Three dimensional unsteady analysis of a miniaturized pressure probe for turbocharger applications

Downsizing and turbocharging are nowadays widely spread techniques in automotive small-size internal combustion engines aimed at reducing the specific fuel consumption without affecting the power output. Due to the device small dimensions and to the high temperature of the exhaust-gases feeding the turbine, a relevant amount of heat is customarily exchanged between the turbine and the compressor so that a classical adiabatic approach could lead to an inaccurate estimation of the performance. This paper preliminary investigates the feasibility of an experimental procedure aimed at computing the exchanged work as variation of the angular momentum via a three-hole probe located at the impeller outlet. Because of the very reduced machine dimensions, torque measurements could be difficult, as the intrusive nature of the measurement could significantly affect the accuracy of the collected data. For this reason, the influence of the probe finite-size onto the flow field is numerically analysed solving the Unsteady Reynolds-Averaged Navier Stokes equations with and without the probe installed at the diffuser inlet. The equations are closed via the k − ω SST turbulence model, while a density-based commercial CFD package is used to integrate the governing equation. Finally, the pressure distribution in the azimuthal direction is analysed to assess the probe intrusive effects which, in the proposed case, result in a 0.47% (resp. 0.69%) difference in the specific work when a miniaturized probe with a diameter of 1mm (resp. 1.5 mm) is employed.