Turbocompresseur | EPFL Graph Search

vignette|Turbocompresseur sur un moteur de poids lourd (Renault Magnum). Un turbocompresseur (dit « turbo », en langage courant) est l'un des trois principaux systèmes connus de suralimentation généralement employés sur les moteurs à combustion et explosion (essence ou diesel), destinés à augmenter la puissance volumique — les deux autres étant le compresseur mécanique et l'injection gazeuse. Le rôle du turbocompresseur est d'augmenter le taux de dioxygène () dans chaque cylindre en comprimant l'air d'admission. Le principe est d'augmenter la pression des gaz admis, permettant un meilleur remplissage des cylindres en mélange air/carburant (rapport stœchiométrique), permettant soit d'augmenter la puissance d'un moteur atmosphérique soit de réduire la consommation avec un moteur de plus faible cylindrée. Ce type de compresseur est entraîné par une turbine (d'où son nom) animée par la vitesse des gaz d'échappement sortant du bloc-moteur, qui cèdent une partie de leur énergie cinétique

THE ROLE OF IMPELLER OUTFLOW CONDITIONS ON THE PERFORMANCE OF VANED DIFFUSERS

Jürg Alexander Schiffmann

Highly-loaded impellers, typically used in turbocharger and gas turbine applications, exhaust an unsteady, transonic flow that is non-uniform across the span and pitch and swirling at angles approaching tangential. With the exception of the flow angle, conflicting data exist regarding whether these attributes have substantial influence on the performance of the downstream diffuser. This paper quantifies the relative importance of the flow angle, Mach number, non-uniformity and unsteadiness on diffuser performance, through diffuser experiments in a compressor stage and in a rotating swirling flow test rig. This is combined with steady and unsteady Reynolds-Averaged Navier Stokes computations. The test article is a pressure ratio 5 turbocharger compressor with an airfoil vaned diffuser. The swirling flow rig is able to generate rotor outflow conditions representative of the compressor except for the periodic pitchwise unsteadiness, and fits a 0.86 scale diffuser and volute. In both rigs, the time-mean impeller outflow is mapped across a diffuser pitch using miniaturized traversing probes developed for the purpose. Across approximately two-thirds of the stage operating range, diffuser performance is well correlated to the average impeller outflow angle when the metric used is effectiveness, which describes the pressure recovery obtained relative to the maximum possible given the average inflow angle, Mach number and the vane exit metal angle. Utilizing effectiveness captures density changes through the diffuser at higher Mach numbers; a 10% increase in pressure recovery is observed as the inlet Mach number is increased from 0.5 to 1. Further, effectiveness is shown to be largely independent of the time-averaged spanwise and unsteady pitchwise non-uniformity from the rotor; this independence is reflective of the strong mixing processes that occur in the diffuser inlet region. The observed exception is for operating points with high time-averaged vane incidence. Here, it is hypothesized that temporary excursions into high-loss flow regimes cause a non-linear increase in loss as large unsteady angle variations pass by from the rotor. Given that straight-channel diffuser design charts typically used in preliminary radial vaned diffuser design capture neither streamtube area changes from impeller exit to the diffuser throat nor vane incidence effects, their utility is limited. An alternative approach, utilizing effectiveness and vane leading edge incidence, is proposed.

Amer Soc Mechanical Engineers2016

The Role of Impeller Outflow Conditions on the Performance of Vaned Diffusers

Jürg Alexander Schiffmann

Highly loaded impellers, typically used in turbocharger and gas turbine applications, exhaust an unsteady, transonic flow that is nonuniform across the span and pitch and swirling at angles approaching tangential. With the exception of the flow angle, conflicting data exist regarding whether these attributes have substantial influence on the performance of the downstream diffuser. This paper quantifies the relative importance of the flow angle, Mach number, nonuniformity, and unsteadiness on diffuser performance, through diffuser experiments in a compressor stage and in a rotating swirling flow test rig. This is combined with steady and unsteady Reynolds-averaged Navier–Stokes (RANS) computations. The test article is a pressure ratio 5 turbocharger compressor with an airfoil vaned diffuser. The swirling flow rig is able to generate rotor outflow conditions representative of the compressor except for the periodic pitchwise unsteadiness and fits a 0.86 scale diffuser and volute. In both rigs, the time-mean impeller outflow is mapped across a diffuser pitch using miniaturized traversing probes developed for the purpose. Across approximately two-thirds of the stage operating range, diffuser performance is well correlated to the average impeller outflow angle when the metric used is effectiveness, which describes the pressure recovery obtained relative to the maximum possible given the average inflow angle and Mach number and the vane exit metal angle. Utilizing effectiveness captures density changes through the diffuser at higher Mach numbers; a 10% increase in pressure recovery is observed as the inlet Mach number is increased from 0.5 to 1. Further, effectiveness is shown to be largely independent of the time-averaged spanwise and unsteady pitchwise nonuniformity from the rotor; this independence is reflective of the strong mixing processes that occur in the diffuser inlet region. The observed exception is for operating points with high time-averaged vane incidence. Here, it is hypothesized that temporary excursions into high-loss flow regimes cause a nonlinear increase in loss as large unsteady angle variations pass by from the rotor. Given that straight-channel diffuser design charts typically used in preliminary radial vaned diffuser design capture neither streamtube area changes from impeller exit to the diffuser throat nor vane incidence effects, their utility is limited. An alternative approach, utilizing effectiveness and vane leading edge incidence, is proposed.

American Society of Mechanical Engineers2017

Heat Pump driven by a Small-Scale Oil-Free Turbocompressor – System Design and Simulation

Adeel Javed, Jürg Alexander Schiffmann

Small-scale oil-free turbocompressors driven by high-speed electric motors and supported on refrigerant vapor bearings represent a promising technology to increase the performance of domestic heat pumps. Gas bearings enable high rotational speeds with low mechanical losses. Furthermore, turbocompressors can reach high compression efficiencies and offer a compact and lightweight design. This paper evaluates the performance of a heat pump using a small-scale radial turbocompressor rotating on gas bearings. The turbocompressor has been optimized for R134a and achieves pressure ratios ion the order of 1.5 to 3.5 at rotational speeds of 160 to 280 krpm with isentropic efficiencies of up to 75%. The impeller diameter is 15.2 mm. A system model of the heat pump has been programmed in the Engineering Equation Solver (EES) software. The model uses effectiveness-NTU models for the heat exchangers and polynomial fit approximations for the non-dimensional compressor map data. The heat pump produces 4.0 kW of 30°C water from 10°C ground heat with a predicted COP of 8.1 and 53.4% 2nd law efficiency. Simulation results, the design of the turbocompressor impeller, as well as the layout of the experimental setup are presented. First experimental measurement results will be expected in the beginning of 2017. The system serves as a proof of concept before stepping forward to a two-stage heat pump cycle with two turbocompressors reaching heat sink temperatures of 55 to 65°C.

2017

The Role of Impeller Outflow Conditions on the Performance of Vaned Diffusers

Jürg Alexander Schiffmann

American Society of Mechanical Engineers2017

THE ROLE OF IMPELLER OUTFLOW CONDITIONS ON THE PERFORMANCE OF VANED DIFFUSERS

Jürg Alexander Schiffmann

Amer Soc Mechanical Engineers2016