Time-averaged pressure from Robotic Volumetric PIV

Pressure represents a physical magnitude which allows the characterisation of flow behaviour. Its study isof great interest for engineering purposes and is broadly reported in the literature. The practical implementation of pressure measurements in industrial wind tunnel facilities involves the use of intrusive pressure probes only able to retrieve pressure confined in a two-dimensional space. The interest of the industry is, however, centred on three-dimensional large-scale flows. Although they are proven to be a reliable and established technique, direct pressure measurements can also be time-consuming or provide insufficient information when considering the relatively large measurement regions in industrial wind tunnel testing.Pressure measurement using flow velocity data from PIV represents a viable alternative to direct pressuremeasurements. A literature survey identifies the successful measurement of pressure using 2D and 3DPIV techniques. Nevertheless, limitations in terms of maximum measurement volume, setup complexity and computational time make its application in the industry impractical. The introduction of Helium Filled Soap Bubbles and novel particle tracking algorithms allows for larger measurement volumes and affordable computation times which, combined with the arrival of Robotic Volumetric PIV, open the possibility of large-scale industrial measurements. While the technique has been successfully demonstrated, its performance in terms of pressure reconstruction has never been reported in the literature. Feasibility of 3D pressure measurements in large-scale industrial environments opens the possibility to substitute intrusive direct pressure measurements.In order to prove the feasibility of non-intrusive pressure reconstruction from PIV, the practical implementations are investigated and assessed through a wind tunnel experiment in the wake flow of a wall bounded finite cylinder. The proposed approach is based on the combination of velocity information with flow governing equations to obtain and solve the Poisson equation for pressure using first Neumann and then Dirichlet boundary conditions on the edge of the domain. The analysis is performed at flow speeds of 10 and 25 m/s where time-resolved and double-pulse acquisition strategies are used respectively. PIV-based pressure measured in a 24 L volume is compared with state-of-the-art direct pressure measurements along planes inside the same volume, serving as reference data. Total pressure is retrieved from a Kiel probe survey and static pressure is measured through pressure taps installed in the test section.The results show a good agreement between PIV-pressure from time-resolved acquisition and direct pressure measurements at 10 m/s, while for the case of double-pulse PIV-pressure at 25 m/s, it does not fully agree with the reference data. The current system capabilities demonstrate the possibility of substituting traditional pressure measurements in large-scale industrial environments for speeds up to 15 m/s. Moreover, larger amounts of pressure information are available in a similar time-scale, which ultimately confers superior flow characterisation capabilities. For higher flow speeds, increased performance of double-pulse acquisition strategy along with dedicated pressure reconstruction approaches might represent a viable alternative for pressure measurements in the future.Aerospace Engineering | Flight Performance and Propulsio