The hydrodynamic characteristics of a rigid, single, circular cylinder in a three dimensional, incompressible, uniform cross flow were calculated using the large-eddy simulation method of CFX5. Solutions to the three ...The hydrodynamic characteristics of a rigid, single, circular cylinder in a three dimensional, incompressible, uniform cross flow were calculated using the large-eddy simulation method of CFX5. Solutions to the three dimensional N-S equations were obtained by the finite volume method. The focus of this numerical simulation was to research the characteristics of pressure distribution （drag and litt forces） and vortex tubes at high Reynolds numbers. The results of the calculations showed that the forces at every section in the spanwise direction of the cylinder were symmetrical about the middle section and smaller than the forces calculated in two dimensional cases. Moreover, the flow around the cylinder obviously presents three dimensional characteristics.展开更多
This paper presents hybrid Reynolds-averaged Navier-Stokes （RANS） and large-eddy-simulation （LES） methods for the separated flows at high angles of attack around a 6：1 prolate spheroid. The RANS/LES hybrid meth- ...This paper presents hybrid Reynolds-averaged Navier-Stokes （RANS） and large-eddy-simulation （LES） methods for the separated flows at high angles of attack around a 6：1 prolate spheroid. The RANS/LES hybrid meth- ods studied in this work include the detached eddy simulation （DES） based on Spalart-Allmaras （S-A）, Menter＇s k-ω shear-stress-transport （SST） and k-o9 with weakly nonlinear eddy viscosity formulation （Wilcox-Durbin＋, WD＋） models and the zonalANS/LES methods based on the SST and WD＋ models. The switch from RANS near the wall to LES in the core flow region is smooth through the implementation of a flow-dependent blending function for the zonal hybrid method. All the hybrid methods are designed to have a RANS mode for the attached flows and have a LES behavior for the separated flows. The main objective of this paper is to apply the hybrid methods for the high Reynolds number separated flows around prolate spheroid at high-incidences. A fourth-order central scheme with fourth-order artificial viscosity is applied for spatial differencing. The fully implicit lower-upper symmetric-Gauss-Seidel with pseudo time sub-iteration is taken as the temporal differentiation. Comparisons with available measurements are carried out for pressure distribution, skin friction, and profiles of velocity, etc. Reasonable agreement with the experiments, accounting for the effect on grids and fundamental turbulence models, is obtained for the separation flows.展开更多
The massively separated flow past triple cylin- ders （TriC） in tandem arrangement is simulated using the improved delayed detached-eddy simulation （IDDES） method based on the shear stress transport （SST） model, ...The massively separated flow past triple cylin- ders （TriC） in tandem arrangement is simulated using the improved delayed detached-eddy simulation （IDDES） method based on the shear stress transport （SST） model, coupled with the high order adaptive dissipation scheme. The spacing between adjacent cylinders is sub-critical （1.435D）. IDDES prediction of two cylinders （TC） with the same spacing is compared to experimental data for validation, and the numerical results agree well with the available measurements, except for the asymmetry in the gap region. The flow past TriC is investigated using the same method. Generally, the mean flow quantities past TriC, such as the velocity, pressure, and vorticity, are similar to the corresponding components of TC. However, the pressure fluctuations on the TriC surface are uniformly larger than those on TC. Meanwhile, the instantaneous flows past TriC are much more complex. The periodical blockage in the first gap region is found in the TriC case and leads to the up-and-down movement of shear layer in the second gap region.展开更多
In order to correct the unphysical log-layer mismatch commonly encountered in detached eddy simulation(DES) of flows with attached boundary layers,a function M,ML,which has a multi-layer structure with scaling laws in...In order to correct the unphysical log-layer mismatch commonly encountered in detached eddy simulation(DES) of flows with attached boundary layers,a function M,ML,which has a multi-layer structure with scaling laws in each layer and a plateau related to the Kármán constant,is defined.The height of this plateau is found to be crucial for obtaining the correct log-layer.A target scaling function is designed which equals M,ML in the near-wall region,but with the height of plateau determined analytically from the classical log-law.This scaling function is used as a target function according to which the resolved turbulent fluctuations are renormalized,in order to recover the height of plateau prescribed by the log-law.The renormalization procedure guarantees the height of M,ML required by log-law,resulting in correct log layer slope.The method is also shown to maintain similar turbulent properties in the large eddy simulation(LES) region of DES method.Hence it predicts the turbulent intensity correctly.The results demonstrate the relationship between constant M,ML and log-law profile of mean velocity,and relate the Kármán constant to turbulent fluctuations,implying a complete description of turbulent structural ensemble dynamics.The proposed method can be extended to more general flows with log layers since it uses only the log-law with Kármán constant as the input,while the intercept of log layer depends on the solution of Spalart-Allmaras(SA) model in the near-wall field,where Reynolds-averaged Navier-Stokes(RANS) solutions are accurate.展开更多
文摘The hydrodynamic characteristics of a rigid, single, circular cylinder in a three dimensional, incompressible, uniform cross flow were calculated using the large-eddy simulation method of CFX5. Solutions to the three dimensional N-S equations were obtained by the finite volume method. The focus of this numerical simulation was to research the characteristics of pressure distribution （drag and litt forces） and vortex tubes at high Reynolds numbers. The results of the calculations showed that the forces at every section in the spanwise direction of the cylinder were symmetrical about the middle section and smaller than the forces calculated in two dimensional cases. Moreover, the flow around the cylinder obviously presents three dimensional characteristics.
基金The project supported by the National Natural Science Foundation of China (10502030 and 90505005)
文摘This paper presents hybrid Reynolds-averaged Navier-Stokes （RANS） and large-eddy-simulation （LES） methods for the separated flows at high angles of attack around a 6：1 prolate spheroid. The RANS/LES hybrid meth- ods studied in this work include the detached eddy simulation （DES） based on Spalart-Allmaras （S-A）, Menter＇s k-ω shear-stress-transport （SST） and k-o9 with weakly nonlinear eddy viscosity formulation （Wilcox-Durbin＋, WD＋） models and the zonalANS/LES methods based on the SST and WD＋ models. The switch from RANS near the wall to LES in the core flow region is smooth through the implementation of a flow-dependent blending function for the zonal hybrid method. All the hybrid methods are designed to have a RANS mode for the attached flows and have a LES behavior for the separated flows. The main objective of this paper is to apply the hybrid methods for the high Reynolds number separated flows around prolate spheroid at high-incidences. A fourth-order central scheme with fourth-order artificial viscosity is applied for spatial differencing. The fully implicit lower-upper symmetric-Gauss-Seidel with pseudo time sub-iteration is taken as the temporal differentiation. Comparisons with available measurements are carried out for pressure distribution, skin friction, and profiles of velocity, etc. Reasonable agreement with the experiments, accounting for the effect on grids and fundamental turbulence models, is obtained for the separation flows.
基金supported by the National Natural Science Foundation of China (Grant 11372159)
文摘The massively separated flow past triple cylin- ders （TriC） in tandem arrangement is simulated using the improved delayed detached-eddy simulation （IDDES） method based on the shear stress transport （SST） model, coupled with the high order adaptive dissipation scheme. The spacing between adjacent cylinders is sub-critical （1.435D）. IDDES prediction of two cylinders （TC） with the same spacing is compared to experimental data for validation, and the numerical results agree well with the available measurements, except for the asymmetry in the gap region. The flow past TriC is investigated using the same method. Generally, the mean flow quantities past TriC, such as the velocity, pressure, and vorticity, are similar to the corresponding components of TC. However, the pressure fluctuations on the TriC surface are uniformly larger than those on TC. Meanwhile, the instantaneous flows past TriC are much more complex. The periodical blockage in the first gap region is found in the TriC case and leads to the up-and-down movement of shear layer in the second gap region.
基金supported by the National Natural Science Fund of China(Grant No. 90716008)the National Basic Research Program of China(Grant No. 2009CB72410)
文摘In order to correct the unphysical log-layer mismatch commonly encountered in detached eddy simulation(DES) of flows with attached boundary layers,a function M,ML,which has a multi-layer structure with scaling laws in each layer and a plateau related to the Kármán constant,is defined.The height of this plateau is found to be crucial for obtaining the correct log-layer.A target scaling function is designed which equals M,ML in the near-wall region,but with the height of plateau determined analytically from the classical log-law.This scaling function is used as a target function according to which the resolved turbulent fluctuations are renormalized,in order to recover the height of plateau prescribed by the log-law.The renormalization procedure guarantees the height of M,ML required by log-law,resulting in correct log layer slope.The method is also shown to maintain similar turbulent properties in the large eddy simulation(LES) region of DES method.Hence it predicts the turbulent intensity correctly.The results demonstrate the relationship between constant M,ML and log-law profile of mean velocity,and relate the Kármán constant to turbulent fluctuations,implying a complete description of turbulent structural ensemble dynamics.The proposed method can be extended to more general flows with log layers since it uses only the log-law with Kármán constant as the input,while the intercept of log layer depends on the solution of Spalart-Allmaras(SA) model in the near-wall field,where Reynolds-averaged Navier-Stokes(RANS) solutions are accurate.
