Modification of turbulent channel flow by passive and additive devices.

摘要

Three devices are examined independently in this study: increasing the Reynolds number (passive device), injection of high molecular weight long-chain polymers (additive device), and introduction of micelle rods (additive device). This experimental investigation focuses on how the velocity statistics in a turbulent channel flow are modified by these devices. Two optical measurement techniques, laser Doppler velocimetry (LDV) and particle-image velocimetry (PIV), are used to obtain accurate measurements of the instantaneous fluctuating velocities in a 5.08 cm {dollar}times{dollar} 61.0 cm rectangular channel.; A two-component laser Doppler velocimeter, with high spatial and temporal resolution, was used to measure the instantaneous streamwise and normal velocities for six different Reynolds numbers; {dollar}Resb{lcub}b{rcub}{dollar} = 5100, 9200, 12400, 20300, 31200, and 48800 (based on the bulk velocity and half-height of the channel). Results are presented comparing the streamwise mean velocity, the root-mean-square of the streamwise and normal velocity fluctuations, Reynolds shear stresses, and the streamwise and normal power spectral density functions. The ideas of inner and outer scaling are supported by the measurements. Scaling of the power spectral density function of the streamwise and normal velocity fluctuations shows that the energy contributed by large frequencies increases with increasing Reynolds number, indicating larger contributions from smaller turbulence structures.; In this investigation, the instantaneous streamwise and normal velocity fluctuations were measured with LDV over a large range of drag reductions (10% to 69%) and polymer concentrations (0.25 ppm to 50 ppm) for {dollar}Resb{lcub}b{rcub} simeq{dollar} 20300. The polymer used was Percol 727, a copolymer of polyacrylamide and sodium-acrylate. Comparisons of the turbulence statistics obtained for the different polymer solutions were made to measurements for water at the same Reynolds number. The velocity statistics were found to be quite different for low drag-reduction ({dollar}{dollar}60%).; Solutions of surfactants in water can be formulated so that rod-shaped micelles are created, which can reduce the drag over what would be experienced with a Newtonian fluid flowing turbulently at the same rate. A solution of 2000 ppm tallow-(tris-hydroxyethyl)-ammonium acetate (or Ethoquad T/13/50) and sodium salicylate is investigated in this study. The instantaneous streamwise and normal velocity fluctuations were measured using LDV for four different Reynolds numbers; {dollar}Resb{lcub}b{rcub}{dollar} = 13300, 19100, 3200, and 49100. For a fixed volumetric flow the pressure drop is reduced by 62 to 76 per cent when compared to a Newtonian flow with an equal wall viscosity. Measurements were made of the mean streamwise velocity, the root-mean-square of the streamwise and normal fluctuating velocities, the Reynolds shear stress, and the spectral density function of the fluctuating velocity in the streamwise direction. (Abstract shortened by UMI.)