摘要 :
This work explores the possibility of reducing the dominant noise source in a rectangular supersonic jet by enhancing its interaction with other coherent modes. As a first step before running Large-Eddy Simulations, we use Lineari...
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This work explores the possibility of reducing the dominant noise source in a rectangular supersonic jet by enhancing its interaction with other coherent modes. As a first step before running Large-Eddy Simulations, we use Linearized Euler Equations (LEE) to provide the transverse profiles of the various flow perturbation parameters across the jet and normalize these profiles such that it is a function of the Strouhal number and local momentum thickness. This, along with other appropriate transverse shape assumptions enable us to reduce the full governing equations into a set of ordinary differential equations (ODE) describing the interaction among the various coherent modes in the jet as well as with the mean flow and background fine-scale random turbulence. This work is an extension of previous works for a compressible shear layer, but the theory is extended into 3D with the use of LEE instead of the Linear Stability Theory to obtain the transverse shape of the coherent structure. ODE solutions are presented for the case of fundamental-subharmonic interactions between Strouhal numbers 0.20 and 0.10. It is concluded that adding the subharmonic can reduce the fundamental at an optimal initial phase angle and when both initial amplitudes are large.
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摘要 :
The use of Linearized Euler Equations for direct prediction of supersonic jet noise issued from a rectangular nozzle is explored and noise directivity is compared with the previous traditional approaches of Large-Eddy Simulations ...
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The use of Linearized Euler Equations for direct prediction of supersonic jet noise issued from a rectangular nozzle is explored and noise directivity is compared with the previous traditional approaches of Large-Eddy Simulations accompanied with Ffowcs-Williams Hawkings method. A new versatile Linearized Euler Equations solver is developed using the OpenFOAM API named "leeFoam". Special treatment of boundary reflections such as implementation of non-reflecting boundary condition along with a sponge zone is introduces. Artificial Acoustic Damping is implemented as a source term to prevent spurious numerical instabilities. It is shown that a finite-volume numerical scheme coupled with proper boundary treatment can produce a stable solution nearly free from reflections. Verification is conducted against analytical results for the propagation of an acoustic pulse in uniform flow. Applicability of this approach to real jets is explored by taking the inflow disturbances to be related to the fundamental frequency of jet and comparing with experimentally measured noise.
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