Computation of the Flow of a Dual-Stream Jet with External Solid and Perforated Wedge Deflectors for Noise Reduction

We present a methodology for the computation of flow fields involving complex perforated surfaces in propulsion applications. Of particular interest is the treatment of perforated flaps used as wedge-shaped fan flow deflectors for reducing jet noise of a supersonic turbofan engine. A three-dimensional Reynolds-Averaged Navier-Stokes solver is used to compute the flow field of the external jet plume with solid and perforated deflector flaps, the latter with 50% porosity. Flow computation for perforated flaps presents a particular challenge and is handled by use of a localized body force model in the momentum equation. The study is conducted at two operating conditions: a cold condition at which mean velocity surveys were conducted and against which the computational code is validated; and a hot condition that corresponds to the takeoff engine cycle. The code predictions replicate adequately the mean velocity fields of the cold experimental flows. The code is then extended to the conditions of the actual engine cycle to study the impacts of the deflectors on the turbulent kinetic energy (TKE) distributions in the jet plume and on the aerodynamic performance of the nozzle. Consistent with findings of past studies, the solid flaps decrease the TKE on the underside of the jet and increase it at the top of the jet. The perforated flaps mitigate the TKE increase on the top of the jet, thus reducing the potential of excess noise from that region. The thrust loss of the perforated flaps is approximately one half that of the solid flaps.