Emel Selamet

Simulation of surge in the air induction system of turbocharged internal combustion engines

A computational approach has been developed to accurately predict compression system surge instabilities within the induction system of turbocharged internal combustion engines by employing one-dimensional, nonlinear gas dynamics. This capability was first developed for a compression system installed on a turbocharger gas stand, in order to isolate the surge physics from the airborne pulsations of engine and simplify the ducting geometry. Findings fromthe turbocharger stand study were then utilized to create a new model of a twin, parallel turbocharged engine. Extensive development was carried out to accurately characterize the wave dynamics within key induction system components in terms of transmission loss and flow losses for the individual compressor inlet and outlet ducts. The engine was instrumented to obtain time-resolved measurements for model validation during surge instabilities, and simulation results agree well with the experimental data, in terms of both the amplitude and frequency. The present quasi-one-dimensional approach relaxes many of the assumptions inherent to earlier lumped parameter surge models; therefore, it provides the flexibility to model advanced boosting systems with multiple turbochargers and complex ducting geometry.

Fluid instabilities in turbocharger compression systems

Turbochargers increase the power density of internal combustion engines, which allows the displaced volume to be reduced and the fuel efficiency to be improved for the same level of performance. However, the demand for turbocharger centrifugal compressors to deliver increasingly elevated boost pressures, over a wide air flow range, results in unfavorable flow fields that generate narrow and broadband noises within the engine air induction system. The present study is a combined computational and experimental effort, focusing on identifying unsteady fluid-flow instabilities in a turbocharger compression system installed on a bench top stand. This work concentrates primarily on prediction of mild and deep surge instabilities, since they limit the low-flow operating range. Surge occurs near the Helmholtz resonance frequency of the compression system (including a compressor inlet duct, centrifugal compressor, compressor outlet duct, plenum, plenum outlet duct, and a valve) and results in low frequency pressur...

Three-dimensional computational fluid dynamics prediction of mild surge in a turbocharger compression system vs. experiments

The flow instabilities in a turbocharger compression system are studied numerically by employing a compressible, three-dimensional computational fluid dynamics code. The model represents the full compression system of a turbocharger test stand, consisting of a compressor inlet duct breathing from ambient, a centrifugal compressor, an exit duct connected to a plenum, followed by another duct which incorporates a valve restriction. The detailed compressor model includes the full rotating impeller and resolution of the clearance gap between the impeller blades and shroud. The simulation begins at a converged, stable operating point, where the flow rate at the outlet boundary is gradually reduced and maintained at the final value. Characteristics of mild surge are captured as the mass flow rate is reduced below the stability limit, including a discrete low frequency sound peak near the Helmholtz resonance of the compression system. The predictions are then compared with experimental results obtained from the ...

Simulation of surge in the induction system of turbocharged internal combustion engines

A computational methodology has been developed to accurately predict the compression system surge instabilities within the induction system of turbocharged internal combustion engines by employing one-dimensional nonlinear gas dynamics. This capability was first developed for a compression system installed on a turbocharger flow stand, in order to isolate the surge physics from the airborne pulsations of engine. Findings from the turbocharger stand model were then utilized to create a separate model of a twin, parallel turbocharged engine. Extensive development was carried out to accurately characterize the wave dynamics behavior of induction system components in terms of transmission loss and flow losses for the individual compressor inlet and outlet ducts. The engine was instrumented to obtain time-resolved measurements for model validation under stable, full-load conditions and during surge instabilities. Simulation results from the turbocharger stand and engine agree well with the experimental data fr...

Acoustics of a Helmholtz Resonator Aligned Parallel with Flow: A Computational Study VS. Experiments

Acoustic attenuation of a Helmholtz resonator (HR) placed parallel to the flow path is investigated computationally with and without mean flow and compared with experimental results. The time-dependent flow field is determined by solving three-dimensional unsteady, laminar/turbulent, compress-ible Navier-Stokes equations using Pressure-Implicit-Splittingof-Operators algorithm of STAR-CD. Computations are performed by di erent finite difference schemes such as central and upwind for momentum equation. Predictions with central differencing, a blending (with upwind) factor 0.5, and fine mesh reveal results that are consistent with the experimental observations. The effect of flow on the acoustic attenuation characteristics of HR has been illustrated both computationally and experimentally. The predictions for transmission loss exhibit reduced attenuation at elevated flow rates.