Volumetric velocity measurements (V3V) on turbulent swirling flows
Résumé
This paper presents some results of Volumetric V3V 3D3C velocity measurements on a turbulent flow from a swirl burner. The flow out from the burner used is highly three-dimensional. The study aims at using a system of instantaneous 3D velocity measurements in order to characterize the turbulent swirling flow. The burner used consists of two coaxial tubes with a swirler placed in an annular part supplying the oxidant flow. The central pipe delivers the fuel radially (in the case of reacting flow) through eight holes symmetrically distributed on the periphery of the tube. The burner is placed at the bottom of a combustion chamber and the flow develops vertically along the confinement. The Volumetric 3-component Velocimetry V3V® technique commercialized by TSI is used for 3D velocity measurements in a non reacting flow. The measurement volume above the burner is located at 1.3Db (=49.4 mm) and is 50×50×22 mm3. The operating conditions considered in this study are 4.67 m/s of bulk velocity, Re=7531 of Reynolds number and Sn=1.4 of swirl number. There are very limited works on the application V3V technique on fluid flows. This paper presents the first results concerning an isothermal non-reacting gas flow. Instantaneous and mean velocity 3D3C volumes are measured and shown. Streamlines and velocity iso-surfaces are also analyzed together with different velocity profiles. The results are compared to previous SPIV (Stereoscopic Particle Image Velocimetry) measurements performed by the authors. A good agreement is found between the results of both techniques; the discrepancy did not exceed 10%. V3V results allowed a fine description of 3D aspects of the flow including the recirculation zone and the annular zone with swirling jet effects. The swirling part of the flow and the central recirculation zone are clearly identified by 3D fields of velocities and streamlines. Velocity volume indicates the presence of a central zone with a negative longitudinal velocity, which can reach −1 m/s at the burner center. Under the swirl effect, the tangential velocity is relatively high, particularly in the annular zone of the burner. Indeed, this velocity is varied between 3 and −3 m/s for a bulk velocity of 4.7 m/s.