Turbulent axisymmetric base flows: Symmetry and long-term behavior

This thesis deals with the flow around truncated bodies of revolution. Such flows are encountered in a variety of engineering applications relevant to the aerospace transportation industry, notably to space launcher vehicles. The work focuses on the unsteady behavior of the wake and particularly on the dynamics of the recirculation region behind...

Low-frequency wake instability of an axisymmetric bluff body in pitch

The backflow instability in the wake past a cylindrical blunt-based body in pitch is investigated at a Reynolds number ReD = 6.7 · 104 based on the cylinder diameter. Time-resolved stereoscopic particle image velocimetry measurements have been performed in a cross-flow plane located 0.3 D downstream of the model base. An increasing displacement...

Very-low frequency wake dynamics of an axisymmetric body

The so-called very-low-frequency (VLF) azimuthal meandering of the reversed-flow region has been shown to contribute significantly to the unsteadiness of the turbulent wake flow past a bluff body of revolution (Rigas et al. 2014; Grandemange et al. 2014). Such an erratic behavior causes a continuous change in the wake topology and, particularly...

Experimental assessment of PIV/PTV-based pressure reconstruction techniques applied to a low-speed base flow

Quantification of surface pressure is critical for the efficient design of aerospace structures. One way of measuring pressure is PIV/PTV-based pressure reconstruction [1]. In this approach, PIV/PTV data are used to determine the material acceleration and subsequently pressure via the momentum equation. In recent years, the technique has become...

Low-frequency behavior of the turbulent axisymmetric near-wake

The turbulent wake past an axisymmetric body is investigated with time-resolved stereoscopic particle image velocimetry (PIV) at a Reynolds number ReD = 6.7 × 104 based on the object diameter. The azimuthal organization of the near-wake is studied at different locations downstream of the trailing edge. The time-averaged velocity field features a...

Time-dependent behaviour of the recirculation region behind an axisymmetric bluff-body

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...

Organization of an axisymmetric turbulent wake in presence of a central protrusion

Stereoscopic Particle Image Velocimetry (PIV) was used to study the wake of an ogive-cylinder with after-body at a diameter-based Reynolds number ReD = 6.7 · 104. The vertical fluctuations reduced from a maximum of 0.18 U? in absence of rear-protrusion, up to 0.12 U? and 0.1 U? when the main-body to after- body diameter ratio d/D was increased...