Binghu Piao

The Effects of the Wall-Layer Models on the Outer Turbulence Structures in Large Eddy Simulation of Pipe Flows

Reproduction of the outer turbulence in Large Eddy Simulation (LES), when the wall-layer model is adopted in the inner layer, is investigated to validate the hybrid RANS/LES as an approximate near-wall treatment. Special emphasis is on the possibility of Detached Eddy Simulation (DES) for the reproduction of outer large (∼ R) and very large (∼ 10 R) streaky structures typically observed in the pipe turbulence. LES and DES of fully developed turbulent pipe flows at the friction Reynolds number up to 5000 are conducted using a very long analysis region to capture entire outer scales. It is found that the outer scales are properly captured in DES independent on the unphysical super-streaks in the RANS region near the wall, as long as sufficient height for the DES buffer layer is maintained. Our results shed light on the origin of the outer structures, which are rather autonomous similar to the inner sublayer streaks, and these two structures with different scaling exists in the isolated manner.Copyright

Numerical Analysis of Moving Boundary Problems Using Cartesian Grid Method

Recently, the Cartesian grid method was used on simulations of fluid flow around the complex geometry problems. In this paper, the Cartesian grid method with cut cells are used to simulate incompressible viscous flows around moving objects. In this study, the small cut cells are merged with neighboring cells. The code was developed based on Fractional Step Method on Finite Volume Method. In time integrate, the second order explicit Adams-Bashforth method was used for the convective terms and second order implicit Crank-Nicholson method was used for the diffusive terms. Some moving boundary problem are simulated using the presented code and compared with other previous numerical and experimental results.

Flow around a Pitching Wing with a Bending Motion in a Uniform Flow.

Flows around a pitching wing with a bending motion in a uniform flow are studied numerically. A finite difference method based on Marker and Cell (MAC) methods is used to calculate the two dimensional incompressible Navier-Stokes equations. The third order upwind finite difference scheme is used. Body-fitted grid generation with moving boundaries is used to obtain the numerical solutions of the flow fields. The effects on the flow field of Reynolds number, pitching frequency and bending angles are studied numerically. The effects on CD of pitching motion and bending oscillation are obtained. The results shows that a thrust is generated on the pitching and bending wing.