Flow field investigations in rotating facilities by means of stationary PIV systems

Abstract

The flow field inside rotating test sections can be investigated by means of particle image velocimetry (PIV) operated in the phase-locked mode. With this experimental approach, the measurement system is kept fixed and it is synchronized with the periodical passage of the test section. Therefore, the direct output of the PIV measurements is the absolute velocity field, while the relative one is indirectly obtained from proper data processing that relies on accurate knowledge of the peripheral velocity field. This work provides an uncertainty analysis about the evaluation of the peripheral displacement field in phase-locked PIV measurements. The analysis leads to the detection of the levels of accuracy required in the estimation of both the angular velocity and the position of the center of rotation to ensure correct evaluation of the peripheral displacement field. In this regard, a simple methodology is proposed to evaluate the center of rotation position with an accuracy below 1 px. Finally, a procedure to pre-process the PIV images by subtracting the peripheral displacement is described. The advantages of its implementation are highlighted by the comparison with the performance of a more standard methodology where the peripheral field is subtracted from the absolute velocity field and not directly from the PIV raw data.

Effect of Rotation on a Gas Turbine Blade Internal Cooling System: Experimental Investigation

“…For the data acquired under rotation, error introduced by the image processing has to be taken into account. In accordance with the analysis proposed by Armellini et al [32], the velocity uncertainty must be increased by 1% of U b (Eq. (5)).…”

“…Concerning the measurements under rotation, it has to be underlined that the present PIV system is stationary; therefore, a phased-locked configuration has been adopted. Since the measurement output is the absolute velocity field, a more complex preand postprocessing procedures [31,32] were adopted in order to get an accurate reconstruction of the relative velocity field inside the test section.…”

Flow field inside a leading edge cooling channel with turbulence promoters in rotating conditions

“…However, it is worth noting that the laser and cameras are not inbuilt with the rotating equipment (see Figure 4), hence tests in rotating conditions are carried out in phased-locked configuration i.e. synchronizing the acquisition of the image pair with the test section transition through the measurement zone 26 ). For this reason, image processing and relative velocity field computation required the development of a dedicated technique whose description is available in Furlani et al 5 Concerning PIV data accuracy, an estimate of the mean velocity uncertainty was previously performed 5 and resulted to be less than 2% and 5% with respect to U b (95% confidence level), for the static or rotating measurement, respectively.…”

Effects of Rotation at Different Channel Orientations on the Flow Field inside a Trailing Edge Internal Cooling Channel

“…The test rig allows measurements to be taken under both static and rotating conditions with the PIV image acquisition performed in phase-locked mode (i.e., the measurement chain is fixed, not rotating with the test section). A good accuracy of the data is obtained by applying a particular image preprocessing procedure as described in detail in [27,28]. All the statistical flow quantities result from a time average computed on 1000 samples.…”

“…velocity values. According to the analysis proposed in Armellini et al [28], the velocity uncertainty must be increased by 1% of for the data acquired under rotation. Finally, referring to the stereo-PIV measurements, a crosscomparison with 2D data reported in [27] proved a satisfactory accuracy (5% ) also for the stereo-data.…”