Digital Filter-based Turbulent Inflow Generation for Jet Aeroacoustics on Non-Uniform Structured Grids

Abstract

Inclusion of the nozzle geometry with a turbulent inflow boundary condition is essential for realistic jet noise simulations. In the current study, a digital filter-based turbulent inflow condition, extended in a new way to non-uniform curvilinear grids, is implemented to achieve this. The proposed method has several key features desirable for jet noise simulations, with some limitations. To validate the method, a quasi-incompressible zeropressure-gradient flat plate turbulent boundary layer is simulated at a high Reynolds number. The boundary layer produced by the current method is shown to agree reasonably well with theory and a recycling-based turbulence injection method. The length of the adjustment region necessary for synthetic inlet turbulence to recover from modeling errors is estimated. A low Reynolds number wall-resolved jet simulation including a round nozzle geometry is performed. The method is shown to be effective in producing sustained turbulence on a non-uniform, non-Cartesian grid at a barely turbulent Reynolds number. The effect of variation of the inlet integral length scales on the recovery of turbulent fluctuations is studied and recommendations are made for choosing these parameters. A possible spurious noise source is identified near the turbulent inlet for the current method. It is shown that this spurious noise does not affect the acoustic field outside of the jet significantly, though it is recommended to attenuate this noise artificially by using a sponge zone.Downloaded by CORNELL UNIVERSITY on July 30, 2015 | http://arc.aiaa.org |

Analysis of Converging-Diverging Beveled Nozzle Jets Using Large Eddy Simulation with a Wall Model

“…As discussed in ref. 36, the required length is a function of the inflow BL thickness, δ 99i . For flat plate BLs, 8δ 99i is sufficient when using the wall model 47 and 11.5δ 99i works well for wall-resolved simulations.…”

“…For flat plate BLs, 8δ 99i is sufficient when using the wall model 47 and 11.5δ 99i works well for wall-resolved simulations. 36 A conservative length of 13δ 99i is used here. There is also another difference between the simulations and experiments.…”

“…35,38,42 Furthermore, an approximate inflow turbulent boundary condition [43][44][45] provides turbulent boundary layers on the interior nozzle walls. 36,37 For wallresolved LES, the methodology has been found to work well for a variety of problems including subsonic converging nozzles 35,36 and supersonic converging-diverging (CD) nozzles. 46 Also, a simple equilibrium wall shear stress model has been developed and validated for nearly incompressible flat plate BLs 47 and subsonic jets.…”

“…[34][35][36][37][38] The implementation relies on the SPIKE algorithm for solving banded linear systems in parallel. 39,40 A shock-capturing method based on local application of a weighted essentially non-oscillatory (WENO) characteristic filter 41 has also been included for supersonic flows.…”

Equilibrium Wall Model for Large Eddy Simulations of Jets for Aeroacoustics

“…To this end, a highly-parallelizable modular Fortran code is being developed at Purdue University to perform such calculations utilizing high-order numerical methods. [21][22][23][24] For wall-resolved LES, our current methodology has been found to work well for a variety of problems including subsonic converging nozzles 22,23 and supersonic converging-diverging nozzles. 25 Wall-resolved nozzle boundary layers, however, become prohibitively expensive for jet simulations at realistic Reynolds numbers.…”