Control of diffuser jet flow: turbulent kinetic energy and jet spreading enhancements assisted by a non-thermal plasma discharge |
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Authors: | N Benard N Balcon G Touchard E Moreau |
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Institution: | (1) Laboratoire d’Etudes Aérodynamiques (LEA), Université de Poitiers, ENSMA, CNRS, Bld Marie et Pierre Curie, Teleport 2, 86962 Futuroscope Cedex, France |
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Abstract: | An axisymmetric air jet exhausting from a 22-degree-angle diffuser is investigated experimentally by particle image velocimetry
(PIV) and stereo-PIV measurements. Two opposite dielectric barrier discharge (DBD) actuators are placed along the lips of
the diffuser in order to force the mixing by a co-flow actuation. The electrohydrodynamic forces generated by both actuators
modify and excite the turbulent shear layer at the diffuser jet exit. Primary air jet velocities from 10 to 40 m/s are studied
(Reynolds numbers ranging from 3.2 to 12.8 × 104), and baseline and forced flows are compared by analysing streamwise and cross-stream PIV fields. The mixing enhancement
in the near field region is characterized by the potential core length, the centreline turbulent kinetic energy (TKE), the
integrated value of the TKE over various slices along the jet, the turbulent Reynolds stresses and the vorticity fields. The
time-averaged fields demonstrate that an effective increase in mixing is achieved by a forced flow reattachment along the
wall of the diffuser at 10 m/s, whereas mixing enhancement is realized by excitation of the coherent structures for a primary
velocity of 20 and 30 m/s. The actuation introduces two pairs of contra-rotating vortices above each actuator. These structures
entrain the higher speed core fluid toward the ambient air. Unsteady actuations over Strouhal numbers ranging from 0.08 to
1 are also studied. The results suggest that the excitation at a Strouhal number around 0.3 is more effective to enhance the
turbulence kinetic energy in the near-field region for primary jet velocity up to 30 m/s. |
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