Dynamic Response in Transient Operation of a Variable Geometry Turbine Stage: Influence of the Aerodynamic Performance

Abstract

The transient response of a radial turbine stage with a variable geometry system is evaluated. Mainly, the consequences of the variations of the aerodynamic performance of the stage on the response time are checked. A simple quasi-steady model is derived in order to formalize the expected dependences. Then an experimental campaign is conducted: a brutal step in the feeding conditions of the stage is imposed, and the response time in terms of rotational speed is measured. This has been reproduced on different declinations of the same stage, through the variation of the stator geometry, and correlated to the steady-state performance of the initial and final operating points of the transient phase. The matching between theoretical expectation and results is surprisingly good for some configurations, less for others. The most important factor identified is the mass-flow level during the transient phase. It increases the reactivity, even far above the theoretical expectation for some configurations. For those cases, it is demonstrated that the quasi-steady approach may not be sufficient to explain how the transient response is set.

Transient flow in infinitely thin airfoil cascade

“…Nowadays, flow unsteadiness is considered damaging for turbine performance. However, Gugau & Roclawski (2012) suggest that an over-torque can be recovered by the rotor, while Binder et al (2013) notice that the rotor response is unusually high for some opening of guide vane. However, no explanation is given on the nature of the physical phenomenon.…”

Transient performance of the mixed flow and radial flow variable geometry turbines for an automotive turbocharger

“…The lower inertia results in faster transient response, refer to Binder et al. 17 For the given size of the rotor, the rate of increase in turbine MFP is higher with MFVGT compared to the RFVGT. The rate of turbine MFP rise contributes to an increase in turbine power and hence the faster transient response. The combined turbine efficiency plays a major role in the transient response of the turbine.…”

“…Binder et al. 17 studied the dynamic response for the radial flow VGT through the experimental and the simulation using the quasi-steady approach. The impulse response of the turbine is expressed using the identification functions, the rise in pressure at the inlet and the rotor rotational speed evolution.…”