Rick Dehner

Noise at the mid to high flow range of a turbocharger compressor

The acoustic and performance characteristics of an automotive centrifugal compressor are studied on a steady-flow turbocharger test bench, with the intention of identifying operating regions associated with flow noise within the compressor and connected ducting. Near choke, discrete tones including rotor-order frequency and its harmonics (bladepass) are observed. As the flow rate is reduced, the current compressor exhibited a broadband elevation of noise in the 4-12 kHz band, which was evident both in the upstream compressor duct and external sound pressure level (SPL) measurement locations. At all rotational speeds studied here, the total SPL in this frequency range demonstrates a strong dependence on the incidence angle of the incoming flow with the blades at the inducer of the impeller. When the incidence angle is further increased (mass flow rate is decreased) beyond a critical value, the temperature near the inducer tips increases sharply, suggesting local flow reversal, and the total SPL in the 4-12 kHz range suddenly reduces.

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...

Effect of Fin Orientation and Length on the Rayleigh-Benard Convection

Abstract: Natural convection driven by the temperature difference of horizontal top and bottom surfaces of an enclosure containing air, Pr = 0.7, and fins of different arrangements at different lengths is studied numerically for Ra = 10 and 5 × 10. Evolution of heat transfer rates (Nusselt number) is illustrated along with various, steady or unsteady, cellular flow structures and temperature patterns. The effect of fin length and placement on flow regime and heat transfer is established. Different fin orientations at the walls are observed to introduce considerable unsteadiness in some cases, requiring close investigation in order to design systems for specific purposes.

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...

Whoosh noise measurements from an automotive centrifugal compressor

Broadband noise, accompanying the flow separation and turbulence, is studied for an automotive centrifugal compressor on a steady-flow turbocharger bench facility. When operated in the mid-flow region, the current compressor exhibited elevated broadband noise at high frequencies, which was evident both in the upstream compressor duct and external sound pressure level (SPL) measurement locations. Viewing SPL data as a function of the flow angle relative to the leading edge of the inducer blades (incidence angle) reveals a relationship which is nearly independent of the rotational speed. As the incidence angle is increased, broadband noise levels first go up gradually, nearly level off, and then decrease sharply at a critical incidence angle.