below the stability limit, including discrete sound peaks at low frequencies along with their amplitudes in the compressor (downstream) duct and plenum. The predictions are then compared with the experimental results obtained from the cold stand placed in a hemi-anechoic room. The computational results are shown to be capable of reproducing a number of key experimental observations, including the details of low-frequency pressure fluctuations in the compressor ducts and plenum; and the transition from stable operation to oscillating mild surge.Zero-dimensional (lumped parameter) models have been developed to predict the surge behavior of both axial [3] and
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