Abstract
Unsteady three-dimensional flow phenomena must be investigated and well understood to be able to design devices to control such complex flow phenomena in order to achieve the desired behavior of the flow and to assess their performance, even in harsh industrial environments. Experimental investigations for flow control research require measurement techniques capable to resolve the flow field with high spatial and temporal resolution to be able to perceive the relevant phenomena. Particle Image Velocimetry (PIV), providing access to the unsteady flow velocity field, is a measurement technique which is readily available commercially today. This explains why PIV is widely used for flow control research. A number of standard configurations exist, which, with increasing complexity, allow capturing flow velocity data instantaneously in geometrical arrangements extending from planes to volumes and in temporal arrangements extending from snapshots to temporarily well resolved data. With increasing complexity these PIV systems require advancing expertise of the user and growing investment costs. Using typical problems of flow control research, three different standard PIV systems will be characterized briefly. It is possible to upgrade a PIV system from a simple planar to a “high end” tomographic PIV system over a period of time, if sufficient PIV expertise can be built up and budget for additional investments becomes available.
Highlights
Flow control involves passive or active devices to affect a beneficial change in wall-bounded or free shear flows [1]
Individual flow structures and their contribution to the flow properties can be identified and can be used as an indicator for flow control efficiency in the device optimization process. This example shows that tomographic Particle Image Velocimetry (PIV) provides the most complete information on the tree-dimensional velocity field of all three PIV systems discussed in this paper
PIV has become an indispensable tool for the investigation of complex unsteady flow fields
Summary
Flow control involves passive or active devices to affect a beneficial change in wall-bounded or free shear flows [1]. All data must be acquired non-intrusively so that no interference of the flow field by the measurement is to occur The availability of such high quality experimental data does provide insight into the fluid mechanical phenomena involved in controlling the flow and supports the validation of the results of numerical calculations. Based on the considerations made above and as example for the potential of image based measurement techniques applied to flow control, an overview of the measurement of flow velocities employing different configurations of PIV systems will be given next. The performance of PIV systems such as planar PIV, stereoscopic PIV, tomographic PIV and corresponding modifications utilizing high-speed cameras for recording to achieve the required temporal resolution will be presented and their application to flow control research will be described briefly.
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