Experimental Investigations Into the Nonuniform Flow in a 4-Stage Turbine With Special Focus on the Flow Equalization in the First Turbine Stage

Abstract

Control stage turbines are in widespread use to control turbine power output in power generation and industrial applications. Depending on the point of operation and the turbine design the inflow to the multi-stage turbine is highly non-uniform. It is important to know how the inhomogeneities in mass flow and temperature distribution develop and attenuate inside a multistage flow passage. The object of this study is to experimentally measure and report the inhomogeneous flow structure and attenuation in a multistage turbine, especially in the first turbine stage. In a scaled down original turbine consisting of a control stage with cross-over channel and a 4-stage turbine velocities, pressures and temperatures are extensively measured at the 360° circumference at the inlet, within the first stage and at the outlet of the multistage turbine part. By closing a 20% sector of the control stage a circumferential flow inhomogeneity with significant pressure, velocity and temperature gradients is created at the inlet of the multistage turbine. For analyzing the equalization of the mass flow distribution in the first stage, the experimental results are normalized with a reference case at full admission in order to separate flow phenomena created by the turbine geometry. The results show that the flow inhomogeneity at the inlet of the multistage part is significant, but the flow is basically equalized after the third stage. Most of the flow equalization takes place within the first turbine stage while the guide vane is the main driver for this process. In opposite to this the temperature inhomogeneity does not attenuate significantly within the multistage turbine part.