Coral Gables

Calculation of transonic flows using WENO method with a low diffusion E-CUSP upwind scheme

A low difiusion E-CUSP (LDE) scheme is applied with 5th order WENO scheme in this paper. The E-CUSP scheme can capture crisp shock proflle and exact contact surface. Several numerical cases are presented to demonstrate the accuracy and robustness for the E-CUSP scheme to be used with the WENO strategy.

Delayed Detached Eddy Simulation of a Stall Flow Over NACA0012 Airfoil Using High Order Schemes

Delayed-Detached Eddy Simulation (DDES) is conducted to simulate aerodynamic stall flow over NACA0012 airfoil at 45 ◦ angle of attack. DDES is an improved version of DES97 to avoid Modeled-Stress Depletion (MSD) in attached boundary layer by redefining the length scale of DES97. The test of DDES for the flat plate shows that the delayed LES function facilitates DDES to preserve eddy viscosity even with a severe grid that makes DES to undergo MSD. For comparison, DES97 and URANS also were conducted for the stalled NACA 0012 airfoil flow. DDES and DES predicted the drag coefficient accurately, while URANS overpredicted the drag by 33.6%. Both DES and DDES appear to be satisfactory to simulate the stalled airfoil flow at high angle of attack, in which the large structure of vortex are dominant.

A Novel Airfoil Circulation Augment Flow Control Method Using Co-Flow Jet

Anovelsubsonicairfoilcirculationaugmenttechniqueusingco-∞owjet(CFJ)toachievesuperioraerodynamicperformanceforsubsonicaircraftisprovednumericallybyCFDsimulation. Theadvantagesofco-∞owjetairfoilincludehighliftathighangleofattack,ultrahigh Cl=Cdat cruise point, and low penalty to the overall cycle e‐ciency of the airframe-propulsion system. Unlike the conventional circulation control (CC) airfoil which is only suitable for landing and taking ofi, the CFJ airfoil can be used for the whole ∞ying mission. No blunt leading and trailing edge is required so that the pressure drag is small. No moving parts are needed and make it easy to be implemented and weight less. The jet to enhance the circulation will be recirculated. Compared with the CC airfoil, the recirculating CFJ airfoil will signiflcantly save fuel consumption because: 1) the power required to energize the jet is less; 2) no penalty to the jet engine thrust and e‐ciency due to the disposed jet mass ∞ow since the jet mass ∞ow is recirculated. For the NACA2415 airfoil studied, at low AOA with moderate momentum jet coe‐cient, the co∞ow jet airfoil will not only signiflcantly enhance the lift, but also dramatically reduce the drag, or even generate the negative drag (thrust). The mechanism is that the co∞ow jet can control the pressure drag by fllling the wake, and could generate negative pressure drag greaterthanthefrictiondrag. Thismayallowtheaircrafttocruisewithveryhighaerodynamic e‐ciency. AthighAOA,boththeliftandthedragaresigniflcantlyhigherthantheairfoilwith no ∞ow control, which may enhance the performance of taking ofi and landing within short distance.

Numerical Simulation of Flow Induced Vibration Based on Fully Coupled Fluid-Structural Interactions

Afullycouplednumericalmethodologyisdevelopedforcalculatingthe∞ow-structureinteraction problems. The Roe scheme is extended to moving grid and used with the flnite-volume method. The unsteady solutions march in time by using a dual-time stepping implicit unfactored line Gauss-Seidel iteration. The unsteady Navier-Stokes equations and the linear structural equations are fully coupled implicitly via successive iteration with pseudo time stepping. Themovingmeshandmeshdeformationstrategyisbasedontwomeshzones,aflnemeshzone surroundingthesolidbodywithoutmeshdeformationandacoarsemeshzonesurroundingthe flnemeshzoneanddeformswiththesolidobject. Thismeshdeformationstrategycanmaintain the orthogonality of the mesh near the wall and save CPU time for re-meshing. The study cases presented include a vortex-induced oscillating cylinder, a forced pitching airfoil, and an elastically mounted transonic airfoil. For the elastic transonic airfoil, the ∞utter boundary is calculated. Otherphenomenacapturedincludethelimitcycleoscillation(LCO)andthesteady state ∞ow conditions, under which the aerodynamic forces and moments are balanced by the structure. Thecomputationalresultsagreewellwiththeexperimentsandthecomputedresults of other researchers. The methodology is demonstrated to be accurate, robust and e‐cient.

Prediction of a Supersonic Wing Flutter Boundary Using a High Fidelity Detached Eddy Simulation

Delayed Detached Eddy Simulation of supersonic flutter of a 3D wing is conducted at free stream Mach number of 1.141 using a fully coupled fluid/structure interaction (FSI). Unsteady 3D compressible Navier-Stokes equations are solved with a system of 5 decoupled structure modal equations in a fully coupled manner. The low diffusion E-CUSP scheme with a 5th order WENO reconstruction for the inviscid flux and a set of 4th order central differencing for the viscous terms are used to accurately capture the shock wave/turbulent boundary layer interaction of the vibrating wing. The predicted flutter boundary at supersonic Mach number achieves excellent agreement with experiment. It appears to be the first time that a numerical prediction of supersonic flutter boundary matches with experiment accurately.

Fully Coupled Fluid-Structural Interaction of a Transonic Rotor at Near-Stall Conditions Using Detached Eddy Simulation

This paper presents a numerical methodology to study the mechanism of stall flutter at near stall conditions using high fidelity detached eddy simulation (DES) in conjunction with a fully coupled fluidstructural interaction (FSI) model. At near-stall conditions, the flow is highly unsteady due to tip leakage vortex and may induce stall flutter. Such problems often involve shock wave-turbulent boundary layer interaction and flow separation due to rotating stall. In order to capture the possible flutter at near stall conditions, the DES is performed in a single passage domain with circumferential periodicity. The CFD techniques used include: a 5th order WENO scheme with a low diffusion Riemann solver for the inviscid fluxes, a fully conservative 4th order central differencing scheme for the viscous terms, a fully coupled fluid-structural interaction methodology, and a massive parallel procedure. The structural solver employs the efficient and accurate modal approach with five major mode shapes for the rotor blade. The work described herein will lay the foundation for the future work of simulating non-synchronous vibration.

3D Simulation of a Transonic Wing Flutter using an E-cient High Resolution Upwind Scheme

The∞utterboundaryofthe3DAGARD445.6Wingiscalculatedbyusingane‐cientupwind scheme,ZhaCUSP2,inmovinggridsystem. The3DReynoldsaverageNavier-Stokesequations aresolved. ClosureoftheReynoldsstressesisprovidedbytheBaldwin-Lomaxturbulencemodel. The modal approach solver is used to calculate the structural response under aerodynamic forces with second-order accuracy. The CFD and structural solvers are fully coupled implicitly via successive iterations within each physical time step. The numerical results show that this method is capable of capturing the aeroelastic properties of the ∞exible wing e‐ciently. The computed∞utterboundaryofAGARDWing445.6forfreestreamMachnumbersrangingfrom 0.499 to 1.141 agrees well with the experiment.

Investigation of Co-Flow Jet Airfoil Mixing Mechanism Using Large Eddy Simulation

This paper uses large eddy simulation (LES) to investigate Co-Flow Jet (CFJ) airfoil flows at high angle of attack (AOA). The standard Smagorinsky model with Van Driest damping is employed to resolve the subgrid scale stress. The 5th order WENO scheme is used for the reconstruction of the inviscid flux and the 4th order central differencing for the viscous flux. The momentum coefficient(Cµ) is chosen as a parameter to control the jet flow of the CFJ airfoil. LES simulations were carried out for the different momentum coefficients. The LES results at 30 o AOA are compared with the experiment to understand the flow structure of the jet mixing and flow separation. The numerically captured qualitative flow structures are very similar to those obtained in experiment. The quantitative prediction of lift and drag agree very well with experiment.

A hybrid Cartesian-body fitted grid approach for simulation of flows in complex geometries

A novel approach of automated hybrid Cartesian-body fltted grid (HCBFG) for simulations of ∞uid ∞ows in complex geometries is suggested. Based on a Cartesian background grid, the new approach automatically searches a near wall boundary(NWB) at any instant when a geometry is given. Within the NWB, a body-fltted mesh is generated using an e‐cient algebraic method with the skew angle between any two mesh lines guaranteed between 45 ‐ and 135 ‐ . This is attributed to the fact that only the mesh lines tangential to the solid surface needs to be generated. The mesh lines in the other two directions are from the background Cartesian grid. Outside of the NWB, the Cartesian grid is used. On the NWB, the grid points are one-to-one connected with the Cartesian grid. Hence, a consistent discretization scheme for structured grid can be used with no interpolation needed at the NWB. The fully conservative ∞ux calculation can be achieved. This new approach has the advantages of the Chimera grid and Cartesian grid methods to treat complex or moving geometry, but overcomes the drawbacks of those methods requiring interpolation on the difierent mesh boundaries. Beneflted from the HCBFG, all the rigorous numerical techniques developed for body-fltted grid, which are essential to achieve high order accuracy, can be used. The mesh size of the proposed hybrid grid approach will also be substantially smaller than that of a Cartesian grid method or unstructured grids since a highly stretched grid can be used near walls. This new approach may open a door to a new class of CFD technique for e‐ciently and accurately simulating steady and unsteady ∞ows, furthermore, solving moving grid and ∞uid-structural interaction problems with complex geometries. This paper presents several examples of the HCBFG for representative geometries. The transonic RAE2822 airfoil is calculated using an implicit line Gauss-Seidel iteration to demonstrate the feasibility of the method.