Determination of instantaneous pressure in an axisymmetric base flow using time-resolved tomographic PIV

Quantification of mean and fluctuating surface loads is critical for the efficient design of aerospace structures. To measure surface pressure in experiments, wind tunnel models are typically equipped with pressure transducers, which offer high sampling rates and high sensitivity. In order to have a sufficient spatial sampling of the surface pressure such that the instantaneous surface loads can be determined, a large number of transducers is required. From a practical point of view, the installation of transducers can be costly and can pose significant challenges due to spatial limitations inside the wind tunnel model. An alternative for measuring pressure is PIV-based pressure determination [1]. In this approach, PIV data are used to determine the material acceleration, which is related to the local pressure gradient via the momentum equation. Whereas the mean pressure field can be obtained from a series of uncorrelated velocity fields (e.g. [2]), the availability of time-resolved PIV data allow for the determination of instantaneous pressure fields. Recent developments in PIV measurement capabilities, in particular tomographic PIV [3], have made this technique increasingly feasible and appealing. A particular advantage of the technique is that it provides simultaneous velocity and pressure data in the full flow field, thus enabling a better understanding of the relation between fluid dynamics and the corresponding pressure field. The ability of PIV to determine the material acceleration, from which the pressure can subsequently be obtained, has been the subject of extensive study. Using two or more velocity fields closely separated in time, the material acceleration can be determined using traditional Eulerian or Lagrangian formulations (see e.g. [1] for details). An improved estimate of the material acceleration may be obtained using fluid trajectory tracking (FTC) which correlates more than two consecutive reconstructions [4, 5]. The present study builds on these efforts by using time-resolved tomographic PIV to obtain instantaneous pressure distributions in a low-speed axisymmetric base flow. Results are compared to simultaneous unsteady pressure measurements using microphones and mean pressure measurements using static pressure sensors