Instabilities of the separated wake flow in the base region of

a space launcher BackgroundDue to the abrupt change in geometry on the base, the flow past a space launcher is characterized by a massive separation.During the lift-off at transonic speeds, the resulting turbulent flow can excite structural modes and generate unsteady side loads both on the base and on the nozzle (buffeting).Aim of the researchIn order to contain structural problems without over-designing the launcher, it is necessary to investigate the effects of different geometric configuration and flow regimes on the separated flow. Particular attention is addressed to the case of Ariane 5.

Proper Orthogonal Decomposition (POD) were used to identify the most energetic modes associated to the motion of the wake.

Research MethodologyThe flow field in the separated wake behind the launcher is studied considering different geometric configurations and different flow regimes. The effect on the organization and coherence of turbulent structures are considered.The flow field behind the launcher is obtained by means of Paticle Image Velocimetry (PIV).

Progress Tomographic PIV was used to investigate the flow field behind a simple truncated base rocket model at uncompressible regime.Different flow velocities were considered in a range including both laminar and turbulent regimes.The main purpose was to study the spatial organization of turbulent structures inside the wake in the plane parallel to the base of the model (Azimuthal Plane).

PhD Candidate: Valeria GentileDepartment: AWEPSection: AerodynamicsSupervisor: F. Schrijer, B. van OudheusdenPromoter: F. ScaranoStart date: 03-12-2012Funding: Tinker Bell Scholarship

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Coherent structures downstream of a cylinder with a cylindrical after- body at high subsonic regime (Deck and Thorigny, 2007)

ObjectivesThe results obtained for the uncompressible case are to be used for next experiments at transonic regime.Modifications of the basis and the after- body of the model are to be considered in order to obtain a geometric configuration closer to the one of Ariane 5.

Ariane 5 Lift- Off

Axial Velocity Field -0.25 diameters past the base – V=20m/s

Axial Velocity Field 1.75 diameters past the base - V=20m/s

Axial Velocity Field 1.0 diameters past the base - V=20m/s

POD Mode m=1- 0.25 diameters past the base

POD Mode m=2- 0.25 diameters past the base

POD Mode m=3- 0.25 diameters past the base

POD Mode=4- 0.25 diameters past the base