pression and load evaluation from optical measurements – EVAPOR

This project is aligned with the "fluid, structures" axis along with "fluid dynamics" and "propulsion and energy flow" sub-axes’ themes of the DGA. Its principal aim is to assess the pressure and force in the near and far fields from non-intrusive volumetric measurements of velocity. Despite the substantial progress made by numerical simulation in fluid mechanics in the last two decades, the study of these complex phenomena by experimental approaches remains essential to the understanding of the underlying physical mechanisms and the study of problems of industrial interest. While different tools exist for flow measurements, one of the most commonly used today remains PIV (particle image velocimetry), which is applied in almost all areas of fluid mechanics. This technique offers the double advantage of simultaneously providing non-intrusive flow visualization and quantitative measurements of velocity. Recently, the development of Tomographic-PIV has demonstrated the ability to obtain three-dimensional measurements of velocity fields in a volume of significant size. Although some limitations of this measurement technique remain today, such as the sensitivity of the reconstruction calibration and the need to have sufficient optical access to the measurement domain from multiple cameras, the resulting three velocity components that are measured in volume is a major asset. This allows the evaluation of quantities such as pressure fields and forces in aerodynamic or hydrodynamic flows.
In the framework of this project, the collaborating partners, having benefitted from the experience of a European project on a related problematic, propose novel approaches for 3D pressure assessment. These approaches will be compared to the state of the art and the forces in the near field and far field will be evaluated. This work will be decomposed into three stages. The first stage will be the development of pressure and force evaluation tools that will be validated with the results obtained by numerical simulation. The resolved pressure from a standard integration of the Poisson equation will be compared to methods that either integrate the pressure gradient calculated from the projection of the velocity field on a polynomial basis or that solve a coupled Poisson – boundary condition integral equation. For the calculation of forces, near field approaches based on the momentum equation or on the concept of impulse vorticity and far field approaches based on the calculation of the generating pressure from the speed and the static pressure will be developed and compared with direct measurements of forces using mass balances. The remaining two stages of the project will be the application of these methods on a flow around a flexible hydrodynamic foil, that presents the difficulty of non-stationary and variable surfaces, and the flow around a generic UCAV model in an aerodynamic wind tunnel, which approaches industrial applications. The final objective of this project is to compare the developed methods on these two types of flow and make the tools sufficiently simple and flexible in order to disseminate and apply them in industry.