Keith Miazgowicz

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.

Effect of inlet vanes on centrifugal compressor acoustics and performance

The effect of inlet guide vanes (IGVs) on the acoustic and performance characteristics of an automotive centrifugal compressor is studied on a steady-flow turbocharger experimental facility. Broadband noise accompanying flow separation occurs as the flow rate of the compressor is reduced and the incidence angle of the flow relative to the leading edge of the inducer blades increases. The addition of IGVs upstream of the inducer imparts a tangential (swirl) velocity component in the same direction of impeller rotation, which improves the incidence angle particularly at low to mid-flow rates. In the present study, experimental data is compared for three compressor inlet geometries, including a no-swirl baseline along with two different IGV configurations. IGVs were shown to slightly improve the surge line at the highest rotational speed considered in this study, while compromising the maximum flow rate at all rotational speeds. In the high-flow range, IGVs are observed to increase compressor inlet noise levels over a wide frequency range. At the more common low to mid-flow range, however, broadband whoosh noise is reduced with the addition of IGVs in the 5-12 kHz band.

Time domain computational modeling of viscothermal acoustic propagation in catalytic converter substrates with porous walls

Models for viscothermal effects in catalytic converter substrates are developed for time domain computational methods. The models are suitable for use in one-dimensional approaches for the prediction of exhaust system performance (engine tuning characteristics) and radiated sound levels. Starting with the “low reduced frequency” equations for viscothermal acoustic propagation in capillary tubes, time domain submodels are developed for the frequency-dependent wall friction, frequency-dependent wall heat transfer, and porous wall effects exhibited by catalytic converter substrates. Results from a time domain computational approach employing these submodels are compared to available analytical solutions for the low reduced frequency equations. The computational results are shown to agree well with the analytical solutions for capillary geometries representative of automotive catalytic converter substrates.

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.

Acoustics of automotive catalytic converter assemblies

In an automotive exhaust system, the purpose of the catalytic converter is to reduce pollutant emissions. However, catalytic converters also affect the engine and exhaust system breathing characteristics; they increase backpressure, affect exhaust system acoustic characteristics, and contribute to exhaust manifold tuning. Thus, radiated sound models should include catalytic converters since they can affect both the source characteristics and the exhaust system acoustic behavior. A typical catalytic converter assembly employs a ceramic substrate to carry the catalytically active noble metals. The substrate has numerous parallel tubes and is mounted in a housing with swelling mat or wire mesh around its periphery. Seals at the ends of the substrate can be used to help force flow through the substrate and/or protect the mat material. Typically, catalytic converter studies only consider sound propagation in the small capillary tubes of the substrate. Investigations of the acoustic characteristics of entire ca...