Large eddy simulation of compressible turbulent channel and annular pipe flows with system and wall rotations

Abstract

The compressible filtered Navier-Stokes equations were solved using a second order accurate finite volume method with low Mach number preconditioning. A dynamic subgrid-scale stress model accounted for the subgrid-scale turbulence. The study focused on the effects of buoyancy and rotation on the structure of turbulence and transport processes including heat transfer. Several different physical arrangements were studied as outlined below. The effects of buoyancy were first studied in a vertical channel using large eddy simulation (LES). The walls were maintained at constant temperatures, one heated and the other cooled, at temperature ratios of 1.01, 1.99 and 3.00. Results showed that aiding and opposing buoyancy forces emerge near the heated and cooled walls, respectively, while the pressure gradient drives the mean flow upwards. Buoyancy effects on the mean velocity, temperature, and turbulent intensities were observed near the walls. In the aiding flow, the turbulent intensities and heat transfer were suppressed and the flow was relaminarized at large values of Grashof number. In the opposing flow, however, turbulence was enhanced with increased velocity fluctuations. Another buoyancy study considered turbulent flow in a vertically oriented annulus. Isofiux wall boundary conditions with low and high heating were imposed on the inner wall while the outer wall was adiabatic. Comparisons were made with available experimental data. The re­ sults showed that the strong heating and buoyancy force caused distortions of the flow structure resulting in reduction of turbulent intensities, shear stress, and turbulent heat flux, particularly near the heated wall. Flow in an annular pipe with and without an outer wall rotation about its axis was first investigated at moderate Reynolds numbers. A non-uniform grid in the radial direction yielded very accurate solutions using a reasonable number of grid points. The mean and turbulent quantities of the non-rotating annular pipe flow have been compared with the available exper­ imental and numerical data. When the outer pipe wall was rotated, a significant reduction of turbulent kinetic energy was realized near the rotating wall and the intensity of bursting effects appeared to decrease. This modification of the turbulent structures was related to vor­ tical structure changes near the rotating outer wall. It has been observed that the wall vortices were pushed in the direction of rotation and their intensity increased near the non-rotating wall. The consequent effect was to enhance the turbulent kinetic energy and increase the heat transfer coefficient there. Secondly, a large eddy simulation has been performed to investigate the effect of swirl on the heat and momentum transfer in an annular pipe flow with a rotating inner wall. The numerical results are summarized and compared with the experimental results of previous studies. The simulations indicated that the Nusselt number and the wall friction coefficient increased with increasing rotation speed of the wall. It was also observed that the axial velocity profile became flattened and turbulent intensities were enhanced due to swirl. This modification of the turbulent structures was closely related to the increase of the Nusselt number and the friction coefficient. As a part of the study of rotation effects, large eddy simulation of a rotating ribbed channel flow with heat transfer was investigated. The rotation axis was parallel to the spanwise direc­ tion of the parallel plate channel. Uniform heat flux was applied to the channel for two rates of rotation. The results showed that the rotation consistently altered the turbulent structures near the walls. Near the stable (leading) side, the turbulent intensities and heat transfer were suppressed, but turbulence was enhanced with increasing shear stress and turbulent kinetic energy near the unstable (trailing) side.