LES-based evaluation of a microjet noise reduction concept in static and flight conditions

AbstractThe Large-Eddy Simulation (LES) numerical system established since 2002 for jet-noise computation is first evaluated in terms of recent gains in accuracy with increased computer resources, and is then used to explore the relatively new “microjet” noisereduction concept (injection of high-pressure microjets in the vicinity of the main jet nozzle exit), which currently attracts significant attention in the aeroacoustic community. The simulations are found to capture the essential features of the flow/turbulence and the far-field noise alteration by the microjets observed in experiments, and to reveal the subtle flow features responsible for the effect of injection on noise. They also confirm the experimental observation that in static conditions microjets provide a noise reduction comparable with that from chevrons in the low-frequency range, and probably have a less pronounced high-frequency penalty. This positive evaluation of the microjets concept is, however, mitigated by results of simulations in flight conditions, which were never studied experimentally. The latter results, which are awaiting an experimental verification, make a practical use of the concept in its current form rather unlikely

Simulation of a Shear Coaxial GO2/GH2 Rocket Injector with DES and LES Using Flamelet Models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97098/1/AIAA2012-3744.pd

Comparison of RANS, DES and DDES Results for ONERA M-6 Wing at Transonic Flow Speed Using an In-House Parallel Code

The very first thought that comes to the mind with the application area of the DES and DDES schemes is a massively separated flow with highly unsteady flowfield. However, for various complex three dimensional cases, there is no prior knowledge of the flowfield in the domain and it may have mild separation or no separation at all with a steady domain. This study is carried out to see that what will be the behaviour of the DES and DDES schemes in comparison with the URANS scheme if they are applied to a steady state case. An in-house mpi code DG-DES is used for the present study. Three different flux computational schemes named Roe, AUSM and HLLC schemes within DES formulation are compared to check the response for the flows without massive separation and unsteadiness. The cases are run in both single and double precision mode for DES formulation using Roe flux computational scheme to appreciate the accuracy of the solver. A good comparison of pressure distribution with the experimental data is obtained for all URANS, DES and DDES simulations. The pressure distribution results for DES scheme using single and double precision agree well with the experimental data. The pressure distribution predicted by DES using Roe, AUSM and HLLC schemes agree well with the experimental data. The computed values of Cl and Cd are also in close approximity to the other studies. The drag predicted by all DES and DDES simulations is lower than the URANS scheme. It indicates that the DES and DDES schemes generate lower dissipation due to switching to the LES mode and hence result in lower drag prediction as compared with the URANS solution. There is no anomaly observed in the flow due to the use of DES or DDES for steady flow case

Improvement of delayed detached-eddy simulation for LES with wall modelling

Adjustments are proposed of the Delayed Detached Eddy Simulation (DDES) approach to turbulence. They preserve the DDES capabilities particularly for natural DES uses, and resolve the mismatch of the logarithmic layers discovered earlier for the basic DES technique when used for Wall-Modelled Large-Eddy Simulation (WMLES) of attached flows. The adjustments are defined both for the Spalart-Allmaras and the Menter SST models. The first one concerns the definition of the LES length scale in general for anisotropic grids near a wall, and makes use of the wall distance along with the grid spacing; it clearly benefits even the Smagorinsky model. The second one manages the blending of RANS and LES behaviour within a WMLES to advantage, greatly increasing the resolved turbulence activity near the wall, and finely adjusting the resolved logarithmic layer. This is seen in channel flow over a wide Reynolds-number range, and through some grid variations. Tests show that the new method, although somewhat more complex, returns the desired behaviour not only in channel-flow LES, but also in channel-flow RANS, in a backward-facing-step case with side-by-side LES and RANS regions, and over an airfoil in deep stall