Different Measurement Techniques for Wider Small Radial Turbine Performance Maps

Garcia

International Journal of Heat and Fluid Flow

2019

The characterization of tip leakage flow plays an important role for one-dimensional loss modeling and design in radial turbine research. Tip leakage losses can be expressed as function of fluid momentum and mass flow passing through the tip gap. Friction-driven flow and contrariwise oriented pressure gradient-driven flow are highly coupled. However, these numbers are mostly unknown and dependent on tip gap geometry and turbine running condition. Based on a commonly used definition of a non-dimensional tip leakage momentum ratio, a novel correlation has been derived. This allows a consistent characterization for variable tip gap sizes over a wide range of operating conditions. The correlation has been validated by means of CFD data with high variety in reduced speed tip gap geometry and expansion ratios. Results of the novel number show significant improvements of quantitative and qualitative results over a wide range of running conditions in comparison to existing correlations. Furthermore, correlations for tip leakage velocities, that can easily be used in one-dimensional models, have been derived. Finally, it has been demonstrated, that the influence of inlet flow momentum on the tip leakage flow can be analyzed with presented correlations.

Section: Introductionmentioning

confidence: 99%

Contribution to tip leakage loss modeling in radial turbines based on 3D flow analysis and 1D characterization

Garcia

International Journal of Heat and Fluid Flow

2019

“…Later, Terdich [6] was able to maintain the turbocharger speed at low turbine power with an electrically assisted turbocharger. Salameh et al [7] used a mirrored compressor as a second turbine for powering the turbocharger shaft while the turbine is operating at high blade speed ratio (BSR) conditions. Finally, an industrial applicable measurement technique has been presented by Serrano et al [8] and deepened in Serrano et al [9].…”

Section: Introductionmentioning

confidence: 99%

Turbocharger turbine rotor tip leakage loss and mass flow model valid up to extreme off-design conditions with high blade to jet speed ratio

Garcia

2018

Energy

“…For the testing of common turbochargers a modification towards a electrically assisted assembly is not feasible, as the thermal characterization changes and the effort is remarkable. Salameh et al [22] replaced the compressor wheel with a designed turbine wheel to supply extra energy to the shaft.…”

Section: Introductionmentioning

confidence: 99%

Radial turbine performance measurement under extreme off-design conditions

Tiseira

et al. 2017

Energy

During automotive urban driving conditions and future homologation cycles, automotive radial turbines experience transient conditions, whereby the same operate at very high blade speed ratios and, thus, at very low power outputs. Under those conditions, the turbine power output might not be enough to feed the mechanical power needs of the compressor. Typical fast one-dimensional full engine simulations rely on steady-state performance maps to characterize the turbocharger. Due to the restricting compressor braking power, extreme off-design measurements cannot be obtained in standard gas stands without using an external brake instead of the compressor or without using a motor attached to the turbocharger shaft. Such turbocharger assemblies cause shaft balancing issues inherent to the connection to a brake operating at high rotational speeds or need basic changes of the turbocharger geometry. This paper presents a novel approach for turbine performance map measurements at very low expansion ratio and very low mass flow without the aforementioned issues. The method uses the turbocharger compressor as a centrifugal turbine, providing mechanical power to the shaft and enabling turbine performance measurements from points of very high expansion ratio up to very low pressure ratio. It is even possible to measure at almost zero flow rate in the turbine when it consumes shaft power instead of producing it. This experimental procedure that can be applied to whatever turbocharger produces valuable information for the development and validation of turbine performance models aiming to extrapolate its behaviour at off-design conditions.