Abstract
Techniques for increasing the rate of jet mixing in axisymmetric nozzle flows have been studied in the present work both experimentally and computationally. Near-field jet development from a “clean” axisymmetric nozzle is used as a datum against which to judge mixing effectiveness. A combination of water tunnel and high-speed airflow facilities are used to assess the near-field jet behaviour experimentally. Classical solid tabs and “fluid” tabs (i.e. discrete radially discharging jets at nozzle exit) are examined. Both measurements and CFD calculations demonstrate that fluid tabs reproduce the same streamwise vortex formation process as solid tabs. For a tab jet flow rate of around 1% of the core nozzle flow, similar potential core length reductions and increased centre-line velocity decay rates are observed in the near field. Since fluid tabs can be switched off when not needed, hence avoiding associated drag/thrust loss penalties, this technology is a promising technique worthy of further development.
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