Abstract
A feasibility study of velocity field measurements using the Particle Image Velocimetry (PIV) method in an axial air turbine model is presented. The wakes past the blades of the rotor wheel were observed using the PIV technique. Data acquisition was synchronized with the shaft rotation; thus, the wakes were phase averaged for statistical analysis. The interaction of the rotor blade wakes with the stator ones was investigated by changing the stator wheel’s angle. The measurement planes were located just behind the rotor blades, covering approximately 3 cm × 3 cm in axial × tangential directions. The spatial correlation function suggests that the resolution used is sufficient for the large-scale flow-patterns only, but not for the small ones. The scales of fluctuations correspond to the shear layer thickness at the mid-span plane but, close to the end-wall, they contain larger structures caused by the secondary flows. The length-scales of the fluctuations under off-design conditions display a dependence on the area of the stator and rotor wakes cross-sections, which, in turn, depend on their angle. The obtained experimental data are to be used for the validation of mathematical simulation results in the future.
Highlights
Accepted: 10 June 2021Due to the crucial importance of steam turbines in the current “electric age”, there are a large number of scientific studies concerning the flow through these admirable machines
The flow past a single turbine stage is affected by the wake of the rotor, and by the wake of the upstream stator. The interaction of these two wake systems can be studied statistically by using the phase averaging of the data obtained at the same rotor angle
A slight rotation of the stator allowed us to distinguish natural waves in the rotor wakes from those caused by the stator wakes as illustrated in Figure 3, presenting the phase averaged data at three different stator wheel positions
Summary
Accepted: 10 June 2021Due to the crucial importance of steam turbines in the current “electric age”, there are a large number of scientific studies concerning the flow through these admirable machines. The flow inside an axial turbine is highly dynamical, consisting of an important periodical component, which is connected with moving wakes behind the rotor blades, and a truly turbulent component. These two components play very different roles in the flow dynamics, including mixing properties and flow stability behavior. The pressure and/or velocity fields are reconstructed from the multiple point measurements. This method is suitable only for the evaluation of statistical characteristics while supposing stationarity during the whole measuring procedure, and for the application of averaging or phase averaging strategies
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