Investigation of a Twinjet Configuration with and without Flow Control

Abstract

Jet noise has been an active area of research owing to public health concerns and aviation regulations. This problem is further amplified with the use of multiple engines placed in closed proximity to each other. In addition to significantly altered farfield noise as compared to a single-jet, previous experimental results show high levels of dynamic pressure fluctuations in the inter-nozzle region which can cause structural damage. In this work, Large Eddy Simulations are performed to study the dynamics of a supersonic twinjet configuration, with and without flow control. Results indicate that relative to single-jet configuration, twinjets show decrease in column lengths due to significant modifications in shear-layer properties. The simulations also corroborate previous experimental observations of very high levels of dynamic pressure fluctuations in the inter-nozzle region relative to a single-jet configuration for identical flow parameters. The phenomenon of noise shielding along the plane containing the two jets has been reported for all the twinjet cases explored in this work and trends of sound pressure levels obtained at various polar angles indicate an increased efficiency of shielding at lower polar angles. The sensitivity of the dynamic pressure fluctuations on the nozzle-exit boundary layer thickness is also characterized. Simulations are also performed to mimic the effects of Localized Arc Filament Plasma Actuators at different excitation frequencies (St=0.3 and 0.9) actuated in an axisymmetric fashion (m=0). Close to the nozzle exit, toroidal structures formed as a result of control result in significant increase in jet spreading leading to the formation of a recirculation region along the symmetry plane, relative to the uncontrolled case. This excitation scheme increased the levels of dynamic pressure fluctuations closer to the nozzle exit in the inter-nozzle region. In contrast, the near field shows significant reduction in pressure fluctuations, especially for the higher Strouhal number case.