Jingbo Huang

Numerical Dissipation Effects on Massive Separation Around Tandem Cylinders

Three spatial schemes, the original Roe scheme and two high-order symmetric total variation diminishing schemes,whose dissipations aremultiplied by a constant parameter or a function (called ), are coupledwith delayed detached eddy simulation to investigate the numerical dissipation effects on the massive separation flow around tandem cylinders. From the comparisons between the computations and the available measurements, the numerical dissipation has a significant influence on the mean and instantaneous flowfields. The original Roe scheme is too dissipative to predict the small scale turbulent structures, and it strongly suppresses the growth of resolved turbulence. The S6WENO5 schemes with constantand adaptivetimes of dissipation have similar performances and they well match the measurements. However, the S6WENO5 with constanttimes (0.12 here) of dissipation is too empirical, and the small constanttimes of dissipation cannot generally suppress the numerical oscillations near the wall and in the far fields. The S6WENO5 with adaptive dissipation provides the best performance.

Investigation of Flows Around a Rudimentary Landing Gear with Advanced Detached-Eddy-Simulation Approaches

Unsteady and massively separated flows past the rudimentary landing gear are investigated using delayed detached-eddy-simulation and improved delayed detached-eddy-simulation based on shear stress transport model. To eliminate the unfavorable influence of large numerical dissipation, a high order symmetric total variation diminishing scheme with adaptive dissipation approach is implemented. Three sets of grid, including the coarse, medium and locally refined grids are applied. It is observed that the grid density effect is weak on the mean flows, but significant on the instantaneous quantities. Both approaches present acceptable agreements with the available experiments. Due to its wall-modeled large-eddy-simulation mode, improved delayed detached-eddy-simulation can deliver slightly larger secondary separation and smaller horseshoe vortex on the aft wheels, predict the shear layer instability a little more upstream and resolve smaller instantaneous structures. There are strong interactions between vortic...

Study of Delayed-Detached Eddy Simulation with Weakly Nonlinear Turbulence Model

This paper presents a parallel computation with hybrid Reynolds-averaged Navier-Stokes and large eddy simulation methods. Two types of hybrid approaches, referred to as detached eddy simulation and delayed-detached eddy simulation, are investigated through introducing length scales into the weakly nonlinear k-w turbulence model. Before the implementation of hybrid methods, the baseline weakly nonlinear model and k-w shear-stress-transport model are validated in the transonic RAE-2822 airfoil and ONERA-M6 wing cases. The numerical results show satisfactory agreement with the available experimental data. The Reynolds-averaged and hybrid methods based on the weakly nonlinear turbulence model are then applied to calculate the high Reynolds number transonic separation flows around NASA TN D-712 wing fulesage For the higher angle of attack case (a = 26.2 deg), both hybrid methods deliver good results when compared with the experiment; for the moderate angle of attack case (a = 12.5 deg), the results obtained with the delayed detached eddy simulation are satisfactory, whereas the starting point of the wing vortex breakdown predicted with the detached eddy simulation is too far upstream.

Comparisons of Three Improved DES Methods on Unsteady Flows Past Tandem Cylinders

Three advanced DES-type models coupled with adaptive dissipation scheme, DDES-2003/2006 and IDDES, are applied to predict the unsteady flow past tandem cylinders. The main differences among them are the shield functions and length scales, which leads to significant differences in mean turbulence kinetic energy, root mean square of pressure, instantaneous vorticity, and so on. The computational results are compared with almost all available measurements. These three models show good capability for the massive separation flows. IDDES performs relatively better than other two SST-DDES models. Furthermore, IDDES matches well with the measurements with trips on the rear cylinder surface.

Investigation of Practical Flow Control Methodologies with RANS/LES Hybrid Methods

Passive flow control methods, such as vortex generators (VG) on supercritical wing and before a cavity, spoiler in a large expanded diffuser, boat-tailed or multi-step afterbodies are numerically investigated with RANS or RANS/LES hybrid methods. The basic turbulence models are two-equation k-( models, such as shear stress transport (SST) and with Durbin’s three-dimensional correction (WD+) models. Before applying the flow control methods, the fundamental flows are explored and validated firstly. The flow-fields with flow control methodologies are compared with those of fundamental flows. The results show that the VGs can effectively restrain the separations induced by shock wave and boundary layer interaction on the supercritical wing. VG or VG pair can affect the shear layer instabilities after the leading edge of the cavity. The spoiler appropriately located can eliminate the separations in a diffuser. The boat-tailed and multi-step afterbodies can effectively increase the pressure at the base showing a significant reduction in the base drag.

Numerical Investigation of Massively Separated Flows past RLG Using Advanced DES Approaches

Unsteady and massively separated flows past the Rudimentary Landing Gear (RLG) are investigated using Delayed Detached-Eddy-Simulation (DDES) and Improved-DDES (IDDES) based on Shear Stress Transport model (SST). To eliminate the unfavorable influence of large numerical dissipation, a high order Symmetric Total Variation Diminishing (STVD) scheme with adaptive dissipation approach is implemented to better resolve the turbulence. Three sets of grid, including the coarse, mandatory and locally fine grids with 3.6, 11 and 13 million grid points, are applied to predict the massive separation and we find that grid density has a weak effect on the mean flows, but has a significant influence on the instantaneous flows. After investigating the flow features, both DDES and IDDES present acceptable agreements with the available experiments for the mean pressure, pressure fluctuations and surface flow patterns, and only small differences in some local regions occur. Due to the wall-modeled large-eddy-simulation (WMLES) mode, IDDES presents slightly more reasonable secondary separation and range of horseshoe vortex on the aft wheels than those by DDES. Furthermore, IDDES can present more reasonable root mean squares of pressure coefficients on the wheels, predict the shear layer instability a little more upstream and resolve smaller instantaneous structures than DDES.

Study into Effects of Vortex Generators on a Supercritical Wing

Flows around vortex generators (VGs), which serve as one of the important flow control methods, are investigated by solving Reynolds-averaged Navier–Stokes (RANS) equations. The influences on the main flow of VGs are intended to explore. Firstly, the flow around a single VG on a flat plane is computed to validate the schemes and to acquire basic knowledge of this kind of flow. Secondly, the effects of a row of VGs mounted about 25% local chord on a supercritical wing are analyzed in transonic condition with strong SWBLI. Lastly, VGs are mounted more upwind (about 3.5% local chord) to explore the effects at low speed and high incidence condition. The numerical results show that seven VGs can effectively suppress the separations behind the strong SWBLI and decrease spanwise flow and wing-tip vortex in transonic condition. VGs also can decrease the large scope of separation over the wing at low speed with high angle of attack.

Prediction for Separation Flows around a 6:1 Prolate Spheroid Using Hybrid RANS/LES Methods

This paper presents some hybrid Reynolds-Averaged Navier-Stokes (RANS) and large-eddy-simulation (LES) methods for the separated flows at high angles of attack around 6:1 prolate spheroid. These hybrid RANS/LES methods including detached eddy simulation (DES) based on Spalart-Allmaras, Menter’s k-ω shear-stress-transport (SST) and k-ω with weakly nonlinear eddy viscosity formulation (Wilcox-Durbin+, WD+) models and zonal-RANS/LES methods based on SST and WD+ models through a flow-dependent blending function are implemented to switch smoothly from RANS near the wall to LES in the core flow region. All the hybrid methods are designed to have a RANS mode for the attached flows near the solid wall and have a LES behavior for the separated flows in the core flow region. The main objective of this paper is to apply the hybrid methods for high Reynolds separated flows around prolate spheroid at high-incidences. At the same time, fourth-order central scheme with particle 4 th -order artificial viscosity and fully implicit lower-upper symmetric-Gauss-Seidel with pseudo time sub-iteration are taken as the spatial and temporal methods, respectively. Comparison with measurement is carried out for pressure coefficients, skin friction, profiles of velocity and the surface flow patterns, etc. Reasonable agreement with the available measurements, accounting for the effect on grids and fundamental turbulence models, is obtained for these separation flows. I. Introduction lo air th ws around ships, submarines, torpedoes, hot balloons, ships and aircrafts are usually very complicated and entirely ree-dimensional (1-D). At high angle of attack (AOA), 3-D flow separation has been an interesting and challenging problem in fluid mechanics. Undesired effects such as loss of lift, increase of drag, amplification of unsteady fluctuations in the pressure fields and uncontrolled yawing moment caused by the asymmetric fore-body vortices always accompany when the 3-D separation takes place. 2-D separation flows are mainly dominated by the adverse pressure gradient, flow reversal, etc. In 3-D separation flows, the separation features can be sensitive to the body configuration, roughness of surface, AOA and Reynolds number, etc. In addition to the complex topology of the flow patterns, the 3-D separation flows strongly challenge experimental equipments, analytical and predictive tools. The prolate spheroid, with a 6:1 major-minor semi-axis ratio, has very simple configuration; however, the flows past it present almost all the fundamental transition and separation phenomena of a 3-D flows. The flow separating from the leeward side of the spheroid rolls up into a strong primary vortex on each side of the spheroid and reattaches at the symmetric plane. The primary vortex is always accompanied by one small secondary vortex, which separates and reattaches adjacent to the body. The flow transition includes not only the stream-wise Tollmien-Schilichting (T-S) wave instability but also cross-flow instability, which is lack of effective predictive tools with the transition models until now. The flows around prolate spheroid have been studied both experimentally 1,2,3 and computationally using Reynolds-Averaged Navier