Vélocimétrie Instantanée Volumique pour les Ecoulements Tridimensionnels – VIVE3D

The majority of flows, which have significant interests for academic research and are representative of industrial situations, reveals the presence of unsteady three-dimensional flow structures. Even if numerical modelling has done substantial progress in fluid mechanic during the last two decades, experimental approaches of these complex phenomena remain essential to understand the physic of fluid mechanisms and to investigate problems of industrial relevance.. Today, experimental studies are based mainly on one-point velocity measurements (Hot Wire Anemometer HWA, Laser Doppler Velocimetry : LDV), pressure taps and more recently two-dimensional optical diagnostics : Particle Image Velocimetry : PIV, which provides instantaneous velocity maps in a slice of the flow. These latter diagnostics have shown their ability to assess complex flow structures and are becoming essential tools of fluid mechanics research. Nevertheless, even if holographic techniques have done significant progress during the last decade and open new ways to think of measuring all components of velocity vectors in volume, the three-dimensional features and unsteady behaviour of flow structures are still more or less out of reach of experimental techniques. Recently, new developments in the field of optical diagnostic [1,2] have demonstrated the possibility to get measurement of three-dimensional velocity fields in a volume of significant size. These original experimental approaches open new tracks for studying the three-dimensional topology of turbulent flows. The aim of the present project is to develop, adapt and apply two complementary optical diagnostics which offer substantial potentials for measuring the instantaneous three components of a vector field in volume: - The tomographic particle image velocimetry [1,2] - The digital in-line holography [3] The first part of the project will be devoted to the development of the two techniques. The development of tomographic PIV will be focused on the reconstruction of 3D distribution of particles, the calibration of the optical system and the extension of the PIV algorithms to the 3D velocity measurement. Recent works have shown the great interest of such a technique, which could provide the full spatial resolution of the velocity with time resolution [2]. For the development of the digital in-line holographic technique, the project will benefit from the experience of the consortium in the field of holographic methods associated with recent technical improvements of high resolution CCD camera. That will permit to adapt holographic velocity measurement to volume size of 10x10x10 mm3, with the final objective to reach measurement volume as small as 1x1x1 mm3 in order to access accurately to velocity profiles very close to wall for measuring the wall shear stress. In the second part of the project, the three-dimensional techniques will be applied in real flow conditions. The partners have identified a set of 4 test cases of flow with complex 3D structures, which are difficult to figure out by using one-point or two dimensional velocity measurement techniques: - Turbulent boundary layers in large wind tunnel at LML - Stabilization of lifted turbulent flame at CORIA - Measurement of 3D velocity gradients in an optical viscosimeter at LEA - Pulsed jet in crossflow at LEA These experiences will be carried out in collaboration with all the partners in order to benefit from all the cross developments and the knowledge the partners acquired working on that project. The association of skills of three laboratories, internationally identified for a long time as leader in the field of optical diagnostics developments for fluid mechanics will guarantee the success of the project. These teams have collaborated and collaborate regularly in the framework of various programs, such as European projects. These collaborations have settled privileged scientific links between the partners, which are evidenced today, through numerous scientific exchanges, mutual confidence and the loans of scientific equipments. This last point will be essential for the project success where sharing of high cost scientific equipments will be necessary. In particular, these teams will take advantage of the fact that already contribute to the 'Plateforme de Métrologie Optique de Lille (MEOL) [1] Elsinga, G. E.; Scarano, F.; Wieneke, B. & van Oudheusden, B. W. (2006), 'Tomographic particle image velocimetry', Experiments in Fluids V41(6), 933—947 [2] Schröder A., Geisler R., Elsinga GE., Scarano F. and Dierksheide U. (2006) 'Investigation of a turbulent spot using time-resolved tomographic PIV', 13th Int. Symp. Appl. Laser Tech. Fluid Mech., Lisbon [3] Malek, M.; Allano, D.; Coetmellec, S.; Ozkul, C. & Lebrun, D. (2004), 'Digital in-line holography for three-dimensional-two-components particle tracking velocimetry', Measurement Science and Technology 15(4), 699-705