Study Of Unsteady And Massively Separated Flows Past Rudimentary Landing Gear Using DES-type Methods

Massive separation flows could be found in many fields such as aviation,navigation, spaceflight, wind engineering, and so on. Flows with massiveseparation always cause to unsteady vortex shedding which accompanies withunsteady force, generation of acoustics, and vibrations of solid frames whichmay lead to fatigue sometimes. Detached eddy simulation-type methods(DES-type), which combine the advantages of RANS and LES, are suitablefor predictions of massive separated flows in engineering.Development of DES-type methods is summarized in this article, and theformations of DES, DDES and IDDES based on two equation k-ω-SSTturbulence model are present. The characteristics, advantages anddisadvantages of the above DES methods are analyzed in detailed. The keyparameter CDESin DES-type methods is recalibrated through computing thedecay of homogenous and isotropic turbulence case (DHIT). The effect ondissipation of spatial schemes is investigated through both DHIT and tandemcylinders cases. It suggests that excessive dissipation may speed up thedecaying of turbulence, prevent the production of small-scale turbulentstructures in the separated regions, suspend the flow separations from thesurface, and shorten the range of power spectral density of pressure.A symmetric TVD spatial scheme, combining6thcenter scheme and5thWENO interpolation is taken as the spatial scheme when solving N-Sequations. To capture more detailed turbulent structures, the dissipation of thescheme could be reasonable decrease depend on the flow fields, which issuitable for DES-type methods. Differences between DDES and IDDES whenpredicting the unsteady flows around tandem cylinders based on the adaptivedissipation scheme, are compared with experiments. The results show thatIDDES including WMLES could reflect the effects of upstream turbulenceinformation in the boundary layer, expedite the switch from RANS to LES, and take better performances than DDES on the locations of flow separationfrom the surface and the distributions of turbulent kinetic energy in the gapregions between the two cylinders. The effects of the transition trips on thecylinder surface are studied using DDES with quasi-laminar (DDES-QL)method initially. The differences could be found on the distributions ofturbulent kinetic energy (TKE) in the wake of rear cylinder, and TKE basedon DDES-QL matches the measurement with transition trip on the rearcylinder better.The unsteady flow past rudimentary landing gear (RLG) is investigatedusing DDES coupled with adaptive dissipation scheme. Features of surfaceflow such as distributions of mean and root mean square of pressure andfriction lines and flow fields in space such as mean velocity, resolved andmodeled Reynolds-stresses and instantaneous vorticity are obtained. Therelation ship between the characters of surface flows and space flow fields isanalyzed. The maximum sound pressure level (SPL) locates at the bottom sideof the axle and ground inner side of the rear wheels which are related with theunsteady vortex shedding from upstream.