Influence of thermal flow field of cooling tower on recirculation ratio of a direct air-cooled system for a power plant

In order to get thermal flow field of direct air-cooled system,the hot water was supplied to the model of direct air-cooled condenser(ACC). The particle image velocimetery (PIV) experiments were carried out to get thermal flow field of a ACC under different conditions in low velocity wind tunnel,at the same time,the recirculation ratio at cooling tower was measured,so the relationship between flow field characteristics and recirculation ratio of cooling tower can be discussed. From the results we can see that the flow field configuration around cooling tower has great effects on average recirculation ratio under cooling tower. The eddy formed around cooling tower is a key reason that recirculation produces. The eddy intensity relates to velocity magnitude and direction angle,and the configuration of eddy lies on the geometry size of cooling tower. So changing the flow field configuration around cooling tower reasonably can decrease recirculation ratio under cooling tower,and heat dispel effect of ACC can also be improved.

LES Investigation of Drag-Reducing Mechanism of Turbulent Channel Flow with Surfactant Additives

In this work,the drag-reducing mechanism of high-Reynoldsnumber turbulent channel flow with surfactant additives is investigated by using large eddy simulation(LES)method.An N-parallel finitely extensible nonlinear elastic model with Peterlin’s approximation(FENE-P)is used to describe the rheological behaviors of non-Newtonian fluid with surfactant.To close the filtered LES equations,a hybrid subgrid scale(SGS)model coupling the spatial filter and temporal filter is applied to compute the subgrid stress and other subfilter terms.The finite difference method and projection algorithm are adopted to solve the LES governing equations.To validate the correctness of our LES method and in-house code,the particle image velocimetry(PIV)experiment is carried out and representative measured results are compared with LES results in detail.Then the flow characteristics and drag-reducing mechanism of turbulent channel flow with surfactant are investigated from the perspective of drag reduction rate,mean velocity,fluctuation of deformation rate,shear stress,transport and dissipation of turbulent kinetic energy,and turbulent coherent structures.This research can shed a light on the application of turbulent drag reduction technique in district heating,petroleum transport,etc.

The influence of the leading-edge angle of subgrade on the aerodynamic loads of a high-speed train in a wind tunnel

The purpose of this study is to establish the correlation between the boundary layer over the subgrade and the aerodynamic loads act-ing on the train model in conventional wind tunnel tests.Firstly,flow characteristics around the subgrade with different leading-edge angles(15°,30°and 45°)are investigated through the particle image velocimetry(PIV)experimental test method.Then,wind tunnel tests of the aerodynamic performance of a high-speed train are carried out.The results are compared with previous experimental data obtained by moving model tests.Results show that,due to the presence of a boundary layer,the pressure acting on the lower part of the train head decreases,while other locations are not significantly affected.This is the reason for the reduction of the aerodynamic drag and lift on the train.In addition,the reduction effects become more obvious when the thickness of the boundary layer increases.The experimental results obtained could serve as a calibration of aerodynamic forces for wind tunnel tests on high-speed trains.